Why you can't go faster than light (with equations) - Sixty Symbols

[@urinstein1864]

With 4 years between videos, it's also a series on how Professor Merrifield changes over time.

[@beeble2003]

Four years in what reference frame?

[@Naijiri.]

ΔMerrifield

[@sillysausage4549]

I'm a big fan of all the original Sixty Symbols profs. I'm totally Old School.

[@JacobRy]

4 more years

[@AdnanCucak]

I laughed way too much when the Minute Physics music started to play

[@tehweine]

That bit got me :P

[@harshraj460]

If we imagine that an object is moving with speed of light then it's mass will be infinity How it is possible??? And also it's length will decreases as it approaches speed of light??

[@TheLucasBurgel]

@@harshraj460 It's lenght will decrease, but remember that mass is equal to energy (E=mc^2), so every time you get closer to lightspeed, you need more energy to accelerate the system, and thus not being able to get this infinite energy (in our real universe), you won't get the "infinite mass"

[@ThainaYu]

Me too

[@harshraj460]

Can we use dark energy theory to approach that speed?

[@adamlatosinski5475]

About why the speed of light is so big, I think we need to think the other way around. The speed of light is an universal constant. The question we should be asking is "Why all the velocities we observe in normal life are so much smaller than the speed of light?" The answer for that is linked to the binding energies of chemical molecules - anything that moves to fast is prone to break apart in collisions, so only things that move slowly can create complex chemical compounds and subsequently, life. So the next question is, why the binding energy of chemical molecules is so small compared to mc^2? And the answer for that is another universal constant, called the fine-structure constant. It is a numeric (dimensionless) constant, approximately equal to 1/137, and it describes the strength of electromagnetic interactions. The chemical energies depend on in, and since it is much smaller than 1, the chemical energies are much smaller than the energies of particles moving with relativistic velocities. As far as we know, there's no reason why the fine-structure constant has this value and no other, but I believe that it is the thing that is ultimately responsible for why we don't see many relativisitc effects. If it was bigger, the chemical compounds would stay stable in much higher temperatures, and a lot higher temperature would be required to have chemichal reactions, and the whole life would ahve to happen in much higher temperature. And in that temperature, the atoms could actualy move so fast that we would be able to notice relativistic effects.

[@ChenfengBao]

+ You said it brilliantly. Talking about changing a dimensionful physical constant isn't really meaningful. They're pretty much just a normalization. It only makes sense to talk about about dimensionless constants like the fine structure constants. I really wish they could make a video on this topic.

[@ChenfengBao]

+Pan Raphael Just FYI, it's a common understanding in the physics community that values of dimensionful constants aren't meaningful. We routinely put all of them to simply 1 in advanced textbooks and research papers. In fact, every time you see a popular science outlet talking about "what would happen if the speed of light is slower", they are actually always talking about the fine structure constant. They just never explain this point, because most laymen don't care about the fine structure constant, whereas "changing the speed of light" sounds much cooler (even though it's meaningless).

[@vivigesso3756]

This is a lie. Why is there no proof we landed on the moon?

[@antman7673]

pp rr Why is there no proof you are not a bot?

[@adamlatosinski5475]

+Pan Raphael Yes, all our measurment units are based on the physical objects or phenomena, so if everything (space, time, mass etc.) got rescaled, but all the ratios (dimensionless quantities) stayed the same, there would be no way to see a difference. Because of that physicist like to use so-called "natural unit system", in which the most fundamental quantities (speed of light, Planck constant, gravitational constant, and several others) have all value of 1. However the dimensionless constants cannot be fixed in this way, and their values are determining the behavior of physical systems. Those include most importantly the fine-structure constant and other constants that describe the strength of fundamental interactions, as well as ratios of masses of various elemental particles. Some of them are related to each other, but many of them cannot be calculated from any known laws and are true parameters that decide the laws of physics.

[@onbored9627]

Professor Mike Merrifield is one of the best, love to see him on here.

[@TheOddSavants]

Should have said "my drawings aren't quite up to speed"

[@solapowsj25]

His nose 🐽would bump into the torchlight front when his speed is close to 'c', and he'd know that the speed of light is constant. Strange way? Warped space travel?? Dunno. '

[@RealCadde]

The clock speed of the universes CPU is the speed of light. When you approach maximum load, the game has to slow down time to compensate.

[@garethdean6382]

But it's the same no matter how many players I have onscreen at once?

[@AltisiaK]

@@garethdean6382 Entropy goes up and more players means more entropy.

[@javierbenez7438]

r/outside

[@00BillyTorontoBill]

Thats multiplayer or solo? or is it the same?

[@mikeandtherest]

But what about OCing the base clock speed? Would it then go beyond the light speed limit? :)

[@hotkonto]

I truly enjoy listening to Professor Merrifield explain things.

[@JayDizzle00]

Pr. Mike is my absolute favorite. He'll take on any question to the best of his ability. It's very illuminating for someone outside the world of theoretical physics like me.

[@legofranak]

My understanding from reading about the universal constants is that they're dimensionless, meaning they only represent ratios between, e.g., the speed of light and the electric force of an electron. So if all of the components of the ratios were changed together, there would be no observable difference between that changed universe and ours.

[@garethdean6382]

Yes, but you'd need to change everything in lockstep; changing for example alpha, the fine structure constant, would alter how electrons sit in atoms, warping chemistry. And how atomic nuclei function altering fusion in stars (And quite possibly making elements heavier than helium impossible to produce.) Perfectly cancelling everything is harder than it looks.

[@insainsin]

The speed of light is a dimensional constant. This is important because only dimensional constant have changes that cancel stuff out. Scientist like to replace these constants with one because it makes stuff easier. The other constants like the electric force are actually important to the standard model.

[@elisilver97]

Thank you for doing some math on the channel! The disconnect between engaging the public with interesting physics and actually teaching them physics is an important one I think. Would you consider making a video going into ways to self educate and learn more than the surface level usually covered in the chapter? Even the professors talking about their favorite Newtonian Mechanics textbooks and ways that they help their students learn the basic foundations would be well received. I love the content, just wish your channel gave the tools to go deeper as well.

[@macronencer]

I used to get terribly confused about this when I was a child. My epiphany happened when I realised that there is nothing special about light (in this context). The universe has a speed limit because of the nature of spacetime. Light happens to travel at that speed limit (because it's massless, I think), but that's all. I think there would be less confusion about this issue if people didn't constantly say 'you can't travel faster than light', but instead said 'nothing can travel faster than the Universal Speed Limit'. With hindsight, I'm pretty glad that there is a speed limit in some ways (despite its sucking for space travel), because if there weren't, that would mean that some unknown physical process could accelerate matter to such insane velocities that it would pose a terrifying threat to our own planet if it arrived from elsewhere and hit us.

[@leonardogyn]

Quoting Minute Phisics and playing its soundtrack was simply awesome!!

[@MPSpecial]

“Sorry we don't serve particles faster than light” A tachyon walks into a bar

[@harleyspeedthrust4013]

there is no evidence of tachyons

[@ryanbell6672]

@@harleyspeedthrust4013 not with that attitude there isnt

[@russellwarren9595]

@@harleyspeedthrust4013 watch star trek, every episode they are using a tachyon beam or a quantum something. unless I have been deceived my entire life star trek, star wars and anything written in comic book form is true! although during surgery a few years ago I lost a lot of blood and needed to have a transfusion of 3 pints. imagine my disappointment when I realised that I hadn't gained super powers. I guess it must not have been radioactive!

[@leobarlach]

The way I finally learned relativity in first year of undergrad was starting from the speed of light and working back. It's much easier to remember whether you should multiply or divide by gamma when you remember that the consequence should be the speed of light.

[@BenTajer89]

I think the point they are missing here is that the speed of light is not just the speed of light, it is the speed of all causality. Moreover, not only is the speed of all causality the speed of light, it is the only speed at which anything happens in the universe. The reason that everyday objects cannot move at the speed of light is because their very existence is dependent on interactions that are constantly happening at the speed of light. Moreover this is why time slows down when you approach the speed of light, because the total velocity of any interaction happening with in an object can only be the speed of light, any velocity perpendicular to the main axis of motion needs to decrease (it's trigonometric). Another takeaway is that all causality can be reduced to a spatial translation of information. Veritassium made a great video about this a couple years back.

[@alwaysdisputin9930]

Why do you say c is the speed of all causality?

[@glarynth]

If the speed of light were walking pace, perhaps we would keep food fresh in centrifuges rather than refrigerators.

[@vishalmishra4408]

@Eldain - Rob meant time-dilation inside the centrifuge will slow down the aging of food so it will stay fresh much longer according to the clock outside the centrifuge. So yes - it is an interesting thought :D

[@egooidios5061]

Yeah Iran has some centrifuges for sale if you feel like investing in this idea. Plus their radiation will keep germs at very low levels!!!!

[@jorgepeterbarton]

but when we eat it, we'd die before the energy was transported around our body due to the time dilation occuring in the flow of our blood.

[@funkyflames7430]

@@jorgepeterbarton I really don´t understand what you are saying, I don´t think that is how it works.

[@garymitchell4719]

As an avid enthusiast of mathematics I must say- and not in arrogance- that we can fall into the trap of stating unequivocally that statement A is true because our maths says so. On a philosophical note, I believe we should not be so entrenched in what we think is true just because we say it is. Fact is, I think we are so wrapped up in proving that c is a maximum that we tend to not embrace the possibility that it isn't.

[@willemm9356]

I think the reason why the speed of light is constant is actually quite simple: All processes, chemical/physical interactions, etc. depend on the speed at which particles move, which directly depends on the speed of light. So time (something that is measured by a physical process) depends on the speed of light so therefore it will always come out the same.

[@mukundabharadwaj852]

Logic should be well-defined with mathematical reasoning 😁.

[@alexmcgaw]

I wonder if, had the speed of light been slower, if the "speed of life" would have been slower too. Do all physical and chemical reactions happen at some fraction of the speed of light, so if c was slower, the rest of the universe would be slower, so someone existing in that universe wouldn't notice?

[@BatMandor]

I'm not sure but I think it would perfectly work out the same. Our numbers are not special or anything, they're just there to describe stuff and did you know that most people in modern physics take speed of light = 1 and then derive meter and all that. The seconds come from radioactive decay which is perfectly uniform. So yeah. Actually I don't think it would even change the numbers, even if we don't take c=1 because our brain slows down and what seems slower seems fast (relative to this world) so it cancels out (the things change by same). You never know if speed of light is just changing (crazily) or not *I think*

[@rykehuss3435]

The speed of light has nothing to do with light itself. Its more accurately called speed of causality. Go watch PBS Spacetime video about it if you want to know a little bit more about c.

[@Borednesss]

Changing the speed of light (and everything else) would either act like a linear transformation and everything would change accordingly so that we wouldn't be able to tell the difference, or things would be wildly different because of all the squared terms in physics formulas. Regardless I think it would change the amount of energy in the universe, which would either again cancel out because everything else changes at the same ratio or completely change some bigger picture of the universe such as the shape or size or density. Or perhaps it works the other way around, and the size/shape/density of the universe influences the speed of light. I'm sure many people with a lot of physics knowledge have asked and mathematically answered the question with many different results. No one knows!

[@jeremysale1385]

Well, it has something to do with light, don't you think?

[@marktero]

If the speed of light would be slower, wouldn't the dopler effect be more noticeable at lower velocities?

[@IceMetalPunk]

My (very limited, but curious) understanding is that the speed of light comes directly from two fundamental constants of the universe: the permittivity of free space (ε0) and the permeability of free space (μ0). The first is basically "how hard is it to change an electric field" and the second is "how hard is it to change a magnetic field". And it's an inverse square-like law, where c^2 = 1/(ε0μ0), so if either of those is higher (i.e. it's harder to make change the field), then the speed of light would be slower. Which makes sense: if it's harder to change "the next part" of the field in front of a light wave, we'd expect it to take longer and thus propagate slower. And since light is a wave in the electromagnetic field, which is "made up of" the electric and magnetic fields, it makes sense, too, that a change in either would have the same effect on the speed of light, since it's really the same change in the overall EMF. In other words, the speed of light isn't mysterious, it's just a consequence of how hard it is for the electromagnetic field to change. In fact, in a system of "natural units" (units based on only physical constants rather than human-defined properties), you can end up with ε0 = 1, μ0 = 1, and c = 1 and all the math still works and models the universe accurately. Which means it's only the units that separate ε0 and μ0 in the first place; they're likely actually different measurements of the same field (and as I read more about this, my brain begins to implode considering the effects of relativity on electric and magnetic fields... did you know that relativity implies that magnetic fields and electric fields both exist, but that they actually are the same thing, even though they're actually different things? Or something like that... I'm getting confused trying to understand this stuff >_< ).

[@thedeemon]

But it's not just about light. Any massless particle moves with this speed, even if it's not related to magnetic fields at all. And all massive particles are affected by this speed of light limit and resulting time dilation effects. It's about geometry of spacetime itself, not just particular field.

[@SolaceEasy]

Klee Irwin at Quantum Gravity Research has new videos for you on time.

[@stevenadam6489]

To follow the last question Brady asked. What would be the consequences if the speed of light was, let's say, 10x the actual value ? or a 100x ? Will it fundamentaly change something on some laws of physics that will mess up the universe ?

[@Charlie-jp6cc]

I'm not too sure. Many things depend on the speed of light so many things would surely be affected. However, I would imagine any catastrophic change would be brought about by a change in important energy scales relative to each other. For example, DNA (and other organic molecules) have evolved so that at body temperature the molecules don't have enough thermal energy to rip themselves apart. If something were to suddenly increase the temperature of everything on earth by a lot, aside from the obvious death of everybody, the molecules that originate life wouldn't even be able to form. So perhaps there is some energy scale that is dependent on the speed of light (like electrical potential) that would change drastically relative to some other energy scale (maybe thermal energy?) that would make some systems, that would otherwise be stable, unstable. Sorry for the novel!

[@garethdean6382]

It could be quite a mess. YOu'd alter mass-energy equivalence, which would alter the output and efficiency (and size and stability) of stars. The size of atoms also depends on light speed, increasing it increases their size and changes how strongly electrons are bound and thus chemistry and as a side effect van der waals bonding. (Making most organic substances gasses.) On all scales from astronomic to atomic things would alter drastically.

[@CrniWuk]

We would all be gasses! What awesome life forms we could be!

[@davecrupel2817]

Me patting you on the back would probably feel like getting a pat on the back from The Iron Giant.

[@insainsin]

Nothing would change. Energy isn't based on mass. Mass is based on energy. Gravity is based on energy. Change in actual distances caused by the change of light wouldn't be noticeable because relative distance would stay the same. Mass would change, but mass is only important when it comes to do with ratios of energy transferring. Both sides of the ratio are scaled equally when the speed of light is changed. (In other words, relative mass stays the same.) Speed wouldn't change either because time changes according to the speed of light which is cancelled out by the change in length. In fact in the standard model, the speed of light is really only used when it comes to relativity.

[@pohkangyu]

Just started my undergraduate studies.. Unfortunately not in physics which I had a keen interest in. The practicality of how this world works pretty much forced me to this standstill. Thanks for the clear video and the refreshing knowledge. It is always amazing, learning new stuff about this subject.

[@Gh0stClown]

Physics is pretty employable, not just in research but also in finance and industry.

[@sirbruce1970]

While I appreciate your videos, I have to say that the title of this video is misleading. Nothing here explains why you can't go faster than light, only that the math of Relativity (which is true as far as we have tested) tells us the speed of light is constant in all reference frames. That's a start, but that doesn't really address the question of why something else can't go faster than light.

[@johnchappell4492]

It's not so much that nothing can exceed the speed of light, it's that nothing (including light) can exceed the speed of causality. Causality simply means that a "cause" proceeds the "effect". When something happens, the effects of that event must happen some amount of time later (even if infinitesimal). Otherwise everything in the universe would happen all at the same time. The life of the universe would be a single instant. So logically, there must be a maximum speed of causality. What it turned out to be is some arbitrary underlying restriction of the basic laws of interaction between particles or fields. It had to be something. Since light is massless , ( zero mass), it travels through a vacuum at the maximum speed of causality. Another way it's commonly described is the maximum speed of information transfer.

[@NoActuallyGo-KCUF-Yourself]

If something did move faster than light, how would you measure its speed?

[@akostarkanyi825]

@@johnchappell4492 "everything in the universe would happen all at the same time" And our Universe is not like that - although this does not mean it couldn't be like that. Anyway, causality could work faster than the speed of light - as the scientist said, we have no explanation why it is C that has to be the upper limit.

[@johnchappell4492]

@Reed Morris....It is an axiom (an underlying assumption) from which he derived the rest of his theory.

[@johnchappell4492]

@Reed Morris....I'm not sure if you mean neutrons or neutrinos, but since both have mass, they can not reach the speed of light. Any particle that has mass can not reach the speed of light, and the closer to the speed of light they are accelerated, the more energy it takes to accelerate them more. You are correct, that even using all the energy in the universe, you can't accelerate a particle that has mass to the speed of light. There was a brief time where people THOUGHT they had observed neutrinos moving slightly faster than light, but it has since been proven that they do not.

[@Inferryu]

The scratchiness of that marker, just remembering the feeling gives me goosebumps, great ASMR 👌.

[@trinitrojack]

Love the questions at the end!!!

[@JustOneAsbesto]

Every Prof Mike video is the best video.

[@edwardkim6389]

hahaha minute physics double base! nice touch

[@Jerome...]

The conclusion of this video is such a great movie idea.

[@anon8109]

A wonderful book describing what life would be like if the speed of light were 20 miles/hour is "The New World of Mr. Tompkins" by physicists George Gamow and Russell Stannard. It's written as a series of fanciful stories, but based on actual physics.

[@TommiHimberg]

I was going to post this very comment - then decided to scroll down the comments as I was sure someone _must have_ mentioned Gamow and Mr Tompkins here.

[@rarebeeph1783]

When you plug in values above the speed of light you get fun things like "the train moving forward slows it down" and "it has infinite/undefined speed if the train is moving backwards at the right speed"

[@Valdagast]

Maybe I'm strange but when I spot a "hole" in relativity I usually think that I'm the one who has made a mistake. I understand that there are lots of people who think the other way around - all the physics professors who have lived since 1905 have been wrong and they're right. Seems arrogant to me.

[@mykofreder1682]

I think it is an accepted theory now that space itself is expanding at different reference points from us approaching the speed of light at the edge of the visible universe and probably beyond light speed outside that limit which remains invisible because it is moving away from us faster than light can travel. And that the visible universe's diameter (if we could instantly get updated on what is happening on the edge) is actually close to 90 billion years because of expansion.

[@sarahbell180]

@Enter the Braggn' No, it wasn't, though I do have a suspicion you herd about 'redshift quantization' from Dr. Humphrey, am I wrong?

[@original0143]

In an earlier video deriving the lorentz transformation, it was necessary to assume the speed of light is invariant. In this video, the Lorentz transformation is used to show that the speed of light is invariant. Does independent justification for light's speed invariance stem from its derivation from Maxwell's equations and the assumption that the laws of physics are independent of inertial reference frame?

[@grainfrizz]

4:06 - the moment I heard the background music I almost burst!

[@avinotion]

Did I miss anything?

[@HerrLavett]

Thank you for this very likable and relaxing video!

[@KFRogers263]

This seems like a big of circular math. I thought that special relativity (aka the lorentz transforms) come out of the positing the speed of light has to be the same in all reference frames. (From Maxwell Eq's)....guess I should've watched to the end. You say that :) Still is circular math then.

[@Mike-zf4xg]

I am not sure that is circular as the axiom just states that speed of light in a vacuum is constant in all inertial reference frames. I am not seeing how it's apparent from it that you can't boost some frame faster than the speed of light. Really, a geometry of spacetime that enforces those axioms has transformation rules that don't allow you to boost any framer faster that c. Not a very satisfying answer, but it is fundamental at least.

[@TyTheRegularMan]

That last cancel that leaves us with "c" is mind-blowing and beautiful.

[@pancakelegend]

Minute Physics bassline win

[@kenphil8389]

This is really something to me. He didn't really give a direct lucid physiological reason an object can't travel faster than light, but just a cursory explanation shrouded in obtuse mathematics. I go through many of these videos and it's always the same thing. It's really amazing to me that they just cannot explain these things in a practical way that the unscientific laymen can understand it.

[@olfmombach260]

4:08 Love that music easteregg!

[@BC3012]

Olf Mombach editing is lit AF today 👌

[@matts8249]

FYI you can go faster than light if you are space itself. Light is only the limit within the medium of space.

[@claushellsing]

That bass lol XD

[@WylliamJudd]

A great way to explain the speed of light, which I got from PBS spacetime, is that the speed of light is really the speed of causality. It shouldn't be thought of as a cosmic speed limit, so much as the default speed at which causes cause effects when they're not impeded by something like mass (or drag on any fields of energy).

[@AceNallawar]

Thank you for the equations, I don't understand why you always hate equations..

[@markgigiel2722]

I'm new here and American. If there's no exponent it's prime, no need to keep saying it. I'm not from the UK, I guess that's your convention. I'll refrain from further comment. I used to breeze through this physics stuff, now I'm getting old and it's a bit harder and kind of fast for me. But I'm glad I found this channel. Thanks for what you do.

[@cyberexile3507]

this is like the non braindead version of asmr

[@ErikJohnsonFMA]

these technical videos are my favorite.

[@olekrarup9570]

Here's an argument for why it's impossible to exceed the speed of light: In relativity the energy of a particle is given by E^2=(pc)^2 (mc^2)^2, where p is the momentum *relative to you*, m is the mads and c is the speed of light. Imagine speeding yourself up, so were moving at the same speed as the particle. Now the momentum, p, relative to you is zero and the energy is determined by the rest mass. E=0 + mc^2 However photons have zero mass, so their energy is given by E=pc +0 If it were possible to speed up and cruise alongside the photon, its momentum relative to you would be zero. But then E= 0+0 = 0 and you would effectively have annihilated the photon by doing nothing other than changing your own reference frame! In other words any particle with zero mass *must* move at the highest speed allowed by the universe in any reference frame to escape this "death by lorentz transformation".

[@thedeemon]

So you've just shown that speed of light must be invariant if you use equations from the theory that's based on the idea of speed of light being invariant. Okay. ;)

[@peculiarlittleman5303]

Beautiful.

[@solarisone1082]

"Inside the photon"? Meaningless. The photon HAS NO frame of reference. That's the whole damn point of special relativity! If it had a frame of reference, you would be able to catch up to it, since there would be a frame where said photon was at rest--that's because you're always at rest within your own frame of reference.

[@DavidAndrewsPEC]

Have some dressing to go with that word salad.

[@vishalmishra4408]

Every photon in our universe has no life (At speed = c - the entire universe is just a point due to length-contraction and time has stopped due to time-dilation). So sad.

[@AstroRamiEmad]

You ended this video with an Oscar winning idea! ... It's mine, no one else is allowed to steal it!

[@oldcowbb]

this proof is circular reasoning, the gamma factor it self comes from the premise of speed of light is constant, and you just use it to proof that speed of light is constant

[@anda3487]

oldcowbb maths prof wouldnt be happy

[@CorwynGC]

This wasn't a proof, just an explanation.

[@oldcowbb]

A not satisfying one

[@CorwynGC]

Which parts did you find unsatisfying? Perhaps I can recommend a video to fill that gap.

[@dilanovich]

This was not a proof. The derivation is built on the axioms of relativity. It merely demonstrates that relativity is consistent with it's own rules, specifically that the speed of light is the same in all reference frames (which is one of the axioms).

[@Say-Yesh-to-the-Mesh]

This video is amazing. Please do more math in sixty symbols!

[@alexconlon1935]

4:00 haha, and then the music is the icing on the cake!

[@michaelzoran]

QUESTION: Thermodynamics tells us that at the Temperature of 0 Kelvin, there is no movement at all - both Space and Time stop. So, there is a "Minimum" Temperature 0 Kelvin. However, Thermodynamics also tells us there is no "Maximum" Temperature. As a result, it would theoretically be possible to have a Temperature so high that an object moved faster than the speed of light. Is this correct? According to Thermodynamics and this concept of "No Maximum Temperature," it would theoretically be possible for an object to have a Temperature so high that it occupied all points of Space in the Universe simultaneously at all moments of Time. I realize there would never be enough energy to do such a thing. However, let's just say that a form of technology has been invented so matter no longer contains mass, which allows it to be moved with virtually no energy. And, let's just say the technology has been invented so an object can be heated by a device that has access to an alternate dimension filled with an infinite supply of energy. In that scenario, would it be possible to move faster than the speed of light? ... I realize that to "observers" the object would only be "seen" moving at the speed of light. However, the object itself that had such a high Temperature would be travelling much faster than the speed of light, wouldn't it?

[@taascheee]

I love the musical minute physics reference :D

[@michaelzoran]

QUESTION: Let's say there is a transparent ship moving away from you. The ship is traveling at 100,000mph. On board this ship, a flashlight is also shined away from you. This means the photos from the flashlight are moving at the speed of light (186,000 miles per second) plus the speed the ship is moving at (100,000mph) according to the Theory of Relativity. I fully realize that according to the Theory of Special Relativity, the photons "seen" by you at your location will only be traveling at the "speed of light" rather than "the speed of light plus the speed of the ship." However, there seems to be no doubt the photons from the flashlight on board the ship are actually moving at "the speed of light plus the speed of the ship." In fact, all photons from all objects on the ship will be moving at the "the speed of light plus the speed of the ship" when those photons are traveling in that particular direction away from you. With that in mind, my "question" is whether or not is is possible to actually be "moving" faster than the speed of light, even though you would not actually be "seen" moving at only the speed of light? In other words, I'm saying it seems to be possible to travel much faster than the speed of light and reach your destination, even though it would "appear" to take much longer to an observer. For example, let's say I left the planet Earth in a ship using technology where all matter is changed so that it no longer contains mass and requires very little energy to move. This ship has the ability to travel at a speed of 1,000 times the speed of light. I reach my destination on another planet in 10 hours. I live on this planet for many years and build a home on this planet. In about 1,000 years telescopes on the planet Earth will be able to "see" my home on this planet, even though my home on the planet will have existed that entire time. As far as the planet Earth is concerned, the images from that planet are like looking 1,000 years into the past, just as looking at the Sun provides an image about 8 minutes into the past. From the point of view of people on Earth, they will be able to see me in their telescopes and see the "photons" from my ship traveling to the planet for 1,000 years, even though it only took me 10 hours to get to the planet. The reason for this is because the "photons" from my ship would be traveling at only the speed of light, while the ship itself would be traveling at a rate of 1,000 times the speed of light. Is that example accurate? Please tell me why the example would not be possible to actually move faster than the speed of light, even though others would only "see" me moving at the speed of light due to the fact that the photos from my ship would be traveling at only the speed of light.

[@feynstein1004]

If anyone is interested in special relativity, Brain Greene's lectures from World Science University are the best thing I've seen so far.

[@rykehuss3435]

PBS Spacetime is superior.

[@feynstein1004]

+asusminor I've never heard of viascience before. I'll check it out.

[@Nothing_serious]

Because Brian Greene is already an expert on it. He did explain in a complicated level once in Late night show

[@feynstein1004]

+asusminor Well, I did check the channel out and while it's pretty awesome and math-heavy, Greene's lectures are better for developing intuition and easing into the theory. To me, they're both great in their own way.

[@sciencefreakdog]

Please make a vidoe/videos about symmetries in physics. They are important and the more basic ones, I believe, shouldn't be too hard to visualize.

[@artmyb]

Actually this video more concernes the engineering side of the subject. You take the formula, substitude the values, calculate it and see the result. You don't understand it fundamentally unless you know what the formulas based on and how they was derived. The reason that speed of light is c is not "because when you put lorrentz factor it is so...". It is becuase lorrentz factor was calculated based on the constancy of the speed of light. There is no logical explanation for why it is constant for all frames of references. The constancy of speed of light was the biggest impact to the human intuition. And why you can't go faster than light can be explained simpler and more fundamentally. It's just because you have to exert a force to accelerate a body and since there is no force carried faster than light, the force carrier particles simply cannot catch the body to accelerate it more.

[@thedeemon]

But then you'll have to explain why those force carriers cannot be accelerated faster than c.

[@Hunnter2k3]

", the force carrier particles simply cannot catch the body to accelerate it more." Jokes on you, I have a warp engine in the back, I can just eject it and let it explode, because apparently that makes an explosion more powerful than warping space, you know, antimatter and matter explosion vs changing the fabric of reality to cheat around lightspeed. I always hated that one bit in Star Trek. Of all the sci-fi nonsense that has been in it, that bit stands out as my biggest annoyance because even in its own universe of physics it makes no sense.

[@taylorwestmore4664]

Ya'll should check out the quaternion mathematics of Maxwell and the differential equations of Whittaker c. 1910. Null electromagnetic bi-vectors, also called phase conjugate photons, can described as an extra scalar potential energy term contributing to the metric tensor (Einstein's field equations describing curvature). This is essentially describing a vacuum state that is composed of phase conjugated EM waves, or 'time-reversed' waves (sometimes called retroreflection). The sub-structure of spacetime in this deterministic treatment of the quantum vacuum is dynamic and gravity is a composite force with a composite particle called a graviton. Gravitons are phase conjugate pairs of photons. The reason for the relativistic mass increase as you reach the speed of light in this framework is straightforward; Objects with mass and volume, displace the vacuum and decouples or phase-shifts the pairs of gravitons in the vacuum field to constantly produce an outpouring of EM energy in the form of charge and radiation. Objects that accelerate interact with Doppler shifted pairs of gravitons so they absorb additional vacuum energy in the direction of travel and also less than average vacuum energy on opposite side. The asymmetrical vacuum interaction on the surface leads to forces on the particle (caused by the dipole moment of the vacuum photons). These forces approach the speed limit of c by summing the forces of increasingly blue shifted + red shifted vacuum photon interactions on the inertial mass. This polarized vacuum energy state may be responsible for inertia itself. Something to think about: if you can engineer the appropriate phase conjugated EM wave fronts with a radio source, you could change the vacuum expectation value and cause a curvature in the metric tensor of spacetime, positive or negative, warping space around any hypothetical vehicles you wish to trek around in.

[@artmyb]

thedeemon when we say "the speed of light" we actually mean the speed of force carrier particles "photons". And yes, I cannot explain why the photons cannot travel faster than light as we cannot explain he constancy of the speed of light. All our formulas are based on simple axioms and you can't go further than them. A great majority of classical mechanics' equations are based on f=ma. But we don't know why is acceleration propotional to force and inversely propotional to the inertia. It is a property of the universe. Of course it's obvius to our intuitions that it's hard to accelerate a body with great inertia(~mass) but the scientific explanations get obstructed somewhere. Maybe in some universe, the mass helps the body accelerate more and that formula would become a=mf.

[@markgigiel2722]

OK Doc, I'll bring the Delorean.

[@occhamrazor]

Nice touch with the Minute physics Bass segment :)

[@GreaterDeity]

I have two pet tachyons that disagree... Now I cannot find them. I saw them once.

[@jari2018]

Watch at the timeline before you birth , they must have been playing hide and catch there.

[@danhaynes446]

If you knew their velocity, you never knew exactly where they were in the first place. This could make writing the Lost and Found ad quite tricky.

[@Triantalex]

ok?

[@andresfernando3342]

this type of videos are the best in sixty symbols

[@reillybrangan2182]

Say that I am in a bus (frame of reference), this bus is travelling at 99% the speed of light on a vector that we will just call north. If my friend stands at the south side of the bus and I stand on the north side, and he turns on a torch towards me in the north direction, will the light coming out of his torch then travel towards me at 1% the speed of light relative to my perspective? Will all of the light being emitted from my friend come to me at 1% the speed of light (relative)? will there be a huge delay in my visual perception of his actions, even though there is but a bus length between us?

[@M104-q9y]

In your perspective the light from the torch would move at 100% the speed of light. The person standing still outside the bus would see something different.

[@nicosmind3]

Thats the perspective of a person from the outside. I think cause your time has slowed down from their perspective then it doesn't matter to you about that accumulative speed and it still equals out as the speed of light to you.

[@mina86]

ytmoog, the colour won’t change. Everything happens in the same inertial frame of reference thus everything behaves just as if the bus was stationary (just as Chris pointed out).

[@dliessmgg]

To you, the light would travel normally, because both of you are in the same frame of reference. To someone outside of the bus, there would need to be some sort of compensation, since the bus is moving so closely to the speed of light. If I'm remembering correctly, to them the bus would appear squashed in the direction it moves, so it would look like a flat rectangular pancake that travels northwards at unimaginable speed.

[@Sopel997]

Consider an object in the universe that out planet travels with 99% of the speed of light relative to (there are such objects). Then you have the same situation as you described, yet we observe the speed of light to be the same in every direction. The longer you think about the situation you presented the less sense it makes. With there being a 'speed limit' relativistic theory is an elementary and required principle.

[@anubhav21dec]

That explanation of the second postulate is really cool, I never saw it that way.

[@ludovanalst]

But these Lorentz transformations are created using the fact that the speed of light is the same in all reference frames. So this is just circular reasoning..

[@thedeemon]

There's no circle: you can't reach speed of light because light speed is invariant, same in all frames of reference. The last fact comes from observations, not from some logic, so it's not circular.

[@ludovanalst]

thedeemon the first statement is exactly what I said and it is called the second postulate of Einstein. From this the Lorentz equations are derived. So saying the speed of light is the same in all inertial frames when looking at those equations is circular reasoning.

[@garethdean6382]

Indeed, but the thing is we KNOW such things happen. The equation for gravitational acceleration relies on gravity being constant at Earth's surface and the result of that equation is things falling at a constant acceleration (With a predictable speed after a certain time.) The reasoning is ok because there is alternate proof outside the circle.

[@DMitsukirules]

It is not circular reasoning, it's describing to you why you cannot go faster than the speed of light. What the video does not do is imply what happens when you assume the speed of light is not the same in all reference frames. So while the reasoning is not circular, the explanation is perhaps poor. We did not start from the idea of Lorentz transformations, we ended up there, and the implications of all of it is exactly what special relativity is. In other words You cannot go faster than the speed of light, that is a fundamental truth. From that truth, you describe the universe, and you can demonstrate the truth with the descriptors such as these equations. You cannot use an equation to prove a fundamental truth. That would be circular, because where would the equations be derived from?

[@ludovanalst]

DMitsuki That is my problem. This is exactly what he does at 7:50.

[@jongyon7192p]

We need more general relativity examples using walking speed as the speed of light. I find it easier to wrap my head around that...

[@tomdrowry]

Why does Einstein always get the sole credit for special relativity when it was Lorentz and Poincare first came up with math behind it ?

[@STOG01]

Not enough PR.

[@BatMandor]

I read somewhere that you can come up with general relativity easily with special relativity but you can't by using Lorentz and all his relativity math. Einstein used his own ways i suppose. But Lorentz explained it quite well and predicted too.

[@hectarsavoie8166]

@Manasv Chhabra I think it's the opposite. The step from Special Relativity to General Relativity took gigantic leaps of genius, whereas the step form Lorentz and Poincare's ideas to Special Relativity had a smaller leap.

[@Veon1]

Mostly because he was the one who gave it a proper physical interpretation, the other two still thought "ether" was a real thing, for example. Though for a long time there were quite a few people who gave Poincaré the credit for SR (he himself never acknowledged Einstein).

[@wenkeli1409]

"The structure of scientific revolutions" by Thomas Kuhn talks about this quite a bit, worth a read...

[@philcorrigan5641]

I think a lot of the confusion about c comes from describing it as ‘the speed of light’, when a more accurate description would be the cosmic speed limit, which is constant throughout the universe and never changes. The nature of light means that it can travel at that speed in a vacuum. Looking at it that way you see that c is an aspect of the universe itself, rather than light in particular.

[@MrHarsh3600]

Sooooooo

[@SophiaAstatine]

LolGuy SoooOooo

[@Jobobn1998]

Great video! I really love the camera work!

[@Sphere723]

His "x" makes me angry.

[@levinb1]

Maxwell’s equations/math reduction show that the speed of light as it is, in a vacuum. Speed of light philosophically contradicted the idea of Galilean relativity, adopted by newton, in that objects have any range of speeds in the universe.

[@brokoli3d]

Professor is getting older oh no 😰

[@takshashila2995]

Death.

[@IvanCADtutorials]

if point A is moving in one direction and point B is moving in opposite direction (started from same point), both at speed of light, can point A register light from point B (after moment in time they started , t>0), or light from B can never come to A? That way point B will seem immovable to A as A will always see only light that B emitted at t=0... This can lead that speed of B observed from A is C, but just observed speed. Real relative speed is 2*C but it can not be observed.

[@husnainanwaar1992]

This a much better way of learning.

[@husnainanwaar1992]

make a playlist and save it universities are no longer relevant

[@hjembrentkent6181]

this nub

[@rjstegbauer]

Great video! I loved the last couple of minutes about why the speed of light couldn't be slow.

[@MaxPower2719]

Minute Physics... will you disable comments soon?

[@JustinKoenigSilica]

ohfuckoff.jpg

[@MaxPower2719]

Justin Koenig Link to jpg doesn't work. Pls post again, while comments are still up.

[@MaxPower2719]

ytmoog It was a joke because Minute Physics disabled comments on one of their videos because they couldn't handle the criticism they got over that video.

[@MrClivesinger]

You say "criticism", others might say "offensive and occasionally threatening language." Either way, that has nothing to do with this video.

[@MaxPower2719]

Kyle Baldwin "Offensive language" and similar phrasings are just cop-outs KZbinrs and other content creators use to silence any negativity. Don't fall for that easy excuse, please. And no, it has nothing to do with this video. I already mentioned it was a joke.

[@ThePinkus]

One point I'm particularly interested about in the discussion of special relativity is acceleration: what is the relativistic, or kinematical, effect of accelerating reference frames that special relativity implies? Recalling the 'twins paradox', a pair of twins, one travels to alpha centauri and back at a relativistically non-trascurable speed, which one is younger when they get back together due to relativity? If You only consider velocity effects, the answer is not well defined, it would be different in each of the brothers' reference frame, violating the requirement that proper age is a well defined, objective (frame invariant), property (here, objective is regarded as a requirement for a realistic interpretation). But if You include the effect of acceleration then the results are equal, there is no paradox, age is objective (everybody agrees who's older and how much) and it is therefore legit to think that age is 'real' (existing 'out there', without the need to reference a particular observer to determine its value). That is to say, the discussion of special relativity does not stop at the discussion of velocities, kinematic effects of acceleration is a necessary part of it. The point is important in view of the special to general relativity discussion. There are two aspects to Einstein's equivalence principle, one is the equivalence of inertial and gravitational mass, the other is that gravitational force is (experimentally, in a small volume of space w.r.t. curvature) the same as the pseudo-force in an accelerating frame. What is the latter? Kinematics effects of special relativity, which are non-trivial! Indeed one narration to solve the twins paradox is to invoke the equivalence principle (I disagree with this, though, as I want to see how special relativity solves it, and it does, and how far does it get, before invoking general relativity itself). Thus, my interest is kinematics effects in view of how much of general relativity is implicit in special relativity. The point is also relevant for QFT, as particles are representations of the special relativity transformation groups, how much do they encode not just special relativity but also general relativity? Or, how far does special relativity really brings us toward general relativity, i.e. geometrodynamics, i.e. gravity, and, specifically, how far does it brings us in quantum field theories?

[@unom9515]

FIRST!

[@milanarybethwindictive3969]

sir, got a question. our sun together with the whole solar system orbits the center of the galaxy... with certain speed which i believe is very high. which means the time fluctuation applies to us whenever we go forward (in the direction of the orbit) or backwards. Would this difference be so high it would be measurable even to todays space speed of rockets and satellites?

[@nicepajuju3900]

What is a time fluctuation?

[@adamsmith2719]

Damn it! I was just planning a trip at 1.2c so now I have to change my whole itinerary .

[@Alpha-Alpha]

When 2 particles traveling at the speed of light away from each other, then they are traveling faster than the speed of light relative to each other. And in actual sense the distance apart at given time are are increasing faster than the rate of speed of light. How u explain that.....

[@EnglishMike]

Yes, the distance is growing at double the speed of light, but nothing is traveling greater than the speed of light, even if you measure the speed of one photon from the frame of reference of the other.

[@DGaleano]

Brady, your questions are always very good but today you just excelled yourself. Excellent questions. (chicken or egg? Great!!)

[@Humble_Merchant]

What's keeping us from putting in a variable the same way as c represents the speed of light but instead x for the speed of a bowling ball?

[@itsawonderfullife4802]

The "speed of light" is actually the speed limit for prorogation of causality and it is called "c". The speed at which anything mass-less (in vacuum) would have to travel. But light can sometimes (effectively) go slower than c as in water or a piece of glass, but the speed of causality is always "c". By far, the best source for advanced physics on the KZbin are professor Leonard Susskind's lectures.

[@youtou252]

the questions at the end are really great

[@FransHenskens]

Thank you all very much for doing this for so long. Helping to educate us plebs is really amazing and powerful work. I've heard that there's some variation in the fine structure constant as viewed across the universe. How different would that be to a variation in the speed of light? My understanding is that it would result in a variation in the rate of star formation in the early universe. Is that right? If not, what would it actually change? If so, how much deviation would be acceptable without dramatically changing the formation of heavy elements such that er couldn't exist?

[@locouk]

I wish when I was at school, I could have gotten my head around equations. As soon as my physics teacher wrote an equation on the blackboard, he may as well have been speaking Icelandic. It’s an awesome subject, I just can’t figure out the basics like numbers.

[@theproplady]

I have a weird question: if you were watching a live streaming video from someone in a rocketship millions of miles away and they had found a way to send the video stream to you instantaneously (they beam the signal through a wormhole or something,) would you watch them talking in slow motion (since time for them is moving a lot more slowly relative to you?) Also, would the pitch of their voice change lower as they talked (or would it only be the speed of the voice that was affected, not the pitch?)

[@thedeemon]

Yes, you'll see and hear them in slow motion (assuming they move at relativistic speed).

[@henrytjernlund]

In the 1000+ page book GRAVITATION, c is described to be the conversion factor between measure of space and measures of time. (nothing to do with light, necessarily) So one second of time is space-time equivalent to 300,000,000 m (proximate.) Light/energy moves that fast because of this equivalency.

[@vinayakj023]

As far as I can understand, the only statement in this video which explains "Why you can't go faster than light" is the statement that the Einestine expected the laws of physics to remain the same regardless of the frame of reference. All the equations in this video explain to us, how you would do the calculations to ensure that the speed of light remains constant regardless of the frame of reference. I have a question, what law of physics would change when the frame of reference changed if the speed of light would change with the frame of reference? Or is it that Einestine expected the speed of light to be a low of physics?

[@jnhrtmn]

Skeptical points: 1.) How do 2 observers, each with a 'frame', expect to be slower than each other? (intoxicating) 2.) If physical constants change proportionately with energy, there is no need for a 'Time'. What is time outside of your brain's ability to remember and anticipate? 3.) Speed is just a potential energy that you can see, but acceleration is absolute. Maybe you should start thinking in terms of absolutes! 4.) Math is an analogous overlay that will hide the truth from you when you use incidental variables that have no causal role. 5.) Relativity uses transform equations to change reality before it is even considered, so if I were a professional physicist, I would look into reality first by replacing time with a cause/effect marker. It would just be a question of creating a rate. Start over and try to come to the same conclusions. Don't let a legacy direct you!

[@UPu-tq8zm]

I like this "equations idea" very much

[@louigi6001]

Intresting thing: if the speed of light was walking speed it would mean that anything with mass could never go as fast as walking speed ... gravity would also have to do something funny otherwise you would need to be really far away from anything in order to orbit a walking speed ... and also the observable universe would be much much smaller

[@Tnbeazy]

Interesting! Especially the questions at the end!

[@Veptis]

I got a question. we are inside the reference frame of earth, or solar system for that matter with our probes all our measurements in time and space are related to the speed and acceleration we take through spacetime in reference to the universe(?) and the speed of ligth as fundamental constant. I would like to know and understand, if it is possible to find a reference frame with lower speed and acceleration, in which spacetime isn't bent to be smaller form an outside view like the gamma triology shows with moving trains, but in which the earth is faster and basically the moving train. Where would such a frame of reference be and how would it see things like speeding up and slowing down time. Is there a limit to how slow you can go?

[@EtzEchad]

I love the Minute Physics bass riff. :)

[@charlesbrightman4237]

Speed of light is the speed of light, maybe because the pulsating, swirling photon is the energy unit of this universe and everything in existence is 'light' (photons and interacting photons), 'gravity' being a part of the photon. 'Gravity' being the force that makes the sine wave of em expand and contract and would basically act 90 degrees to the em forces which of course act basically 90 degrees to each other.

[@82spiders]

Anybody have any idea why the "Show More" button"no longer works on KZbin? Or why since it doesn't work, they have not removed it from the page?

[@alleneverhart4141]

Hi 60 symbols, long-time fan. After watching this video I am concluding that it shows how the speed of light cannot be 'hacked' but it goes a bit thin on the premise of the title, why YOU can't go faster than light. I find that many people get boloxed up on that point - just because light behaves that way doesn't necessarily mean that matter is also confined to STL (slower-than-light), right? So I think I have a unique solution to 'splain just why that it so - matter is, in effect, frozen light. You see, when matter annihilates with anti-matter what happens? Two photons emerge traveling in opposite directions! Also, it is a well-known fact that the reverse of this process, two photons coming together to produce matter/antimatter particle pairs also happens. Thus, if matter were able to exceed light speed then you could convert photons into matter, whisk them away to remote locations FTL, then convert the matter back into light. Clearly this would violate the principle that the speed of light cannot be hacked, so matter must also be limited to travel no more than lightspeed BECAUSE it is a form of light.

[@DrumBeat231]

Thank you a lot. I was having trouble with my intro to special relativity homework, and this video helped a lot. I had the formula being u'=(u-v)/(1-uv/c^2). I guess I was confused on what u meant in relation to u'. Thanks again.

[@marlongerbes1613]

Is it light itself OR the fact it's massless the more fundamental property in the speed limit? Check this perspective: kzbin.info/www/bejne/o6S5pnZ7qJ2MmtE