I like how Sean Carroll explains these complex ideas in a way that is well within reach of the minds of non-physicists. Well done sir.

I always thought Sean Carroll was one of the best science communicators. Great to see him in his element like this

It is always a joy to watch and listen to professor Carroll. Complicated concepts are clearly explained and visualized. Thanks for this very informative lecture.

I don't really care for Great Courses. Just clicked for our boi younger Sean Carroll

He's one of the few people I disagree with in fundamental physics but still listen to for general discussion.

That was really a great lecture to watch. I got my own CONE out of intuition. LOL. Joke aside, To grasp such an idea of spacetime isn't easy as you might think ,but Mr. Carroll nailed it. Thank you sir.

Me: "Hey Sean, What time is it?" Sean: " *Yes* ."

Amazing lecture This man has a wonderful voice

Great job explaining complicated material! I find it interesting that our modern model of (space-) time, with its forward and backward looking light cones, looks so similar to one of our oldest timekeeping devices, an hourglass

Really very helpful to understand time... his explanation is very precise and even a layman can also understand the concept and importance of relativity and time

I now know that as much as science interests and amazes me especially astrophysics...astronomy...I will never fully grasp it, if I still mostly struggle even listening to Sean...still enjoyable..thanks for trying Sean Carrol...does anyone know anything that someone, who struggles like myself, could watch and maybe find easier to understand.

i’ve been on this rabbit hole for months now.. this is the best explanation i’ve ever heard!! seems like others almost try to make it more confusing than it needs to be ? idk

Excellent lecture, thank you!

So many of these kind of. Vids yet this one, actually explains things in the most wonderful way, I'm impressed and grateful

Awesome explanation! And the way speaks is so clear! Thoroghly enjoyed this lecture

prof. Carroll is phenomenal

"There's no such thing as one moment spread through out the universe that everyone can agree on" [Sean Carrol] Interestingly the word moment despite being defined as "..a brief period of time" is in fact a brief period of an event because moment comes from momentum which is tantamount to events. Meaning that periods \ duration are of events not time. So events have duration that are measured by time as space has distance that's measured by the metric system or imperial units. What we perceive as the passing of time is just the passing of events.

I would’ve never had the brains or knowledge to study any sort of physics but I’ve been really intrigued and really really REALLY inspired by Mr Sean Carrol In quantum physics i feel like I’m closer and closer to finding the perfect combination in spirituality physics science and geometry and symmetry and etc etc👌👍🙌

I wish I had words to express how much I want to understand all of this. Why can't it be explained? You are the very best I have seen. I like the way you present (OMG, can I say that now?) and pace what you say. I am rather intelligent in everything else! WTF? Help!!!

Can I go back in time and learn this fascinating science in school....when I should’ve been learning it?

Sean always crushes a good lecture

Very clear and entertaining....thank you!

How did he do it ? He looks so much younger. We, the people, believe he knows of, and has practised, time travel. Either that, or this one really old video.

It's interesting to think from the muon's perspective, where the earth is moving towards it at close to the speed of light. The earth still reaches it before it decays though, since the earth experienced less than 2 microseconds of time along the way.

Thank you !❤

Simply wonderful.

Absolutely wonderful lecture , thankyou great courses plus for bringing these insightful sessions available to everyone 🙏 .

Simply brilliant, they way he explains it all

Man it’s amazing listening to you guys

this video or channel this is my first watch,this is a fantastic and brilliant video thankyou for great lecture sire

Thanks. I appreciate the time and effort to put all these information.

12:37 - they came back with 'different reading' of time is because they were affected by different forces by each going through different path/speed/trajectory, while the TIME remains the same everywhere which is an abstract thing that nothing can change it, i.e. it is absolute. So the Newtonian theory seems to make sense.

Terrific explanation

This particular “chapter” was extremely bright for me. It explains space and time relative to my life, past, present and future. Thank you very much, I fear less the more and better I understand. My brain is racing in an exciting way, with thoughts and analysis. Thank you Professor Carroll!

Great description of time and space

Well explained sean

In multi body problems each axis has it's own time function depending on its acceleration therefore spacetime are bending and changing in multi body problem is mind boggling. Meaning our time is not known by another outside of our body and so are the other bodies. Just like the same harddrive memory could be used by many clients on same physical drive but the time of CPU and access time are different could get different data because of accessing method just like existence is different

You may b able to move your "light cones" around. but you can not change the origin of your light cone. If your light cone cone starts on Earth, it is always based on Earth, relative to your change of position in the solar system or galactic plane. Your space-time come from your relative place in the universal plane. Remember it's all relative to where you are.

Excellent video...

"If it's Dec. 7th, 1941 here in Casablanca, what time is it in New York,?" "I don't know, boss. My watch stopped."

Bravo....

Thank you for a better nomenclature.

I never move from my couch while in my trousers. I guess time flies by so fast in my experience.

THANK YOU DR.CARROLL...!!!

Nice video and presentation. Siddhartha Gautama conceived the principle of wisdom from meditation. Einstein conceived the principle of relativity from thought experiment. They both adored and worship by their disciples around the world.

He summarises this very well.

Thanks for the great explanation! And for the undeniable proof that the past exists - the tie :)

Thank you Teacher.

I don't know who Ponkray is but I have studied Poincare. An exceptional mind.

Inside an atomic clock an oscillator emits about 4GHz photon that reaches a Cesium atom, which absorbs and emits about 4G photon times per second. If I place a second atomic clock near a mass the Cesium atom emits 4G - a small value of photons per second. The mass influences what? The frequency of the photon of the oscillator? The oscillation frequency of Cesium? How ? By lengthening the space between the oscillator and the atom?

Why is it easier when Sean explains it?

Light and the speed of it play the most important part of time!

Best courses

Time is fascinating. I worked the subway stations for nearly 10 years. From one end of the city to the other. Every so often I would notice the city would be saying that, "Today just flew by" or "The day was just dragging along." How can an entire city, with no interaction with each other until they used the subway, complain about the same time paradox unless it was effected by it? Maybe a time distorted bubble the earth passes through in its revolution around the sun. Maybe random waves of time distortion hitting the earth? Maybe they're given off by the sun. Maybe they're from outside our Terran system and reach us in intervals. ???? 🎶"Ti-i-i-ime, is on my side. Yes, it is!"🎶 If you can think of a better way to do a blind survey of an entire city, in the small window of opportunity, I'm all in. Until then, I invite you to spend a couple years in the subways, between 2pm-10pm and you'll see for yourself. Just listen as an entire city gets off of work and gets out of school. You'll see it's more than a, "coincidence of circumstances" ;-P

Excellent

You lost me at lightcones. But blew my mind with the muon thing.

Fantastic lecture!

In Galileo system, x=vt, if only if dx/dt is constant. Lorentz transformation goal is distances (x, x’) x=f(v,t)and x’=g(c, t’) are mathematically equal in both systems with symmetry. So c is not Galileo or classic velocity, and t’ is not classic time. In Galileo, v varies, t is uniform at any point in space; whilst in Lorentz, t’ varies, c is constant in space. c =eu , is really the property of the space, or medium, or Ether. It is not velocity in Galileo.( v, C),(t,t’), they are (Apple, Orange), (Peach,Grape) in two math systems. People are still thinking they are same things. That causes confusion. Saying 1) if an object moves at speed of light, time stops. Moving object slows clock, etc. That’s wrong. It should be said t’ in Lorentz stops, or equal to 0. In Galileo, t is uniform, it doesn’t stop or slow. 2). Speed of light C is constant from any observer at different speeds. That is wrong. c in Galileo changes from observers, C in Lorentz as the property of space is constant. Then there is no ambiguity, confusing, both accurate in their own system for/from measurements. Time dilution, space-time curvature, etc. are all bogus by mixing concepts in two systems. If you use Fourier series to express a signal S, it is not the signal in time domain, it’s amplitude A in frequency domain. Nobody treats A-S as “signal dancing”. But sigma of all these series by frequency goes back to the value of signal in time domain. They are just mathematically equivalent, not necessarily physically same. There are many ways to do it mathematically, too. Relativity is just another way of measuring of the nature using electric magnetic wave in Lorentz system. It has advantages over Galileo system in Astronomy, because Maxwells equations describe electromagnetic wave in vacuum with eu as constant, which is the space property and its value equals to speed of light in Galileo. In Algol events, it can prove that light speed varies with observer’s speed( visit Algol website)

Time started when Dielectric energy decayed from the Inertial Plane/Counterspace. Inflation. Dielectric energy decays into Dielectric Voidance Field/Magnetism. The Grand Expand. Gravity is centripetal acceleration into the Inertial Plane. Gravity is Magnetism/Dielectric Voidance Field returning to Dielectric energy, then the Inertial Plane/Counterspace.

I love all physicists because they are the real heros I love space and time

The sky isn't the limit, your light cone is! Lol!

The 'clocks on spaceships' reference as a test idea, but then it was sad that relativity shows us that you can't measure time throughout the universe as one single moment that everyone agrees on. Key words here are "everyone agrees on" I feel. We should also hold to the importance of the idea that we can still identify a single 'moment in time', at least in principle. Say you freeze all of spacetime and look at it as a whole from a god's eye point of view. That's your single moment in time. Sure, the clocks of those spaceships and their viewpoints with each other will be different from their starting location, but that's just their rate of cause and effect (their time) changing. You can still justifiably state that picture as "a single moment in time", which if everyone could also look back and view, could all then agree upon that picture as well. Please correct me if I'm somehow wrong on this idea.

I’ll have to watch this a few more times and see what happens. Seems like a better way to explain it but I just can’t grasp it. It seems to me from the perspective of light time does not exist so how could there be a cone? I keep trying to understand it but I’m probably not smart enough.

What’s time? There are two times here. One is universal, the other is relative, t and t’ , which have the relationship t’=r(t-Kxv). At speed of light, or at black hole, r=0, so t’ stops. But t goes as usual. t’ is the time you observed through light. it is different from an object’s objective time t. Because c is considered as constant at any reference frame, so t’ and t are not synchronized. space-time. It is really just a Lorentz transformation of t. Just remember that when people talk time stops at black hole, or moving at c, that time is t’. A moving object, it’s time running faster or slower, that’s t’. Spacetime is curved, that also is t’. We really should not think only t’ is so called time. (Actually t is the base time, because v and c are calculated by t, not by t’). t and t’ have the relationship t’=r(t-Kxv). So, both t’ and t can not go back. People forget the conditions of Lorentz transformation and special relativity: point to point, inertia reference frame. What that means? It means that v in the above relationship, in Lorentz T , is constant, no acceleration. The object observed cannot have acceleration. If an object has acceleration, the Lorentz T and SR are NOT DEFINED. What clock measures is the synchronized events. Atomic clock measures atom vibration events, electronic watch measures quartz frequency, watch measures mechanical vibration events, the earth spins a turn as a day, moves a turn around sun as a year. We humans use different synchronized events to express different time. t’ and t, both are man-made.

Relativity is the time differential of light to create mass. Everything moves at the speed of light except when slowed down.

Maybe space becomes a point in time inside of a blackhole because it's so compressed that there is no vacuum for the quantum field to propogate inside what we call, "time".

At the end Dr. Carroll refers to General Relativity. Does he have another lecture specifically about GR?

We can send the different kind of time function and not the counting time so it can change it's time by applied new formula of time function each time it receive and calibrate two system one mechanical time and one on atomic clock

when ti,e becomes personal / where does the space go to contain the observer

He explains very well, but I just don't understand. I am relatively dumb. :(

Very very good

Can we define an absolute equal time for all reference system using Lorent's equations? A definition of absolute time can be given in accordance with the Lorentz equations Time dilation is not a good interpretation. see this demo The traveling clock is characterized by its position x=vt and the time observed from the stationary system dt' = dt/g. g is the relativistic factor we will write (dx, cdt')= (v, c/g) dt. c= light velocity (dx, cdt') = C dt C is a vector of magnitude c. after a time T all frames of reference have a timeline length equal to T. C is the transport vector towards the future, but the future has different directions (those of C) but the same magnitude, time dilation has no basis. Seeing the evolution at an angle, you can see a component that is used to give speed to the moving system and a component in the direction of the future of the stationary system t'. kzfaq.info/get/bejne/gtiGpbyTztPOY30.html

Exactly constant varies in space but event is real.

Studying special relativity and have watched Sabine Hossenfelder, and Brian Greene etc. Coming back here for a review. What amazes me is that none of these folks ever try to define TIME. Why is that? I know our brains did not evolve to understand it, just to use it to survive. But really, these science folks have got to try to define TIMEt in words. It appears to our brain as some kind of "gap" between events. Is that the best we can do? Hossenfelder states that time dilation is caused when movement is on a parabola which is by definition, acceleration. See Hossenfelder on KZfaq. I see Carroll has a video called "What is Time." I'll check that out.

Time as we think we know it is only a concept of the human mind. Time neither starts nor ends. Relativity effects of time appear only when we try to make measurements.

Good explanation of incongruous blather

Time is symmetric only insofar that the operator that has us move forward through time has an inverse operator that moved us backward through time. Yet, as soon as you bring moving objects into the picture, you can’t just rotate the time axis and expect to get the same picture. There’s actually a phase shift. One has to wait until the curvature of the object‘s time axis has inverted its direction on my space axes. Also, in the real world, the falling object would collide with something eventually and thus produce heat, i.e. entropy.

Did Newton really have all that hair? I am skeptical. Love the “running back” analogy…the profound insight of relativity for me (that took me years to comprehend) is that C is the only constant, it’s space and time that are mutable, light speed never varies ever.

saw this so long ago. big up Sean. Level of stripes!

Great courses changed their name to Wondrium.

I need help with my new years resolution. I've figured out how to change the stars. My idea for changing the stars includes Orion and Pleiades (Subaru). I figure it's time to put something up there that's relevant to us, don't you think? Take Orion's belt and Betelgeuse becomes the head with a baseball hat. Below the belt are two legs bending at the knee. The feet aligning perfectly under the bent knees. The 3 stars of Orion's belt align perfectly as the 3 fat belt loops on a baseball uniform. The spear pointing at "Subaru" is the bat being swung and "Pleiades" is the baseball flying away after being hit. Put it all together and you get, "THE ALL-STAR." In my case, I see a left-handed batter and I imagine a "7" on the jersey. Which makes him, "Mickey." (As it should be ;-) But you can put any number you want, making, "THE ALL-STAR," any player you want. It'd be wrong of me to not, at least, try. This is me, trying. Pass it on, please and thank you. Don't worry, where I come from, crazy is a compliment! ;-P

I think what Einstein did was an observation. He interpreted the results well. We however lack similar observation and interpretation

Question : If the universe is expanding with more entropy. Is time speeding up, which we cannot measure?

I have been investigating propagating Electromagnetic fields for many years. My investigations revealed that these fields and the information in these fields propagate nearly instantaneously when they are created and reduce to the speed of light as they propagate into the farfield. According to Albert Einstein, if the speed of light is not a constant, then his theories of Special and General Relativity are wrong. This can be seen in Einstein's time dilation result due to a moving observer: t=r t' and the length contraction result: L=L'/r, where t and L are reference to the stationary frame, and t' and L ' are reference to the moving frame, and r is the Relativistic gamma factor: r =1/Sqrt(1-(v/c)^2). These results are easily derived using Einstein's light clock thought experiment using simple algebra. But if propagating EM fields with infinite speed near the source are used in the derivation, then c = Infinity, and r=1. If propagating EM fields far from the source are used, then c = the speed of light, and r= the standard Relativistic gamma factor. What comes out of this is that the effects on time and space are completely different depending on whether one uses propagating fields near or far away from the source, which can't be true since time and space are real. So the conclusion must be that Einstein's Relativity is wrong and time and space do not change with respect to moving reference frames, Galilean Relativity is correct, and that Einstein's equations just enable us to back calculate to the correct answer, givin the time delays observed by the propagating EM fields used in measuring the effects. But these results do not account for the time dilation observed by moving atomic clocks in airplane experiments, but can be accounted for using variable light speed theory (VLS), origionally proposed by Einstein, and later improved by Robert Dicky in 1957. In this theory, spacetime is not curved by gravity as suggested by General Relativity, instead Newtons theory of gravity is correct and the many other known effects of gravity are due to the affect of gravity on the of light speed. For instance the observed bending of light by mass, which caused General Relativity to be accepted, can be explained, by the gravity generated by the mass, changing the speed of light, causing the light to bend around the mass. This effect is analogous to the bending of light in glass. Since lasers are used in atomic clocks to measure time, then the observed time dilation in atomic clocks in moving airplanes can be explained as due to the effects of light speed changes in the clocks due to changes in gravitation as the plane goes up and down. It should also be noted that several researchers have shown the relation E=mc^2 can be derived without Relativity using Newtonian mechanics, and the Michelson Morley experiment can be explained using the Doppler effect, ref Nathan Rapport 2021 In summary, this research shows that Einstein's theories are wrong and that time and space do not change with respect to moving observers, Galilean Relativity is correct, Newtons theory of gravity is correct, and many of the other effects of gravity can be explained as gravity simply changing the speed of light. The importance of this research is that it completely changes our understanding of time and space and gravity, and simplifies our theories. Perhaps this new understanding will finally enable researchers to finally unite Gravitational theory with quantum mechanics which have been incompatible since scientists accepted Einstein's theories for Special and General Relativity. For instance, Relativity is incompatible with quantum entanglement, which requires communication faster than light, but can perhaps can be explained by superluminal propagating fields between entangled particles. It should be mentioned that this superluminal effect is also observed in the propagating gravitational fields generated by an oscillating mass using Newtonian gravitational theory, and is nearly infinite near the source and reduces to speed of light far from the source. This matches very well with observations of the stability of the planets, which would not be possible if gravity propagates at light speed, and was origionally proposed by Simone Laplace in his famous book: Mécanique Céleste in the late 1700's, where he estimated the speed of gravity to be 7x10^6 times greater than the speed of light.

at 08:47 -- Suddenly I think that Simultaneity is impossible. Every lightray in the eye has wandered through space, and space is only possible because of individual time. ... or ...

My idea so I get to name it! What I mean is, no one has claimed it so I'm officially calling, "Dibs." Voyager 1 is now in the, "Milky Way's interstellar time" or "Mikey's Time." "V-ger's" message has sped up now that it's outside our Sun's, "Time Bubble," or, "Terran Time." It will be faster, still, when "V-ger" sends a message from beyond the Milky Way's time bubble. Then there's Outside the Local Group time bubble. So on and so on until we get outside any influence and into the, "True Interstellar Time Standard." Or, "T.I..." ;-P Now that "V-ger" is outside our Sun's reach, in interstellar space, it's now in the Milky Way's faster moving, Interstellar Time or "Mikey's Time." This can be proven by turning off everything except its clock and transmitter. Have "V-ger" read time for as long as possible. They WILL show the flow of time speeds up the further away you get from any celestial bodies. Until you reach the Milky Way's time standard or "Mikey's Time." •Our sun's time bubble: "Terran Time" we know and have measured. In a lifetime, our head is one second younger than our feet. •Milky Way's time bubble or "Mikey's Time." The rate/flow of TIME outside any influence but within the Milky Way: We just got there and are still figuring what the difference is. Wild guess I'd say time will increase in speed, now and until V-ger is outside the Ort cloud. •Local Group's time bubble or the rate/flow of time outside of any influence but within the Local Group: Name still open and unknown. Wild guess .08 P-22% to a couple seconds faster, maybe. Used just for reference. •Outside any influence in the, "True Interstellar Time Standard." (or T.I...) ;-P This name is NOT up for grabs. The rate/flow of time is fastest here. (Time flows fastest here so it's best to use a motor boat and hold tight. Always applies when you're in T.I....) ;-P A minute is a minute in all. It's the rate/flow I'm talking about. Heck, rivers of time flowing differently might explain dark energy and dark matter. The Milky Way's Interstellar Time Standard will be known as, "Mikey's Time." Pass it on, please and thank you!

It appears that the universe started as something tiny and started to expand to what we can observe and detect today. It also appears that anything we can observe or detect is made from extremely tiny particles which interact and combine with each other based on some fundamental predetermined rules. We have identified quit a few of these extremely tiny particles and have identified quit a few of the rules these particles follow to interact and combine. Perhaps most of the particles and most of the rules but there probably are more. We also discovered that anything that we can observe or detect is made from the same basic stuff and we call this stuff energy. We know this because we have figured out how to calculate a value or quantity of energy for anything that we can observe or detect. I think we can say the fabric of the universe is space time but we can also say that the fabric of the universe is energy time because we now know that space is not empty and is also some type of energy and we can calculate or at least estimate how much energy is in a given volume of space. It also appears that after the universe started to expand, no more energy was added or removed as it continued to expand. We do not know what the rules were that determined the amount of energy in the universe nor what caused the energy in the universe to start expanding. The rules for how energy expands, transforms, interacts and combines cause energy to cycle from concentrated to diluted states. Although the cycles can be repeated almost an infinite number of times, there will be a time when they stop because as the cycles keep repeating, the total amount of energy in the universe keeps becoming more and more diluted. We call this rule entropy. At some point in time, all the energy will become so diluted that it will not be able to cycle back into more concentrated states and we think this is when the universe ends. We still do not know the rules before the universe started to expand and we still do not know the rules after the universe ends and there are probably still many rules that we do not know about what causes the energy in the universe to cycle back and forth from concentrated to diluted states as it continues to expand and dilute.

Thanks! I'm going to utilize this more. We would have time. ... Yeah, We are choosing the best choice for all of us. (Sorry for a unexpected message.)

So how would length of an object is measure. By placing it against standard scale, its one end is marked on scale then other end. The difference in value of two ends is length. One thing is assumed here that an object is at rest with scale which is also called as coordinate or frame. Now if an object have some speed against the scale or frame then does its length could be measured accurately. No, because it's not possible to mark both ends at same time and if object and scale have relative speed then one of end either contract or expand the measured length of object. This is relative measurement and when object is at rest with scale is proper or absolute measurement. Now relativists says that both measurement are correct and more than that if either object or scale is moving then relative measurement is giving actual description of object's physical quantity. So whether length contract or expand that relative measurement define physical state of object as by relativists. Further than that, in most conditions there is no frame moving with light speed and some events happening in it. Observation of planet is not relative because observer with scale like clock and angular scale is on earth. In case of far objects it's not possible to directly measure object so light is used. But relativists says that speed of light is constant whether source or observer have relative speed or not. First thing, general science laws doesnt allow it, second it require that light should have special quality which it has not so. In classical relativity that replaced by theory of relativity which we know now, has no problem with measurement of distant objects because its absolute and relative measurements are same so no problem. All problems start with insistence of relativists that speed of light is constant so they change fundamental quantities like length, time, mass. Suppose some children are playing in ground which is stationary. Now if an observer moving with quarter of light speed measure length of ground as per theory of relativity, found that length of ground is small as compared to what is told. Another observer with half light speed measure length of ground and found that length is contracted and also differ from first observer, then who is right, observer at rest with ground or moving observers. Does measurement of moving observers that differ from rest one, in any way affect or give actual representation, no. Same thing is with time, moving observers says children are slow. Does clock of moving observer change the movement of children on ground, no. Question is why they are doing so inspite of evidences against their theories. Reason is that constancy of speed of light is required for their model of universe, if that is changed then their model collapse.

I'm looking for a video titled "relativity is finally proven". Have you seen it?

Okay, so rate of time is affected by rate of speed, acceleration. And we think muons have enough time to reach us, despite their rate of decay, because time for them has slowed due to their acceleration. But what acceleration is that? From the moment a muon comes into being, as a pion decay product, is it accelerated and by such a value that would meaningfully slow time for it?

please check the settings of the subtitles, I tried to change the subtitles in English but they are stuck in the Korean language. Great video though.

Best people

One of the best teachers I've seen. Absolutely brilliant explanation for someone (like myself) who is just starting to explore relativity. Many thanks

Time and space emerge from motion. We live in a universe of motion. Matter has an "inward" motion (gravity) and forces have an "outward" motion

Respected sir, can we collapse time and space through our imagination? Through our imagination we change the reality with out taking any action.

BAM!!!

If a photon were to wear a watch (silly but hear me out), that watch would never tick. Since the photo is massless and thus traveling at c, its movement in space-time is all in space and not at all in time. So in the photon’s context, time is still. And it’s not even traveling, because you can’t travel without time. The photon, to itself, is simply everywhere at once. Yet in our context, we see the photon move on the edge of the time cone. Therefor, I believe time itself is traveling at c. Light is riding the wave of time… How am I wrong?

Using the same robots experiment we could send diferents robots with sincronize clock to different directions and follow the path where time moves slower and faster. That would be the true arrow of time

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