Special Relativity: Crash Course Physics #42

[@crashcourse]

We made quiz questions to help you review the content in this episode! Find them on the free Crash Course App! Download it here for Apple Devices: apple.co/3d4eyZo Download it here for Android Devices: bit.ly/3TW06aP

[@TheSnakeboy11]

"You already know that V x T = D" *you overestimate me*

[@_zerofox]

This is too funny XD

[@mrhatman675]

Sorry but that s as easy as a squack

[@neetbucks521]

I think they are speaking to you as if you are watching each episode chronologically that concept was covered earlier in the series

[@rld8258]

No you underestimated yourself

[@VyvienneEaux]

I’m pretty sure you did already know that one. I walked at a speed of 3 miles per hour for one hour. How far did I go?

[@jessicaonymous4352]

0:23 I love how Bob is flying backwards, presumably from air drag, even though he's in a vacuum

[@dr.bipinmandar3458]

After watching this, I realized why Einstien is regarded a genius.

[@rh16]

My mind is so fucked right now i forgot how to hold a spoon

[@RatherBeEmbed]

There is no spoon lol

[@ChimneyCrab737]

RatherBeEmbed is that a gamechild reference

[@staubsauger2305]

@@ChimneyCrab737 - is from the movie The Matrix.

[@guigaingamkamei9654]

I'm dead lil

[@varinderarora3238]

spoon!! how to breathe

[@twentytwo1290]

My bicycle can't travel faster than light, it's two-tired

[@guigaingamkamei9654]

I see the pun

[@michelef406]

So underrated.

[@taseenahnaf]

@Michael Terrell II tyre = tire xD

[@randomstuffyouwontseeinyou8786]

I don’t get it

[@jeremyjohngraham]

😑🤣

[@JugheadJones03]

Dr. Somara, I cannot imagine how mindbogglingly hard it must have been to get through all of this in school and UNI. Thanks for trying to make this palatable for people like me who are fascinated by it, but just not driven enough to take it on! Really cool stuff.

[@AndroxDpl]

Jughead Jones She said at the beginning of the course, she studied fluid dynamics. Which is still a bitch, because the math gets very complex.

[@TheScientificCookie]

Special relativity can be taught at secondary school its quite simple. Fluid dynamics on the other hand...... oh dear god save us all.

[@fossilfighters101]

+

[@anirudhkrishnan1797]

Wojciech Morawiec 😂😂😂😂

[@mayankgupta7342]

Jughead Jones yups I think the same!

[@fernandes1431]

How Einstein conjured this madness up. Wish I could :-D

[@equivalenceprinciple1982]

L F The speed of light in a vacuum being constant is actually a prediction of Maxwell’s equations, which describe electricity and magnetism. Einstein computed the effects of this in Special Relativity. In addition, there was experimental evidence at the time that seemed to indicate this fact about light. A famous example comes from the Michelson-Morley experiment, which tried and failed to detect the ‘aether’, a special medium in which it was thought light travelled. This in no way diminishes Einstein’s achievements, however! To paraphrase Newton, everyone stands on the shoulders of giants.

[@rustysim]

English is my first language and she still spoke fast as hell...

[@spookeymo]

that's the first video on spcial relativity that explained it so well i understood! most people don't include maths in their explanation because they think it'll make things more complicated but it actually made it so much easier to comprehend. thank you for your series!

[@alekdaniels]

I just dropped by to tell you I'm only looking for a special recipie to cook for relatives and got subjected to a serious mental injury by clicking this video.

[@swiftlymurmurs]

Man, that is... Mindbending. We're used to thinking time and space are constant, and can't be shaped to our will. But when you realise it's all conatantly warping and stretching it gets... a bit confusing

[@TheDemisemismiles]

Subhobrata Chakravorti Einstein didn’t invent, he discovered.

[@amosandrecantini3453]

I'm the only one who's watched this video twice and lowered the speed to 0.5 to understand something??

[@iaexo]

0.5c

[@DavidGonzales-eq2oi]

Don't forget closed captions!

[@erkive2201]

I did and still didn't understand anything 😂

[@katejohnson9737]

But from the perspective of the video, it perceived you observing it twice as fast.

[@manofcultura]

Is this real life or is this just fantasy? Caught in a land slide, no escape from reality.

[@drg8687]

Open your eyes, look up to the skies and see..............................

[@Mr8lacklp]

Jebuslives mom's spaghetti

[@vikneshmaniam5618]

im just a poor boy i need no sympathy

[@vikneshmaniam5618]

brendon's version playing in my head

[@afroman8626]

Mr8lacklp- Nice, love the Queen ref destruction. Good old EMINEM

[@matyourin]

nothing gets easier to understand by telling it faster... while I somehow enjoyed crash course history and philosophy, these physics crashes just seem to me like a futile attempt to reduce complex topics and speed them up to make them somehow fit this format - so that the result is only understood by those who alrdeady understood it in the first place. maybe that's just my impression as a physics teacher...but I would take a complete series of videos instead of one to get each of these topics.

[@oldcowbb]

i recommend drphysicsa, he explains really well, and i like his accent

[@j-theorythequantummechanic6025]

matyourin Or read The Elegant Universe..

[@mfpope7431]

j-theory the quantum mechanic I’m reading that right now and I just got done with the general relativity section, and still don’t understand it. I mean I understand that time changes according to the something is going, but I don’t understand why. Maybe my understanding of time is wrong or something. But I watched this video to get another point of view or explanation.

[@davidscott5903]

I fully agree with you. This covered the topic about as well as a Hollywood movie, but most likely just scared more people away from ever really learning about it. Most people are going to watch it and say to themselves, "Wow that was a lot, and I understand that time changes based on how fast you're going, but I don't understand the rest, so I guess I just can't understand that and I guess that I am just not smart enough to learn about that." And that's when they decide that they can't do it, and quit trying.

[@paulpaul8861]

I don't understand the need to speak so fast. It doesn't make it easier to learn, so not sure who it's benefiting.

[@benhurston]

I've watched several videos in attempt to understand special relativity/time dilation, and either (a) all of the previous videos have been slowly adding to my understanding to the point where when I watched this video, it finally made sense, or (b) this video does the best job of explaining special relativity that I've found yet! It's probably a little of both, but either way, great job, and THANK YOU!

[@Kithairon]

If Bob is moving at a constant speed through a vacuum, why are his arms draged behind him?

[@Basilisk2077]

Probably going insane due to the high g's he would be experiencing.

[@charlesreisner6681]

Warlord25100 that would assume that he is not moving at a constant speed. G-forces require change in velocity

[@Basilisk2077]

Charlie Reisner He had to get to that insane velocity somehow.

[@o.p.rajput655]

Umm.... Why is no one mentioning inertia here ?

[@abduljawwad1620]

um inertia?

[@luizbertoncini]

westworld anyone?

[@JP-yl4ts]

Cole Sawyer same

[@wmjessemiller]

yeah... i caught that too lol

[@theazkii]

Luiz Bertoncini why?

[@ThZuao]

Sort of. Not enough BOOBS.

[@manojj888]

Luiz Bertoncini same thought

[@oliverlovelltas]

Hi. I believe that one of your examples is incorrect. At 6:36 you say, ‘We already know that time moves faster for you than for Bob. Whilst 666 nS has passed for Bob, only 577 nS passed for you.’ These two sentences are contradictory. If ‘time moves faster for you than Bob’, then the amount of time elapsed for you (person on the platform) must be greater than for Bob. The time elapsed for the observer on the platform should be 769ns, not 577ns. This is also consistent with the twin’s paradox and the idea that ‘a moving clock runs slow’. From the twins paradox, we expect the observer on the fast moving object (in this case, the train) to age less than the stationary observer (person on platform). Thus, time elapsed for Bob on the train must be less than for the person on the platform. From, ‘a moving clock runs slow’, we also anticipate that Bob’s recorded time will be less than that recorded from the platform. To summarise, if Bob records 666 nS from the train, you record 769 on the platform. Happy to be corrected, but I believe that this is correct.

[@bradyblake6573]

been waiting on these types of vids for a while. I love this kind of advanced physics

[@Teo-uw7mh]

Brady Blake this is as basic as it gets compared to generell relativety. But i guess you're not studying physics

[@colbillington]

kevin randleman and I guess you're not studying grammar

[@bradyblake6573]

Thanks Was, also Kevin I'm graduating with a mech engineering degree in 8 months and I still find relativity goofy af

[@IceMetalPunk]

+kevin randleman And general relativity is as basic as it gets when compared to quantum mechanics. Just because there's something more advanced out there doesn't mean everything else is basic.

[@amritanshuray]

Yeah, but this is relatively more advanced than the previous episodes. Woohoo, hope you caught the pun. K bye.

[@Donezekiele]

Did anyone else see a resemblance between the animation with the train and Westworld?

[@dorkmax7073]

Juan Vallejo Doesn't look like anything to me.

[@atombaxter1975]

Juan Vallejo Yes! That's what I thought when I saw the thumbnail!

[@veggiekeef]

Dominic Sosa Perfect comment lol

[@mihailung1720]

Juan Vallejo How van you possibly believe that was not intentional? And yes, literally everyone saw it

[@jeza8138]

No. No one saw it. It's really hard to spot. You must be so clever to have spotted it.

[@Worgak]

Oh my god, Special Relativity finally makes sense! I've tryed to wrap my head around it several times now, and had it explained to me in several diffrent matters. Yours is the one that finally made it click! Thank you so much! The world is confusig as ever, but at the same time, it makes just a little more sense to me.

[@Worgak]

No, seriously, yall are the best. Thank you so much. You're wonderful.

[@anamwaseem6693]

I still don't understand special relativity 😭😭

[@asoor]

This video is pure gold! Thanks for the clarity in the explanations and the amazing motion graphics that accompany them.

[@dorkmax7073]

Thought Bubble...doesn't look like anything to me.

[@toffeesky6227]

I see what you did there

[@abandonedchannel8981]

Thomas Binch I dont

[@CthulhuFhtagn138]

nah its just a "WestWorld" reference

[@benjaminazmon]

Dominic Sosa, what do you mean?

[@abhinavajith92]

Chris Todd aha thanks m8

[@atombaxter1975]

Westworld influence in the animation?

[@Nablabla1]

at 0:30, when the train is moving in a vacuum, why is Ford dancing so crazy?

[@timothymclean]

Have _you_ ever ridden a relativistic train in a vacuum? That's not dancing, that's spasming.

[@fossilfighters101]

+

[@claudettedelafayette9979]

Inertia The resistance to sudden changes in motion. Just like pulling a piece of paper below a glass of wine in a short amount of time.

[@matthewdockter2424]

You guys did a good job on explaining this. This and PBS Space Time are two great videos on the topic.

[@GuyusSeralius]

Wow, she talks near the speed of light! If only she was traveling near the speed of light, relative to me, then I would observe her time dilate, which would cause her to speak much slower from my point-of-view, so I could more easily take in all that she is explaining.

[@samjw1999]

This stuff is fascinating, why my class chose to do astrophysics over this I'll never know.

[@nasserderakhshan3211]

Why are you speaking at the speed of light?

[@splitpitch]

i can't wait until they start mass producing these new hypothetical trains. It will cut travel time immensely.

[@timwhite1783]

This was perfectly timed. I just started special relativity in Year 12 physics yesterday.

[@harry_page]

Year 12? Mate you're so lucky, I'm in year 13 and my physics class does its best to avoid even calculus for some reason, it's quite depressing.

[@wackywally69420]

Year twelve is I'm assuming like the year after senior year in high school? I'm only in my second year of high school/secondary school and I'm really hoping we do more than just Newtonan physics and math only relating to that.

[@wackywally69420]

Grade 10 I mean lol

[@AbdulBasit-we9lf]

Einstein was, without a doubt, in a league of his own. The simple fact of light travelling in a constant speed was taken into consideration, yet he brilliantly revolutionized Newtonian physics by applying certain case scenarios which were, back then, impossible to allocate to. Pure genius!!!!!

[@megametagrossard3342]

@Justa Fool that is only if the speed of light were not constant ..... But it is ... And thats the hard part ... Why ?

[@manu1434u]

@Justa Fool what do you mean "proven"? Gravitational waves were proven to exist which were predicted by general relativity, atomic clocks are proving special relativity..should it be something tangible to be considered as proof..no one has seen an atom..but it's existence is proven by experiments.. should I say it doesnt exist because it cant be seen by a microscope or my eye..

[@manu1434u]

@Justa Fool yes Einstein made mistakes..his assertion that universe is static by cosmological constant is false, but the idea that speed of light is absolute is true..been proven again and again..if light speed is absolute, spacetime should be variable and it's a theory..and it has been proven correct..see the article above..how do you refute it? Or do you have any other theory to explain it?

[@manu1434u]

@Justa Fool why is it not rational when it's explaining all the things it was supposed to do so? Black holes, gravitational waves, light bending around massive object's, time dilation, length contraction..all are out of relativity..and are proven correct..what evidence DO you have to prove it false?

[@manu1434u]

@Justa Fool Either way..Prove it wrong then! Thinking it is wrong doesnt make it wrong..PROVE IT WRONG if you think so. Relativity hasnt been proven wrong yet, so come back when that happens.. or stop making assumptions of your own with no backing.. How is LIGO fraud when after it detects gravitational waves and then they focus the telescopes towards that location, they are able to find electromagnetic radiation coming from those events as EMR might travel a bit slower due to gas and dust present in between. You have literally got no footing..

[@TheAbominableChappal]

this is by far the best explanation on this topic I've ever seen.

[@AnthonySiarkiewicz]

Just just love when Bobs arms go up cause he's train has been hit by lighting.

[@Pepperball909]

So Robert Ford was nicknamed Bob in his younger years?

[@WhiteBudWidows]

5:23 when my boyfriend thinks i was hitting on someone but i was just being nice

[@Soulofyoga]

regarding 4:42: if the distance in the moving reference frame is shorter, it should take the light a shorter period to travel up and down (what you also mention at 4:10). Why is it longer than in the stationary reference frame (according to the formula)? If gamma was 2, then if 10 seconds pass in the stationary rf, 20seconds would have passed in the moving rf. Should it not be the other way around?

[@blownspeakersss]

Why does Crash Course insist on making its videos so short? It seems like a topic like this could benefit from a 20 or so minute video. 9 really is not enough, in my opinion.

[@Nothing_serious]

blownspeakersss Because Crash Course really means fast or short lesson or something like that.

[@Mr8lacklp]

blownspeakersss because animations are a metric shitton of work

[@blownspeakersss]

Well, a 20 minute discussion of Special Relativity would inevitably still be a "crash course." And I get that animations require a lot of work to make, but then they could just use more footage of the host talking or whatever with simple animations (showing equations and so forth).

[@arstgkneio]

20 minutes is running kind of long. ideally, this wouldn't be your only source for studying this material.

[@mohangrewal1466]

Because people would be bored out of their mind if the video went on longer.

[@jonathanblackwell42]

Thank you so much for this episode. Even in my college physics classes, we never got into anything relativistic so I never really understood it. This was much needed. Great work, y'all!

[@McHaven07]

This has always bugged me, and it still does.

[@EdwinLuciano]

My preschoolers are going to love this video. Thanks for posting it.

[@elmothemilkman99]

I think you guys made a mistake with labelling the formula at 4:38. Tv is the reference frame of a stationary observer, and To should be the moving reference

[@crossfire1403]

That formular just tells how long the same time-duration of stationary frame needs in the moving frame to pass from the view of stationary frame (clock-ticks). E.g.: T0=1sec, v=0,5c, how long do you have to wait/measure, to be sure that T0=1sec has also passed in the moving frame? ==> from perspective of stationary frame it takes a duration of approx. 1,15sec to pass on the stationary clock, to be sure that the T0=1sec-duration in the moving frame has passed. It's a little missleading, but the formular does not mean, that if in stationary frame 1sec has passed, that in the moving frame already 1,15sec have passed...

[@crossfire1403]

Otherwise: while in stationary frame 1sec has passed, you know at 0.5c of moving frame, that in the moving frame only 0.86sec have passed...

[@srdanmilic4952]

@@crossfire1403 And everything she said is based on ASSUMPTIONS and therefore I must ASSUME that everything she said is true. Sorry but my world is based on facts not assumptions.

[@coldfinger459sub0]

Over the past couple years I've heard this and seeing this explained many different ways but with your visual effects and a combination of your method of explaining I just had that " Ah ha !" moment. The lightbulb has just been switched on I completely see and understand now it's so simple. Keep up the good videos

[@pinco_pallo]

Thank you very much! I'm an Italian student and I can't find videos like his in my Country. The graphic of these videos is superb and the explanations are excellent. Well done!

[@Snidebark]

I came to this video with a competent understanding of the subject, yet found the video hard to follow. It all makes sense because it's all correct and well-scripted, but the editing and fast speech make it difficult to take in what she's explaining. The 'breathing time' between utterances is removed, and that time that it takes to inhale, although short, is just enough to allow us to process each piece of information before the next piece comes. Without it, all of this correct, well-scripted information is a rush of sound. No documentary maker or teacher talks this fast and without pauses between pieces of information, so why do it here?

[@atfchannel3425]

Snidebark مقزميزثز ي عرمربنتؤخعؤ😈😈😴😆

[@bouguezinemohamed767]

Snidebark I don't know but I just paused the video every now and then

[@MegaLotusEater]

You couldn't have had a competent understanding of the subject, as this vid is really clear and easy to understand. I had a limited understanding of the subject and understood it perfectly

[@FknAzzMuncher]

@Irritable Jon Syndrome lol yeah socialism is relevant here

[@nawra77]

Pause and replay button: AM I A JOKE TO YOU?

[@pytle]

I love listening to these while at work, and I keep thinking Symmetra is teaching me this inbetwen matches.

[@Unassuming_Gay]

Ah, Finally the interesting stuff.

[@oldcowbb]

classical is also interesting, but modern physics is indeed more interesting

[@harry_page]

Tell me about it. Mostly boring old classical theories in physics at sixth form, and what little of quantum mechanics that's touched upon is left horrendously unexplained ;-;

[@yssacnton95]

Rigid body rotations is interesting, how rotational bodies can do wonderful stuff, gyroscope etc...

[@gyurmarajzfilm]

You explained this better than my physics teacher. Also: You helped me solve my homework 💚 Thanks!

[@stasacvetkovic6464]

It is fascinating how you can understand so much and don't understand a word at the same time.. but you are incredible teacher ❤

[@Jaydoggy531]

You described this in a way my brain could finally wrap around. Thanks.

[@anjulichaudhary1325]

who feels this did a better job than pbs space time??

[@michaelsommers2356]

Space Time hasn't covered special relativity.

[@tahmidt]

They are catered for different audiences.

[@bigdre9042]

anjuli chaudhary for me VSauce is who usually makes me understand them

[@isabellelindblad2835]

Thank you! Im still confused but this is helping me dwell into the metaphysics of time.

[@jeremymiller4189]

This episode needs placed in your physics playlist.

[@DaveGaming99]

FINALLY! Only took 42 episodes to get to one of the most interesting parts of physics to me! :) Thank you!!!

[@MusikCassette]

4:34 wait a minute, "stationary reference frame" "moving reference frame" ? I thought we established, that it is indistinguishable which one is moving. From the perspective of bob, the platform is moving. So from bobs perspective the time on the platform is dilated the same way. How can that be? That would mean that also t0=yt ( while still t=yt0) so t0=y²t. Something is wrong here. (I used y for /gamma to type it on a normal keybord)

[@secondo92]

It is indistinguishable because Bob sees the train station move past him. If he is not accelerating he would not be able to tell if it is himself moving or if the train station is moving(like when you're in the backseat of car next to another car moving at a constant speed, and the other car slowly decelerates, you can't tell if you're slowly speeding up or they are slowing down). So noone can actually prove who is moving unless one of them were to be accelerating, but then special relativity wouldn't hold. In Bobs' perspective he sees the world differently(everything has shrunk in size), but the train station sees Bob as if he shrunk in size. This gets more interesting once you investigate the twin paradox and that photons "experience" the world as if time had stopped entirely.

[@MusikCassette]

I think you did not understand the question: bobs time is running slower that the stations time the stations time is running slower than bobs time ergo the stations time runs slower than the stations time ??? how does that work?

[@secondo92]

That is not the case. They perceive these things differently. Imagine that theres a clock on the train station and on the train where Bob is. Bob will see that clock is moving slower on the train station, while his own clock is running perfectly "normal". The train station sees that Bobs clock is running slower, while their own clock is running perfecly "normal".

[@robertf7881]

I am having the same problem. if t = yt0 where y is always positive then t > t0. According to the formula t = time in moving reference frame (clock in train) and t0= time at stationary reference frame (clock at train station) --> Then t>t0 means that more time will have elapsed on the moving train than at the stationary train station. In other words clocks are faster on the moving train... This cannot be true because the whole point is that clocks slow down as you approach the speed of light on a moving train. I suppose if you switched t and t0 like MusikCassette did then the formula would work out. Not sure if t and t0 are improperly labeled in the video or if I am misunderstanding the concept. Anyone help?

[@MusikCassette]

Well, that does not help. you just repeaded the thought experiment, the question was a little more specific than that: Imagine the equation t=yt0 Imagine the equation t0=yt now Imagine the conclusion t=y²t and now Imagine me having a problem with that. The Problem is not, lack of imagination, but how to use those equations.

[@doronbarzilay590]

Not stopping for even a second between sentences to give the viewer a moment to digest what you said while talking about one of the most complicated ideas in phisics is an excellent idea!

[@NiknAknO]

If only there was a button to stop the video...

[@doronbarzilay590]

@@NiknAknO a video that needs to be stopped every few seconds should not be an educational video.

[@jamestaylor8217]

Best illustration of these concepts I've seen in 60 odd years. Thanks

[@adamcampagnolo3896]

Crash Course is my favorite thing on KZbin! Please fund this!

[@Creamagination]

Love her British akcent, really good.

[@yourfriendlyneighbourhoodh4700]

Hidden driver no such thing as a British accent. What you're referring to is queen's English.

[@afroman8626]

What about Irish or Scottish, or Welsh? They're British too. I think that's what they may have been meaning.Cause I don't think she has an Irish accent

[@Bugatti1]

And this is why my major is computer science...

[@IceMetalPunk]

I'm also a computer scientist, but I've always loved special relativity :)

[@oldcowbb]

what if you have to programme a satellite

[@IceMetalPunk]

+oldcowbb Then he'll use a relativity library to handle that part of the math :P

[@theindianremix9404]

I have to take this course for comp sci :(

[@dphorgan]

Quantum computing?....

[@benjaminazmon]

I love that spacetime is the 42nd episode. now we know the meaning of life the universe and everything

[@sajadkhosravanis.8288]

Thank you so much for your ideal development of every aspect of the tutorial.

[@Not_here1234]

I'm sending this to my friends to mess with their heads :/

[@nah7749]

Brianna Amador huh, I’m sure you’ll stump em, I’m confused out of my mind! 🤣

[@GeorgeCopperfield]

She's so cute !

[@substitoad7069]

Torin Webster cute

[@rolandomarinhdez8262]

Torin Webster she is...

[@torpezaincreible8692]

ikr😍😍😍😍😍😍❤️❤️❤️❤️❤️

[@ashboon1625]

Please do nuclear, atomic and quantum physics next!

[@j-theorythequantummechanic6025]

ash boon I think general relativity is next right? If they're going in order.. Then quantum mechanics..

[@braddboy5]

I don't understand the statement about simultaneity. I get that bob observes the lighting at two separate moments and the person on the platform sees the lightning at the same time. But that doesn't mean its isnt a simultaneous event. Since the person on the platform is equidistant from both bolts of lightning and the speed of light is constant, it happens at the same time. For bob the distance and time are different for each bolt. This doesn't mean that it wasn't a simultaneous event. If someone claps their hands right next to me and someone else does the same but further away and i observe the sound from the closer clap first it doesnt mean that the claps didnt happen simultaneously. This means that even though bob sees the lightning that is closer first, both bolts still strike simultaneously.

[@p3nf9ld]

Everything depends on the frame of reference. Simultaneity can only be judged from the single reference point. That is, you observed the claps occurring at different times so not simultaneous to you. At least one of the people clapping heard non simultaneous claps. However, one of the clappers may have heard the claps at the same time so he correctly assessed them to be simultaneous to him. There is no such thing as describing an event as irrefutably simultaneous.

[@harshgoyal7098]

Hi Crash course team, at 4:38 she says that time in that moving reference frame = time in your reference frame * gamma, plz check it again because I feel there is some error in that equation. it should have been like: time in your reference frame = time in that moving reference frame * gamma

[@ronblaess1]

No, they are actually right. Time is dilated in the moving frame, so you have to multiply the time in your frame by gamma.

[@Spartanruler729]

Raumzeit - Vlog der Zukunft time moves slower as you approach the speed of light

[@crossfire1403]

That formular just tells how long the same time-duration of stationary frame needs in the moving frame to pass from the view of stationary frame (clock-ticks). E.g.: T0=1sec, v=0,5c, how long do you have to wait/measure, to be sure that T0=1sec has also passed in the moving frame? ==> from perspective of stationary frame it takes a duration of approx. 1,15sec to pass on the stationary clock, to be sure that the T0=1sec-duration in the moving frame has passed. It's a little missleading, but the formular does not mean, that if in stationary frame 1sec has passed, that in the moving frame already 1,15sec have passed...

[@crossfire1403]

Otherwise: while in stationary frame 1sec has passed, you know at 0.5c of moving frame, that in the moving frame only 0.86sec have passed...

[@TheRealFOSFOR]

They always talk about how things depends on the point of view. Everything is relative. Or something... But if I fly a rocket at the speed of light. Why is time slowing down for me? Why not the rest of the universe? Who chooses witch one of us is moving. Me in my rocket or everything around my rocket? I specifically remember reading somewhere that it is impossible to ever measure the absolute speed for anything because you don't have any reference point.

[@alexneff3512]

You can only measure things through what is called an inertial reference frame, or non accelerating point of view. If this is true, you can measure the other things acceleration, telling you that it moved, not you. This is actually the exact scenario that led Einstein to create general relativity, which takes acceleration into account

[@ahmaquindi]

This video came out right when I needed. In a couple of hours my physics teacher is going to give a lecture on this and I'm so exciteddd physics is the best

[@maksphoto78]

I kinda had an epiphany myself about how the speed of light (in vacuum) remains constant no matter what. Speed is distance divided by time. The speed of light remains constant through the stretching of time (making the taveller's local time slow down).

[@antoniobaker3828]

I was so ready to pay attention and try to understand this then instantly got distracted on how beautiful she is

[@kcwidman]

If I am in a spaceship flying to alpha Centauri, would the 4.1 light years I need to travel contract if I move at a significant fraction of C? So I would actually travel less distance on my way there from my perspective?

[@DaveGaming99]

The distance is always the same; the distance never changes, it is only the amount of time that you experience while traveling that distance at a certain speed.

[@kcwidman]

Everyone experiences their OWN time to be normal. So if I were watching someone in a spaceship at 99% c I would see their clock tick slower. Since the people IN the ship are experiencing time normally, doesn't that mean that from their perspective they don't travel the distance they calculated at the start of the trip?

[@secondo92]

If someone was to be moving at 99% of the speed of light, the distance between the earth and alpha Centauri would be length contracted so much that it would seem only a foot length away in their frame of reference.

[@kcwidman]

secondo92 but the thing is, it doesn't seem like it is 1 foot away. From the perspective of the spaceship, it is objectively, 100%, the actual distance, 1 foot away.

[@secondo92]

Yes to correct myself, it is 1 foot away. It's all about how you perceive things. That's why it is called relativity.

[@samdaniel9595]

From Hist to Philo. From Econ to Poli Sci. Now with theoretical physics!!! You guys are the best!

[@masterhidsert1043]

Cool! I'm more of a chemist but physics is phenomenal

[@Oliver-fu1go]

AHHHHHHHHHHHHHHHHHHHHHHHH! Interesting... brain dead... but interesting

[@pietrocelano23]

watch the "would headlight work at lightspeed?" video by vsauce

[@torpezaincreible8692]

that's so relatable hehe😂😂😂😂😂😂😂

[@zes3813]

wrg

[@netahamiel4304]

we just gonna forget about how mass increases as you get close to the speed of light? fine

[@science-y9209]

Mass increases? ??

[@daena9289]

Yes, because according to Einstein’s famous equation, E=mc^2. (Where E is energy, m is mass, and c is the speed of light.) Because of the equivalence of energy and mass, the more energy an object has due to its motion would add up to the mass. (Therefore, as the energy required for motion increases, so does mass.) And that is why mass would increase as you approach the speed of light.

[@eliirrii]

This is actually considered to be incorrect now. According to the OpenStax text book (Volume three, section 5.8), it says under relativistic momentum: "The relativistically correct definition of momentum as p=γmu is sometimes taken to imply that mass varies with velocity: mvar=γm, particularly in older textbooks. However, note that m is the mass of the object as measured by a person at rest relative to the object. Thus, m is defined to be the rest mass, which could be measured at rest, perhaps using gravity. When a mass is moving relative to an observer, the only way that its mass can be determined is through collisions or other means involving momentum. Because the mass of a moving object cannot be determined independently of momentum, the only meaningful mass is rest mass. Therefore, when we use the term 'mass,' assume it to be identical to 'rest mass.' "

[@talalzero1418]

I’ve watched 10s of videos explaining/mentioning time dialation and this video was the only one my brain was able to digest. Thank you

[@littlepix101]

You guys might have saved my life. I'm in the middle of my first exam period of my degree (biomedical engineering), I failed my first physics exam- and need to retake it, on Tuesday. I have seen the two theorems for the time/length thing, and was never sure which was for the stationary system... Your explanations were very clear and helped my understand why I kept getting these questions wrong... I think I love you

[@cuzco08]

Explained as beautifully as she is.

[@j-theorythequantummechanic6025]

Marcus Taylor She's mine!

[@pet3590]

I don't think I need to start saving for retirement, I'm still in school.

[@pet3590]

I like this series but please don't advertise insurance companies, do charities or something education related like the great courses

[@skrenos]

First off, it's never too early to start saving for retirement. Second, content creators don't always get to choose who sponsors them. If it's a choice between an insurance company and no sponsorship, you bet your sweet bippy they'll pick the insurance company.

[@ajeuscher7988]

somebodys gotta pay the bills right? At least its at the end and doesnt impact the rest of the episode at all

[@marrs1013]

Sameopet I guess it depends on who is actually willing to pay for the slot. Just becouse you are not paying for it, it doesn't mean it's free. But I'm sure there are ways to support the show...

[@marrs1013]

Sameopet By the way, the later you start to save the harder it gets, as you need to put aside more and more to make an actual difference by the time you retire. So do yourself a favoure, and start saving the first day you start to work. You can't imagine how happy and grateful you will be later. This should be part of curriculum, so in a sense it IS educational.

[@kattyseraphin3812]

Shouldn't time and distance be directly proportional? I mean if "v*t=d" when time increases, the distance should also increase right? Why is it inversely proportional now? Can someone please explain

[@LudusYT]

Ann-K Seraphin - I cover this in chapter 2 of my special relativity series. Feel free to take a look if you want a more in-depth understanding of SR. Here's the short version to hopefully clear things up for you. If you stand still and measure the speed of a light pulse, you would get the speed of light "c". Let's now say that another observer is moving in the direction of that light pulse , at a velocity v, and also measuring it's speed. Intuitively, you would assume that they measure the speed of the pulse to be c-v relative to them. The problem is that, in reality, they also measure the speed of light to be moving at c. So how do you account for this? Since v=d/t, you could accuse them of measuring either distance or time incorrectly. In order for them to increase the velocity from c-v to c, they must have either measured a longer distance or a shorter time... or maybe both. In my chapter 2 video, we find out that the answer is both, and that is the roots of length contraction and time dilation. I hope this helped! Let me know if you are still confused.

[@shehryarzia9661]

Time dilation is just like our teacher lecture. For us it is of 45 minutes but for him it is only 5 minutes.

[@Robert-qw9hp]

6:33 "Time goes faster for you than for Bob", but later less time passes for you than for Bob, what??

[@TheRandomEnthusiast]

Robert Vincent Struggling with the exact same thing here!

[@alexneff3512]

Allen Dowe I thought the same thing. Not completely sure but I think the logic in relating time dilation to length contraction is flawed, or at least i don’t understand it. How can you maintain that the stationary perspective measured longer in the time dilation example, if in the length contraction example you say that in d = v * t, the moving observer measures longer?

[@extizt6677]

If time is passing faster for you than bob then the same event should take less time to occur for you while it takes more time for bob

[@hartog2332]

then if you take this scenario to like a year long journey Bob would have aged more than you? as it seems more time has passed for him so he would have thus aged more?? This is not the standard answer to the scenario, where fast movement= less fast ageing.

[@MalakTumeh]

Hello Robert, I've taken time to calculate this, and the video is, indeed, wrong. If 667 nanoseconds pass for Bob, 770 nanoseconds should have passed for the still reference frame. I believe they have made a mistake when defining t and t0. It should be as followed: t= Time for still reference frame t0= time for moving reference frame

[@abrahamlincoln9869]

I'm in love with her..

[@RockRita09]

Right! Smart and pretty!

[@audreykea7771]

@@RockRita09 yea well im in love with barack obama

[@katerinavachova6217]

My brain is crying but I’m loving it

[@cough5431]

i’d just like to point out the irony in that last comment... “that’s because we’re used to seeing the world at much much slower speeds than light” 😂😂😂 great vid btw

[@bianca-jj4mc]

i did not understand fiskskxkd

[@jadonbertholf547]

My brain hurts

[@IceMetalPunk]

The short and simple version: you know distance = speed x time, yes? And you know that in a right triangle, the hypotenuse length C is longer than the base length B, right? So if light travels the same speed in a vacuum no matter what (which it does), then if someone shines a light as they're moving past you, they'll only see the light form a straight baseline, while you'll see it trace out the hypotenuse of a triangle. So if speed is constant and the distance is longer, then time must be changing between you and them--specifically, since you see the light moving a longer distance, it'll seem like their time is slower than yours (since it takes longer to travel). Similarly, if the time something takes to pass you is longer, but it's moving at the same speed for both of you, then it will seem to that object that it's longer than it seems to you--which means from your perspective, it's "shrunk" or contracted.

[@o.p.rajput655]

@@IceMetalPunk dude. Cheers for the effort

[@nimrod9640]

You are becoming a famous yt channel, and I think that a lot of people from different nationalities are watching you interesting videos. So it could be realy amazing if you give us some french, spanish, german, or italian subtitles. Thanks for reading !

[@tiborcongo]

awesome, ads suck, but this is our world so if it's what it takes to get this content out, I'm in! What's killing me though is the Hafele-Keating experiment, cannot get past the paradox of the clocks not having the same change relative to each other (I'll keep reading)

[@310iq6]

Brain.exe has stopped responding.

[@alexneff3512]

Not completely sure but I think the logic in relating time dilation to length contraction is flawed, or at least i don’t understand it. How can you maintain that the stationary perspective measured longer in the time dilation example, if in the length contraction example you say that in d = v * t, the moving observer measures longer? Time should be longer for the stationary perspective, hence the twins paradox, so how is the distance for stationary measured shorter if d = v * t? That would imply that the time multiplier is shorter, but it’s not. An solution to my confusion would be greatly appreciated

[@alexneff3512]

Also this video gets the lack of simultaneity wrong. That example simply demonstrates light being the fastest means of communication. With telescopes, we can see the early universe because the light has taken that long to reach us, but we still know it happened billions of years ago; it is not out present, we are just seeing it now.

[@davezimmer9053]

Yeah I was also confused by that.... I tried to put that calculation into the equation but couldn't get that right.

[@ronblaess1]

What she failed to mention is that the clocks used for measuring the time it takes the train to pass are BOTH with the stationary observer. Bob sees a certain time pass on a clock at the train station (he concludes that his train is 100 meters long) yet Sarah? measures less time on the same clock as for her Bob's train is length contracted. That really was an oversight in an otherwise pretty good video.

[@crossfire1403]

@@ronblaess1 but why does the "moving-frame-observer" measure its own "plattform-pass-by-duration" by using a relative to him moving clock? This outer clock-readout therefore will result in a wrong "time-duration-measurement", because the outer clock is in a different reference-frame from the perspective of the "moving-frame-observer". How can it be right to make time-measurement by using an "outside-the-own-referene-system-clock"?

[@chickenbro8086]

would this mean when we run this happens? and does your math consider how fast we blink to capture light?

[@SSGranor]

Sure, it happens when you run; but, the gamma factor in that case is about 1.0000000000000002. And, blinking is irrelevant. All these effects are measurable with instruments that have no need to blink.

[@KevlarSammy]

PBS was there when I was a kid and is still there when I’m an adult.

[@thomasrivera8626]

She is Beautiful and I like her but what happened to John Green?

[@recklessroges]

I don't think Physics is John's strong suit. He does books n' stuff. Hank could probably do Physics, but I really like Dr Shini Somara

[@thomasrivera8626]

LOL Ohh thanks.

[@kudos4201]

id' rather have someone who has a doctorate in physics to explain. even if it is scripted.

[@NateManPro]

First ha ha what a meme

[@Nana-kw2qo]

Correct me if I’m wrong but special relativity is when time warps to accommodate the speed of light since usually we live at a rate slower than the speed of light

[@cerealkiller1939]

Best physics vid yet