Lecture 1 | Modern Physics: Special Relativity (Stanford)

[@yoondami1127]

I consider him my mentor even if he doesn't even know me. You're amazing, Leonard.

[@jitendeka5619]

Actually susskind has taken many of ours heart , I love this guy very much

[@parthadx7ster]

Undoubtedly the best.

[@AlmostBasian]

This is exactly what youtube is for. Allowing people to take their education into their own hands is key to social mobility. Things like this are making our society a better place.

[@rigomiller5465]

... I just woke up and he's still talking and where did this headache come from! The science channel made it look so much easier. Hats off to all that study this.

[@jwoya]

This is one of the fathers of string theory here :-) Listening to him, you get insights which never come out in a more straightforward explanation.

[@kaganesa]

i think its fantastic that stanford shares the brilliance of such great lecturers for free for everyone! thanks stanford!

[@CapyBrotha]

I watched Prof. Susskind's TED talk about Richard Feynman. It was very elegant listening to him talk about such a great man, and from what he described a great friend. I'd love the opportunity to sit in a lecture hall and listen to him describe this, however this is good enough! Thanks Stanford!

[@bostaurus1]

I love the way he is eating in all his lectures.

[@sirisaacalbertmravinszky2671]

So do I! I am not the only one! 😀

[@StaticBlaster]

Thanks for inspiring people to pursue science. We need more professors like him.

[@Cfx45321]

The simplest and most elegant derivation of SR I've ever seen !!

[@pierfrancescopeperoni]

Although the constancy of the speed of light is usually an axiom, I prefer to think of it as a consequence of trying to represent time and space with the same units, so that they are the same thing, and assuming that in such units there is interchangeability in the equations of physics, which means there is symmetry with respect to the bisector, which represents a point moving at speed c. So c is the same in every reference frame. And if we assume space and time are the same, it makes no difference to invert the space and time axes. So a particle moving at speed V>c is perceived as a particle moving at speed v

[@redpillmath]

The Absurdity of Special Bullshit Relativity Theory kzbin.info/www/bejne/gKndmaKJjKenndk. The falsity of Einstein's thought experiments, the thought Light-Clock, Lorent's equations, and the interest of the Elite, a selected coterie, to impose their Relativistic-Chaos stuff in our educational system to manipulate, control, and exploit vulnerable people.

[@pierfrancescopeperoni]

@@redpillmath lol

[@MrNopperaBo]

WOW, Leonard! After more than 6 years of university physics studies, only now I understand sinh/cosh :) Plus got another perspective on the derivation of special relativity equations. Mind blowing.

[@drb_physix]

Professor Susskind is a wonderfully clear lecturer, what a great resource this is.

[@Lakanyon]

I have school tomorrow and I could not sleep and so I looked up lectures to make me bored and sleep, I accidentally learned something and staid up another like hour and a half

[@usefulbobcat]

Use your tidbits of knowledge to realise. It's ok to stay up all night thinking because one day you could achieve something great even if no one will ever know. Knowledge is not to change the world but only to satisfy your own curiosity. It's your choice wether to share your thoughts or not

[@usefulbobcat]

But so long as your able to accept in the end is the only that really matters in the end

[@Mnemonic-X]

But this theory is full bullshit.

[@pphilosophy2156]

@@Mnemonic-X What theory is bullshit and why? What specifically? Special relativity?

[@feuzzionarts8129]

..goodmorning

[@amarah89]

i like how within the first five minutes, right after he announced that he won't be describing in detail what an inertial reference frame is, he actually takes 2 minutes to do just that.

[@TheGreenCommunity]

I absolutely appreciate all of great videos of the University Of Stanford ,they are profoundly useful.

[@prawn1535]

LOL

[@ik0ygj]

Thanks professor Susskind, I followed so many of your lessons at home that you are one of the family !

[@sepijortikka]

Thank you Leonard Susskind and Stanford university. I'm studying physics at Helsinki University, and these Lectures are really helpful!

[@Mnemonic-X]

But the special theory of relativity is full bullshit.

[@JohnLemieux]

"One plus one, over two, equals one. At least it did yesterday. (looks at equation) Yep, still does."

[@Elitecataphract]

He made it seem like such a stupid question haha

[@ellis2726]

i've been watching this on a daily basis as im really enjoying it, im just turning 16 and the whole special relativity thing has really got me hooked into science, so thank you for giving me an interest.

[@fahadalbalawi1828]

What are you studying now ?

[@ellis2726]

@@fahadalbalawi1828 Wow can't believe this popped up, I went on to study chemistry and I now teach chemistry/physics a-level

[@fgrv]

Admiro muchísimo que a través de internet tengamos el alcance de presenciar a personas tan prestigiosas, de universidades tan importantes como Stanford y hablando sobre temas tan avanzados e interesantes. Saludos desde Caaguazú - Paraguay! Viva la tecnología!

[@rsmith7710]

Love is the wormhole through which we can travel faster than the speed of light across spacetime in order to gain each other's perspective. Love is not one dimensional. Love is all dimensions. Love is all perspectives. Love is how we gain perspective. Memory is how we retain perspectives we have gained. Perspective is how we solve problems. If I find myself faced with a problem I cannot solve, then all I must do is first let go of my present perspective so that I may gain another.

[@flyingdutchman2649]

OMG!!! That's Professor Leonard Susskind!!!

[@pinoypangit]

I'm a working young adult with kids so the I had to take classes online. I'm currently taking Modern Physics. So far this video gave me a lot of help. Thank you very much. Vincent Villar

[@ritemolawbks8012]

I could listen to Professor Susskind for days. I even started walking like him. He's a brilliant man. I can't match his knowledge of relativity and string theory, but even I know you can't see sound 👉🏾[ 1:02:01 ]. No disrespect, but I know my five senses very well.

[@JasonW7467]

I definitely understand where your coming at. I get annoyed specifically when people try to explain other ways of going about the math than the professor is doing, which slows down the lecture.

[@shivaniits]

These lectures are so helpful, thank you stanford for making these lectures available 🖒

[@AETHERscience]

@UniversumExNihilo If I may: 1. It's not that the aether really does not do anything. Among others, it is the medium that conveys the electrostatic interaction between two charges placed in vacuum. And is the medium that carries the magnetostatic interaction between two parallel current-carrying conductors placed in vacuum.

[@artembluntzki7376]

Thank you KZbin for allowing me to view amazing lectures which my school doesn't have =]

[@adamx20]

Thank you Standford! It's fun understanding the principles of what is being said, but hearing the math behind those principles is just as fun. XD

[@caseros85]

Measurements in one inertial frame can be converted to measurements in another by a simple transformation through the Lorentz transformation in special relativity.

[@2OQP]

@AngelofAntistupidity Be sure, Red/Blue shifts occurs because of the Doppler effect. In that, when the speed of a moving source of a detected radiation(from 0Hz to petaHz, doesn't matter) impacts the actual distance that is has to travel to get to the detector, hence creating a perceived change in frequency. Now, stand corrected. Redshift occurs because distance augments and then frequency diminishes, it does not increase. it would if the source would reduce the distance.

[@AETHERscience]

Dear Prof. Susskind, At minute 1:00:50 of this video, you started to discuss about the aether. This was a big surprise for me because I study the aether. With due respect : - The speed of sound in air does not change if you move with respect to it (min. 1:02:04). What changes to an observer moving relative to the air at rest is the frequency of the sound (Doppler effect). - M-M experiment proved that we are at rest with the aether at all times. Respectfully, Ionel DINU, M.Sc., Physics Teacher

[@dmthom23]

These lectures are extremely useful! Thanks Stanford & Professor Susskind.

[@WorldClassLogic]

Math is awesome. Thanks SU and Professor Bloch for giving me free knowledge :)

[@Omnibus101]

From the above it follows that the ``Principle of Relativity`` requires that the mass m which a body has in a given system, be represented by the same mass m in any other system. On the contrary, Lorentz transformations require that a body of mass m in one system be represented by mass beta^3m in another system. Therefore, the ``Principle of Relativity`` contradicts the Lorentz transformations which invalidates it in its entirety.

[@magmigmag]

@Astro27Phys : there are couple of them online, but they are all 2nd and 3rd year status courses. In first year you will be concentrating on calculus, Chem, introduction to engineering, basic static and dynamic of mechanics, C++ (programing) etc. Things you might find online which will be useful later on are lectures on, thermodynamics, fluids, dynamics of machinery, solids, aerospace materials and so on

[@FlavoredCoffeeGuy]

@gamesbok C can be local, and in plasma physics, there is a set of equations that all use time to explain how the plasma borrows energy from it's own future. My point, is that it is upsidedown. It punches energy into the past. The vibrational energy of electron and ion temperature relates to why and how based upon C being local from a moving emission point. The borrowed energy is a product of present and superposition where C is local. It revolves around relativistic plasmas.

[@AETHERscience]

@UniversumExNihilo Yes, I am talking about the Michelson-Morley experiment. It showed that the Earth carries the aether with it (at least below the ground, in the basement where it was done), not that there is no aether at all. Later, Miller found that at higher altitudes there is a small aether motion.

[@TimTeatro]

@Madhusudan Mudhol You say "The students, i think are more mathematically proficient than Susskind." Would it change your opinion if I told you that Prof. Susskind is one of the fathers of superstring theory? He's also responsible for identifying the black hole information paradox.

[@TimTeatro]

Well, that explains things. You're arrogance is just a symptom of your youth. What year are you in? What is your favourite area? Trust me, Prof. Suskind is no slouch. Seriously, read his papers. He's not 'producing a few papers on a theoretical problem', he's the father of one of the most active areas in theoretical research, and the most mathematical theoretical framework that we have. I can't believe you're a physics student if you don't appreciate that. You say "Well I knew...and I still think he 's a terrible teacher." --- You didn't say he was a terrible teacher, you said he was mathematically ignorant. "The fact that he couldn't recall Kepler's or Newton's laws is..."---I don't recall him not remembering Kepler's law, and I'm certain he didn't forget Newton's law. But the details of Kepler's laws are easy to forget unless you teach first year physics. It's a bit of a toy model that gets used for historical reasons more than practical value. It is, however, useful to derive Kepler's laws from the deeper models that we do currently use to solve real problems. There is insight to be gained there. You really should watch some more stuff from Prof. Suskind. By the end of it, you may not appreciate his style any better, but you'll certainly have a different opinion of him. By the way; since you seem keen to compare credentials, I'm a physicist, but I'm currently working on a PhD in applied math in an engineering faculty. My background is in computational quantum mechanics.

[@TimTeatro]

***** Oh, well as long as you've taken physics classes, I bow before the master! I'll take my lousy physics degrees and a continue my little PhD, humbled by someone who's taken \*gulp\* physics classes. We're done here. Good day.

[@MrKmanthie]

You can't talk any sense to young children. They think they know it all. You just have to let them grow up & find out for themselves that they actually know very little and that their opinions mean very little.

[@legalfictionnaturalfact3969]

Maybe you farts should look up the flynn effect. Sorry.

[@edtExodus]

c is independand from the actual speed of light. It is a constant equal to the speed that light travels with in a vacuum. It is like a hard cap for the maximum velocity of massless particles (at least those we know). It is named speed of light because light just happens to reach the maximum possible velocity of massless particles when unhindered and undisturbed.

[@FlavoredCoffeeGuy]

@gamesbok C can be local, and in plasma physics, there is a set of equations that all use time to explain how the plasma borrows energy from it's own future. My point, is that it is upsidedown. It punches energy into the past. The vibrational energy of electron and ion temperature relates to why and how based upon C being local from a moving emission point.

[@signorellil]

Muller is very good if you want to get a general understanding of the topic, but thse lecture from Susskind are much better if you want to really learn the subject

[@krawte89]

@tnguyen318 The ball doesn't hit the back of the car because it too, is traveling at the same speed as the car. The laws of physics apply to any inertial reference frame. An inertial reference frame is one where it is not accelerating. Since the car is traveling at a constant speed, the laws of physics can describe the ball as if you were not in the car.

[@TheBobathon]

If d(tau)squared= dtsquared+dxsquared, then time would have the same properties as space in the theory: it'd just be another spatial dimension. You'd be able to rotate your finger from pointing East to pointing back in time, just as you can rotate from East to North. That sign difference is the only thing that makes time different from the other three dimensions. Because of this "(+ - - -) signature of spacetime", once you're moving forwards in time, you have to stay moving forwards in time.

[@MrUnkownperson]

Seems to be funny, But the ways of teaching is very good. His lectures helps me alot..............Thanks to Leonard and Stanford University.

[@johnliamten]

@krennolls it's not that the time spent out flying around at a constant velocity that makes the twin any younger, it's the acceleration he requires to get to that velocity. That is why the twin who goes off to space is younger.

[@jattymaniac]

x=vt is just the equation of the line following y=mx+c. M is being represented as V, and since the line crosses T at the origin c=0 therefore it is not included in the equation.

[@nadavdanieli]

40:07 this describes -x = t not x = x = -t, lets keep the visual consistent to the formula :) The bottom line is that relativity formula's just satisfy c = 1 for all observers. Clocks don't run any slower, bot inertial and moving observers clocks are at sync all the time.

[@fjolsvit]

Regarding Galileo's concept of an inertial frame, see Taylor and Wheeler, Spacetime Physics, 2nd Ed. Page 53. That makes it absolutely clear that Galileo had a concept of the invariance of physics between inertial frames.

[@AETHERscience]

@UniversumExNihilo 2. And it is not that it does not offer resistance: it offers resistance to objects accelerating through it - this is how you can explain Newton's second law that you need a force to make an object increase (accelerate) its speed in vacuum. The mass of the object is the constant of proportionality between the force applied and the acceleration produced.

[@AETHERscience]

@UniversumExNihilo Thanks a lot for your comments. So it seems that there is no relative motion with respect to the aether at all. But to conclude from this that there is no aether at all is as if one would say that just because there is no (air) wind there is no air at all.

[@CACBCCCU]

Suppose you're watching a star explode from a distance thousands of light-years away that you can easily track the lateral pace of the expanding flash as it's shown by its reflections off surrounding sparsely-scattered reflective dust. Forget that it takes millenia for the light to arrive here, note that lateral displacement over the course of a few years produces negligible relative increase in distance. One can say opposite ends of the ring separate at 2c, but it's only reflections off dust.

[@BlastOfPhurie]

for me its fun to watch this because i get these lectures in dutch so its a good way for substaining my english by watching this course

[@clayishamoeba2]

The work i do has absolutely nothing to do with physics but I still enjoy watching this infinitely more than CNN.

[@Curt1678]

I'm in Oxford University doing physics at the moment, in my first year. Our SR lecturer isn't great, so I came to watch this, and it's SOO much better. Stanford better than Oxford? Possibly...

[@AhmadKhan-sp3qb]

SR in 1st year?!

[@FlavoredCoffeeGuy]

@gamesbok C can be local, and in plasma physics, there is a set of equations that all use time to explain how the plasma borrows energy from it's own future. My point, is that it is upsidedown. It punches energy into the past.

[@guitarfighter]

@robbietea/Pt.1 "youtube needs a rewind button!!!"Hover your mouse pointer over the time bar which is located under the video.The time at which your mouse is at will pop up.Know that the circle at the end of the time line is representative of the exact point the video is at,still or in motion.Move the ball back and forth for instant rewind or fast forward.One can also read the time and left click along the time line for quick adjustments, which eventually becomes 2nd nature.DependsOnPtOfRef.

[@AlecBrady]

@RadostinaChipanova Spacetime has this unusual form of the Pythagoras theorem. It's what makes the time direction different from the other three. In this four-space, the hypotenuse represents the time direction for the observer moving along it. Hope that helps.

[@2OQP]

@freshfreenlovinit It depends what you mean by 'on' the train. Nothing is 'on' anything. The photons are emitted from the flame. Once they leave, they are on their own, just like the balls. And there is no 'beam' per se. Once they left the flame, they are on their own and will be impacted by medium, phase shift, dispersion in the chromatic and polarization space. The torch has a speed because of the train, the photons will leave at that speed plus C. No matter on which frame you are.

[@PresCalvinCoolidge]

@cubeloveme33 The challange in this first lecture is not the math, he only used algebra and trig. However, you cannot learn physics from simply watching these lectures, you need to be working problems. So if you have already done some problems these lectures are great supplement.

[@ronocko]

@TarverEngineering It's quite different to state that the universe had a beginning and stating that the universe had to be created by an external AND sentient being. One of the principals of science is that it doesn't matter who says it, it's what can be demonstrated to be true, currently the event/s before the big bang are unknown.

[@TarverEngineering]

@ronocko My reference is "The Meaning of Relativity" by Albert Einstein and my training MSEE. Relativity is based on Maxwell's Equations with Time decoupled from Space creating a 4th dimension. Internet links to the Copenhagen Observations do not exist. To quote Einstein, "Quantum and Relativity prove that a Sentient Being outside the Universe is required to make the Universe real". The competing Copenhagen observation claimed that Probabilities are determinant, a notion falsed by John Bell.

[@AETHERscience]

@UniversumExNihilo What I have said at point 2 makes very much sense, it can be put in an equation. There is an equation in hydrodynamics that is the key to the understanding of mass. And this fact is one of the reasons why I think the aether is worth everything from a scientific point of view.

[@RTVFX7oD]

@Fidde F. general cannot be confused with special relativity A ship accelerates away from Earth - unlike constant Velocity (special relative) the Inhabitants of Earth stay at the same inertia/gravity - it's not a reciprocal experience & thus the time dilation is not cancelled out A trip away and back ACCELERATING to velocities approaching C (relative to Earth) means the ship underwent MASSIVE inertia/gravity experience = slowed clock relative to Earth w/ it's unchanged inertia

[@d3l1a4973]

@baaroodii i am almost 16 also and i enjoy learning physics 1) b/c i enjoy learning new stuff @)its interesting to me 3) i enjoy not understanding something (i.e special relativity) and then i enjoy the feeling i get once i finally understand it

[@CACBCCCU]

My comment below was about an expanding ring of a light flash seen reflected in dust around an exploding star. Suppose glowing masses are ejected along with the light, and two such masses head off in opposite directions at the same speed, and both appear to move 2/3 as fast as the expanding ring in the same direction. The two glowing masses appear to have a differential velocity of 4/3 c, and it's an actual superluminal relative velocity. This is basically Beckenstein's perspective, afaik.

[@freshfreenlovinit]

@2OQP I do not believe the photons are like a ball. The ball exists before it is thrown and is on the train before it is thrown. The photons do not exist until they are emitted from the torch. Since observation has shown that the speed of light is constant for all frames of reference, I think it makes more sense to reason that the light does not gain momentum from the train because it is never on the train, rather than come up with a theory which involves time slowing down.

[@freshfreenlovinit]

@2OQP I did not say the photons come out of thin air. I said they emanate from the torch and they could well get their energy from an electron stepping down a lower ring. I am not debating how they get their energy which represents itself as light rays. I am debating whether they should also be getting momentum from the train since I don't believe they are ever "on" the train. You must be on the train to get momentum from it.

[@youcefyahiaoui1465]

I cannot believe that this respectable professor goes with the student argument that x' is bigger than x to modify the equations! A little more rotation of the second frame in either direction will make that argument go down the drain. The coordinates in the new frame are found by simply knowing that the unit vectors of the original frame are multiplied by e(jΘ) and concluding that x' = xcos(Θ) + ysin(Θ) and y' = -xsin(Θ) + ycos(Θ)

[@businessmonkey4726]

@ 1:29:30 someone notices that there's a non negligible adjustment to time dilation when "X" is very large. Had to pause the video and ponder on that for a second. Would that mean that two observers separated by a large distance would experience time dilation even if they had no relative motion? Of course not, right? The coordinates are arbitrary anyway so this shouldn't be the case. I'm sure I'm missing something about what X represents in this sense...

[@AlaskanSingers]

Knowing that he is at least trying to understand it is really what is important. Knowledge is something you should be proud to have not use to brag or show off but something you should use to enlighten other people so that they may be just a smart as you. By the way, sense when does it matter what grade your in anyway?

[@yamatushre]

wow! thanks. This is really great upload for science freaks like me. I hope to see more such uploads.

[@martinskanal]

At 10:00 Susskind refers to some lecture on relativity and electro magnetism supposedly accessable on the internet... Tried to google it, but failed to find the vid(s) in question. Does anybody know where to find this lecture?? Thx

[@aeroscience9834]

It's on KZbin but it's mislabeled. The titles of the lectures are "Lecture __ Quantum entanglements part 3" even though they are about relativity. You can also find it on his website: thetheoreticalminimum.com. It's the 2007 relativity series which is under the supplemental courses tab.

[@Oh4Chrissake]

@@aeroscience9834 Much obliged.

[@ugowar]

@Mrjbauer5 These lectures were meant for the interested general public, not exclusive to students. Susskind described the attendees in one video as ranging mostly from 40-70 year old people, people interested in physics. Not theoretical physicists or physics students.

[@RyanNorrington]

x prime is just a different measurement, you could technically replace it with any letter it is just to show that it is an unknown value which is different to x

[@ChristopherSyn1]

@kerkoky From Wikipedia: "Note that some of the lecture names are a little mixed-up: "Quantum Entanglements Part 3" is in fact a lecture series on special relativity and electromagnetic theory,

[@RealNRD]

@LoveGovernment The light from both of your flashlights will be moving at the same speed. It is my understanding that because you are in motion your time is slowed (compared to that of your stationary friend) and distance is compressed in the direction of the motion. This video explains a scenario similar to the one you presented: "Time Dilation | Einstein's Relativity"

[@TarverEngineering]

@ronocko Probabilities and the Theory of Relativity are Creationism. Einstein said so in 1927. (Copenhagen Observations 1927)

[@pjdatayan341]

Leonard Susskind would've made a great Tywin Lannister.

[@nmarbletoe8210]

PJ Datayan Hawking as Bran Stark

[@multimotyl]

PJ Datayan Ehm! Jonathan Banks. Ehm!

[@pukamon1681]

+PJ Datayan Old Man Marley from Home Alone

[@albericrex9005]

🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣

[@DrLafranz]

@sirrigs okay .. so .. u have the angle .. the new coordinate system .. can be expressed into separation of vectors .. if u dont understand that.. dont try to use pythagorean theorem to figure out how to separate the systems.. now .. he did something that maybe confusing to some people.. adding in the speed of light to the cosh and sinh functions.. the thing was that he was using a coordinate system in where every 1 unit is equal to the speed of light.. he added it back on later

[@krebit8899]

i am pretty sure when he gave this lecture he was not expecting an 8th grader to watch this but here we are

[@fermionplasma]

Special. General Relativity will be way over your head unless you are fluent in the language of tensors (which you won't learn until late in your undergraduate years).

[@FarFromEquilibrium]

Leonard is the best.

[@TheMathKing]

Ever read "Hitchhiker's Guide to the Galaxy?" They had an idea of forcing the Hilbert wave function of our bodies to have a 100% chance to warp somewhere instantaneously. It's true too, since our wave function's "probability to be somewhere" does extend throughout the universe, the thing is that it's approximately zero, outside a very small distance past our bodies lol. We need to see if we can control Schrodinger wave equations completely, I think.

[@2OQP]

@freshfreenlovinit Photons are created when a ring-elevated electron, steps back to a lower ring, in the process emitting a photon. They might appear as coming out of thin air but in reality, if the atom that contains the electron that is stepping down, is moving, than that photon shall have that extra velocity, however small an unsignificant in most cases, beside theory developments. The issue goes along those lines; it's decided that C can't change thence time' linearity is questioned...

[@liviur23]

I found: "Consider this warning from Wikipedia: Note that some of the lecture names are a little mixed-up: “Quantum Entanglements Part 3″ is in fact a lecture series on special relativity and electromagnetic theory, and the order in which the lectures were given is 1, 4, 5, 6, 7, 2&3, 8 and 9 (in terms of the numbers given on the videos). There is no ..." On that site there also is other information, like lecture notes

[@Bibchetoo]

@harvellt In the highschools in my country we study some elementary level of mechanics, movement generally kinds of movements and the different lows. Of course the 3 principles of mechanics we don't study quantum and the things from the mechanics we study them in 7th class and in 8th class we study mostly about cinetic and potential energies. Then in 9th class we study Electrostatics, Electric current, Electromagnetism, Oscillation, Light and we finish with Nuclear Physics.

[@fateplus1]

why don't the audience members just allow this great man to teach...

[@TarverEngineering]

@ronocko The story of Jacob is very old and I used it for that reason only. I can probably find a more obscure reference in another tribal history, but I find everyone can read the story of Jacob in the Western world. I believe Einstein's conclusion as to the meaning of the mathematical models of our universe in 1927 was intended to battle the Evolutionists who would deliver the Halocaust to Europe a few years later.

[@mnightsky]

@jmidesigns yes , u r right and thats what the physicists call it "mass-energy equivalence", where you can tell about an object content of energy if you know its mass.

[@hydropen1]

I'm just 12 years old but I understand some of his lectures clearly.

[@theophrastusvonhoenheim4022]

Do you get it now that your 21

[@AlternativApproach]

Special Relativity is a part of Doppler effect. Common formulas -> Unified Doppler effect..

[@csmcmillion]

@jmidesigns "If atoms are mostly empty how can things be so solid." Electromagnetism! The electrons surrounding each atom repel each other as the atoms get close.

[@CACBCCCU]

Following up, with the same perspective as below, if it's now a pair of exploding stars sitting spaced apart by a few light years, using the same best possible observer reference frame, i.e a safe and relatively nonmoving observation point thousands of light-years away, then there are observable two glowing masses with an actual superluminal differential velocity of 4/3 c, supposedly, colliding together. In the frames of these two masses, relativity prevails: everything's slowed to sub-luminal.

[@jeffcherytv6154]

that was awesome lecture.thanks a lot

[@bartkwezelstaart9306]

At 57:55 Susskind proves that the 2 equations (the first one's below this) obey the condition x'^2-t"^2=x^2-t^2. So you have: x'=x*cosh(omega) - t*sinh(omega) and t'= -x*sinh(omega)+t*cosh(omega) You want to test if they fit for: x'^2-t"^2=x^2-t^2. To do that, you want to square the first 2 equations and substract them from eachother respectively. Then you get: x'^2-t'^2= 0 ( because cosh^2 - sinh^2 = 1). Susskind says that therefore it is easy to see that the first two equations are right because they obey the condition x'^2-t"^2=x^2-t^2. Unfortunately i don't get that logic :3 Could someone show me on what logic that is based? Thanks in advance!

[@MotorFlaps]

(x')^2=(x)^2·cosh^2(ω)+(t)^2·sinh^2(ω)-[2·x·t·sinh(ω)·cosh(ω)] (t')^2=(t)^2·cosh^2(ω)+(x)^2·sinh^2(ω)-[2·x·t·sinh(ω)·cosh(ω)] Then, (x')^2-(t')^2=[(x)^2·cosh^2(ω)+(t)^2·sinh^2(ω)] - [(t)^2·cosh^2(ω)+(x)^2·sinh^2(ω)]= =(x)^2·[cosh^2(ω)-sinh^2(ω)] - (t)^2·[cosh^2(ω)-sinh^2(ω)] And finally, (x')^2-(t')^2=(x)^2-(t)^2

[@bartkwezelstaart9306]

Thanks for the response! I did, however, not formulate my question correctly. I already got the algebra, but i couldn't see WHY you can proof that they fit for the condition by this manipulation, but i can now ^^. It was actualy a very elementary fault and you might not even be able to see my confusion because it was just a little mind twist i had to come over. I did some practicing in calculating the relative velocity between some frames of reference that were apparently moving relative to oneanother with greater then c when one added up the velocities. Shall i post an example? Have a nice day!

[@MotorFlaps]

Bart Kwezelstaart There is no need, you too!

[@Gunner3210]

@cubeloveme33 If you really want to understand everything you need at least multivariable calculus (usually 2nd year university level calculus). The derivations for time dilation and length contraction can be done by knowing simple trigonometry.

[@belalakaperal]

@jmidesigns That does appear to be the case. I know we've changed matter into energy with nuclear bombs, but I don't believe we've ever changed energy into mass. Not only does mass give rise to gravity, but so does energy, that's all in the general theory of relativity.

[@Olconer]

am i the only one that likes to fall asleep to this . makes me comfortable

[@TheLiz217217]

"Susskind the plumber" and black holes. This guy is good.