Time Dilation - Albert Einstein and the Theory of Relativity
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Video Description:
Two spaceships are traveling together through the galaxy at close to the speed of light. Mounted on one ship is a laser that can fire pulses of light, and on the other, a mirror. The pilot of the first ship fires a pulse at the mirror, and watches as it is reflected back. A clock on board measures how long the round trip takes.
But now suppose that he does this as the ships are passing an observer on a nearby asteroid. According to relativity theory, this observer sees the pulse moving through space at exactly the same speed that the pilot does -- namely, the speed of light. But he also sees the pulse traveling a longer distance, because from his perspective, he must add the forward motion of the ships to the motion of the pulse between them. So he measures a longer time interval for the round trip than the pilot does, because he is watching the pulse go farther without going any faster. This effect is called time dilation: if one observer is moving with respect to another, each perceives that the other's time is flowing more slowly.
National Science Foundation
Tags for this video: Albert dilation Einstein of Physics Relativity Science Theory time
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| Comments for this video on YouTube |
| Oh. Just realized ... ( 1 week ago by Flashman2006) |
| Oh. Just realized you took those quotes from the video. Either way, thanks for posting them. |
| good thinking, ... ( 1 week ago by toosas) |
| good thinking, cause if the speed of light is constant, the pulse that has left the ship (which is flying in a direction at 90 degree angle, at speeds near to c) is already a bit behind both ships so they would have to compensate for the light to hit the mirror and again the receiver.. |
| Thanks for the kind ... ( 1 week ago by jalcide) |
| Thanks for the kind words Flashman, funny thing I didn't think I was using any quotes from the video. Actually most of the analogies were paraphrased from Brian Greene's "The Elegant Universe", fantastic book. I guess a lot of these concepts get distilled down to pretty universal sounding sound bites. ;-) Special and General Relativity is such a mind blowing, wondrous thing. It's taken quite some time for me to wrap my head around it, and still am, which it why I love this dialog. Cheers! |
| To clarify ... ( 1 week ago by jalcide) |
| To clarify something in my "part 3" post: The reason the space travelers would come back to a "much aged earth" is assuming they have been traveling near the speed of light. Time, relative to those on earth would have flowed more slowly for them, as much of their space-time motion is being used moving in 3 dimensions, they would have aged less. Gravity of the earth is actually helping those on earth age slower too, just not as significant an amount as a space traveller moving near lightspeed. |
| What did the ... ( 1 week ago by Neithax) |
| What did the michelson morley show? That light speeds away with c from its emission point!!!! That is true galilean invariance! |
| But that doesn't ... ( 6 days ago by BelieveIt1051) |
| But that doesn't mean humans that travel at light speed will come back to an aged Earth. Time does not slow down as you approach the speed of light. This is where Einstein's genius ran out. Traveling faster doesn't make you age any slower. If you went billions of light years in one second, you would be one second older, as would the Earth be one second older. The time the Earth ages is the same amount of time you spend away from it, and that time passed is also your added age as well. |
| Strange as it may ... ( 6 days ago by jalcide) |
| Strange as it may sound, this "traveling into earth's future" would indeed happen. In fact, you may be using it everyday without knowing it as a similar effect due to gravity, required engineers to compensate for it to get GPS systems working. Back to your e.g. You'd be one sec. older within your frame of ref. only. If you could get enough energy to accelerate your mass to 0.9999998 of 'c', after 8 of your years, 1840 would have flowed back on earth, effectively "traveling" into earth's future. |
| Sorry, but that ... ( 6 days ago by BelieveIt1051) |
| Sorry, but that just doesn't follow logic. Speed does not make a person age slower or faster. It moves them through space in less or more time. What you're talking about is actually speeding up one's own time frame to be faster than the normal passage of time, which is beyond our comprehension at this stage of human knowledge. In this case the person would age faster than everything else, or if he slowed time down for himself, he would age more slowly. Has nothing to do with light speed though. |
| It has everything ... ( 6 days ago by jalcide) |
| It has everything to do with the speed of light ('c') insofar as the fact that 'c' is constant, that's the kicker. In the video, it's that photon plus the speed of the ships still being 'c', not c + ships 'v'. Because it's constant it's this somewhat odd relationship between space and time exists, it's called spacetime. There's an inextricable bond between the two that says when something's moving though the space "axis," less is moving through the time "axis" relative to an observer. |
| (cont) We say " ... ( 6 days ago by jalcide) |
| (cont) We say "relative to an observer" because when something's in constant, unchanging motion they can make the claim they're not moving at all. So to really enjoy the "lasting" effects of time dilation's time travel side-effect you'd want to move in a non-constant, continual acceleration away and then back towards earth. When you're *feeling* the effects of acceleration (just like gravity) you can't make "an equal and valid claim" that you're at rest and so your clock definitely slows. |
| But the real kicker ... ( 6 days ago by BelieveIt1051) |
| But the real kicker is that the speed of light is set. It is not infinate. If it were infinate, THEN maybe you'd have a point, but lightspeed is set. It takes 8.5 minutes for the light of the Sun to reach Earth. If a human traveled from the Sun to Earth at the speed of light, he or she would age 8.5 minutes, and things on Earth would age at the same rate. The rate doesn't change just because of human perception of space. |
| If we sped by Earth ... ( 6 days ago by BelieveIt1051) |
| If we sped by Earth at the SoL it might seem that Earth was standing still but then again we would only see Earth for a millisecond at the most. The fact is that it would keep spinning at the same rate and we would age at the same rate. I agree that the faster you move the less time you spend in 1 point in space, but as you leave 1 point you enter another, and so on. So time remains constant. Time travel is only possible by stopping time itself. Traveling from 1 point to another in 0 seconds. |
| SoL is set, but ... ( 6 days ago by jalcide) |
| SoL is set, but time is not, it changes in two ways: first, "relatively" if the motion is constant and secondly "for real" if the motion is accelerated or under a gravitation field (accelerated motion and gravity are the same thing). Strictly speaking a human or anything with mass could never travel at the SoL as mass increases exponentially with speed, at 99.9% SoL it's 224 times, as the decimal points get longer it's get's even more drastic to the point of infinity (more energy than exists). |
| (cont) But let's ... ( 6 days ago by jalcide) |
| (cont) But let's say you could actually travel at 'c', you wouldn't age 8.5 minutes to get to the sun, you'd age zero minutes. Light doesn't age at all. All of light's "motion" is expended moving through x/y/z dimension(s) with none left over for the time dimension. Time is "frozen" for light. But back to the spirit of your e.g.: If someone with a stopwatch *accelerated* toward the sun increasing close to light speed and then back again the watch, upon inspection, would not agree with earth's. |
| This same effect ... ( 6 days ago by jalcide) |
| This same effect had to be compensated for by engineers in GPS satellites. Just as acceleration "pushes you back" in your seat, so too does gravity. Gravity IS "accel.," only sitting still. The satellite's higher orbit causes it to "feel less" accel., it's "moving" less (in gravity) than someone standing on earth, this "less moving" means more of it's time is "moving," that is, the clock is running faster for it. This (tiny) time diff. had to be accounted for to get our GPS gadgets working. ;-) |
| I don't understand ... ( 4 days ago by humbertojimmy) |
| I don't understand why they say that if you move at the speed of light and then come back to Earth, everybody has aged more than you. Shouldn't it be otherwise? Imagine 2 guys inside a locked room. 1 moves at normal speed and the other moves at light speed. Wouldn't everything around the fast guy slow down? Wouldn't the fast guy be able to do a 1000 things while the other only blinked an eye? So, since the "inner time" of each remains constant, the fast guy is the one aging quick.. makes sense? |
| Hi, In your e.g. ... ( 3 days ago by jalcide) |
| Hi, In your e.g. where "...everything around the fast guy would slow down...", true, but from his perspective only. The things he passes can make the same claim about him. There's no "common thread of time" to "know" that one guy is faster. It's all relative based on motion. Ergo, this "earth's future" thing would only work if the traveler's speed is in continual acceleration, such that they feel a force and therefore can't make an "at rest" claim. It's all about the acceleration (or gravity). |
| humbertojimmy: ... ( 1 day ago by gwarkan) |
| humbertojimmy: Google search this: "resoultion of twin paradox with spacetime diagram" you'll find an animated diagram - pretty easy to follow. |
| Of course you don't ... ( 1 day ago by Neithax) |
| Of course you don't age slower. Einstein tried to give the Lorentz transformation which serve the Lorentz covariance for the Maxwell-Lorentz-Gibbs electrodynamics, a "physical" explanation and kinematical justification. It is too bad his SRT is so absurd and Einstein told everyone to abandon it in 1911. I am already talkin too way too much people to explain it further. But if you want a real broad picture, read Maxwell and Lorentz first before starting with Einstein. |
| It has everything ... ( 1 day ago by Neithax) |
| It has everything to do with making a Field theory galilean invariant and since field theories use Eulerian coordinats and the Maxwell-Lorentz partial time derivatives which are based on a static ether, this coordinats require scale changes. Scale changes arenot necessary for particle theories which are exact galilean invariant. These scale changes are explained by "SRT" for the laymen. Albeit I do not approve it because the derivation is absurd. |
| Ow you do know that ... ( 1 day ago by Neithax) |
| Ow you do know that (x-xs)=c*t is galilean invariant. (With x the tip of the lightwave and xs, the sun inside the physical inertial frame the sun. Now apply an active galilean boost to both the tip of the wave and xs to another star (let say Proxima centauri) and one obtains true galilean invariance. We cannot determine absolute motion locally but we can do so globally!!! We do it globally because of doppler effects of the 3K background radiation. That Radiation has c - v with respect to Earth. |
| can anyone answer ... ( 23 hours ago by qawra2008) |
| can anyone answer me howcome a twin travelling to space and back at high speed seens his brother younger on arrival.. Also from his brother frame of reference his brother is also younger than him... Isn't this a contradiction.... |
| before someone ... ( 23 hours ago by qawra2008) |
| before someone answers me by saying that only one brother accelarated and made a u-turn... can i put forward a situation where both brothers were in a rocket and both brothers accelarated and made am identical u-turn and met again in the same departing spot.... |
| So here's a paradox ... ( 7 hours ago by humbertojimmy) |
| So here's a paradox within itself: Imagine a car racing show (Nascar style, circle loops) advertised as being an hour show. The audience is there, the cars are there, but these cars have enough potency to go at almost light speed. The pilots have wrist watches to know when an hour has passed, so do the people on the audience.. when the race ends, how come the audience didn't realise they have been sitting there for a FEW YEARS? |
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