Einstein, Gravity, and the Twin Paradox (Einstein's 1918 Solution)

[@EugeneKhutoryansky]

First of all, it was not "my" explanation, but Einstein's explanation. You are claiming that Einstein was wrong, which you are welcome to do, but please realize that this is what you are doing. As for the specific criticism, a uniform gravitational field throughout the entire universe does not need a cause, because it is consistent with Einstein's Field Equations. This is the same way in which, even if there were no electric charges, a uniform electric field throughout the universe is consistent with Maxwell's equations.

[@dialectphilosophy]

Einstein did not develop his theory overnight -- his opinion on multiple aspects of his theory changed over time, and his 1918 paradox solution was part of his working through ideas. Certainly he later recanted on his advocacy of the General Principle of Relativity, a principle which your video wrongly espouses. Please do not discredit our video simply because you failed to sufficiently research yours. And a real field does need a source -- this is a fundamental principle of what defines "real". You can have all sorts of fictitious fields that are consistent with field equations, this does not mean that they are real. And a "uniform electric field throughout the universe" is consistent with Maxwell's equations? An electric field cannot originate without a source, so if you are implying that a universal electric field can spontaneously come into existence and cover the entire universe you perhaps ought to take a second look at Maxwell's equations.

[@EugeneKhutoryansky]

@@dialectphilosophy Einstein did not recant the General Principle of Relativity. This is what the entire General Theory of Relativity is based on. As for the analogy to Maxwell's equations, a uniform electric field has a divergence and a curl that is equal to zero everywhere (for both the E field and the B field). This simultaneously satisfies all four of Maxwell's equations in a universe with no electric charge.

[@dialectphilosophy]

@@EugeneKhutoryansky Eugene, you need to re-read the works of Einstein, if you've even read them at all. Perhaps focus on the 1918 years, and the response to the criticism he received from Kretschmann. While Einstein certainly hoped to put acceleration on equal footing with all other types of motion, and while it indeed motivated his development of GR, he openly acknowledged that he did not achieve such a result this with his theories. Acceleration is absolute in GR, and it can be objectively identified by any observer in any frame. Any novice student of GR knows and recognizes this. It is disconcerting that you, as a self-purported expert of physics, do not understand this basic concept. The idea that a uniform gravitational field covering all of the universe, which arises when an observer accelerates, can be interpreted as real is not Einstein's idea. Furthermore, it is not even an idea that is accepted or espoused in mainstream physics. It is one-hundred percent your idea. And given the untenable lengths you have to gone to to uphold it -- via invoking a poorly contextualized electric field analogy -- it is clearly not an easy idea to defend. In fact, let's take a look at why your electric field analogy is simply bad physics: 1) You are confusing a static situation (i.e. a constant uniform electric field) with a dynamical one (a field which at first does not exist, then arises to cover the entire universe, then disappears again) 2) Maxwell's equations, which clearly couple all fields to matter (with the exception only of propagating radiative solutions), certainly permits 'vacuum solutions' for local patches of space with no matter inside them, in which divergence and curl are zero. But it is implied, via the other equations, that fields which exist in these local patches still have sources outside of the region of consideration. There is nothing in Maxwell's equations which allows us to expand this local patch of space to encompass the entire universe, especially since boundaries conditions are infinity must at some point be factored in. Furthermore, empirically speaking, no electric field has ever been observed without a source, so your claim that it exists and can be real is highly dubious. 3) Even if we expanded our local region of space to cover the entire universe, and make the absurd assertion that a sourceless uniform electric field contained within it could still exist and "be real", this still doesn't change the fact that this field is and constant and static, and therefore does not apply to the situation we are discussing. The situation we are discussing involves a dynamic field, one that changes over time, since the field is not at first present, then arises, and then disappears again. This changing flux throughout the entire universe is in no way analogous to a "constant uniform electric field", and to continue to make that analogy is poor physics. As a promoter of physics with a wide and numerous audience on KZbin, you have a responsibility to convey concepts of physics with accuracy and precision, and not to simply promote the lowest-rung misconceptions which permeate many a newcomer's understanding. By continuing to senselessly spout arguments that bear no relevance to the actual concept at hand, and to make claims which you have clearly not researched and cannot actual back up with any sources other than your own self-endowed authority, you are clearly failing in that responsibility.

[@EugeneKhutoryansky]

@@dialectphilosophy Please provide the reference where you believe Einstein recanted the General Principle of Relativity.

[@corwin-7365]

@@dialectphilosophy said: _"An electric field cannot originate without a source."_ That is a statement of _opinion_ on your part, not a statement of physics principles (although I guess it depends on what you mean by a "source" since you didn't really specify that). Under Maxwell's Equations, electric & magnetic fields are defined simply as valid SOLUTIONS to the equations. From the formula an electric field can arise from electric charges, changing magnetic fields, as a uniform constant, or as as an appropriate combination of these.

[@jrv634]

I follow multiple physics channels weekly and I can say this is the only video I've seen that actually throws some light on the twins' paradox

[@mikkel715]

Put "Paradox" in double quotes. Because there is no paradox. As Sean Carrol explains in "Biggest ideas in the Universe"

[@michaelbariso3192]

Time and distance cannot be relative to other objects in space-time as that would violate the law of conservation of energy. To travel distance requires potential energy, an observer can have no effect a moving objects kinetic energy-Relativity debunked. Testing the speed light in on Earth is like riding a bicycle up hill, gravity will show you down. The biggest threat to humanity is human stupidity. The theory of everything according to humans that believe their intellect evolved from a monkey's brain. If the light waves from the sun were 8 minutes and 20 seconds in a past dimension of Einstein's space-time then people on Earth are just imagining the infrared warmth of the sun coming up on the horizon. The communications delay between Earth and Mars is approximately 20 minutes. We're either viewing the light from Mars in the future, Einstein's past dimensions of space-time or in real time, which do you think is more logical? Einstein's relativity is wrong light has no limitation of speed; it cannot be slowed down because it isn't moving. From every vantage point in the universe light is omnidirectional-instantaneously traveling in both directions. Light and electromagnetic waves are independent of each other. According to Einstein's relativity-time dilation's, photos taken of the Earth from the Discovery Space station traveled from the past to the future violating the laws of physics, conservation of energy and common sense. According to Einstein's projectile light particle proton light has a (constant speed) of 186,000 miles per second moving through spacetime, but if light has a (constant speed) then moving clocks cannot run slow through spacetime! :-) The speed of light according to Einstein's relativity is 186,000 miles per second, but according to physics if two mechanical watches were synchronized on earth and one traveled across the universe and back, there would be no difference in time between the mechanical watches proving the speed of light is instantaneous as the only way a mechanical watch will run slow is if you tighten the main spring. Big Bang, Einstein's relativity-time dilation and nearly all of science debunked. Using optical clocks, lasers and GPS to prove Einstein's time dilation-space-time curvature is like using a metal detector to find gold at Fort Knox. The closer you are to the electromagnetic fields, mass and gravity of the earth the more light bends aka gravitational lensing. If the speed of light is constant then past and future dimensions of spacetime and an expanding universe would not be possible, obviously destroying the twins paradox as each twin cannot move faster or slower than the other. A mirror is a wave reflector that flips images from left to right, but according to Einstein the images you see are the result of projectile light particle photons being transported into past and future dimensions of space-time. Explain how particle light photons can re-converge their molecular structures in mirrors and how this is done without violating the law of conservation of energy. From every vantage point in the universe light is omnidirectional-instantaneously traveling in all directions (forwards and backwards through Einstein's space-time) while violating the law of conservation of energy. Explain how Einstein's projectile light particle proton can travel all directions having a (constant speed) of 186,000 miles per second. Einstein would have made a great used car salesman :-). Light waves can stretch, bend-curve and occupy a state of superposition, whereas the hypothetical Einstein projectile light particle (photon), a particle that has never been observed cannot. Unlike a TV or computer monitor the images we are viewing in the universe are in real time, not a series of frames that create the appearance of a moving image. There are no DCU digital convergence circuits in space yet Einstein's disciples believe the light and moving images they see in the universe aren't really there, they're just video recorded images of the past 13.8 billion years. You could lead a cult to water, but you can't make them think. Neither time, energy nor mass can create itself into nothing, reside in nothing or expand into nothing simply because nothing has no properties. Time and space are independent of each other, not material bodies or fantasy unions that magically stretch Time, energy, and matter like a rubber band into space-time dimensions. Einstein's projectile light particle proton has a (constant speed) of 186,000 miles per second moving through spacetime and because so wavelengths of light cannot stretch through spacetime! Red-shifts are simply the result of decelerating electrons, as moving electrons of charged electromagnetic waves-light travel through the plasma of the universe each lump (or "quanta") of energy in the electromagnetic waves are charged then discharged to the next lump, eventually the energy dissipates causing the delay in radio communications giving the appearance of time dilation - longer wavelengths in red shift. Will the James Webb Telescope view the birth of the first galaxies? Nope, the universe goes on to infinity. Neither time, the atom, energy nor mass can create itself into nothing, reside in nothing or expand into nothing simply because nothing has no properties. The James Webb Space Telescope is not a time machine, you can’t travel back in time to view the beginning of the universe with telescopes that were made in the future :-). Light and electromagnetic waves are independent of each other. If science uses Einstein's wrongly theorized speed of light like an odometer to calculate past dimensions of distance and time, then using that same method to calculate forward dimensions of distance and time would mean the Big Bang was created and expanded in the future before time existed. Unlike a television or computer monitor the images we are viewing in the universe are in real time, not a series of still image frames that hypothetical Einstein projectile light particles photons create to give us the appearance of a moving image :-). The speed of electromagnetic wave is 186,282 miles per second vs Einstein's projectile light particle proton at 186,000 miles per second. Is this a coincidence or did Einstein plagiarize yet another phenomenon to fit the math of relativity? Electromagnetic waves in space can neither slow down or speed up, this is consistent with the law of conservation of energy. If light slowed down, its energy would decrease, thereby violating the law of conservation of energy so the speed of light is instantaneous and cannot travel slower than it does. If Einstein's projectile light (particle photon) had mass it's light could not travel across the universe, high speed particles traveling at 186,000 miles per second would break the Hubble and James Webb telescope mirrors, debunking the speed of light, Big Bang, Einstein's relativity and any science that uses relativity in their theories. Similar to a mirror light is a real-time wave reflector where light and images travel in straight lines-in all directions in space as they do on earth. The faintest stars and galaxies are neither in a past or future dimension of Einstein's space-time, they're in real-time. Everyone knows cell phone electromagnetic radio waves travel both ways, yet Einstein's disciples believe time energy, mass and light can only travel one way back in time. If you simply run the Big Bang theory in reverse you reveal the insanity of Einstein's relativity and Big Bang theory. If the expansion of the Big Bang were true, time, energy, mass and light would be in the future from the vantage point of an expanding singularity-Big Bang and planet Earth would now reside in a past dimension of Einstein's time dilation (moving clocks run slow) space-time 13.8 billion years ago :-). From every vantage point in the universe light is omnidirectional-instantaneously traveling in both directions (forwards and backwards through Einstein's space-time) while violating the law of conservation of energy. Explain how Einstein's projectile light particle proton can travel in both directions having a (constant speed) of 186,000 miles per second :-) It's truly amazing how the science and politics of the left are able to keep people denying reality, there are no DCU digital convergence circuits in space, yet Einstein's disciples believe the light and moving images they see in the universe aren't really there, they're just recorded images of the past 13.8 billion years. Pretending not to notice the gross contradictions-pseudoscience in Relativity is typical of Einstein's disciples, devaluing the source of any information that's in contradiction with their beliefs-theories. You could lead a cult to water, but you can't make them think. If the light from the universe travels to past dimensions of time then it's light is also traveling into future dimensions of time (instantaneously). “And God said, Let there be light: and there was light.” a state of superposition where time and gravity run inwardly, outwardly, in all directions in the same time frame, similar to the electromagnetic field having no beginning and no end. The Doppler effect is wrongly conflated with cosmological Redshift. As one approaches a blowing horn the perceived pitch is higher until the horn is reached, then becomes lower as the horn is passed. This phenomenon is caused by the physical movement of a mechanical soundwave traveling through the medium of air, similar to throwing a rock in a pond, the rock creates physical movement in the medium of water. Cosmological Redshifts are merely the GoPro fisheye effect where wavelengths appear to lengthen-stretch from the phenomenon of gravitational lensing. "I am the Alpha and the Omega, the First and the Last, the Beginning and the End" Magnetron

[@mikkel715]

@@michaelbariso3192 Writing a conspiracy book in a comments doesn't give all the viewers and readers you want. I didn't read all carefully. But the Doppler effect is actually by the Quantum Wave function properties and combined with Maxwell's equation, it is real with a fixed speed of light, and non fixed speed of observer. Eugene Khutoryansky explains this in his Particle/Wave duality video. ("Waves: Light, Sound, and the nature of Reality") Eugene Khutoryansky is making a good explanation of conservation for different observers in his relativity videos. ("Einstein's Gravito-Electromagnetism, Gravity of moving mass in General Relativity") In his video about Quantum Entanglement and Bell Inequality is very good explanation about instantaneous and relativity. It's at the end of that video. ("Quantum Entanglement, Bell Inequality, EPR paradox") .

[@michaelbariso3192]

@@mikkel715 Time and distance cannot be relative to other objects in space-time as that would violate the law of conservation of energy. To travel distance requires potential energy, an observer can have no effect on a moving objects kinetic energy-Relativity debunked. Light travels in both directions, anyone having a conversation with their friends understands this simple phenomenon yet Einstein's disciples believe people on earth are time traveling backwards and forwards in space-time relative to one another. Don't drink the Kool-Aid folks :-) Testing the speed light in on Earth is like riding a bicycle up hill, gravity will show you down. The biggest threat to humanity is human stupidity. If the light waves from the sun were 8 minutes and 20 seconds in a past dimension of Einstein's space-time then people on Earth are just imagining the infrared warmth of the sun coming up on the horizon :-) Traveling at a different speed from the stationary clock having no universal time, all the stars, planets and galaxies would be in a different place in the universe so distance for the observer could never be calculated. Twins paradox debunked again Einstein Relativity 1=2 Fantasy Physics, Wave-Particle Duality, Photon, ... kzbin.info/www/bejne/ZpTNc5eKrKtprJo via @KZbin Special Relativity is Einstein's Biggest Blunder! First Principles Persp... kzbin.info/www/bejne/eZTRqpyCe9Z_Y7M via @KZbin

[@michaelbariso3192]

@@mikkel715 When Einstein's disciples are unable defend relativity they deflect from having to answer questions by redirecting the questions on you aka deflection-misdirection. When disciples discover you're onto their tactics they'll use character assassinations, ad hominem attacks or call you stupid to avoid cognitive dissonance, the reality of knowing everything they've ever believed that was a lie.

[@youlio10]

I love you and your videos, I thought of being crazy trying to understand the paradox from other KZbin videos or articles. Please hurry up with the sequel, I need it for my school thesis!

[@bacsi8337]

Howdy Giulio Ferraro. Consider this. The deeper the gravity well, the slower time passes with respect to those farther away. The faster an object travels away from a gravity well, the slower time passes with respect to those stationary with respect to the gravity well. Imagine that I can slow down time 99.999% in a sphere 9 inches in diameter surrounding a lit candle. From the outside, all you would see is a black hole because you would only be able to see a photon of light escape .001% of your time frame. What would an ant see if it was on the side of the candle? It would see a cloud of light in the form of a million years of photons arriving in almost an instant. The reason Black Hole slows down time so much is its gravity. Light is emanating from a Black Hole, only our time frame is so much faster that we cannot spot the photons as they leave and pass through our time frame. When we see a galaxy farther away from the Universe center, we see it accelerating away from us because it is farther away from the collective mass of the Universe. Persons in the distant galaxies look at galaxies closer to the Center of the Universe and see them traveling much slower because their perspective of time is moving faster than ours. We look at stars closer to our galaxy center and see them orbiting the Galaxy’s Black Hole so slowly that we wonder why they don’t fall into it. If we were standing on a planet orbiting a star close to that same Black Hole, we would wonder why the stars on the outer edge of the Galaxy don’t fly off into space because they are traveling way too fast to stay in orbit. Many scientists attribute those phenomena to Dark Matter and Dark Energy. But its really General Relativity.

[@chrisracer2007]

My friend from school really recommended you and I just wanted to let you guys know that I am really impressed! Your work is amazing

[@bacsi8337]

@@jasond8953 Always have fun with quantum technologies :) q off

[@echoromeo384]

Your videos have the most exacting and thorough ideas of GR and physics on KZbin. Others just hope the viewers don't pick apart their arguments and philosophies while you have an excellent real world grasp on the subjects. Thanks brother, keep em coming.

[@mdoliner526]

I never understood why the paradox was not presented with the twins in symmetrical motion. What if both traveled in opposite directions, turned at the same time, and returned. During the periods of constant motion each would see the others clock as going slower. Whatever happened when they turned would happen to both. Then when they returned at constant speed each would see the other's clock as going slower. When they meet each twin should be younger and older than the other.

[@titsorass4553]

they'll both be the same age

[@justopastorlambare2933]

Relativity gives a precise and unambiguous solution for that case too.

[@РайанКупер-э4о]

13:38 Shouldn't be acceleration in gravity assist maneuver also absolute?

[@Chris.Davies]

I am absolutely loving the deep explanatory power of the River Model of General Relativity. But now I am very much wanting to know what properties space must have for it to work correctly. It seems space drags on mass, to create the effect we feel as gravity, and I refer to this as being "slammed by space", because when you jump off a rooftop, it is the flow of space which slams you to the ground, instead of apparently breaking Newtons Laws - because we know gravity is not a force. I love the fact there is absolute time, and absolute space - and that Einstein's E=mc^2 explains rest mass and relativistic mass explains the apparent dilation of time due to the conservation of momentum, as all vibrations and oscillations show down as mass increases. I love the fact there is no so-called Twins Paradox. Because Paradoxes are almost universally a problem with the language itself or a failure of logic.

[@bismajoyosumarto1237]

16:02 "Don't leave! I'm still confused, dam**#@!" Same, bro, same.

[@justopastorlambare2933]

So far, the best twin paradox discussion I've seen. Congratulation!

[@justopastorlambare2933]

@@nadirceliloglu397 Sorry, anyone who understands special relativity knows the solution to the paradox. I like the video because it explains Einstein's confusion with his gravitational theory. He initially thought GR resolved the relative motion problem proving Mach's principle. It turned out that he was wrong, he could not prove Mahc's principle but found a wonderful gravitation theory that is called "General Relativity" only for historical reasons.

[@Xidnaf]

Wow. I thought I understood the twin paradox. I did not understand the twin paradox.

[@doctor_4]

You're just awesome Dialect. I'm interested in science for years and have never seen such a tough problem like this before. I've been trying to understand how such phenomena exists for hours. For every explanation I've read, I was like "Well, symmetry is still not broken! This explanation can't be right!". People just "accept" what science videos and websites tell them to "believe" but you embrace real skeptical thinking in your perfectly made videos. Keep making these awesome videos pal!

[@Josiejen9]

Like others, I think these are fascinating videos. Can you please hurry up with the next one - I've been waiting over 2 months, lol.

[@dialectphilosophy]

Thank you very much! Sorry for the long wait, and please be patient with us, we promise more to come :-)

[@TheTannertech]

This topic is so immensely complex holy shit, thank you for the breakdowns.

[@imaginingPhysics]

7:46 side note: the "existence" of some kind of gravitomagnetic field is already implied by special relativity when gravity is developed into so called gravitoelectromagnetism (en.m.wikipedia.org/wiki/Gravitoelectromagnetism). Basically it is what you get when you combine Newtons inverse square law (compare Coulomb) with the finite speed of information - - > Maxwell type equations. It is quite inevitable that gravity has to have these kind of effects ("dragging" in this case), whatever their interpretation. And indeed gravitoelectromagnetism is equivalent (apart from a constant) to the linearized version of GR field equations.

[@imaginingPhysics]

As to the "reality" of the induced gravitational field, I would like to compare it to the "reality" of an Electric field induced by changing magnetic field. Both can be seen as relativistic effects of accelerating bodies.

[@imaginingPhysics]

9:29 I do not see why the analogy would break down. The accelerating observer in his rest frame sees distant stars accelerate --> their acceleration induces a changing gravitomagnetic field - - > changing gravitomagnetic field induces the gravitational field. (replace mass by charge and this Is classical electrodynamics). Now If Einstein went around to say that the induced gravitational field is responsible for the acceleration of the starts, that seems circular to me. You would not say such things about accelerating charges would you?

[@imaginingPhysics]

To me all this is a beautiful demonstration of the equivalence principle in action. Laws of physics are the same and produce equivalent outcomes weather we are in an accelerating frame or non accelerating. Now, i do not want to pretend to understand relativity perfectly. These are my private ruminations. (the gravitoelectromagnetism is a real deal however)

[@dialectphilosophy]

To answer some of your questions: yes, in his 1918 paper Einstein does actually assert that the induced gravitational field is responsible for accelerating the stars (shown at 10:01 in our video). But he also in the same paper implies the opposite (that first the stars accelerate) (10:09) so in fact it's a little unclear what exactly his interpretation was, and this is why we assert there is an "analogy breakdown". You could consider the universe as filled with a sort of static gravitomagnetic field that begins to change once the stars accelerate, thereby inducing a changing gravitational field. This still leaves the issue of non-local propagation of such changes; however, the main reason this theory has been dismissed among the current physics community is that in an empty universe, an accelerating rocket ship would still have to observe the arising of gravitational field, and its obvious such a field would have no source. The point of this video is indeed to demonstrate that the equivalence principles does NOT imply the equivalency of the laws of physics in non-accelerating vs accelerating frames. It only asserts the local equivalency of accelerating frames with frames-at-rest in a gravitational field. According to the theory of SR and GR, accelerating frames are privileged and can always be identified by all observers due to the unique form the laws of physics take in them. (Indeed, it is the observance of a gravitational field which always indicates true acceleration in GR.)

[@imaginingPhysics]

Thanks for the answer. Yeah the non local propagation seems dubious. So propably you and the scientific concensus are right. Also, The strength of the induced gravitational field would depend on the mass density of the universe, so in an empty universe the twins would always age the same (in this interpretation at least). And that last contradics GR, which does not care about distant stars (or does it?). Anyhow. The phenomenon/interpretation is still quite beautiful. Is it a pure coincidence or does contain "some truth" about the equivalence principle? I did not know einstein himself had seriously considered it. Enjoyed the video, thanks. Keep them coming.

[@hosh1313]

6:25 3 legs of the journey? What about the initial acceleration and final deceleration?

[@Plus9dB996]

What if you do not use straight lines. When either twin moves away from the other they travel in a circular direction. If only one moves, they will have come back to the other after completing a full circle. If they both move away from each other, they will come back to each other after completing a half circle. In all 3 scenarios the persons that are moving never have to change velocity. In the scenario where both are moving they will come back together in half of the time and half of the distance. 😊

[@user-lb8qx8yl8k]

After thinking about this for a while i began to wonder why there's no mention of the simple concept of the inertial reference frame. The frame where the traveling twin is at rest is not an inertial reference frame. Why? The 'stay at home twin' who can be seen as a free particle (a particle which is not subjected to an external force) does not travel in a straight line. Hence, in that reference frame, there's a fictitious force acting on the stay at home twin which yields the APPARENT acceleration. The frame where the stay at home twin is seen as stationary is, on the other hand, inertial. That's why all the analysis should be done in that reference frame.

[@dialectphilosophy]

We talk about inertial frame in other our videos in our twin paradox series -- unfortunately, due their ambiguous definitions and inherently mathematical nature, they can't be used to determine the agent of asymmetry in the paradox.

[@user-lb8qx8yl8k]

@@dialectphilosophy -- Thanks for the reply. Your videos really made me rethink the twin paradox. And I realize it's resolution wasn't quite as simple as I thought. You're videos are amongst my favorites. That said, I'm really only familiar with one definition of an inertial reference frame. We learn it in a first semester course on Newton's laws of motion. An inertial reference frame is a frame in which F=ma is satisfied where F is the net external force acting on a mass m. That's how it's defined in special relativity with the additional assumption that gravity is not present. This is _equivalent_ to saying that the worldline of a free particle is straight in an inertial reference frame. An object has constant velocity if it's worldline is straight within an inertial reference frame. In the formulation of the traveling twin problem, it is tacitly presumed that one twin, the "stay at home twin," is a free particle and the other is not. We take Bob to be the free particle and Alice to be the particle that is subjected to an external force at the point of the u-turn. The reference frame which Alice is at rest is non-inertial because Bob's worldline is not straight in that reference frame. The reference frame in which Bob is at rest is inertial. Alice's worldline is not straight but Alice is, by definition, not a free particle. I just saw the other video. Maybe I need to watch it a second time, but you seem to dispute the fact that the traveling twin does not stay within a single reference frame.

[@zemm9003]

In GR an inertial frame is a free falling frame. The stay at home twin is not truly inertial due to the acceleration of the ground but it is close enough. The other twin suffered tremendous acceleration by comparison.

[@user-lb8qx8yl8k]

@@zemm9003 -- It's presumed that there are no gravitational sources in sight. The difference between an inertial reference frame in special relativity and an inertial reference frame in Newtonian mechanics is that the former doesn't incorporate gravity.

[@zemm9003]

@@user-lb8qx8yl8k gravity has nothing to do with it. The definition would be the same. The only difference is that the notion of "free fall" would not be intuitively related to gravitational fields.

[@DanielGrubbs1]

At 6:01 you say "Now, because clocks run faster farther out in gravitational fields, distant objects will appear to age very rapidly from his perspective." But I don't think this is true in this case. With this "uniform gravitational field" both of the rockets will experience the same effects with neither clock running faster or slower due to general relativistic effects. There will be a Doppler shift and special relativistic effects, but no gravitational difference. Most sources of a gravitational field come from a particular source with field lines closer together nearer the source. I believe that this is why clocks run slower nearer to the source. I know this doesn't affect your thesis as you go on to show this explanation is wrong, but I thought I should comment on it. If I'm incorrect, lease tell me why. Thanks.

[@dialectphilosophy]

"Real" gravity, i.e., spacetime curvature, must stem from a source. A uniform gravitational field is not real curvature and not real gravity, but rather a "pseudo-field" that is a consequence of inhabiting an accelerating frame. So you are correct to assert that there is no gravitational difference in a uniform field, and the effects of time dilation there are all due to special relativistic phenomena. A rather startling fact: time dilation and curvature (gravity) have nothing to do with each other. Several videos out there on KZbin perpetuate the misconception that they are related, which they are not. You can have a theory of gravitational curvature (Newton-Cartan physics) without any time dilation whatsoever. Clocks run slower nearer to a source because the observers near to that source are in accelerating frames of reference. Thus, due to kinematical effects from special relativity, they "see" clocks farther out running faster than their own.

[@zemm9003]

Time Dilation comes from the Lorentz signature and not from the Riemannian Curvature Tensor.

[@c.s.4273]

At 6:24 you are mistaken when equaling both phases of the constant velocity as the inbound phase is when space traveller sees time on earth running much faster than the slowing of time on earth during outbound phase.

[@shugyosha7924]

You have the best videos about the twin paradox. Thanks so much!

[@uavtech]

A non-hand waving explaination. GREAT WORK!! On to your next video. 😊

[@Swiffah145]

The objective (i.e. coordinate-independent) difference between the two twins is the spacetime interval traversed by their trajectories: The interval traversed by the traveling’s twin is shorter than the remaining twin. The spacetime interval is a (arguably *the*) fundamental property of the underlying (Minkowski) spacetime. And special relativity employs this property in explaining the age difference, namely via clock postulate. This postulate says that the readings on a clock is proportional to the spacetime interval traversed by its trajectory. The clock postulate is not often mentioned as a fundamental postulate of SR, but it really should be - it’s essential to linking the properties of spacetime to observable phenomena. Note how the above explanation does not mention “acceleration” or “coordinate system” or anything else.

[@dialectphilosophy]

We discuss some of these aspects in our video on the twin paradox in curved spacetime. While comparison of spacetime intervals does absolve the asymmetry of the paradox from being solely correlated to a notion of absolute acceleration, the fact still remains that in flat spacetime, shortening the spacetime distance between two spacetime events requires an act of acceleration, which, in the context of SR, is still defined relationally via the 3-acceleration of an accelerometer instrument.

[@tricky778]

Around 10:40: Which 'instantaneously' do you mean? At the same time-ordinate in the proper frame of the spaceship or on the lightcone of the event in which the rocket fires to make a step change in velocity?

[@dialectphilosophy]

The instantaneity would occur in the frame of the genesis of the acceleration; for frames of observers nearby this vanishing would not appear to be instantaneous, but rather the spacetime separation between the events appear to be space-like, which is still in violation of causality.

[@tricky778]

@@dialectphilosophy that doesn't answer the question, I think, to be self consistent it would have to be the same line at arbitrarily small times before and after the acceleration in those moments' respective frames otherwise the acceleration would be asymmetric; I think this forces us to take the usual lightcone for instantaneously, but perhaps it doesn't matter because all we're doing is cutting and pasting bits of equivalent diagrams for an impossible extreme acceleration until we also have some nonrotational equivalent of frame dragging (I don't know anything about this subject I'm just supposing something I might investigate). And unless we're instead going to take the integral of all the step accelerations in a continuous acceleration to find a causal upper bound to the rate of acceleration we're not going to learn much from the exercise

[@dialectphilosophy]

@@tricky778 Hm, not sure we're following your reasoning here, though your line about "non-rotational frame dragging" peaked our interest. Could you reframe the question you are trying to ask in a different way perhaps?

[@tricky778]

@@dialectphilosophy I don't know enough to pick the right terms. I was saying that if we're to make a diagram by cutting and pasting that has one solution for the properties at each point then the two inertial diagrams from before and after the momentum exchange mustn't overlap and so the cuts must be on the light cones. Then I note that it's all a silliness unless we're to introduce some other curvature due to the event which I thought would be a component similar to what we call frame dragging for rotating masses. I hoped to elicit discussion of these matters.

[@tricky778]

Actually, consistency only forces us to paste the first frame inside the past lightcone and the after frame in the future lightcone, we can either have discontinuities at the cones or vary gamma in between. We could vary it in any way such that the integral of cuts and the integral of their valid joining curved spaces satisfies essential laws. Having thought more, I wonder if the Lorentz transform of inertial space is the counterpart to frame dragging and so it's already incorporated. I need to study but I don't have faith that I'll remember anything or that it'll pay off if I do

[@juniorcyans2988]

I'm a sophomore of physics. So far the benefit of being a physics student is that I've been lucky to discern which videos make sense. I just learned special relativity in my Modern Physics class in the past two weeks of this semester, this video makes a lot of sense to me! Actually I love the video because it corrects the misleading other videos made. Science digs for truth, this is why I love science!

[@stewiesaidthat]

This video is misleading also. It doesn't explain why electronic devices in motion run slower than stationary devices. It doesn't explain how acceleration/gravity impacts cellular functions.

[@juniorcyans2988]

@@stewiesaidthat One video can’t cover everything right? Actually it uses Michelson-Morley experiment without explanation, fortunately I learned in my class so I know what it means.

[@stewiesaidthat]

@Junior Cyans one video can cover everything. 1) Motion changes the electromagnetic wavelength, which changes the frequency. 2) Electromagnetic waves travel independently of the source. 3) A change in force on the source necessitates a change in force of the electromagnetic wave. 4) Electronic devices operate at a constant frequency. 5) Clocks measure motion and synchronized clocks measure relative motion. There is no time-dilation. One clock is just moving through space faster than the other. If you want to compare the effects of space travel on the human body, you must reference NASA's data. None of these videos do that. They just run you through silly math problems that are improperly applied. A slower running clock means slower running electronics. You have to look elsewhere to discern if there is a difference in aging due to other forces.

[@juniorcyans2988]

@@stewiesaidthat lol that would be a lot of work to do. Anyways pions decay before they reach the speed of light. What we calculated in class kinda proved time does dilate.

[@stewiesaidthat]

@Junior Cyans lol yourself. Matter gets turned into energy as it approaches the speed of light. Increasing that rate is not time-dilation. Frozen embryos were hatched out 30 years later. Is that time dilation? Plants grow faster on warm sunny days than cold cloudy days. Is that time-dilation? Children reach puberty sooner on a high protein diet. Is that time-dilation. It takes longer to drive 1000 miles than it does to fly 1000 miles. Is that time-dilation. Everything is in time-dilation because everything moves at different speeds - applied force. Solving the twin paradox is just a matter of identifying the frame of reference. Determining what the applied forces are. And how the frame of reference responds to the applied force. To understand why there is no difference in aging, you need knowledge about biology, what is it source of energy is and the rate of consumption. But you first need to reject this notion that motion causes time-dilation.

[@PulseCodeMusic]

Accelerating reference frames have a slower passage of time than inertial ones. You can come to this conclusion quite easily by measuring the the length of ticks of photon clock oriented in the direction of acceleration (or paths of photons in an accelerating photon box). Call that a fake gravitational field if you want, but there is an equivalence between acceleration and staying still in a gravitational field, so why would you choose the one that is clearly not the actual reality of the situation.

[@IanTickle-k1o]

There's no need to invoke any of fictitious forces, inertial frames, accelerations (absolute or otherwise), the "fixed" stars, earth's or any other body's gravity or GR to explain the twin "paradox". In fact it's not even a paradox, rather it's an asymmetry that's entirely an expected consequence of SR alone. It's very surprising that Einstein was apparently confused by this (or perhaps it's better to say that we are in the privileged position of hindsight). The twin asymmetry arises solely because the earth twin's path through spacetime is linear whereas the space twin's path through ST is kinked at the turn-around point (irrespective of the forces and accelerations experienced there), and there's no transformation by a change of coordinates that can straighten the kink (i.e. the rotation of the space twin's planes of simultaneity). It's obvious that the accelerations are irrelevant because one does not need to know the accelerations to compute the difference in the recorded proper times (a.k.a. "dilation"), only the average outward and return velocities. The space twin's ST path has to be kinked because (s)he must return to earth in order to compare clocks at the same ST coordinates, otherwise any comparison is not valid according to SR. Read Sean Carroll's book "The Biggest Ideas in the Universe" for clear explanations of SR and GR.

[@stevemuller8320]

correct! it's all about Minkowski's (not Einstein's) invention of spacetime as a whole (and the resulting Minkowski metric (-(!)1, +1,+1,+1) - there is no space (illusion) and there is no time (illusion) - only spacetime is real. Moving near the speed of light reduces proper-time - not moving at all (relative to the speed of light) maximises proper-time. In a Minkowski Diagramm twin A will stay in the center of the coordinate-system (moving only in coordinate-time - not in space = stationary observer) and twin B will move on a straight line in coordinate time (ct-axis) AND coordinate space (x-axis) - thus reducing his proper-time according to tau^2 = (d ct)^2 - (d x)^2 (would B move with the speed of light, his proper-time would shrink to zero)

[@J7Handle]

I did just think about this, but assuming the idea of absolute acceleration is correct (which it can't be, I agree on that one), then we can create two new twin paradox scenarios. Scenario 1: Ship B leaves at velocity v and after Ship A experiences time elapsed t, Ship B abruptly halts relative to Ship A, and they both measure the distance between them to be d = v * t. Scenario 2: Ship B leaves at velocity v and after Ship A experiences time elapsed t, Ship A abruptly accelerates to match Ship B's velocity, and due to length contraction after acceleration (and the accompanying lack of length expansion that Ship B sees due to not decelerating in this scenario), both ships measure the distance between them to be d = v * t / gamma. When we remove the idea of absolute acceleration and prevent the ships from agreeing on who's accelerating, we suddenly lose the ability to account for why length contraction occurs in one scenario and length expansion occurs for the other. Of course, this is to be expected. If we have a paradox regarding the time of travel, we would naturally also have a paradox regarding the distance of travel, the two being inseparably linked. But it does raise the interesting point: If the twins are able to compare both the distance traveled and the time elapsed between each other, they can conclude which of them has absolutely accelerated and which of them hasn't, but we're not supposed to be able to conclude absolute acceleration. Why am I so adamant that absolute acceleration cannot be? Because in our expanding universe, every object simultaneously observes the others to be accelerating away while also validly claiming they themselves are not accelerating. Thus, acceleration due to the expansion of the universe must be relative due to the irreconcilable disagreements. The only other possible conclusion is that acceleration due to expansion of the universe is not acceleration at all despite working exactly like regular acceleration in every way except for the inability to reconcile disagreements on absolute motion. Which according the the principle of relativity, shouldn't be a problem.

[@dialectphilosophy]

That's an excellent point about relative acceleration and the expanding universe!

[@J7Handle]

@@dialectphilosophy recently, my views on this subject have been changing rapidly. Your video on how time dilation is actually an illusion caused by how we measure time made me think that there could actually be an aether without us ever being able to verify its presence (except if we found a new force that propagates faster than light). And if time dilation and length contraction are both illusions that don't actually happen, then spacetime is also an illusion, as spacetime is the concept that ties together time dilation and length contraction. With those being illusions, the spacetime idea becomes pointless. Which also defeats the idea of gravity being curvature in spacetime. With this revelation, the twin paradox in curved spacetime loses its mystique, as the acceleration due to gravity ends up exactly equivalent to normal acceleration. Thus solution to the twin paradox remains: acceleration. But in order to accept absolute acceleration, I've been forced to seriously consider that the aether really does exist. In a twin paradox scenario with an empty universe save for the two twins, and an undetectable gravitational field causes a twin to undergo an undetectable acceleration at the turnaround point, the twins can no longer determine who will experience more time based on their absolute acceleration (they can't decide who was the one who accelerated). They can only determine their absolute acceleration from their experience of time instead. But absolute acceleration relative to what? They didn't feel the acceleration and didn't observe any influence that could cause the acceleration. They are simply forced to accept that one of them had an acceleration relative to something. In another scenario with a closed universe, they push off each other and eventually reunite due to the circularity of the universe. If their time elapsed are different, they're forced to assume that one of them ended up with a higher velocity than the other. If they experience the same elapsed time, they assume they had the same velocity as each other. If you think its natural that both the starting velocity be zero and the resultant velocities be equal and opposite, think again. If they start with zero velocity and one twin is heavier than the other, their resultant velocities when they push off will not be equal and opposite. Meaning its impossible to guarantee that in every scenario they will experience the same amount of time, and the only source of asymmetry that makes sense for that is aether. The aether is the thing that they measure their velocities against. Even if they can't measure the aether wind directly, they measure it when they meet on the other side of the universe and compare clocks. So the aether exists, and acceleration and velocity are absolute (kind of).

[@J7Handle]

@@nadirceliloglu397 While time dilation and length contraction are real, acceleration cannot be relative. Under any circumstances. I've found that an assumption of relative acceleration in any circumstances always yields an impossible twins paradox. Thus, there cannot be relative acceleration. But if there's no relative acceleration, then the equivalence principle is wrong, space doesn't expand, there is a center of the universe (just near impossible to find), there's nothing beyond the edge of the observable universe (edge is a wrong word choice anyways, there's no restriction on how far away something in our observable universe can be from us except the amount of time it would take to get there), therefore the observable universe is the same as the whole universe, time is absolute, length is absolute, velocity is therefore absolute, and because of the expansion of the universe (not space, but the universe itself expands, as in, the things in it accelerate away from the center), position is also absolute. So no motion is relative. The solution to the twins paradox makes all motion absolute, decidable only by observing the rest of the universe and not by "feeling" it locally. The speed of light is also not constant. Gravity is just a region of space with a reduced speed of light, which just like a prism, refracts light, and because matter is made of waves, these are also attracted by gravitational fields.

[@J7Handle]

@@nadirceliloglu397 All experiments that have been claimed to prove relativity have only proved the Lorentz equations. The assumption of relative motion has always been just that: an assumption. Nothing has ever proven it. And the twins paradox proves it wrong. Acceleration is absolute, and everything else I said follows from that.

[@Paul_Walker]

Hey cannu please explain me my doubt... I beg you pls coz I'm really confused nd I can't sleep without knowing it... So let me start .. Suppose A is the guy which is at earth nd B is the guy which is constantly moving in space at speed 0.5 c... So B comes at earth without stopping nd moving constantly, B crosses Earth and as soon he does it, both A & B starts a stopwatch... B then travel to a star ( remember he was constantly moving always )... The star is 4 Ly away nd as he's moving at 0.5 c, so the A knows he'll reach the star in 8 years... But when B reaches the star (it didn't stop), he stops the stopwatch nd shows a big sign of the clock to C which is near the star... C shows the sign ( suppose he saw that B showed 7 years nd he notes it) Now C comes to earth nd tells A that "by the time B reached the star, he showed that it took 7 years"... But A had calculated already that it must've taken 8 years for him(A) by the time B reached the star... So time took for B to reach the star is 7 yrs nd at that time A/ earth has passed 8 yrs... But NONE of them accelerated ever.... So B can say that he was at rest nd earth moved away from him nd stars/c came closer to him... So he's confused that why A isn't younger than him..... So isn't this make us think it's still a paradox??? Pls explain

[@David-gu8hv]

"Because clocks run faster further out in a gravitational field..." is this true in a uniform gravitational field? Isn't that true for a gravitational body because it's gravity is weaker further out; if so wouldn't the clocks in a uniform gravitational field run at the same "rate"?

[@dexter8705]

Nothing has a uniform gravitational field so your question is mute, but if there was one the answer would be yes, but the world or gravity doesn't work that way so why bring up a scenario with no relevance.

[@caperider1160]

This is where experimental physics rocks! Should we have enough resources to carry out this and all other iterations as experiments and obtain results, all problems will be solved. One day. Hopefully. BTW, this video is the most impressive version of twin patadox explanation i have come across. I personally think the twin will age the same.

[@brianwatson9687]

We already have done the experiment with an airplane flying around the world using atomic clocks. What you personally think is irrelevant. And also wrong.

[@jeremy4ags]

If I can press a button and instantly observe a far away object move towards me, isn’t that “gravity” faster than light? Wouldn’t that break symmetry already?

[@congchuatocmay4837]

The moving object is emitting event information, else you could not know it is moving. And if space has an information transmission rate saturation limit the moving object is using some part of that and that may reduce the rate at which events occur (eg. slow time.) And like I said there are a lot of events happening in a proton per second as the quarks and gluons interact. And that uses up some of the saturation capacity, slowing the event rate (time) the way gravity is known to do. Then you could speculate that an electron must have interacting constituents to have mass.

[@markcollinscope]

I have a slightly lateral question here. Where did the Twins Paradox come from; how was it initially conceived. At a guess (humour) it wasn't from experimental evidence at the time. So it must have been a theoretical 'observation' (i.e. it was calculated mathematically using SR). So if we want to explain the Twins Paradox, shouldn't we go back to the original calculation(s)? I may have missed something here - feel free to enlighten me. If not, anyone seen the 'original calculation' (assuming that exists).

[@stewiesaidthat]

The paradox arose from Einstein combining space and time into one entity. Coupled that with not understanding that mechanical clocks measure motion in space leads to a convoluted fantasy universe where Force does not equal Acceleration. A slower running clock just means that it is experiencing more space (distance). How is thus determined? Because clocks in motion use the same amount of energy as stationary clocks. Where does the energy come from to accelerate cell growth? For egg embryos- the mother hen. Is it constant? No. Seed germination rates are dependent on soil temperature. Is that value constant? No as it changes with energy received from the sun/artificial means. Go back in time and look at who started all this relativity/time-dilation nonsense. A guy who knew nothing about the universe and made everything up in his head with his 'thought' experiments.

[@voteforhamsandwich1112]

Sorry, i got confused. Does acceleration explain the paradox?

[@zemm9003]

Yes. The free falling twin (almost free falling since the Earth stops the fall) has a longer proper time. The traveling twin has a shorter proper time and the reason we know he is not free falling is due to the acceleration.

[@utkuaraskula2348]

if we assume, one particle was seperated to two particle. each particle has same mass and velocity(same momentum) but opposite direction. there no extra particle(mass) to curve spacetime. spacetime is equally curved in this region. some time after, each particle collides same obstacle(same mass, same collision friction) and turn back to initial point. in this scenario, there no gravitational force, no accelarition(or same for each particle), no rocket thrust, first particle say that i am standing still, i am older you are younger, second particle say that i am standing still, i am older you are younger. which one is true?

[@abiuniverse]

Does uniform gravitational field means no change in the value of acceleration due to gravity(g) throughout the universe? Then it means there is no source because if that were the case you would see a decreasing value of g as you move away from it. That means you cannot say clocks far away from you are moving faster because there is no source which centred at you or somewhere.

[@isbestlizard]

The explanation also assumes a straight line out, a turn around (where the paradox-solving magic happens), and a return. What if one twin just travelling in a HUGE circle, constantly accelerating, until they rejoin their twin? There's no turn around point. And each travelled in a huge constant-acceleration circle from the others perspective.

[@isbestlizard]

Or maybe a parabola or orbit or whatever, but a continuous acceleration for the entire trip such that it starts and ends at the same point

[@zemm9003]

This also works fine the instant acceleration just simplifies the problem which is why it is used.

[@QuicksilverSG]

@10:21 - "The arising of the gravitational field is even more problematic, however, because from the space twin's perspective, it appears in a non-local instantaneous fashion throughout all of space." This insight alone debunks the assumption of relativity between the perspectives of the two twins. In order to regard the space twin's perspective as an inertial frame of reference, you have to postulate a gravitational field that propagates instantaneously throughout all of space. This obviously violates relativistic limitations of propagation through space-time, as well as conflicting with recent observations of gravitational fields propagating at the speed of light.

[@Robinson8491]

11:15: is this non-transformability also true for a lagrangepoint? As you cannot deduce the deviation in position from it as it is identical at all directions, so could be mistaken for flat spacetime. While time dilation is still at hand!

[@thalianero1071]

I have found your videos on this topic unclear, even with having watched the bucket video. But my current understanding of your argument is that using acceleration to resolve the paradox requires you to choose an inertial frame against which to define the acceleration (typically, the frame of one of the twins). Is your assertion that any measurement of acceleration on the part of the twins depends on your choice of inertial frame? Do you think each choice of frame is a separate instance of the problem, or that all choices of frame should be valid for the single instance of the problem?

[@rathereasy]

How's this for an explanation of the asymmetry: length contraction. Alice and Bob disagree about the distance that the other person traveled. If we take bob's frame as inertial, he thinks Alice travelled less far. They both agree on the speeds, but Bob's observes the distances to be shorter regardless of which frame is inertial.

[@kingnovak2831]

Man, why does reality have to make everything so complicated?

[@RecursionIs]

It is an exercise in exceptions

[@cisuminocisumino3250]

Or maybe we're the ones making reality complicated.

[@Jaggerbush]

@@cisuminocisumino3250 no - it’s complicated. That’s the point. If you think you can watch a KZbin video and understand it- then you don’t understand it.

[@2tehnik]

@@Jaggerbush I think they were more so making a point about how our theories are incomplete or don't actually map onto the world.

[@dritemolawzbks8574]

"The Universe is under no obligation to make sense to you." -NDT (America's favorite celebrity astrophysicist)

[@Rastlov]

Nice thoughts. But the traveling twin actually feels the acceleration. The twin on earth doesn’t feel any charges. That breaks the symmetry.

[@dexter8705]

I hope you watch his newer videos cause he proves acceleration doesn't resolve or break the symetry.

[@ferdinandkraft857]

The animations are so witty! Good job!

[@dialectphilosophy]

Thank you! :-)

[@berndmayer3984]

The Twin "Paradox" also works without acceleration. The decisive factor is a one-time change of the reference frame for one of the persons involved.

[@dialectphilosophy]

A change of reference frame is proper acceleration, and yes it is required for the paradox. However, the change of reference frame is debunked in curved spacetime, where the non-inertial or frame-changing observer can age more than the inertial one. Check out our video "The Twin Paradox in Curved Spacetime" for more.

[@markcollinscope]

See my 'thought experiment' about 5 comments up. Is that similar to your 'without acceleration' perspective?

[@inteallsviktigt]

@@dialectphilosophyhow would this change if we used two planets that travel away from each other? As in we have two planets in two mirror galaxies that are neighbors, and as the planets travels perpendicular to each other and perceive the other as accelerating away as they both travel a galactic cycle before returning to each other.

[@erinm9445]

@@dialectphilosophy How would the paradox work if one twin were on the earth, and the other were in a long eliptical orbit around the earth, that came very close to the earth on one end of the orbit, close enough that the twins could more or less instantly compare clocks via electronic communication? In that case, neither twin would experience acceleration. Or, at least, neither twin would experience non-gravitational acceleration.

[@keithdubose2150]

​@@dialectphilosophy never heard a change in reference frame defined as proper acceleratoon. Float head physics shows how the paradox is explained with triplets .. where only constant velocities, with only a 'hand off' of reference frame.. can demonstrate the resolution with out acceleration.

[@pedrokrause7553]

Hey Dialect! What do you think about TED-Ed explanation?

[@dialectphilosophy]

Great question. Sadly, despite being a highly-viewed video backed by an accredited institution, the TED-Ed video actually makes the very basic error of conflating time dilation with the doppler effect. Around the 4:45 mark, the video claims that Terra observes Stella aging slowly for 90% of the trip, and then observes her aging quickly the rest of the time. This is VERY incorrect. Terra observes Stella aging slowly the entire duration of the trip. The frequency of Terra's light-messages will be lessened (blue-shifted) during that 90% of the trip because of Doppler effects, however, Terra still has to account for the amount of time taken by the light from Stella to reach her. Terra will know exactly how far away Stella is when each light message was sent, since the message will presumably contain information about where in space Stella was at the moment the message was sent, and therefore Terra can calculate backwards, via her knowledge of the speed of light, how much time actually elapsed between two ticks in Stella's clocks. Doing this, it will be apparent that, from Terra's view, Stella's clocks run consistently slow throughout the entire duration of the trip. An easier way to think about it is that Terra could have a group of assistants, all positioned throughout different points of space along Stella's path, and all at rest with respect to Terra, who measure the rate of Stella's clocks as she passes by them. Later these assistants could all compare notes and everyone would see that Stella's clocks were, from the frame of Terra's perspective, running slow the entire duration of her journey. There's actually studies out there that show a large number of professional physicists don't understand the difference between the Doppler effect and time dilation -- demonstrating that relativity is a difficult topic, even for those who profess to teach it!

[@pedrokrause7553]

​@@dialectphilosophy I believe the video was valid solution to "Who is the older one when both meet again?", but it is true that the video might have conflated time dilation and the doppler effect. But I also think that the video focuses on how Stella and Terra would see each other's aging process, in the original meaning of the word, which is by receiving light - and in that sense the video is correct.

[@pedrokrause7553]

@@dialectphilosophy And it is certainly true that there's a lot of professionals that don't actually know the subject, which is very unfortunate.

[@dialectphilosophy]

​@@pedrokrause7553 With regards to the question of what breaks the symmetry of the paradox, the Ted-Ed video does at least state that what defines Stella's non-inertial frame is her acceleration with respect to the rest of the universe. This is a step above other videos, whose conceptualizations of non-inertial frames are woefully under-defined. However, the video does not get the aging process correct at all. This is due to, as we explained above, the misconception regarding the doppler effect, as well as the fact that multiple meanings of the term "seeing" and "observing" are being thrown around. When we receive light from the very distant universe, we know that what we are "seeing" happened a very long time ago, not at that very instant. Likewise, Terra should know that the light she receives from Stella represents a picture of an event whose occurrence must be ordered and placed in the past, yet the Ted-Ed video falsely implies that the frequency in which Terra receives Stella's messages corresponds to the time intervals on Stella's clock. If this were the case, then Terra would also see Stella traveling the entire return trip distance in a very very brief time, thereby implying that Stella was traveling FASTER than the speed of light! The important take away is that Terra observes Stella's clocks running slow the entire trip, and likewise Stella with Terra. The discrepancies in clock speeds occurs only at the turn-around.

[@LinkenCV]

Questions: 1) In a gravitational field, time flows more slowly. In the Twins paradox: dT`=dT*gamma. Why dT doesn`t changes in "accelerated field"? 2)2 frame of reference: a)gain of mass by you, b)gain of mass by Universe(except you). Curvature of space that makes accelerated whale is bigger than curvature of space by mosquito, therefore time dilations are different(but I saw a video showing symmetrical lines of space-time diagrams for twins) And "Oh boi, hold my beer" 3) Acceleration, increase in mass, the rate of change of the wave function of the object changes (the wave function depends on the energy/mass of the system). And in fact, the change in the wave function is time itself. So, Is there a solution to the twin paradox in terms of quantum mechanics?

[@doBobro]

Great series. It's a real shock to be unable to answer your questions on the basis of my current SR knowledge or a lack of it to be precise :)) One can say I had a shaky ground in the first place, but from my perspective it crumbles and cracks are everywhere.

[@MyName-gl1bs]

Great video series on the twin paradox...this one was tough to follow, though!

[@lifequake]

The symmetry is broken by the behavior of light for the two twins. Suppose the twin in the rocket has a laser beam pointing from the floor to the ceiling. When the twin in the rocket sees the earth accelerate back toward him, the laser beam will appear to curve. This twin can make one of two interpretations. He can retain the idea that light always moves in a straight path in an inertial reference frame and conclude that he is not in an inertial reference frame. Of course, this means motion is not completely relative as you point out in the video. Alternatively, he can assert that he is at rest but then he must reject the idea that light always moves in a straight path in an inertial reference frame. However, to reject this idea is to reject the theory of special relativity, and thus he cannot use the theory to conclude that his twin will age more slowly than him. Correct me if I am wrong, but I think there is a paradox only if we want to say that all motion is relative (including acceleration) and that the laws of physics are the same for all observers. As long as we say only that the laws of physics for the same for all observers moving at a constant velocity relative to each other, we will avoid contradictions. We can then say that our accepted laws of physics hold only for frames of references where the laws have simplest form. This is actually a way of defining an inertial reference frame without referring to constant velocity versus acceleration.

[@finbarcurtin6402]

That's interesting because Eistein's solution would say that the light is curving in the inertial frame of reference because of the presence of a gravitational field. But, as the video argues, that's an insufficient answer.

[@lifequake]

​@@finbarcurtin6402 I don't think light appears curved within an inertial reference frame (excluding the effects of electromagnetic forces). If you are in freefall in gravitational field with a beam of light, the light should appear straight to you (according to GR). Otherwise, you'd be able to tell whether you were in freefall as opposed to floating in empty space. If the twin wants to claim that gravity is causing the light to appear bent, then he would need to conclude that he is resisting freefall by accelerating (in the same sense that everyone on earth is accelerating upward through curved spacetime rather than freefalling toward its center). If the twin wants to assert that he is at rest, I don't think he has any other option then to come up with an alternative theory of light based on the idea that light travels in a curved path when observed within an inertial reference frame. This new theory would have its own version of the Lorentz transformations, and I expect those new transformations would make the same prediction as the twin on earth, that the twin on earth is older. Thus, no paradox. Different observations about who is moving combine with different laws about time dilation to result in the same conclusion about who is older.

[@corwin-7365]

The second viewpoint is General Relativity. Ie, all frames are relative but they differ in the amount that light bends.

[@lamcho00]

You are not considering extreme cases. For example imagine in the twin paradox when acceleration becomes too great of a force for a human to survive it. If the twin in the spaceship suddenly accelerates, he'll definitely feel the acceleration, the back of the ship would be crushing his bones. Now after the round trip is over only one of the twins will be dead. This example should show you where you are wrong and why both cases are not equivalent.

[@lamcho00]

@@narfwhals7843 if the only difference is acceleration, then I guess it answers the *why* question. Unless you can spot another difference?

[@lamcho00]

@@narfwhals7843 the easy answer here would be "because that's how the universe is". The longer one would be, it''s part of a theory and a mathematical model. That mathematical model is what all observations so far confirm. In order to move through space a force needs to be exchanged between 2 objects. This force is received in the form of acceleration. Once this acceleration is acquired, both bodies start moving through space in opposite directions but with different speeds (depending on their respective mass). The funny thing is once an object has experienced a force (received acceleration) and starts moving, that object does not only move through space but also through time. That's what Einstein figured out and that's what all observations confirm. In General Relativity this movement through time is called time-dilation. What it means is for objects which received acceleration, time flows slower (from the perspective of a stationary observer). Also time flows slower in gravitational fields. The stronger the gravitational force, the slower time flows.

[@wafikiri_]

The usual concept of motion, for reasons of analytic convenience in most situations, is that of a changing position of an object as observed from another object called frame of reference. But, when I was entering my teens, as I was analysing some classic paradoxes about motion, I came to another, equivalent concept: there is motion when the distance between two objects changes. According to the latter concept, no frame of reference is needed but at least two objects (e.g., two points) are. The twins paradox is a tale of a distance that first increases from zero, then decreases to zero, and none of the distance ends has any superior quality over the other. Therefore, both of the twins' clocks will agree and they will show no age difference.

[@wafikiri_]

While my above reasoning is valid without gravity, it is not when both distance ends are subject to different gravitational influence, which affects clocks as seen from each opposite end. However, just acceleration, or rate of change of distance, affects both ends equally and should, thus, be not considered.

[@pedrokrause7553]

So the minutephysics explanation is only wrong due to the fact that it doesn't mention that acceleration is absolute? Because in the video you stated that the rotation of planes of simultaneity is a valid solution.

[@dialectphilosophy]

You're correct yes. The rotation of planes of simultaneity determines the magnitude of the time gap between the twin's experiences, but until we know which twin is accelerating, we do not know which twin's planes of simultaneity are actually rotating, and thus who should should be aging slower/faster. We cover this in our video "Still Wrong".

[@stiffyvokes2404]

5:08 literally said out loud one second before that "how does it work?"

[@GumbyTheGreen1]

Maybe force itself isn't the agent of asymmetry - at least not directly. But it seems likely that force at least causes something to happen (like a rotation of an object's direction through time or something weird like that) that is the actual agent of asymmetry. Would you agree?

[@youtubebane7036]

Seems to me that the time I left for both twins would be the same because of the directions of travel. I would think that traveling away would be a different amount of time compared to traveling towards and they would equal out in the end. And doesn't the velocity account for the amount of time too even if it is a constant velocity? So basically it would be the acceleration or the bump or the jolt that caused the effect but why would one be more than the other if they are both at rest in their own framework?

[@hdthor]

What if both twins ARE in inertial frames? One twin can be in a circular orbit around a star and the second twin can be in a highly elliptic orbit around the star such that both orbits tangentially intersect. Since orbits are free-fall, then both twins are inertial. How does each view the other’s clock? My guess is the twin in “high orbit” (circular) will be younger than the twin in “low orbit” (elliptical and nears the star). Just like our GPS satellites around Earth grow younger by 1ns per 1s relative to us surface dwellers. But how does each twin know this? Wouldn’t each twin just think they’re following the geodesic in a curved spacetime and their geodesics merely intersect?

[@rclrd1]

Nobody is puzzled that two vehicles travelling from one event and meeting up at another event find they’ve travelled different *distances* if they took *different routes!* According to relativity the *time taken* for a journey, like the *distance travelled,* depends on the journey's trajectory. Why do people call that a "paradox" and make a ridiculous controversy out of it?

[@alansewell7810]

The idea, expressed in this video, is that the non-relativistic motion of the Earth and stars relative to each other determine that the twin in the fast-moving rocket is the one who moves at relativistic speeds relative to the rest of the Universe and therefore ages slowly, while the one who remains on Earth is non-relativistic and ages at normal speed. This is known as "Mach's Principle" after Ernst Mach of sound barrier fame. Mach lived contemporaneously with Einstein, and Einstein studied his work. Mach's idea, restated, is that relative to lightspeed, the bulk of the visible Universe is essentially at rest. Therefore, any object of mass near lightspeed is the exceptional object relative to the rest of the Universe and therefore is assigned the time dilation, whether it accelerates, changes direction, or remains in an inertial frame of constant velocity. I was assured in the comments with a physicist that the "Mach's Principle" is incorrect, even though it seems logical.

[@dialectphilosophy]

You're correct that Mach's Principle is highly relevant to the topics presented in this video. Einstein was a firm believer in Mach's Principle; upon one occasion he numbered it among the foundational pinnacles of General Relativity. However, there is much dispute over what exactly is the meaning of Mach's Principle, and the different ways it could be interpreted and defined might lead one to saying that it is either "correct" or "incorrect". We have eschewed treating it in our videos up to this point because of this ambiguity, but certainly it seems like a subject worthy of deeper examination.

[@robertmadeo7672]

@@dialectphilosophy Clearly, There is only one solution to the twin paradox. Your video outlines that solution. Mach and Einstein would have to be in complete agreement with you. Therefore, I would suggest that Einsteins' understanding of the English language and his translator's understanding of German have somehow muddled things. My understanding of Mach is that he always thought absolute space was impossible. Now, I am not sure this was really his viewpoint. Perhaps he only wanted to limit absolute space to a local star matrix (a billion light-years more or less.) Beyond this scale of interactions, other forces may become noticeable. Neither he nor Einstein have ever adequately explained these forces that create inertia. My understanding of the twin paradox would be explained as follows: Two assumptions are necessary: 1) light moves at a constant speed, 2) all communication between atomic particles requires the transmission of light. Now, a simple thought experiment can be performed. Imagine you are 8 light minutes away from earth. You take a picture of yourself using a camera with a flash function. As the flash occurs, you now ride one of the photons towards the earth (of course this would be physically impossible but this doesn't matter for our thought experiment.) It is you that is moving at the speed of light. All relatively stationary observers in your star matrix would agree that it is you that is moving at the speed of light. Observers on the earth will have to wait 8 minutes before seeing you, your camera, and your photograph. But what about you? Well, the atoms in your body, including your brain will arrive on earth at the same time as the photo. For you, time will have stopped during your journey. All electromagnetic communication energies of your atoms and molecules will be moving in the same direction that the photon is moving. Perhaps, if possible, you would instantaneously exist as a collection of photons. (I doubt everything can be reduced to photons.) However, in the real world, you could only approach the speed of light. As you approach light speed your mass would increase towards infinity and you may begin to drag your local star matrix behind you! I'm sure the intergalactic police (men in black?) would frown on your journey.

[@alansewell7810]

@@robertmadeo7672 Mass does not increase to infinity as you approach light speed, because an object's gravitational field is constant regardless of its velocity. Also bear in mind that if mass were relativistic, if you increased velocity, the rest of the University would increase velocity relative to you, and you would perceive bizarre gravitational effects from the Universe at large. Because gravity cannot vary, neither can mass. Each object has one and only one rest mass, regardless of its speed. What is changing is momentum; i.e. you are cutting through gamma-magnified lengths of space as your speed approaches light, so your momentum, not your mass changes. On to the main point: he breaking of the symmetry in the twins paradox is the absolute speed of each party. The party that sees the Universe thinner is the one whose time is running slower. I.e. if you're travelling at 87% light speed, the Universe appears half as thick, so it is your time that is running twice as slow as the non-relativistic objects. I believe Mach was correct (there are many interpretations of his informal theories) and that there is an absolute frame of reference relative to the bulk of the Universe.

[@robertmadeo7672]

@@alansewell7810 Way back in the dinosaur age when I first took physics, we identified relative mass (gamma)(m) or gamma time the rest-mass. It was explained that the particle or person or rocket would become too massive (fat?) to be accelerated to the speed of light. Anyway, even if relative mass exists, the object would probably be moving so fast that it wouldn't have time to attract anything. Also, relative mass, if it exists, probably doesn't have the same features as rest mass.

[@alansewell7810]

@@robertmadeo7672 I learned it that way too. The difference between mass and momentum in regard to relativity was not differentiated in those days. Don Lincoln, the head physicist at Fermi Lab, has a video called IS RELATIVISTIC MASS REAL? that explains the current thinking, which is that mass is constant, and momentum = gamma * mass * velocity.

[@synx6988]

Awesome stuff! Been binge watching all your stuff. I need a better case for acceleration not being absolute, as I am not 100% on board with that yet. Also I need to know what we meassure on "twin paradox clocks" in real experiments. Keep up the good work!

[@beamshooter]

There isn't a good case for non-absolute acceleration.

[@marshallsweatherhiking1820]

@@beamshooterMy understanding is that it’s the conservation principles that determine whether a reference frame is allowed to claim it is inertial (non-accelerating). So, a fre-falling frame of reference is inertial. The problem is it is only inertial locally. I.e you have to “zoom in” to the point where the source of the gravitational field as at an infinite distance. On the large scale though, the need to invent an infinitely massive object at an infinite distance to explain the uniform acceleration of a spaceship really doesn’t make sense, especially when in that same reference frame, any real propulsion mechanism would behave in a completely unphysical manner. I mean, normally for a ship to change direction it must eject part of its mass in the opposite direction. In the non-accelerated reference frame this ejected mass has no effect on the ship, which makes no sense.

[@markpmar0356]

Would it be impertinent to suggest that the alleged equivalence of the frames in the experiment is actually false?

[@CenturianCornelious]

"This circular reasoning is somewhat problematic." lol Ya think? AE didn't like the notion of absolute motion. Well, so what. True, everything he tells us is constructed around his personal ideological preference, but what he or anyone likes is irrelevant to what is.

[@Chicken_Little_Syndrome]

Circular reasoning is a sign that the idea is illogically premised. Einstein never describes the real Universe. He describes a brain-teasing fantasy that can never exist. Nikola Tesla was right.

[@FuriadeAquiles1]

The best video about this subject

[@hannutiihonen9175]

I hope my question is not too much off-topic. I have not read many articles (in fact only one), where the travelling twin tries to measure simultaneity this way: He sends a message to the earth at time t1 and then the earth twin sends a message back immediately where he tells what time the earth clock showed. The travelling twin gets the answer at time t2. Then he calculates: (t1+t2)/2 should be simultaneous to the time which earth twin told in the message. All these events during the outbound trip. Is this method generally accepted? It gives results which fit to the dime dilation which travelling twin gets using Lorentz factor. Travelling twin thinks that earth twin ages slower in the beginning of the journey. (The situation changes, if the travelling twin gets the answer during inbound trip. But my question is only about the outbound trip). This method seems so simple, almost too simple... For example: Speed 0.6c. Lorentz factor 1.25. Travelling twin sends a message when his clock shows time "one year". Earth twin gets it when earth clock shows time "two years" and sends a message containing this information immediately back. Travelling twin gets it when the spacecraft clock shows "four years". And he calculates (1+4)/2 = 2.5. His result is that spaceship's time 2.5 years is simultaneous with earth time 2 years. And it is the same result which you get using Lorentz factor. I draw a Minkowski-diagram (hope you can see it, there are a couple of finnish words also. Horizontal axis = lightyears, vertical = years). There are other similar messages drawn too. Dotted lines are calculated simultaneity lines 1.bp.blogspot.com/-c8R_3BDVVuk/X_xJ0hgUW6I/AAAAAAAAd_s/hcsojNQDV-sIpSTLhNCMKWygMesc0IJywCLcBGAsYHQ/s960/Minkowski4.png

[@hannutiihonen9175]

@silverrahul Thankyou. But I have an article, where a well known Finnish professor of cosmology uses this method. The purpose of the article is to explain the twin paradox as simply as possible. It is in Finnish, so I dont give it here. And the method seems to work when you test it with examples. But I was asking this, because I don't understand why I can't find this method elsewhere. Maybe bad googling? (I googled a lot) It resembles "Einstein synchronisation" ( Wikipedia says that "Its principal value is for clocks within a single inertial frame.") en.wikipedia.org/wiki/Einstein_synchronisation. And in my example it is used so, that the travelling twing supposes that he is stationary and earth is moving. Then, (by "normal" reasoning) you can think that light passes similar distance to both directions - first from spacecraft to earth and then from earth to spacecraft - because the message is sent IMMEDIATELY back. But I have become suspicious when I notice I am using "normal" reasoning when speaking about relativity... So I am hoping that somebody could give me more background information about this method, maybe a link to an example where it is used or something. I would be surprised, if it is totally wrong... ???!!!

[@hannutiihonen9175]

@silverrahul Well, maybe because of the relativity? You newer know how is really moving. And you can always think that the other is moving.

[@hannutiihonen9175]

@silverrahul I mean this: If you think that the earth is moving, the lenght of the trip which light signal travels to the point where it meets earth and then the other, back from that point of space to the spaceship is the same, even though distance to the earth is growing all the time, also after the moment when the light signal begins it's trip back.

[@hannutiihonen9175]

@silverrahul My problem is that I don't find that kind of explanation elsewhere. Why? I think it should be mentioned often, because it gives so handy and simple way to measure time dilation of earth twin, in the perspective of travelling twin. The link is here - but no images available. Maybe google translator can help :-) www.mv.helsinki.fi/home/enqvist/artikkeli.dir/kaksos.html

[@hannutiihonen9175]

Yes, I used the Lorentz formula backwads. But If I was the travelling twin, I don't need it. I know when I sent it (year one, spacecraft time) and when I got the answer (year four, spaceraft time). And if if there is information included in the answer: "I got your message when earth clock showed two years" it would be enough to calculate the simultaneity in a very simple way. This brings concreteness. The spacecraft twin has a "measurement" about the time dilation, not only formulae and theory. This answers me the question "Is the time dilation reciprocal REALLY". Yes it is in a way, at least you can measure it (I don't say more) But then, using same method, when beginning to return, the spacecraft twin notices that earth clock has gone much faster. The Earth clock takes even bigger lead than the result is. But then again, when the travelling twin sends more messages during the inbound trip, he notices, that earth clock goes slower, the lead diminishes a bit. Sum of all this is anyway, that earth twin is older. Now I have explained you the article, which I mentioned. BUT as I said, I am wondering, why this way to explain what happens, is so hard to find in the internet. It nags me. 1.bp.blogspot.com/-c8R_3BDVVuk/X_xJ0hgUW6I/AAAAAAAAd_s/hcsojNQDV-sIpSTLhNCMKWygMesc0IJywCLcBGAsYHQ/s960/Minkowski4.png

[@mikkel715]

If the one way speed of light is individual for direction. Will the Time Dilation be going up or down depending of direction compared to the Cosmic Background Radiation? And so needed to define a lowest possible time dilation...?

[@mikkel715]

@@narfwhals7843 Can you explain how Time Dilation shouldn't be per direction, if one way speed of light, changes per direction velocity relative to a reference frame with equal one ways light speeds in all directions. (For info, I'm not talking about a universal rest frame, at least not across the universe)

[@joeboxter3635]

Please explain what and how to covariantly extend SR!!!

[@dragoscoco2173]

My main problem is that there seems to exist a definite directionality to the time dilation effects or they are only apparent in relation to speed. Lets get gravity out of the way entirely and suppose two spaceships A and B with two clocks each sending a light pulse at each other every second. Both close and at rest to each other the pulses are synchronized. B accelerates in 1 second to 0.5c (so as to ignore any time spent in acceleration) and starts coasting. Each will find that the pulses from the other are slower then their clocks are measuring as light needs to travel more to reach them after each second. B decelerates to 0 in respect to A in 1 sec (so as to ignore any time spent in acceleration) and shortly accelerates in the other direction with 0.5c. The interesting thing is what happens when B decelerates and then accelerates back to the frequency of the pulses. It is clear that having zero speed means the pulses will be synchronized again respective to each clock. Then on the back journey the pulses will be faster than their clocks are measuring as light needs to travel less. In the end if they compare the number of pulses they might just find that they totally agree. Thus they are of the same age.

[@riverchess-so7pr]

" _B accelerates in 1 second to 0.5c (so as to ignore any time spent in acceleration) and starts coasting. Each will find that the pulses from the other are slower then their clocks are measuring as light needs to travel more to reach them after each second_ " it is not just slower because of the light travel time. it is also slower because of time dilation due to the relative speed of .5c " _In the end if they compare the number of pulses they might just find that they totally agree. Thus they are of the same age_ " NO. They will NOT totally agree on the number of pulses. The pulses sent by B will be less than the number of pulses sent by A , when they reunite and compare. Because, in A's frame, B's clocks tick slower during the outgoing stage AND during the return stage. i am assuming acceleration and deceleration by B is instantaneous. So, in the end, if A had t seconds elapsed on his clock , B will have a total of t/gamma seconds elapsed on his clock. hence, in the end, if A had sent n pulses, B will have sent n/gamma pulses.

[@Delibro]

9:50 This isn't cause and effect, both, acceleration and gravity are the same. So, no problem basing one on the other and vice versa. The whole video along: "All get the twin paradox wrong". At the end: "All are right at the twin paradox, BUT STILL IT IS SPECIAL RELATIVITY!!!" *stumps on ground

[@hemantjakhar8497]

Sir I have one more doubt... What about length of objects when seen from different frames... I mean will length of objects on earth for person in moving spacecraft will appear shorter or longer

[@dialectphilosophy]

For the constant velocity segments of the trip, each twin will see the other having a shorter length space-craft. At the turn around, if we can "objectively" say one twin is accelerating and not the other, than the accelerating twin will observe the inertial twin's clocks speed up and their lengths dilate, while the inertial twin will continue to observe the accelerating twin as having a shorter spacecraft.

[@prostytroll]

How about following observation. One year from my birthday the Earth will be in the same place relative to the Sun. If my twin rocket flying brother leaves the Earth on my birthday and returns exactly one year later (the Earth in the same place relative to the Sun) why could I be older than him? He returns to the same space-time as I am in after all, right?

[@SpokoSpoko]

What about if we have three siblings instead of twins? One stay on Earth and the other two travel opposite directions. If both of those who are in the rockets can claim that after passing return point they are stationary and Earth started to accelerate toward them, which direction is Earth actually moving? Right or left. Or maybe the space between the three objects starts to shrink?

[@adoion2421]

Post the next video man this is great, please. Of course spacetime is curved at the region of acceleration, acceleration applies an energy density and that curves spacetime. And one more thing, both twins need to agree how old they are after the trip even though the may be blind. Space twin may be in a coke can with no windows when he starts feeling a force from the floor of the rocket and then it will look like he is in uniform gravity field, that's what the equivalence principle says. The source of the gravity is, if space twin knows it or not, the burning fuel of the rocket or whatever accelerates it. So causality goes like, 1. Fuel Burns, 2. Coke can accelerates, 3. Spacetime is locally curved, 4. This should account for the twin being younger.

[@MrCmon113]

Yeah, I've spent some days procrastinating on this issue and the clearest account I can come up with is that the rockets thrust one twin into the future.

[@tudortolciu1396]

So basically, so called solutions of the Twin Paradox work in SR, because in SR acceleration is (correct me if I'm, wrong) absolute to spacetime and breaks the symmetry (basically one of the reasons Einstein was not happy with SR cause it didn't account for gravity). But in GR, the Twin Paradox remains a paradox. Right?

[@tudortolciu1396]

@silverrahul Ok so in GR, you have this "gravitational field" that breaks the symmetry, right.

[@nemvus_]

@@dialectphilosophy Great videos! Thank you so much for making them. I've been resisting this dogma for years because of its incoherence to me, and never got a proper answer from anyone. I'm happy you're making these videos. Excited to see your upcoming one.

[@mikegale9757]

This discussion thread went a bit astray of the premise. The Earth's gravity is incidental because it's constant for the bystander and negligible for the traveller. Anyway, you can easily formulate the problem with no gravitating bodies. I presume you were thinking of Einstein's attempt to break the symmetry with his equivalence principle. I think it's fair to say that he failed in that endeavour, which is the point Dialect is making in this video. It should have been obvious though because GR is indistinguishable from SR in the absence of gravitating bodies.

[@Fixundfertig1]

So help me understand, if you live in a planet with a gravity ten times the gravity of the earth, there you will age slowly? And what does that imply? For good measure let's say both planets share the same star as a source of energy, and that star will die eventually after a certain amount of time, how would agree the two different person about the lifespan of their star? 🤔

[@dialectphilosophy]

When we ask questions about age in relativity, we need to ask them as "aging relative to what/whom?" So if we have two observers on the surface of the same planet, they will both age at the same rates respective to one another, regardless of the gravity of the planet. Now if you go stand on a planet with much stronger gravity than earth, an observer on earth will see you aging much more slowly as a consequence of being deeper in a gravitational well. So yeah, if you want to live longer than your earth-counterparts, move to a planet with stronger gravity! (the greater stress on your body caused by the stronger force of gravity however might counteract the life-extending effect of the time dilation, though 🤔)

[@Fixundfertig1]

@@dialectphilosophy Thank you for your answer, I highly appreciated. In my opinion, that's a nutty field, that I have never seen tacked in any video of this community. I wasn't asking for a formula to live longer, lol, I just was curios on how time (s) work. Apparently in relativity, we can calculate many different times, if the person or the object is subject to different conditions e.g different gravity, velocity, acceleration, whatever. My problem here is that we humans aren't familiar with this "new" concept of time(s), for millennia we took Time as an absolute concept, based on events that we can agree on, e.g a sunset, a full moon, an equinox, those sorta things. So those hypothetical planets, with highly different gravity are gonna have a discrepancy in the relativistic time, but on another note, if they're on the same stellar system, and they can notice events happening to their star, they're gonna agreed on the time when those events happened, so they're gonna share some sort of "shared/absolute" time, aren't they? How can we reconcile that? I've seen videos stating that the moment "now" doesn't exist because universally speaking we can't agree on but, I can't tolerate that notion, the fact that we can't agree on, doesn't imply that it doesn't exist. Everyone is talking about the relativistic time(s), and how mind-blowing is(are), but no one talk about our traditional "universal" time, and how it's set in this new theory of relativity, has still his place to exist? It should, I mean, things move, at least we perceive it that way.

[@dialectphilosophy]

@@Fixundfertig1 We agree. We think there's something fundamentally askew with the notion of relativity of simultaneity. Stay tuned to the channel for the next few months, because we're tackling those exact topics.

[@Fixundfertig1]

@@dialectphilosophy Damn, you already did some videos about it. They're so good, and you talk exactly about what I was thinking. The discrepancies between observers might be like the discrepancies we have while viewing sheer reality in our planet thus, no one can see true lengths, the idea of true length it's just an abstraction we can make by using projection and geometry. I'm waiting for more, thank you again.

[@bhekigin]

An accelarating Mass induces a gravitational field (waves) and visa versa i.e gravitational waves induces acceralation of mass (objects). This means movement from rest a gravitational fuction and all kinetic energy draw from gravitational wave energy. Force is a gravitational wave potential difference.

[@jan_kisan]

and what if there are three twins, one staying on the Earth and the other two going opposite directions and then returning? would the travellers age at the same rate? and consequently, if there are only two twins but they both travel opposite directions with same speeds and accelerations, would they be of the same age upon return?

[@er-klartmathnat794]

Yes.

[@Robinson8491]

I feel the (relative) explanation here given by Einstein is one of perspectives and making them mutually agree, however the actual measurability of differences in clocks at earth (where the *actual* gravity is) is metaphysically ontological (as it is not merely a perspective, but actually measurable). So operationalism (which deals with observables) actually agrees with actual time dilation at earth compared to the experience of the pilot flying away, even though they are obviously mutually inclusive / in agreement as this logically necessarily must per the law of non-contradiction As an underlying argument for this: time in flat spacetime is constant with lightspeed, so it cannot actually move faster than in flat spacetime as would be the case according to you from the viewpoint from the pilot looking at the time elapsing at earth: it would exceed the lightspeed logic of time, which is the natural limit of reality

[@abhilashassariparambilraja2534]

Sir🙏, what about Grand father paradox, please 🙏 give us a clarification 🙏

[@TheZorbeck]

It is very interesting but I still have doubts, related to the equivallence principle, which seems to misbehave. The best way to express this is by a thought experiment. Imagine that the twin traveller travels with a constant acceleration, say 1 g, during the entire trip, or nearly so ( more on this soon), which after a few weeks will lead him to relativistic speeds and consequently with time dilation effects (with each twin claiming he is older as seen from his own reference frame, using the full blown relativity principle). This also means that there will be no difference on the forces acting on them for a very high proportion of the journey's duration. The only difference between the two situations will be, during a relatively short amount of time, an acceleration bigger than g to leave earth's gravitationnal field, later to decelerate (-g) and turn around (+g), and finally approaching earth, with the added event that twice during the entire trip the travelling twin will see up becoming down (once before return point, and another time when decelerating to earth, but we can stretch the experiment a bit by pretending it happened unnoticed during sleep to make the argument realistic :-). Now on what ground can one of the twin claim he is older ? To me the paradox is not solved yet. The only explanation that helps to resolve the paradox, as far as I can guess, relates to geodesics and proper time. But the equivallence principle raises questions...

[@robertmadeo7672]

Think of a star matrix (one billion lightyears in diameter more or less.) Within this space/time frame we find the absolute speed of light. When an object is seen to move in this reference frame close to the speed of light, time dilation occurs. Relatively slow-moving stars and planets may be considered to be motionless. Time dilation only occurs for objects actually moving near the speed of light. The earth is always considered to be motionless. Also, as a spaceship approaches the actual speed of light, its mass approaches infinity. Look out! Here come the intergalactic police (men in black?) They don't like your massive spaceship dragging your star matrix behind it!

[@Josiejen9]

I believe there's a relatively simple and "correct" solution to the Twin Paradox. Travel through Spacetime is always at "c" for everything. If you are stationary in space, you travel at the maximum rate through time. And if you move through space at "c", no time elapses at all. Whatever combination of movement through space and flow of time, the sum of both is always "c", for everything. It is also crucial to remember the classic twin paradox begins and ends at Earth. We know from Special Relativity that In any inertial frame, you will always measure the speed of light at "c", and the frame from which you measure "c" is itself at rest, zero x "c" (stationary). Given the twins both start in an inertial frame (Earth) at zero velocity, Earth twin stays at zero x "c" the whole time, where time flows at its fastest rate (zero travel through Space = maximum travel through time). In comparison, Spaceship twin accelerates through space at some portion of "c". It doesn't matter if some portions are acceleration, constant velocity, deceleration or turnaround. While spaceship twin moves at any speed through space (relative to the starting inertial frame), time will flow more slowly for him (travel through space = reduced travel through time). This is why Earth twin is older and Spaceship twin is younger. It is irrefutable and the correct answer. Bear in mind speed / velocity is relative. The classic twin paradox begins with both twins on Earth. RELATIVE TO EACH OTHER, Earth twin does remain in the stationary inertial frame (max flow of time), and Spaceship twin does travel through space (reduced flow of time). Earth twin is therefore always older. Given the above, does Spaceship twin have the same right to consider himself stationary ? Only with respect to his Spaceship, and all that means is he and the spaceship will experience identical flow of time. But relative to Earth twin, he CANNOT claim to be stationary. He is not in the starting inertial frame (from where "c" was measured) the whole time. We know this, because he accelerates, has some period of constant velocity, decelerates, turns around, accelerates, has another period of constant velocity and finally decelerates to end up back on Earth. He will NOT be able to measure the speed of light as "c" constantly throughout his entire return journey. Even the periods of constant velocity are movement through space (relative to the Earth's inertial frame). Relative to the Earth, he has moved through space and thus experienced less time. This is the correct answer.

[@PADARM]

Exactly, this is the "solution", because there was never a Paradox to begin with! One twin is in a INERTIAL-frame of reference and he never feels any force, in the other hand the twin on the ship is not only in one NON-inertial frame of reference, but in two NON-inertial frame.

[@markrichards5630]

@@PADARM Aren't there actually 4 non-inertial frames of ref? (1) Accelerating up to .5 C, (2)decelerating for the turn, (3) accelerating back up to .5C and then (4) the deceleration to compare clocks.

[@PADARM]

@@markrichards5630 yes, you are right

[@alwaysdisputin9930]

_"He will NOT be able to measure the speed of light as "c" constantly throughout his entire return journey. "_ This bit must be wrong because every teacher says: in a vacuum, EM radiation travels at speed, c for everyone regardless of how they're moving, if they're stationary, or accelerating or braking or whatever it's always the same speed = 300 million m/s

[@TheHesseJames]

You always are travelling through time at the speed of c within your frame of reference. All other frames of reference also are travelling through time at the speed of c. Only when the start to observe each other they realize that there is a difference between their own "c" and the "c" of the object they observe.

[@alchemy1]

[First thing first; what does the term relativity mean in the first place? It means if I am going close to speed of light, you are going close to speed of light. That is what it means.] The problem with this whole relativity thing is as deep as it is wide as they say. Relativity says the following and see if you catch what is wrong here: 1. A stationary object moves in time only. 2. A moving object trades some of that time to move in space. So he moves less in time. 3. In empty space you can never know if you are moving or stationary in the first place. 4. Given two frames (two objects), neither can tell who is moving and who is not. Both see the other moving and it is stationary. 5. There is no absolute frames, meaning there are no stationary objecst in the universe in the first place. 6. In relativistic speed objects are not considered solid. All parts of the objects are all responding at different interval of time. Like traffic jam on the highway. The front car moves and it transfers slowely until the very back car moves, also when the front car stop until the back car stops. It does't happen at the same time. i.e. an object is a frame in motion... that is where the term frame comes from. Put all that together and in your mind's eye see if you can tell what is going on. It is a mess ======================================================================= 1. Forget the Earth and some other planet distraction. You have two objects in empty space. If the distance between the two does not change, it means two things. A. Both moving in the same direction with the same speed. B. They are both stationary. So this means both situations are the same. So neither can tell if they are stationary or if they are moving. Because it could be either one of the two situation. 2. If the two objects distance increase, each object sees itself stationay and the other moving away. If their distance decrease, each sees itself stationary and the other moving towards it. IN OTHER WORDS EACH SEES THE OTHER HAVING TURNED AROUND. 3. The instant distance increase between the objects, that is acceleration. Each sees the other having accelerated away. Coordinate acceleration is relative. Proper acceleration, the force that an accelerating object undergoes is not relative. This does not have any outward effect. Outwardly it becomes coordinate acceleration. This means each can claim the other accelerated. [So-called proper acceleration, applied force on the object does not change its atomic resonant frequency aside from the fact that the measurement is objective, outward that is, which makes the whole thing relative and therefore symmetrical] ============================================================================================= Everything about relativity is a hypothesis, none of it has been proven. It is all a conjucture. The Satellite examples and the muons are not the letter of relativity. What they describe is something other. They don't reflect the actual relativity as taught and what it says in the first place. Muons also see Earth's time dilated, that is relativity. The satellite clock business is not relative to some other clocks. The clocks,,, any and all of them are measured with respect to "at rest frame'", The center the core of the Earth. The core of the earth does not move. The satellites move round and around the center. It is not measured against other clocks. All clocks, the surface on Earth are also measured with respect to this at rest frame. The earth itself moves around this rest center. It is a local rest frame, the center of gravity. The solar system also have "at rest frame" too. It is called the Barycenter, center of mass/gravity of the solar system. This center is used to observe astronomical objects. ================================================================= It is not relativity as you might think.

[@miciglaric]

Twin paradox will only occur if Twins are measuring time with double mirror clock in which light beam is reflected. If they measure time with mechanical clock time will be the same for both twins. With mirror clock after they meet again they can know which one was moving.

[@riverchess-so7pr]

With ANY clock whatsoever, after they meet again, they can know which one was moving. the type of clock does not matter. whether you use mechanical clocks, or atomic clocks or light clocks , that wont change the result. Time dilation changes the flow of time itself, not just the ticking of particular clocks.

[@jacoblloydpaul4853]

It is claimed that the Atomic clocks kept in higher altitude ticks slightly slower compared to atomic clocks kept on the earth's surface.Does it conforms Einstein's gravity explanation for twins paradox?

[@SaintLucifer66]

Ánd when is the motion both constant in some orbital path? then wath?

[@dialectphilosophy]

If both twins are in orbital paths you have to compare the lengths of the spacetime paths they travel. We cover this in our "Twin Paradox in Curved Spacetime" video.

[@fkeyvan]

Thank you. This is incredible.

[@volbla]

10:57 After spending several videos dismissing the notion of absolute acceleration, didn't you just confirm its validity? One twin will observe a ficticious gravitational field. The other twin will not. The one that does is accelerating. The one that doesn't is not accelerating. This is an objective difference that both twins will agree on. This does break the symmetry and resolves the paradox. Well, it in principle resolves the paradox. My issue with various solutions is that no one brings up how to distinguish between accelerating and inertial frames in special relativity. If that distinction can't be made in SR then this is indeed a GR problem, but then all these explanations are still wrong in claiming the paradox can be resolved entirely in SR.

[@stewiesaidthat]

You can solve the paradox when you realize that time is absolute. One doesn't age less just because they travel faster. SR has never been proven and it is easy to distinguish which object is traveling faster simply by comparing the readouts of synchronized clocks. Or, you can just measure your speed against the speed of light. These videos are trying to make mountains out of molehill because they don't understand basic physics and just regurgitate what is written in 'books'.

[@volbla]

@@stewiesaidthat By "books" do you mean all of physics research in the last century?

[@stewiesaidthat]

@Volbla anything doing with Einstein and his relativity theories for sure. Any books that can't distinguish between animal, mineral, and vegetable. The laws of physics are the same. They are just not being properly applied. You can't equate what happens with clocks when the forces acting on it change and apply it to all objects in the room. Shine a light on a plant and it will grow. A clock or animal doesn't care if it's day or night out. Their 'acceleration' rate is dependent on other factors.

[@volbla]

@@stewiesaidthat Ok. Good luck with that.

[@dialectphilosophy]

You're absolutely right that in special relativity how to distinguish between inertial frames and acceleration is left completely unspecified! (We've made whole videos about that, nice to hear someone else say it) But no, we're not confirming the validity of absolute acceleration here, because what defines the fictitious gravitational field is exactly acceleration. So if you are asserting that fictitious gravitational fields break the symmetry, this is the same thing as asserting that acceleration breaks the symmetry. In fact, if you think about it, what "really" seems to define the fictitious gravitational field is that all nearby objects are in accelerative motion relative to you. But this definition couldn't be universal, since a neutral object in a sea of accelerating charged objects would thereby see a gravitational field and thus perceive itself to be non-inertial.

[@elio7610]

I don't see how the explanation given here is any more clear than everyone else's explanations.

[@hemagicmp2773]

thanks for the video....I've been stuck on this paradox for years and everyone seems to be so sure they have the answer but everyone of them is different lol...

[@dialectphilosophy]

You're welcome! Everyone has different answers because no one really understands the problem very well 🤷

[@joeo3377]

@@dialectphilosophy I suspect that everyone has the same answer, but they just have different ways of communicating it. We all agree that the space-time path of the twin who does not stay on Earth is the cause of the age difference, and that to achieve that path, there must be acceleration. It's just a question of how to explain that while also (1) discussing the important features and (2) remaining accessible to people who haven't taken a course in physics. Different people have different approaches to satisfying that. It doesn't make them wrong. Let's be honest, it's a problem that's over 100 years old with a solution that's not difficult if you've studied the material. Do you really think that everybody else has it wrong?

[@dialectphilosophy]

@@joeo3377 You can watch several of the most popular videos on KZbin and discover flaws in each. The Ted-Ed Amber Stuver video, despite the obvious professional level of time and money that went into the video, makes the rookie mistake of conflating time dilation with the Doppler effect - a horrifying thing to consider when you realize it has almost four million views! A large number of even professional physicists confuse many of basic tenets of relativity, so yes, the problem is not well understood. The philosophy and paradoxes of motion have been debated for over two millennia. Do you really think they were solved in one fell swoop by special relativity? Not even Einstein thought so. The current models are incomplete and offer no mechanism by which to determine or define absolute acceleration. It may not be the most pressing epistemological issues facing physics, but it’s certainly there.

[@joeo3377]

@@dialectphilosophy I suggest that you rewatch the Ted-Ed Amber Stuver video, because it does not conflate time dilation with the Doppler effect. It's not something I had watched before, so I just watched it now. The video does make use of the Doppler effect to explain what the twins observe, and does so accurately, but it does not state that the Doppler effect is responsible for time dilation. When you talk about the philosophy and paradoxes of motion being debated for over two millennia, I assume you are talking about Zeno's paradoxes. To answer your question, no I don't believe that Zeno's paradoxes were solved in one fell swoop by relativity. Quite the contrary, I believe Zeno's paradoxes were solved centuries earlier, with the advent of calculus and a rigorous understanding of limits. But even after Zeno's paradoxes were resolved, there were certainly questions that remained about motion. Newton had in his mind an idea of "absolute" motion-motion relative to the "fixed stars"-which was in some ways an answer to the question of Galilean relativity. But we now know that there is no such concept, and that all inertial frames have just as much claim to be "at rest". Coming back to your question about "absolute acceleration", I direct you the the Ted-Ed Amber Stuver video, which very succinctly states: "But when Stella changed direction for her return journey, she entered a different reference frame from the one she started in". There is an objective difference between the two frames of reference for the outward and inbound trips. Because inertial frames are relative, differences between frames are objective. If I measure two objects to be in relative motion (for example, a person walking on a train is in relative motion with the train), then every other observer will also measure those two objects to be in relative motion (although different observers might find the different velocities to be different because relativistic velocity is not strictly additive). But, because we can all agree that different reference frames are in fact different, we can all agree that the Earth-bound twin remains in one reference frame, while the space-bound twin occupies two different reference frames. The only way for this to happen is for the space-bound twin to change reference frames at some point in their journey. We can define this as acceleration.

[@dialectphilosophy]

​@@joeo3377 We suggest you rewatch the Ted-Ed video more closely, particularly around the 4:45 mark. There is a misleading statement made there. If you cannot figure what is incorrect about it, let us know, we can happily explain it to you. We also suggest you watch our other videos, particularly "Do Inertial Frames Resolve the Twin Paradox" if you think we are somehow not aware of the equally problematic idea of defining acceleration through the "changing frames" idea. (Short version: it's circular, since an inertial frame has to be defined through the absence of acceleration.) We've had some of these videos up for two years, and nobody has yet to present a definition of "absolute acceleration" that somehow transcends the relative construct of measurement. (But good luck if you'd like to try.) Ultimately we refer you to our Einstein quote from this video, in which he asserts that, to the consistently-thinking man, the idea of absolute motion makes no sense. So maybe try thinking consistently.

[@stevewhitt9109]

I have always said that symmetry is broken when the moving twin accelerates. In any event we can always see which twin ages. This experiment has been proven decades ago. People would rather argue the theory than accept the facts that have been proven.

[@gravitationalvelocity1905]

@@narfwhals7843 it is not acceleration per se, rather it is being in multiple reference frames. The acceleration is just the means by which the reference frame is changed. To actually calculate the net time change you just need to know the velocity and duration of the two difference reference frames.

[@imaginingPhysics]

I would love to see a video about rotating frames and the Ehrenfest paradox!

[@HuxleysShaggyDog]

Why doesn't a co-moving frame explain this? What about if one uses that and the fact that the accelerating rocket is doing work, spending energy, and for that matter ejecting remass?

[@dialectphilosophy]

In the question of dynamics, one should remember that quantities like energy & work, even if they are assumed to be absolute, are still defined through space, time, and motion, which are all relative. So for instance, to determine energy we have to determine a force applied across a distance, meaning we have to determine first an acceleration which determines the force. The question then become what exactly this acceleration is relative to.

[@HuxleysShaggyDog]

@@dialectphilosophy For the majority of rockets, the rocket's remass flying out of the rear end of the rocket should make things obvious. A comoving frame that has the space ships, earth, moon and any remass coming out of either space ships (or for that matter the planet or moon!) seems sufficient. Is there some very subtle thing I'm missing? In the arguably pathological case of a photon rocket, wouldn't there be an immensely powerful electromagnetic field at the rear end of the rocket, and not at the rear end of the other space ship or celestial objects? You would at the very least be able to observe the rocket heating up.

[@nsfeliz7825]

ok. so why not perform a bunch of experiments to resolve the paradox? too much mathematics confuses 5he issue. the final arbiter is a physical experiment. can it be done on a particle accelerator or a space craft?

[@zvikabar-kochva3641]

I don't understand why the space twin feels force only on the far side of his yrip. Surely, he must feel it outgoing as well. After all, in the beggining of his space trip, he accelerate from 0 to substantial part of the velocity of light. Therefore, he must experince fake gravity twice. On the other hand, this does not happen to the earthbound twin. This is observer independent because accelerated motion, which is csused by a external force, can be measured locally objectively. This means that accelerated motion, caused by an external force should be recognized by all obsevers, i.e., it's an absolute phenomenon, despite the calims of the GR theory. Cotrect?

[@williamwalker39]

The Twin paradox is even more fundamental if only velocities, and no acceleration is involved. Two inertial observers will observe each others space contracting and time dilating, which is a contradiction. Hence the effects of Special Relativity are just an optical illusion. Time space just appear to be flexible, but they are not. Any theory based on Special Relativity, such as General Relativity, must also have the same problem. A more detailed proof is possible, based on experimental evidence. Measurement of the propagation delay between two dipole antennas as the antennas are moved from the nearfield to farfield show that radio waves (light) propagates instantaneously near the source and reduces to the speed of light in the farfield after about 1 wavelength. This corresponds to both the phase and group speed, and the also the information speed. This result is completely incompatible with Relativity. It can be shown that instantaneous nearfield light yields Galilean transformations. So time and space for moving inertial bodies can appear to change using farfield light, but using instantaneous nearfield light will show time and space have not changed. So the effects of Relativity including General Relativity are an optical illusion. Galilean Relativity is the true theory of Relativity where time and space are absolute. So if General Relativity is wrong, what would be a better theory of gravity? General Relativity is known to reduce to Gravitoelectromagnetism for weak gravitational fields, which is all that we observe, so Gravitoelectromagnetism should replace General Relativity since predicts all observed gravitational effects. Particularly important is that Gravitoelectromagnetism is a field theory and can be quantized (graviton) enabling the unification of gravity and Quantum Mechanics. Currently the Copenhagen interpretation is the most accepted interpretation of Quantum Mechanics, which assumes particles are not real until observed. Where as the Pilot Wave interpretation assumes particles are always real, with real positions, and velocities, and are guided by a real pilot wave that acts instantaneously across space with other particles. It is not compatible with Relativity, but is compatible with Galilean Relativity, making it now the preferred interpretation of Quantum Mechanics given the results presented in this post. For more information see my short KZbin presentation and the paper it is based on. William D. Walker and Dag Stranneby, A New Interpretation of Relativity, 2023. kzbin.info/www/bejne/qZazlX1tq7iErLM

[@BuleriaChk]

The correct analysis is that space (x = vt) is not included in the equation to be solved for the "time dilation" equation. (ct')^2 = (ct)^2 + (vt')^2 (solve it for t' for yourselve(s) to understand) and note that this equation cannot be generated from the "space" equation for length in first order (ct') = (ct) + (vt') (draw it on a piece of paper). Hint: If space doesn't exist, the twins don't go anywhere; one of them (the imaginary one) just gets fat in his/her imagination (t'). Which is why Hawking hints that time must be imaginary, but never says why. "Yesterday upon the stair I saw a man who wasn't there He wasn't there again today Oh, how I with he'd go away" - Ogden Nash That is, Fermat's Last Theorem is valid for the case n=2 for all positive real numbers c^2 a^2 + b^2 since in second order (I repeat, sigh. ad infinitum, ad nauseam) c= a + b c^2 = [a^2 + b^2] + [2ab] (Binomial Expansion, proved by Newton) [a^2 + b^2] (why) figure it out and you will be enlightened....😎

[@stewiesaidthat]

(t) is just the measurement of acceleration. Space and Time are separate frames of reference. Clocks measure motion in Space. All this talk of time-dilation by traveling faster in space is flat earth nonsense. Real time-dilation stems from an energy variance. An embryo takes longer to hatch out when the mother hen can't generate enough radiant energy. Seeds take longer to germinate in cold soils. Plants take longer to reach physiological maturity the farther north they are located. E=mc. Energy equals Time and since clocks in motion use the same amount of energy (operating frequency), they experience the same amount of runtime. Einstein couldn't understand a lot of things because he plagiarized most everything and what he is known, he didn't understand even that. The speed of light being the absolute fastest anything can travel and being the same for all observers make it an absolute reference marker to measure all other motion against. Einstein didn't understand that the speed of light might be constant but it's frequency (force) changes in respect to one's motion in space. But what do you expect from someone with an IQ of 20?

[@BuleriaChk]

@@stewiesaidthat Einstein says space and time are orthogonal, but one can only get his equations if time (or spacea0 is imaginary. And if there are no negtive nymbers, there are no square r rots of negative number. There are two equations of a line: 1. x = vt 2. y = Ax + b b is the "constant of integration" which somehow disappears with the derivative The solution is to make y imaginary. And if you believe that I have some great beachfromt property in Florida I will sell cheap for a great profit for you. The "spacetime" diagram is gobbletigook in physics. Much more to this story but I don't have the spacetime to write it here.

[@stewiesaidthat]

@@BuleriaChk Newton's Law of Motion, F=ma, says space (mass) and Time (Acceleration) are separate frames of reference. Each operate independently of the other but within the same postulates of physics. That the laws of physics are equally applicable in ALL frames of reference. So if Force equals Acceleration in the Space frame, then Force equals Acceleration in the Time frame. What Einstein did was confuse Acceleration in Space (change in spatial coordinates) with Acceleration in Time (change in atomic structure). Mechanical clocks don't measure change in atomic structure (radioactive decay). They measure motion in space. So when dreamt up his fantasy universe, he misconstrued acceleration in space (change in one's location within the information stream), with acceleration in Time (biological processes). When the atomic clock came along, his minions misconstrued what the device was telling them. Why is clock's atom being chilled to absolute zero? Why is it being shielded from UV rays? Are the observers afforded the same treatment? What could possibly lead people to believe that they were even in the same Time frame of reference as the clock. You don't put a banana in the freezer and then say, since the banana doesn't age, neither does the observer. I don't know if physicists are just inherently stupid or are playing mind games with the ignorant. This comes directly from NASA. What would a 100 pound person weigh on Mars? Gravity on Mars is about one-third of the gravity on Earth. If you weigh 100 pounds on Earth, you would weigh 38 pounds on Mars. Einstein himself said that gravity comes from Acceleration. Mars Acceleration factor is 97% of Earth's 1480 minutes to complete one revolution vs 1440 for Earth. A 100# person would weigh 97 pounds. Either Nasa is lying or Einstein is. They can't both be right. Galileo proved that gravity is not a fundamental force of nature which is why Einstein resorted to having mass warp space to get his flat earth physics to work. But as any intelligent physicist woukd know, The Laws of Physics are Equally Applicable in ALL frames of Reference. The Earth spinning on its axis is no different than a merry-go-round spinning on its. Both are accelerating their mass outward and forward creating curved space. Mass doesn't warp space. Doesn't doesn't create gravity. Mass doesn't slow down time. Mass doesn't do anything but take up space. F=ma. Mass is not an actionable Force. E=mc. Acceleration creates mass. Not the other way around. That's why Tesla labeled Relativity mathematical nonsense making people blind to its errors. F=ma. Acceleration is the actionable force. Acceleration creates gravity. A person accelerating in space is also being accelerated in time due to the accelerating force being applied to their frame of reference. Physics is twisted up in a knot, it's going to take a generation or two to untangle it. How do you accomplish that? The Church of Relativity isn't going to admit they worship false gods. Time doesn't slow down with increased motion in space. It actually speeds up. Mass comes from Acceleration, it doesn't create acceleration. Take everything the Church of Relativity is preaching, flip it 180 degrees and you have reality. You don't have to jump through hoops to get the model to fit the data. The only piece of the puzzle that is missing is if Acceleration = Acceleration, where did the initial accelerating event originate from? Religion says god and scientists say the BB. Take your pick. Since we exist inside the universe, we will never know how the universe came about.

[@BuleriaChk]

@@stewiesaidthat Pythagoras was wrong. Therefore, so are vectors.

[@stewiesaidthat]

@BuleriaChk what I don't understand is why everyone trots out their spacetime diagram tinkertoy to try and bamboozle people with a bunch of mathematical nonsense. E=mc. That's all you need to understand to resolve the paradox. Energy can be neither created nor destroyed, only transformed. And what transforms it? Acceleration. And what constitutes Acceleration? Time. So E=mc where mass is atomic energy having an Acceleration value < (c) and (c) is radiant energy having an Acceleration value of (c). (c) being the Speed of Light with speed being distance/time so E=mc resolves to E=t or Energy equals Time. Synchronized clocks. Both use the same amount of energy as the both have the same operating frequency. Clocks are instruments that measure motion in space with Space and Time being separate frames of reference. What are the 'age' differences of the twins? From the limited data given, the only correct answer is that both twins are the same age, one just experienced more space as noted by the clock with the lower readout. Force decreases with distance. Less force equals fewer clock cycles. The fewer clock cycles is the result of the photon having to travel a greater distance to reach its target and register a cycle. There are 'age' differences as each twin experiences different forces but to correctly calculate them, would need to know the Force(Energy) values for the Time frame of reference. The stationary twin is assumed to be in a constant 1g environment. How much time above and below 1g did the traveling twin spend? How much cosmic radiation was the traveling twin exposed to. What are the heartbeat differences? Surmise it to say that you need to understand biological processes if you are going to introduce biological entities into your sandbox.

[@eliteteamkiller319]

I wrote this long blurb below showing how IF we assume Bob is traveling to a star, the math works fine without involved acceleration, reference frame changes, OR gravity, and there is no paradox. However, I glossed over the fact that Bob can say Alice and Earth flew off to some region in space, which would mean we could do the exact same calculations and end up with the opposite results. _The Twin Paradox is subtle...._ That said, the solution is still easy: Bob is the one who fired his rocket. We know that creates a force, and we can try to get all Mach all day, we know Newton's Third Law is true. While either one can claim to be at rest, only one felt a force (measurable by an accelerometer), therefore the paradox is solved. Not sure why that isn't good enough for any situation that resembles reality. Sure, if they are featureless points, you'd have a point. *Regardless, when we're talking about spacetime, time, space, and all the things you derive from it, only ONE thing is actually invariant, and that is the SPACETIME INTERVAL. **_That_** is what is key. Whoever travels the longest distance through spacetime is the older twin.* . . Original post: I mean taking into account length contraction, the finite speed of light, and the Doppler effect shows the same slowing and then fast aging of Earth on the return trip from the ship. And it exactly balances to get the right ages when the distance between the clocks is zero (but at other points they will not match). Don't need to calculate accelerations, gravity, or anything else for this to work. Alice and Bob as usual. Bob wants to travel to a star 6 light years away. After slowly accelerating around the planet to get up to 0.6c, he'll head over (as he passes the Earth when the origins coincide and they give each other a high five, they set their clocks to zero; in fact to avoid the relativity of simultaneity, the high five is the very event that sets their clocks to zero). Per length contraction, the distance for Bob is 4.8 cy. Thus the trip to the star takes 8 years to Bob (4.8/0.6). But Alice calculates that the trip will take 10 years (6/0.6). The "paradox" resolves itself by just taking note of what they see (assuming they have the means to see that far). Alice will not SEE Bob reaching the star until 16 years have passed, even though she'll _calculate_ 10 years, because of the signal time for light (Bob takes 10 years to get there, and then it takes 6 years for that light to get back to Earth). That means that Alice will see Bob's clock running at half the speed of her own clock (8 years measured by Bob/16 years seen by Alice). However, when Bob reaches the star and his clock says 8 years have passed, when he looks at Alice's clock, he sees her clock as it was 6 years ago. Or at what her clock read four years (10 years - 6 years). Therefore to him, he sees _her_ clock as moving at half the rate of his own clock (4 years/8 years). _So both see the other as having a clock running at half the speed of their own on the way there._ So, on the way back according to Alice, since from what she sees at the midpoint of the trip 16 years have passed, and because calculation before Bob left showed the trip will take a total of 20 years, she will see Bob come back to Earth in only 4 years (16 + 4 = 20). Moreover, Alice knows Bob's trip must take 16 years according to his own clock (because the trip to the star takes 8 for his clock, 4.8 cy/0.6c, and 8 + 8 = 16). Which means because Alice will see Bob make the six light year journey in only four years, which _should_ take 8 years to _him,_ Alice will see Bob's clock tick at _twice_ the speed of her clock on the way back (8/4). Likewise, back to Bob. Remember, at the star, he sees Alice's clock as it was when it read four years. And from her perspective, the whole trip will take 20 years. So on the way back he will see her clock read 16 years passing, while his will only read 8 passing (20-4 = 16). So once again, Bob will _also_ see Alice's clock tick twice as fast as his (16/8). *So they BOTH see the other's clock tick half as fast as the other on the way there, and they BOTH see the other's clock tick twice as fast on the way back. However, in the end, both will agree that Bob experienced 16 years and Alice experienced 20.* There is no need to bring up either acceleration _or_gravity. All you have to do is take note that the distance is contracted for Bob.

[@dexter8705]

So even if you get bumped into space like a baseball bat hitting a baseball and instantly back in an inertial reference frame. It's not physically possible ATM but theoretically it is and proves acceleration doesn't resolve the paradox, there is no time dilation, gravity stretch's space towards the mass which is the flaw with atomic clocks on satellites because they're more proned to movement unlike ones bolted to the ground. But just because a transmission is stretched taking more time doesn't mean atomic processes are slowed down..

[@kylorenkardashian79]

simple thought experiment: twin A is on earth, Twin B is traveling half the speed of light.. What would a theoretical phone call sound like like between the two? which twin if any would be talking in slow motion? **I understand half the speed of light is faster than the speed of sound. that's why I said theoretical

[@kylorenkardashian79]

@silverrahul that gives me alot to contemplate, thank you

[@kylorenkardashian79]

@silverrahul out of curiosity, why/how would direction play a role?

[@repkins]

@@kylorenkardashian79 Aka, signals from both become redshifted when both sides moving away from each other, no matter who is stationary. And then signal from both become blueshifted when both sides moving towards to each other.

[@mikegale9757]

@@repkins It's a bit more subtle than silverahul suggests because light speed is finite. The traveller hears slow-mo for half the time and fast-mo for the remainder. The bystander hears slow-mo for more than half the time and fast-mo for a shorter period of time thereafter. Couple that with the roundtrip lag and it would be a horribly confusing conversation.

[@al1383]

How can the proton (or electron or whatever is going back and forth) in the time clock be used as an example of why time dilation exist? For one, turn the clock horizontally and you don't have the proton traveling further in space in "someone else's frame of reference". Two, another persons perspective is just that, a perspective. It has no bearing on what is. Its just a perspective. A perspective doesn't make "whatever" so. Three, the time clock that is motionless on earth is far from motionless. Earth is moving at a significant speed. From another observers perspective the time clock on earth may be traveling faster than earth.

[@riverchess-so7pr]

" _For one, turn the clock horizontally and you don't have the proton traveling further in space in "someone else's frame of reference"_ " if you turn the clock horizontally you would get the same result, only the calculation will be a lot more complex. " _Two, another persons perspective is just that, a perspective. It has no bearing on what is. Its just a perspective. A perspective doesn't make "whatever" so_ " well, the other person could say, just as easily, that YOUR perspective is just a perspective. So, it has no bearing on what is. it's just a perspective. so, could a 3rd person. So could every person. so, every person could claim that every other person's perspective is just a perspective. That is the whole point of relativity. That no one person has a special or authoritative or the "absolutely correct perspective". measures of lengths and times will be different for different persons. None of them is absolutely correct.

[@plerpy5]

I've heard that Einstein claimed that gravity is not a force, that no force is acting on an object in free fall (think of an observer in a windowless elevator). Following this line of thought, if the spaceship travels around a massive object e.g. a black hole, and returns to its starting location, it would have done so without any forcreferenceon it. How is the twin paradox explained in this scenario?

[@dialectphilosophy]

We tackle that same question in our "Twin Paradox in Curved Spacetime" video...

[@stewiesaidthat]

Suggest you revist Newton's Laws of Motion. An inertial frame is one that gets its acceleration from an external force. For every action there is an equal and opposite reaction. Gravity is the Reactionary force to an object being accelerated by an external force. An object being dropped in a vacuum chamber is accelerating itself. There is no external force acting on it so no Reactionary force or gravity is involved. Going around in circles constitutes a rotating frame. The top of the frame has more acceleration than the bottom. Thus you have centrifugal-centripetal forces acting on the frame. End result is the rotating mass forms a sphere. Anything above the atmosphere is accelerating itself so in free fall. That takes care of the Space frame. Time is a change in the structure of the mass, aka, radioactive decay. Lead 210, once mined, decays into lead 206. That energy is allowed to escape to the atmosphere so the atoms oscillation rate slows down, transforming the mass from one form of energy to another. That equation is E=mc. Applying the same energy formula to the twins, in order to understand which twin is older, we need to take into consideration the energy value. Both clocks use the same amount of energy so experience the same amount of time. From the information at hand, we can only conclude that both twins are the same age. Now, if you want to factor in g-forces and calories consumed, you can get a better grasp of any age differences. Generally speaking though, Acceleration in Space equals Acceleration in Time so the traveling twin is going to be older unless significant amount of time is spent in a zero g-force environment. What Einstein got wrong is not treating space and time as separate frames of reference and understanding that clocks measure motion in space expressed in units of time. A slower running clock just means it is measuring more distance. F=ma. As mass (distance) increases, force decreases. E=mc or Energy equals Time. Acceleration in Time comes from Energy. The greater one's heart rate, more energy used, the sooner it reaches c - lifespan. Relativity is nothing more than a scam perpetuated by an ignorant patent clerk who plagiarized everything and didn't understand what he was stealing. Motion is absolute to the frame of reference. The observer is not in the same time frame of reference as the clock. Only the same spatial frame.

[@chuckwheatley3227]

Thanks for the Video on Einstein. I hadn’t known all the history of his views on the twin paradox. And after reading all the replies below, it’s clear there are still different opinions on the subject. I found it interesting that no one restated the problem before offering solutions with little proof. The original problem consists of a pair of twins, one of whom (Albert) takes a trip from Earth in a high-speed rocket and returns to earth to find that the twin (Emma) who remained on Earth has aged more. This was viewed as a paradox, which raised two questions (a) is there a paradox and (b) if not, why not? Here’s my simple answer to (a) proving there is no paradox. It assumes Special Relativity is valid and therefore “time interval” (not “time”, which is confusing) dilation and length contraction are real and proven. I think everyone here would agree with that, at least for constant velocity conditions. This has nothing to say about General Relativity which has its own effects, but is not the solution for the twin paradox, which arose from Special Relativity. At the start of the trip, the twins synchronize their clocks and clock rates, agree on a rocket velocity, v, and on a turn-around distance, D, to a fixed object, e.g. a star. Albert travels to the star, reverses course instantly, and returns to earth where their clock times are compared. The formula for length contraction seen from one frame for a length in a second frame with velocity v, is DRelative = DR = D*sqrt(1-v^2). From Albert’s perspective, the Rocket traveled a total distance of 2*DR. And since |v| is constant, that means Albert’s trip time equals 2*DR/|v|. This is what his clock reads at the end of the trip, when Emma’s clock reads 2*D/|v|. The ratio of these two times equals sqrt(1-v^2), which holds for any velocity v and any distance D. There is no paradox. Note that time interval dilation was not needed for this proof. But it is needed in answering question (b), which is what the clocks are doing during the trip. It’s obvious Emma’s clock does nothing except show the time when Albert arrives back at earth. It also seems obvious to me the same can be said for Alberts clock, even though it was subject to an instant reversal in direction at the turn around. The important factor is clock rate, not clock time. I can even quote Einstein on this, after seeing the latest video at time = 16:19 on the bottom of the page. Clock rate is essentially another name for the frequency that runs a clock, and the rest of a clock is just a counter which keeps track of time. The observed frequency from one frame to the other is FR=F*sqrt(1-v^2), which states the clock rate of the other frame is seen to slow down as relative velocity increases. An instant change in the sign of v has no effect on frequency or clock rate, and there is no evidence or reason to believe that the Albert’s clock time will jump.

[@mikegale9757]

You say it's obvious that Emma's clock is unaffected by Albert's antics. But Emma is jumping around from Albert's point of view. How can you tell which perspective is correct, especially if you eliminate other points of reference like the Earth and the fixed stars? The answer is, conservation of momentum. Emma does not feel the force of acceleration when Albert fires his rockets. Being force-free, her time axis runs parallel to the centre of momentum at all times. Albert's does not because he emits rocket propellent in order to get underway.

[@chuckwheatley3227]

​@@mikegale9757 I agree with these two statements "Emma does not feel the force of acceleration when Albert fires his rockets. Albert's does not because he emits rocket propellent in order to get underway" . But can't see how this statement "Being force-free, her time axis runs parallel to the centre of momentum at all times. " is used to solve the problem. The fact that Emma' clock (as seen by Emma) is unaffected by Albert's existence seems obvious to me. But more to the point, not all points of reference were eliminated. one star is left fixed in Emma's frame. Albert travels to that star and comes back. He can observe both clocks at the start and end of the trip and see that his clock reads a smaller elapsed time (see the math in my reply). Emma doesn't even have to know there is an Albert, but It changes nothing if she also observes both clocks.

[@mikegale9757]

​@@chuckwheatley3227 Emma is incidental. She represents the reference frame Albert occupied before he felt the force at the launch event. The time axis of that initial reference frame runs parallel to the centre of momentum (CoM) and conservation of momentum ensures that will always be the case no matter what Albert does with his rockets. To drive this point home, consider the case where both twins go walkabout with equal and opposite velocities. They age at the same rate, but not as fast as a bystander who remains on the launchpad. The upshot is, velocity in the Lorentz transformation is relative to the CoM (i.e. a bystander.) If you pull some other reference frame out of your hat, you have to use the velocity addition formula to deduce the relative velocity in that context from the velocities in the CoM frame. (I suppose you might wonder why time slows down when you depart from the CoM frame. The equations work just as well if it speeds up. I think you have to defer to empirical evidence to settle that argument.) Another good thought experiment is to throw a clock at a wall and then throw a wall at a clock. What's the elapsed time on the clock before it breaks in each case? If you play around with the worldlines on a spacetime diagram for all of these cases, you will see that it all boils down to which reference frame can legitimately strike a perpendicular to its time axis and call that "now over there." i.e. Perceptions of simultaneity are just that - perceptions. Now moments are spacetime events like any other. Their objective reality begins when light is emitted, absorbed or reflected. You can tell if your perspective is skewed by examining the Doppler shift. If the clock over there turns blue or red, your perspective is askew and you must compensate accordingly before arguing with bystanders about when things happened over there.

[@chuckwheatley3227]

@@mikegale9757 I must disagree with this statement. “The upshot is, velocity in the Lorentz transformation is relative to the CoM (i.e. a bystander.).” That’s not true. The velocity in the Lorentz transform is the relative velocity between two inertial frames. If one twin measures the doppler shift on the signal received from the other twin, he/she can back out if and when and where the other twin changed velocity in either frame. No bystander, or observer is needed.

[@mikegale9757]

@@chuckwheatley3227 You're not wrong, but you're missing the point, which is that relative velocity is not invariant. Hence the velocity addition formula. It's all about the initial conditions. If you know which clock is running slow, then relative velocity in that context is sufficient to deduce the speed of the other clock. The harder problem is when you don't know which clock is running slow. In that case, you need to establish the centre of momentum and work forwards form there.