STUDY WITH ME | Special Relativity

Follow along with the special relativity course at brilliant.org/...
In this video I talk about spacetime diagrams, simultaneous events and causality in special relativity.
I make videos about physics, math, astronomy and scientific beauty with a new episode every wednesday and sunday.
💌 Your personal invitation to subscribe: www.youtube.co....
🐦Twitter: / tobyhendy
You might enjoy:
STUDY WITH ME| Math for Quantum Physics • STUDY WITH ME | Math f...
✨

[@ssyyc]

Your voice is so peaceful I’m very much enjoyed it.

[@IOwnThisHandle]

enjoying *

[@supratiksarkar1195]

Yeah. I don't listen to the concepts or anything she teaches. I only see her peaceful face and hear her voice.

[@Joe-bb4yi]

Bob 😐 ily

[@animationspace8550]

hey, nice grammar (at least you're trying)

[@michailtodd8115]

@@supratiksarkar1195 me

[@AndrewDotsonvideos]

So I can't simultaneously disappoint both of my parents so long as one is moving. Good to know!

[@Backpackguy12]

I've seem to have broken physics then

[@mgominasian9206]

The physics meme lord is here

[@satrickptar6265]

Lol

[@ishworshrestha3559]

Ol

[@cyan1294]

@Just Kieran The power of a stars emission doesn't affect the speed of light at all. Photons move at a very constant speed through a vacuum and there may be some evidence that it inst constant, it certainly inst a result from the power of a star. Also, c is a constant for the speed of light in a vacuum, not in any medium. Last thing, the reason people say that c is a constant is not purely because of light... its because the speed of light is the fastest speed at which two entities can "communicate" with each other, in flat space time.

[@CraftAero]

I just leave Tibees on repeat while I sleep. My thesis is nearly complete, but I only understand it in my dreams.

[@984francis]

That's interesting. I play the piano but when I dream about it, I am a brilliant pianist. The funny thing is that I understand what I'm doing when I play the piano in my sleep. Awake, not so much😬

[@eengin6057]

I love that she acknowledges what she is rusty about and makes sure the audience knows where she might fall short, so that they can look for better answers if needed. Tibees, you are a true scientist that values accuracy, keep up the good work. love your videos

[@youtubtc]

Neat video, no music, soothing voice, outstanding knowledge. Pure class

[@WTFhappenedWITHyou]

Can't wait for space battles so I can use this knowledge to outplay my opponent

[@sacsays]

I'm a digital marketer but after listening to your voice I think I must learn special relativity again. Mesmerizing voice and smile.

[@martm216]

Agreed. She is something special.

[@madhurjyagoswami434]

My attendance would have 100 percent if my teachers are like you.

[@sirdan357]

@big fish I don't think he's talking about the information.

[@animationspace8550]

@big fish brilliant premium cost money tho, and sirdan357, what else is there rather than info?

[@40chins_always_wins]

@@sirdan357 Animation Space is getting impatient for an answer

[@arjunarun9147]

@big fish like a teacher using a textbook to teach but this time it's more "modern" so yeah she's still an AMAZING teacher

[@shivamshekhar2497]

Never believed I would make it to the end of this video, but your sweet method of learning and to make us learn, made sure that I end up understanding each concept behind each problem. Thank you very much😍

[@chakshupunj5943]

Relativity is one of my favorite concepts in physics. This video made my Day!! 😀

[@onehitpick9758]

You are humble, knowledgeable, inquisitive, and best kind of professor I could think of.

[@aromview]

Your voice is calming and makes me want to go back to have a look at some of my physics notes from High School.

[@whouse7]

You are awesome! Love your clear calm voice and no music! Thank you!

[@soyouknow8207]

If only you would have been a teacher of mine, I would have gone to my classes more often. Very peaceful and calming voice indeed. Very clear explanations as well. Cheers

[@ItsLucy]

I think you would make an absolutely amazing professor if you ever choose to go that path.

[@anilkumarsharma1205]

path padna pathati pathak pathan pathun path is ways to go, to dp so hindi, sanskrit and you, your, youyam language are common among us that is why Indians and english literature got influence on each other and we are oldest citizens of the world so we are far more superior then any other else

[@mydogbrian4814]

Nope; a sleep Therapist or Hypnotist.

[@mydogbrian4814]

@@anilkumarsharma1205 But of course you are. You can be anything you want in your own mind.

[@superCattaz]

I'm here for the Physics, since I will start the Relativity course next year. Many thanks from Italy.

[@User-jr7vf]

So how are you doing now?

[@zeynep-iu2bt]

So how you are doing now?

[@dijin456]

I study alone .so it's really nice to see what other people are doing..gives me something else to think about I wouldn't on my own..

[@LukeLGK]

I haven't the slightest idea what you're talking about, but I love watching your vids!

[@anapoda3081]

that's 90% of people watching this

[@doublenegation7923]

@@anapoda3081 That is... to say at the least concerning.

[@quahntasy]

Never studied relativity in such a peaceful way.

[@Brandon-ml6ls]

Hi Tibees, Thank you for sharing your videos with us. I thought the following excerpt would be helpful to your studies, as you mentioned a common misconception around 2:40 in the video. From the last paragraph on page 11 of Sean Carroll's textbook, Spacetime and Geometry, "The notion of acceleration in special relativity has a bad reputation, for no good reason. Of course we were careful, in setting up inertial coordinates, to make sure that particles at rest in such coordinates are unaccelerated. However, once we've set up such coordinates, we are free to consider any sort of trajectories for physical particles, whether accelerated or not. In particular, there is no truth to the rumor that SR is unable to deal with accelerated trajectories, and general relativity must be invoked. General relativity becomes relevant in the presence of gravity, when spacetime becomes curved. Any processes in flat spacetime are described within the context of special relativity..."

[@hbm293]

Indeed in SR, when you write Lorentz transformations $X'_\mu = \Lambda_{\mu u} X_ u$ (where the X_\mu are the position 4-vectors in different frames, and the $\Lambda$ tensor what describes the change of frame and will depend on the \gamma factor and on v^2/c^2), it is possible to make \Lambda depending on the instantaneous velocity at the point X_\mu, meaning that you do (now) *local* transformations instead of "global" ones. GR is indeed relevant when your metric tensor vary at each point of space-time.

[@jerrybrennan9327]

Tibees, mathematics has left me behind, looking at the overwhelming schdmatits and diagrams caused my brain to overload with anxiety. Yet somehow I'm able to understand much of you teaching. The pleasant, calm use of your voice relaxes me and I believe helps it sink in. Thank you for all your hard work and generous sharing of you knowledge. Well done young lady. I see many great things comming your way no Matter what path you choose. God Bless.

[@HolyMith]

"The perfect woman doesn't exi-"

[@abdusabdud8218]

This is str

[@tombufford136]

Very useful video. The end example has a reminder of a negative gradient being less than a positive one, taking into account the distance is in the reverse direction. Hence slope and direction should be considered.

[@jad1910]

It has been more than an year since I studied Relativity, good refresher.

[@lolablack1]

Do you know you're doing ASMR? 😜 Lovely video 💖

[@shine-ub6eb]

You're so calming, I really enjoyed this

[@SuperPraveenkumarpk]

I can totally tell the difference when you say girl and gull

[@DougOfTheAntarctic]

In New Zealand, the letter "r" (pronounced "ah") is virtual, unless it's the initial letter of a word.

[@satrickptar6265]

Then ask an Indian to pronounce gull and girl lol

[@lawrencedoliveiro9104]

If the third character had been a ghoul, would that have furthered her goal?

[@lawrencedoliveiro9104]

3:03 That was the one I initially had trouble with, that two observers will always measure the speed of a beam of light to be the same, regardless of how they might be moving. But the Michelson-Morley experiment, among other empirical data (e.g. observations of eclipsing binary stars) all back this up.

[@infinity2infinity401]

I love this I can’t wait to learn more about this in the future ! ! ! Thank you so much, you are truly an inspiration.

[@Robert_11911]

Your voice is very calming, Toby. You make a great teacher!

[@mjnyc8655]

But her looks are too distracting to males.

[@mjnyc8655]

@Izakaro Good question. I invite viewers to offer their opinion.

[@vesuvandoppelganger]

THE PARADOX THAT DISPROVES SPECIAL RELATIVITY: There is a triangle of lights which we will call A, B, and C. They flash simultaneously in the frame of reference that is at rest relative to these lights. There is someone moving at a high rate of speed from B to A. There is someone else moving at a high rate of speed from C to B. There is someone else moving at a high rate of speed from A to C. So A flashes first and then B flashes and then C flashes and then A flashes again. How can A flash twice? When A flashes has B already flashed or not yet flashed? or B flashes first and then C flashes and then A flashes and then B flashes again. How can B flash twice? When B flashes has C already flashed or not yet flashed? or C flashes first and then A flashes and then B flashes and then C flashes again. How can C flash twice? When C flashes has A already flashed or not yet flashed?

[@lawrencedoliveiro9104]

2:33 Make that “constant velocity”, i.e “constant speed *and* direction”. A spinning frame may have every part moving at a constant speed, but the direction is continually changing, so there is still acceleration going on.

[@JustaReadingguy]

She did add the "we are excluding accelerating reference frame."

[@Jirayu.Kaewprateep]

Thank you, I experience once my friend run away from the dromitiry guard and he is riding the bycycle. My friend just run through small gap between drom. but more direct path than the guard that riding around by bycycle. It does not mean my friend running faster than the guard riding the bycycle. And you are correct, sometime the light is bending as sometime its behaviour like particle. Good question.

[@outsideofadream]

Was pleasantly surprised to see this video and one other of yours turn up in the horror movie The Strings!

[@SandeepSingh-vd9in]

Tyson having 2 zeeros in all subject ,fail in all subjects ,but I alway whaching your channel very mind blowing very emprasive , specially in math and physics.

[@theboombody]

It took me FOREVER to accept that time does not flow universally for everyone. Eventually I accepted it. I estimate that forever translates to about two years in this case.

[@VernCrisler]

I can see how the diagrams are constructed, and that there's a difference between inertial and accelerating reference frames. And that the speed of light must be the same in all reference frames. To say I understand it, however, would be an optimistic statement. Why, for instance, is time placed on the y axis rather than the x axis? Is time non-linear? Does the space-time diagram mean time is going upward? But upwardness is a spatial term. The whole thing drives me to drink (more).

[@abhijitganguly5339]

this is a really sweet yet talented girl,I WISH HER SUCCESS IN LIFE!

[@ronaldderooij1774]

One of Einstein's postulates was also "Causality must be maintained, no matter what". By the way, I have looked at a lot of KZbin videos on the Twin Paradox. But nobody seems to agree on whether or not acceleration plays a part in the explanation. Can you shed some light on the role (or lack thereof) of acceleration in the Twin Paradox?

[@Joao50297]

omg i love this channel so much, definitely one of my favorites

[@NothingMaster]

Bob Ross would have been proud of your soothing voice and gentle demeanor. 👍🏻👏🏻👏🏻

[@joshwa6569]

I always had a doubt like "is there a specific college to study THEORY OF RELATIVITY?" or "what job do I acquire if I study THEORY OF RELATIVITY?"

[@redpilled7002]

I'm so thick that working out the girl, gull and guy references threw me completely!

[@sowmyag5142]

Tibees pls make a video on your journey to mit. Plsplsplsplsplsplsplspls You are my inspiration

[@Holobrine]

On the light cone, all events you see as simultaneous form a circle. But the events that seem simultaneous to a moving observer lie in an ellipse. Yay conic sections!

[@samialishah8118]

Special Reletivity , Whenever I study it, I always have the same astonishment as if I were studying it the first time..

[@kaisu8198]

Highly enjoyable thank you!

[@shivalayayadav7685]

Love your voice💞

[@joshuasongate786]

I wished i had a teacher like you when i was a student

[@gordonfreeman8368]

Fascinating subject indeed

[@badrakhariunchimeg1031]

momentum tend to equalize if it's boxed box move all together what ever it is

[@SandeepSingh-vd9in]

Sew,free friction dimention is it one,two,three or multidimensional space

[@johnmills9360]

40 years ago , derive the equation of an electromagnetic field from the equation of an electric field . C is a constant in a vacuum . YES ! 30 marks in the bag ! Uncle Bob lost his mind somewhere along the way :-)

[@mediocreape]

I don't even know what i'm doing here, It's like a brute trying to understand rocket science. I'll gracefully show myself out now.

[@martm216]

Toby - here is a question that has always puzzled me. And I won't explain myself very well. But a test was done to prove Einstein's theory of relativity, and how it affects time. It was something like they flew two atomic clocks around the world on jet airliners, in opposite directions. And both clocks showed a different amount of time having passed. Now, we know that the theory is correct, but I do not understand how this experiment could have proved anything. A clock is just an arbitrary instrument we use gauge the passing of time. It is not time itself. The clock would not KNOW that time was passing differently. It would just keep ticking along at the same rate. If my alarm-clock in the bedroom runs slow because the room is cold, that doesn't mean the coldness has altered time. I am obviously being dense, but can you enlighten me?!

[@martm216]

Just an amendment to my question. I have since learned that while one atomic clock was flown around the world, the other one remained stationery. But my question still remains: a clock, no matter how accurate, is merely an arbitrary measure of time, so that we may agree between us when a certain moment has arrived, e g for an appointment. But our minutes and seconds on the clock are not the actual moment itself. A clock, whether in motion or stationery, cannot KNOW that time is passing at a different rate. A clock is not time. A thermometer, or barometer, senses heat and cold, or air-pressure around it. A clock does not put out 'feelers' in this way. It is a sealed unit. It will tick away at the same rate whatever is changing around it.

[@donaldsheahan600]

@@martm216 Do you agree that if we place a ticking metronome into a moving rocket in which time passes more slowly, the metronome will tick more slowly?

[@martm216]

@@donaldsheahan600 interesting question. So are you suggesting that the effect of movement, especially at extreme speed, has an affect on the metronome making it tick more slowly, and therefore demonstrating that time is also passing more slowly? Yes, I think this begins to help me. I am not doubting that the experiment with the atomic clocks was valid - I'm sure the physicists know what they're about - plus it bore out Einstein's theory, which everyone knows is correct. It was just that I couldn't understand how the moving clock would know that for it, time was was passing more slowly. But I think your metronome postulate helps me. Thanks for your kind reply.

[@donaldsheahan600]

@@martm216 Actually, I'm using the reality of time dilation as a starting point (which can be derived using Einstein's two postulates surprisingly easily, see Wikipedia for example). Then using this result, we can calculate that time should pass twice as slowly in a rocket that moves at 0.866c relative to us; that is to say, after two minutes has elapsed for us, only one minute will have elapsed in the rocket. Then my point is simply this: A ticking metronome (set to 60 bpm, say) depends on time; its physical parts move such that it ticks once per second. Special relativity predicts that, in the moving rocket, a process that takes one second is slowed down and will take two seconds (from our perspective). Thus, if we place the same metronome in the rocket, we should observe that its parts move twice as slowly and produce one tick every two seconds. Same goes for all processes: a ball should fall twice as slowly, a cell should age twice as slowly, etc. Likewise, SR predicts that a clock moving in an airplane should take longer to tick, and this is what we observe in the experiment you mentioned. Hopefully this helps. Edit: mixed up my reference frames at first. lol

[@martm216]

@@donaldsheahan600 yes, I think it does. Seems I was too abstract in my thinking, such as it was. I wasn't grasping the sheer physicality of the process. Thanks for your time and patience!

[@samferrer]

This is very interesting ... are you planing to follow a series? Can we suggest subjects?

[@ffggddss]

Splendid intro to SR! I think the pacing is suitable to a beginning physics student's introduction to SR, who has already achieved some facility with Newtonian mechanics. Seems like we were almost at, or perhaps at the treshold of, defining the spacetime interval, which is an example of a SR invariant quantity. From there, we could move into spacetime 4-vectors; and the Lorentz transformation, which is mathematically just like a spatial rotation, but with hyperbolic rather than circular trig functions. This fact is at the root of most, if not all, of the "weirdness" of SR. This would however, require a passing familiarity with linear algebra. Fred

[@tibees]

Yes looking at invariant quantities came next on the online course. Interesting stuff!

[@ffggddss]

Yes, I must say that, having gone through a touch of SR in undergrad intro physics; then another touch in an upperclass undergrad mechanics course (both when I was majoring in math); then once more in a graduate course (in GR) in physics; the whole thing became much more understandable at that last step, where the late John Wheeler's approach was used. While at this last level, the underlying mathematical structure that was used - differential forms - may be beyond your target audience here; still, most of that could be done with the simpler ideas of vector algebra. Basically, there is a very powerful analogy here between ordinary rotations and spacetime Lorentz transformations. In both cases, looking only at what happens to components, leads to confusion; putting the whole thing in the framework of a vector space, makes some of the otherwise "complicated" formulas, fall out naturally. The intuition is admittedly more natural in the more familiar case of rotations, where the metric signature is all of one sign; as opposed to the Lorentz case, where space and time components take opposite signs; but I don't believe it to be an insurmountable hurdle. I know that you realize fully that learning physics is *not* about memorizing a host of formulas, or even also memorizing when they apply; but rather, learning the concepts from which those formulas flow. I can tell by the way you present these things, and I applaud you for that. BTW, a really fine treatment of SR in this way, at the undergrad level, is in _Spacetime Physics,_ by Taylor & Wheeler. The "Parable of the Surveyors" near the beginning of that text, is a true gem! Fred

[@hbm293]

"Basically, there is a very powerful analogy here between ordinary rotations and spacetime Lorentz transformations" : +1 , in the Lorentz group you have the 3 space rotations generators (cos() and sin() of angles), and the 3 boost generators (rotations in space+time) that are hyperbolic rotations (cosh(), sinh() of a "rapidity" parameter) due to the particular sign assigned in the metric to the time direction.

[@ffggddss]

Yes, The full Lorentz group contains the rotation group, SO(3), as a subgroup. I was referring to the case of a Lorentz transformation that involves only time and one spatial dimension; i.e., a pure "boost." Fred

[@swaroopsuriboyina9911]

most peaceful song I ever listened........

[@sandipdas5684]

Your speaking style is sooooo good.sugest me some computer science books

[@mohammedsalmanali01]

Much awaited topic, eagerly waiting for more videos in this genre

[@devondelgado4147]

Awesome!! Special relativity fascinates me.

[@SandeepSingh-vd9in]

How can I obtained faster speed than light ,no friction, dimention you may like to travel in space?

[@beenay18]

not enough attention span to watch whole video but I want to hit the like button anyway. Hope you make lots and lots of videos.

[@justcurious3653]

I am really not a smart cookie when it comes to math related topics ,which includes physics (so glad when I can get rid of maths after high school hehe)but however you explain physics so beautifully ,that I can actually enjoy it' ^_^

[@new-knowledge8040]

I hate math. I found it much easier to simply discover Special Relativity(SR) by myself, and thus do it without darn math being the primary focus. The goal was basically to figure things out first, and then converting them into mathematical equations as step two. Putting math first, which is common these days, drives me up the wall. I need to fully understand something before any damn math comes into the picture. Besides, if you truly understand SR, you can derive all of the SR equations in mere minutes. How many of today's schools teach people the understanding of SR, and have then allowed these people to derive the equations themselves? Even a high school dropout can do it, if informed of what SR truly is.

[@adityakanase4109]

😀Your smile is just awesome.. 💟😄

[@esa062]

We are used to concepts like "now", that don't really have an exact meaning. That's why actual reality seems weird at first.

[@stiches327]

You should explain blockchain and Crypto to the World. I love your voice

[@SandeepSingh-vd9in]

I feel your heart beat.

[@SandeepSingh-vd9in]

So melodious your voice.

[@SandeepSingh-vd9in]

Symon Clark is helpful for you to understand physics ,and share physics ideas with experment

[@victorvarenium769]

Toby can you do Quantum electrodynamics? I would love a video about it. Thanks for reading this. ;D

[@aidis138]

15:04 "and smashed it!" :O haha)) nice addition.

[@MrTechGamer180]

I have no interest in the specialrelative i just came here for listening to your calming voice its very peaceful.

[@airwolfguy]

Was special relativity covered on you PhD qualifier exam? I've never taken one myself. However I've always looked at the qualifier as the "bar exam" of physics.

[@ronaldjorgensen6839]

so kind to explain all this to me and or us but forget about them now show all math or words are null?

[@jaiguruvlogs1610]

I WOULD LIKE TO KNOW! WHAT YOU'VE BEEN PLANNED FOR FURTHER QUERIES, FOR "SPECIAL RELATIVITY"!? AFTER VIEWING THIS VIDEO IAM APPRECIATE ABOUT YOUR AMAZING IMAGINATIONS. THAT WAS QUICK IMPRESSIVE AND SATISFYING. EVEN THOUGH INFORMATIVE AND I CAN SAY IT WAS AWESOME BICYCLE TO ME TO RIDE ON!! PLEASE LET ME KNOW WHAT YOU'VE PLANNED FOR AHEAD? 👉👈🙄

[@user-vc5rp7nf8f]

if she were my teacher i'd be so distracted.. she's so pretty

[@lawrencedoliveiro9104]

7:58 Q: Why is he called “Crater”? A: Because the only way he can stop is to make one.

[@Wtfukker]

why is it called special relativity? whats special about it? are there other relativities that arent special or classified differently?

[@phatthadol5928]

what are indian calculat when operater cn find disaree of physics all the time

[@thebatmanshown8432]

Thx tibees 😀

[@ericeasterday863]

What's the difference between skillshare and brilliant.org? Just curious which one i should subscribe too

[@noneofyourbizness]

marvelous

[@nadavdanieli]

Why is the speed of light the same for everyone?

[@barryhughes9764]

If two observers cannot agree on the simultaneity of an event, then by definition surely they cannot share the same instant of time, one is either in the others past or future, how then can they communicate? Just curious.

[@MrAlRats]

The theory of Relativity is about how the quantities that are measured by one observer (Alice) relate to corresponding quantities that are measured by another observer (Bob) who are moving with respect to (wrt) each other. The value of some quantities change depending on your perspective; such as the velocity of an object, the time interval/the distance that is measured between a pair of events, the energy/momentum associated with a physical system, the frequency/wavelength of light, etc. Transformation laws describe how the values change from the perspective of one observer (Alice) to another (Bob) depending on how the first observer (Alice) is moving wrt the second (Bob). There is a transformation law for every quantity that is relative (i.e changes depending on your perspective). These transformation laws can be deduced from two experimentally verifiable starting points: a) The laws of physics have the same mathematical form in all inertial frames of reference. b) The speed of light in a vacuum is measured to be the same by all observers. The laws of physics describes the patterns among the quantities that can be measured by any observer in a particular frame of reference. Transformation laws describe how those quantities change from the perspectives of observers in different frames of reference. An inertial frame of reference is any perspective from which no fictitious forces need to be introduced to account for any accelerating bodies. An event is something that can be ascribed a particular set of space and time coordinates wrt some coordinate system associated with an observer. The space and time coordinates of an event are determined by measuring the distance and time intervals between the event in question and some reference event which has been chosen as the origin for the spacetime coordinates. Events which have the same time coordinate are said to be simultaneous wrt that observer. Events which have the same space coordinates are said to occur at the same location wrt that observer. Transformation laws allow spacetime coordinates of events measured by one observer to be transformed into the coordinates that would be measured by another observer for the same events. The time interval between a pair of events (A,B) that occur at the same location wrt one observer will be measured to be longer by another observer who is moving relative to the first observer. The two events (A,B) will also occur at different space coordinates wrt the second observer. The time interval between another pair of events (C,D) that occur at the same location wrt the second observer will also be measured to be longer by the first observer who is moving relative to the second observer. This is time dilation. The distance between a pair of events (E,F) that occur at the same time wrt one observer will be measured to be longer by another observer who is moving relative to the first observer. The two events (E,F) will also occur at different time coordinates wrt the second observer. The distance between another pair of events (G,H) that occur at the same time wrt the second observer will also be measured to be longer by the first observer. This is distance dilation. We define the length of a moving object based on the positions of the end points of the object as they are measured to be at the same time coordinate. Simultaneous events (I,J) such as the end points of the object at a particular time coordinate, wrt an observer for whom the object is stationary, occur at different time coordinates for an observer for whom the object is moving. So by comparing the distance between the end points at the same time wrt one observer (I,J) with the distance between the end points at the same time wrt the other observer (I,K); we are no longer comparing distances between the same pair of events. This results in the length of moving objects being measured to be shorter along the direction in which it is moving. This is length contraction. These are extensions of the idea that the angular size of an object depends on how far it is measured to be from the observer. There is a simple transformation law to calculate the angular size of an object wrt one observer to another depending on the ratio of their respective distances from the object. Measurements made by each observer are equally valid.

[@barryhughes9764]

Al Rats. I appreciate your response to my curiosity. However, I still cannot comprehend how two observers can communicate with each other if they do not agree that they are at they share and are at the same 'instant' in time. How can one observer who has been travelling at near the speed of light for say ten years relative to a stationary observer not conclude, since the stationary observer has aged ten years, that he has been travelling into the stationary observers future? I cannot talk, right now, at this instant to 'yesterdays' you, or even the you as you were a microsecond ago. This all seems a bit confusing.

[@MrAlRats]

It's not meaningful to talk about an "instant of time" without a particular location attached to it. Anything that can be labelled with some particular set of spacetime coordinates with respect to (some coordinate system associated with) any observer is called an event. When the time interval between a pair of events is measured to be zero by a particular observer, those events are said to occur "at the same time" with respect to that observer. This means that both events have the same time coordinate wrt that observer; i.e. the time interval between some third event (the origin) and each of the events in question will be measured to be equal. From the perspective of another observer, the time interval between the two events in question need not be zero. Different observers can measure different time intervals between those pair of events. In fact, for any pair of events that do not have a cause-effect relationship between them, there is no physical significance to any order that any observer may associate with them. For any pair of events that are causally connected, everybody will agree on the order of those events but not necessarily the time interval between them. Our Universe can be thought of as a collection of events. Associated with each event is a subset of all events that occurred in its past; another subset of all events that will occur in its future and a third subset of all events that are not causally connected to it.

[@BestFriendOfJesus]

Great videos

[@mothernature5237]

omg i need that for my physcis a level final exam in two days

[@bassil6138]

Can you give us some equations and exampels with details..on board or anything ..thank you ❤

[@bassil6138]

@Penultimate Hortator i know that and she done a hardwork . But all this informations are general if she can sail with details in the future that is what i asked.thank you

[@jacobbuxton932]

Amazing video!

[@misterwonderful8628]

All I see is a bunch of flirting in the comments section....please. Would Bernoulli equation explain possible influence in the answers that could be provided or is it you feel the number would be too small an amount of variance to consider such an equation as useful determinant towards the answer? ...also... Would it be possible to video explain the answer for my question, but with an even tone dripping with ridicule and with demeaning words of humiliation for me? Thanks.

[@algonte]

I have to see the video at least one more time...

[@MoontyCrabNebula]

I don't really care which axis is used for space or time, that's just convention, but why would they not use ct for the time axis? lol Nice neat bisector line that represents the photon in all the reference frames, and the time increments are not incredibly small.

[@hbm293]

"but why would they not use ct for the time axis?"

[@MoontyCrabNebula]

Yeah your right that it is convention too. But it is a convention where it clearly shows that light has a set worldline for all reference frames, even for ones that have non-orthogonal axis, provided the same distance scales are used. As for c=1, theorists like to. But for people starting to learn SR, not so much.

[@MoontyCrabNebula]

Point being, skipping from non relativistic scenarios with the seagull, to relativistic ones, which include light, we should change the axis scales accordingly.

[@peterbrough2461]

Neither t nor ct give an axis that is orthogonal to the spatial axes. Pick a better one :-)

[@argelisreyes2920]

Fascinating

[@ManrielXiii]

Hi Toby.

[@ranjanmaithani6263]

Toby is a boy

[@allanmanaged3187]

But why should the speed of light be the same for all inertial reference frames ? Is it just an assumption that gives the correct results or is there a more fundamental reason ?

[@jagathmithya719]

Check out the Michelson-Morley experiment that led to special relativity.

[@MoontyCrabNebula]

The Michelson-Morley experiment does not prove Einsteins postulate. The Earth is not an inertial reference frame. The Michelson-Morley experiment was to test whether the aether existed, that is, if light needed a medium in which to propagate. The experiment showed that it did not.

[@allanmanaged3187]

Yes good point, MM showed C didn't change due to the Earth's motion but it still seems a bit of a stretch to say it never changes in an inertial reference frame, at least to me.

[@jagathmithya719]

MoontyCrabNebula: A postulate, if it can be proven at all, will cease to be a postulate. You are right about the intent of MM experiment - which is one of the best, failed experiments in Physics, simply because it assumed _c_ to be variable, but was shown to be constant. (Of course, it also proved the non-existence of a medium *as they had imagined* - aether). The experiment left science in a limbo until Einstein's theory. That's my understanding.

[@MoontyCrabNebula]

That's true. EM is a must. An accelerating charge produces electromagnetic radiation, that is always the speed of c in free vacuum, from Maxwell's classical electromagnetic field theory which can further be explained using quantum electrodynamics which I know very little about. Set up a scenario in the classical situation, electrons on some body are moving at some initial speed, are then accelerated by some internal energy in that body to produce the light, or the speed of propagation in the electromagnetic field. It is the accelerating electron which changes the electromagnetic field, and that change is always c.

[@teamhackersperu3355]

I usually listen to your videos, at first I was hearing that you were talking about a 'gal' (thinking of a girl) and later I heard kratos and I was like hold on... I gotta watch this.

[@markfrancis6508]

Extend space/time continuum.

[@SandeepSingh-vd9in]

Where is black whole situated in our galaxy.

[@nicksu332]

MORE VIDEOS LIKE THISSSS

[@quill444]

Richard Feynman fascinatingly referred to photons as "corpuscles of light" . . . {Hi Toby!} Does a beam of light (photons) therefore 'travel' like a procession of 'coins' dropped out of a hand or pocket, and thus if some of these particular photons should strike my retina, does this preclude those same identical photons from being able to reach (and therefore be 'spent' upon) the retina of another observer? And if so, then how can it really be said that two people ever actually see the same thing? - j q t -

[@elliotheckman7194]

You can think of a photon as just a packet of energy. When the energy is absorbed by your eye, there's none left (in the form of a photon) to be absorbed by someone else's. But a photon is a photon; any two "corpuscles" of the same energy are identical.

[@quill444]

And to what extent therefore are the photons that emanate from something (part of) the thing itself?

[@bunklypeppz]

Photons are spontaneously created near objects as they lose energy equal to that of the photons that are created and they are subsequently annihilated upon any kind of interaction, thereby transferring their information, energy and momentum. In fact, due to the relativistic effects of length contraction and time dilation, photons do not 'experience' space or time, because the length of their journey is infinitely contracted and the passage of time is infinitely reduced (as is the case with anything traveling at the speed of light); they are created and annihilated in the same instant, no matter how far they appear to travel, or how long that journey takes from the perspective of outside observers like ourselves. I don't think it can ever be said that two people see the exact same thing, because a slight difference in perspective will always result in a slight difference in perception, but the changes that macroscopic objects undergo by radiating or reflecting light are so negligible on short time scales, that it is not problematic to claim that an object is essentially the same for different observers looking at it at different times. As for the extent that photons are a part of the thing from which they emanate-- Einstein's famous equation E=mc^2 sums it up (no pun intended), matter is energy, so the photons certainly are/were a literal part of the object, but not necessarily in the form of photons. All objects, from the hottest stars to the coolest rocks are constantly losing some amount of their mass in the form of photons. Furthermore, the speed of light is the speed of causality itself so one could at least philosophically infer that photons are a means by which everything material thing in the universe participates in a sort of cosmic web of causality; in a state of constant physical interaction/contact with all other things by virtue of light speed packets of energy and information for which the distances we perceive between things does not exist. From the reference frame of a photon which travels uninterrupted through the vacuum of space from a distant star, the star and a person on earth who absorbs the photon, are not separated by any distance or time at all.

[@elliotheckman7194]

Well, I guess there not, really. But of course, everything emits black body radiation, and in that case the photons carry away the energy of the object itself. But at any rate, under most circumstances, any two observers will see photons of the same color/frequency/energy which, again, are identical.