Why does time slow down the faster you go?

  • #1

Main Question or Discussion Point

Or is this only true when I am viewing someone else's clock?

Why does time slow down the faster something travels?

How could this apply to the Earth? How would our time on Earth slow down? Would the Earth have to be rotating faster and revolving faster around the Sun?
 

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  • #2
Or is this only true when I am viewing someone else's clock?

Why does time slow down the faster something travels?

How could this apply to the Earth? How would our time on Earth slow down? Would the Earth have to be rotating faster and revolving faster around the Sun?
It's just like politics. Your own clock is always right. It's always the other guy's clock that is wrong.

Why does time slow down the faster something travels?
The other guy's time slows down in order to preserve the laws of physics. If it didn't slow down, the laws of physic would not be preserved and things would be messier than they are.

How could this apply to the Earth? How would our time on Earth slow down? Would the Earth have to be rotating faster and revolving faster around the Sun?
Time is almost exactly the same at sea level, everywhere on the surface of the Earth. Gravity is more at the poles, though.
 
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  • #3
PAllen
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Time is almost exactly the same at sea level, everywhere on the surface of the Earth. Gravity is more at the poles, though.
You are in good company - Einstein was initially confused about this (though his confusion was the revers of yours - he thought time would run slower at the equator, due to rotation speed).

The reality is that the geoid (surface) conforms to be an equipotential surface (this will be true for any body that is shaped by its self gravity - part of the definition of a planet). The oblateness (leading to less gravitational time dilation) at the equator cancels rotational time dilation, so there is no difference (on average) between time flow at the poles versus the equator.

[EDIT: I see this is what you meant. So we are in agreement.]
 
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  • #4
ghwellsjr
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You are in good company - Einstein was initially confused about this (though his confusion was the revers of yours - he thought time would run slower at the equator, due to rotation speed).
He wasn't confused and he was right in what he said concerning Special Relativity in 1905, long before anyone had yet thought of General Relativity:
Thence we conclude that a balance-clock at the equator must go more slowly, by a very small amount, than a precisely similar clock situated at one of the poles under otherwise identical conditions.
He was predicting for the first time what became known as the Twin Paradox and for you to say he was confused makes as much sense as someone complaining about the Earth twin being stationary when we all know that the Earth revolves around the Sun.
 
  • #5
PAllen
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He wasn't confused and he was right in what he said concerning Special Relativity in 1905, long before anyone had yet thought of General Relativity:

He was predicting for the first time what became known as the Twin Paradox and for you to say he was confused makes as much sense as someone complaining about the Earth twin being stationary when we all know that the Earth revolves around the Sun.
Ok, you are right. There are many accounts of this around as a mistake by Einstein, but in historical context it was not. It was a mistaken prediction, but not a misunderstanding of what was then known.
 
  • #6
ghwellsjr
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Ok, you are right. There are many accounts of this around as a mistake by Einstein, but in historical context it was not. It was a mistaken prediction, but not a misunderstanding of what was then known.
It wasn't a mistaken prediction. He said, "under otherwise identical conditions", which means, all other things being equal. It's no different than everyone else ignoring gravity or the earth not being in the same place when they talk about the Twin Paradox.
 
  • #7
PAllen
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It wasn't a mistaken prediction. He said, "under otherwise identical conditions", which means, all other things being equal. It's no different than everyone else ignoring gravity or the earth not being in the same place when they talk about the Twin Paradox.
Now you're quibbling. If cesium clocks existed in 1906, and the experiment were performed to validate SR, it would have been recorded by history as a mistaken prediction (later explained by the development of GR). Scientific history is filled with such incidents - predictions correct based on what was known that turn out wrong due to phenomena not yet known. We don't have to deify Einstein and not use the same language we do for similar historical cases.
 
  • #8
In SR time is only slowing down for the other frame of reference and vice versa?

But isn't it true that time is actually slower in some places than in others? For instance clocks tick slower at sea level than they do at higher altitudes although not by much.
 
  • #9
PAllen
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In SR time is only slowing down for the other frame of reference and vice versa?

But isn't it true that time is actually slower in some places than in others? For instance clocks tick slower at sea level than they do at higher altitudes although not by much.
In SR, if you start with clocks together, separate them, and bring them together, they will generally differ (the path with greater deviation form an inertial path will accumulate less time). The exact same thing is true in GR.

In SR, mutual observation of inertial clocks is symmetric - each sees the other slower. In GR, this is still true for 'nearby clocks' with different inertial motion. Quite generally, SR global behavior becomes GR local behavior.

Finally, for comparing inertial and non-inertial clocks (or two non-inertial clocks) without bringing them together, you have asymmetric effects in both SR and GR. For example, in SR, clocks will run slower at the front of a long uniformly accelerating rocket[edit: compared to the rear of the rocket], and this effect is not symmetric.
 
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  • #10
In SR time is only slowing down for the other frame of reference and vice versa?

But isn't it true that time is actually slower in some places than in others? For instance clocks tick slower at sea level than they do at higher altitudes although not by much.
Right. But that's gravity/general relativity, and special is about no-gravity.
 
  • #11
So where would I actually age slower?
 
  • #12
ghwellsjr
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So where would I actually age slower?
The lower your elevation, the more time dilation you experience.
 
  • #13
ghwellsjr
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In SR time is only slowing down for the other frame of reference and vice versa?
This is the wrong way to express the issue in SR. Time is not going slower for different Frames of Reference. You need to think about a Frame of Reference as extending out to infinity in all directions and including everything and everybody. Observers/objects/clocks at rest as defined by the coordinates of your selected FoR will not experience any time dilation. That is true for all FoRs. The faster an observer/object/clock moves as defined by the coordinates of your selected FoR, the greater their time dilation. So in the FoR in which one Twin remains at rest, he never experiences any time dilation but the other Twin does experience time dilation while he is traveling and ages at a lower rate. You can analyze the situation with any FoR but unless the twins re-unite, different FoR will assign different amounts of time dilation to the two twins with no agreement between them.
But isn't it true that time is actually slower in some places than in others? For instance clocks tick slower at sea level than they do at higher altitudes although not by much.
Yes but that is a GR effect which we usually ignore when talking about SR.
 
  • #14
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Why does time slow down the faster something travels?
It doesn't seem like your question was satisfactorily answered. Which is ok because, afaik, it's an open question in physics in the sense that there's no physical, mechanistic explanation for relativistic differential aging.

If you start with two identical clocks side by side and accelerate one clock to, say, .5 c and then decelerate it and bring it back alongside the stationary clock, then the moving clock will have recorded less time than the stationary clock.

If the clock engines are, say, vibrating quartz crystals, then that means that the period of oscillation of the crystal in the moving clock was, during the round trip, on average greater than that of the stationary clock.

How does this happen? What's the mechanics of it? Nobody knows. It's one of the outstanding mysteries of physics.
 
  • #15
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Why does time slow down the faster something travels?
PAllen's post # 9 gives as precise an explanation as is currently known.

One could also answer "nobody knows" or "because space and time are not fixed (meaning
it's the speed of light that is) for all observers....but our models and mathematics show what happens not really why things happen.
 
  • #16
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PAllen's post # 9 gives as precise an explanation as is currently known.

One could also answer "nobody knows" or "because space and time are not fixed (meaning
it's the speed of light that is) for all observers....but our models and mathematics show what happens not really why things happen.
I agree with what you say, but would like to add that it's precisely because the speed of light is an observationally well verified constant (and an assumed boundary of propagational speed) that it can be inferred that there's an objective/universal meaning wrt distance and time.

Relativistic differential aging is a fascinating phenomenon. It suggests that what's been historically thought of as empty space isn't empty, and that there are currently unknown/unmapped interactions occuring which are the root cause of the phenomenon. The geometrical explanation of relativistic differential aging is, as you note, a certain depiction/description of what happens. As you also indicated, it isn't, however, a physical explanation of how/why it happens in terms of wave mechanical interactions. This is the mystery that remains for physicists to sort out and solve.
 
  • #17
Or is this only true when I am viewing someone else's clock?

Why does time slow down the faster something travels?

How could this apply to the Earth? How would our time on Earth slow down? Would the Earth have to be rotating faster and revolving faster around the Sun?
Well for me personally the best way to "visualise" the answer to your question is to visualise a moving photon clock. Cheers.
 
  • #18
ghwellsjr
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It wasn't a mistaken prediction. He said, "under otherwise identical conditions", which means, all other things being equal. It's no different than everyone else ignoring gravity or the earth not being in the same place when they talk about the Twin Paradox.
Now you're quibbling. If cesium clocks existed in 1906, and the experiment were performed to validate SR, it would have been recorded by history as a mistaken prediction (later explained by the development of GR). Scientific history is filled with such incidents - predictions correct based on what was known that turn out wrong due to phenomena not yet known. We don't have to deify Einstein and not use the same language we do for similar historical cases.
Let me repeat the quote of Einstein's:
Thence we conclude that a balance-clock at the equator must go more slowly, by a very small amount, than a precisely similar clock situated at one of the poles under otherwise identical conditions.
Aren't you using the fact that at sea level, the equator experiences a different GR effect than the poles experience at sea level, correct? But isn't this primarily because the diameter of the earth is greater at the equator than at the poles? And wouldn't it make more sense in order to apply Einstein's stipulation of "under otherwise identical conditions" that we put the clocks at the same distance from the center of the earth and not at different distances? But to be more precise, we should put the clocks at elevations where the effects from General Relativity are the same in order to have "identical conditions". So if we put one clock at the South Pole at the top of whatever mountain is there and found a lower elevation somewhere along the equator that had exactly the same GR effect, then the clock at the equator would run slower than the one at the pole, exactly like Einstein predicted, don't you agree?
 
  • #19
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I was watching a documentary one of these days and it said that we could travel to the future by orbiting a massive black hole and then returning to Earth.

The concept was clear to me: time passes slower near strong gravitational field, for instance let's say an astronaut spends 1 hour orbiting the black hole and when he returns 50 years have passed at Earth. However I have always read that for the man in the spaceship time would pass slower at Earth because he sees Earth at a high speed and the Earth would see time pass slower for him.
For example, in the reference of the Earth he would have been 50 years near the black hole while he would been only 1 hour.
In the man's reference he would have been 50 years near the black hole and only 1 hour would have passed at Earth.

The implications of each scenario are very different. Which one would happen?

I know this question has been asked many times here but I still cannot comprehend its explanation.
 
  • #20
ghwellsjr
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The symmetrical relationship you're talking about occurs when two observers are traveling in more or less a straight line with respect to each other. When one travels in a high-speed circle, it is no longer symmetrical.
 
  • #21
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The symmetrical relationship you're talking about occurs when two observers are traveling in more or less a straight line with respect to each other. When one travels in a high-speed circle, it is no longer symmetrical.
Ok, so let's say the spaceship is leaving Earth in a straight line and at a high speed.
The same paradox would happen; Earth would see the spaceship at high speed, the spaceship would see Earth at a high speed.

Which one would time be slower to?

I have seen other topics where the answer is that both points-of-view are valid, but one of them must happen while the other one not, because the implications are very different for each perpective. Or they both occur at the same time, but being so would make it impossible to detect time dilation.
 
  • #22
PAllen
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Let me repeat the quote of Einstein's:

Aren't you using the fact that at sea level, the equator experiences a different GR effect than the poles experience at sea level, correct? But isn't this primarily because the diameter of the earth is greater at the equator than at the poles? And wouldn't it make more sense in order to apply Einstein's stipulation of "under otherwise identical conditions" that we put the clocks at the same distance from the center of the earth and not at different distances? But to be more precise, we should put the clocks at elevations where the effects from General Relativity are the same in order to have "identical conditions". So if we put one clock at the South Pole at the top of whatever mountain is there and found a lower elevation somewhere along the equator that had exactly the same GR effect, then the clock at the equator would run slower than the one at the pole, exactly like Einstein predicted, don't you agree?
The point is that Einstein obviously didn't know about gravitational time dilation. I'll bet he did know that oblateness of the earth was required by mechanical equilibrium given its rotation. He did not know that this was relevant. So I believe his prediction was meant as something the could (conceivably) be tested in the straightforward way. In 1906 he would have been puzzled by the failure. After 1916, he would have understood that gravitational time dilation plus mechanical equilibrium means that, quite generally, for a realistic spinning body you would get time variations much smaller than those based on his 1905 prediction.

Similar situations in history are called mistaken predictions based on effects not yet known. The same language should be used for Einstein.
 
  • #23
PAllen
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Ok, so let's say the spaceship is leaving Earth in a straight line and at a high speed.
The same paradox would happen; Earth would see the spaceship at high speed, the spaceship would see Earth at a high speed.

Which one would time be slower to?

I have seen other topics where the answer is that both points-of-view are valid, but one of them must happen while the other one not, because the implications are very different for each perpective. Or they both occur at the same time, but being so would make it impossible to detect time dilation.
While the rocket was traveling away, each sees the other slower, and there is no way to way one is preferred. However, once the rocket turns around and heads back to earth, there is a major asymmetry - the rocket turned around, while the earth didn't. Relativity does not say that inertial and non-inertial motion are the same.

If you look just at your literal, un-interpreted image, the difference is immediate. At turnaround, the rocket immediately, visually, sees the earth clock run faster, and this continues until the rocket lands on earth. Meanwhile, the earth observer sees the rocket clock slower until it almost reaches earth, because light from the turnaround hasn't arrived yet. Only when the rocket is close to earth does earth start to see the rocket clock run fast. There are many other ways to understand the asymmetry, but this pure visual appearance explanation is easy to understand.
 
  • #24
ghwellsjr
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The point is that Einstein obviously didn't know about gravitational time dilation. I'll bet he did know that oblateness of the earth was required by mechanical equilibrium given its rotation. He did not know that this was relevant. So I believe his prediction was meant as something the could (conceivably) be tested in the straightforward way. In 1906 he would have been puzzled by the failure. After 1916, he would have understood that gravitational time dilation plus mechanical equilibrium means that, quite generally, for a realistic spinning body you would get time variations much smaller than those based on his 1905 prediction.

Similar situations in history are called mistaken predictions based on effects not yet known. The same language should be used for Einstein.
The actual history is that prior to Einstein, nobody--not Lorentz, not Fitzgerald, not Poincare, not Maxwell--predicted the Twin Paradox. Long after his prediction, which was exactly correct, when many other things became known, nitpickers came along and attempted to denigrate Einstein by claiming that his prediction was faulty.

Tell me, why can't you accept his caveat that "under otherwise identical conditions" takes care of any and all effects that are not the one that he was making the prediction about?
 
  • #25
ghwellsjr
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Ok, so let's say the spaceship is leaving Earth in a straight line and at a high speed.
The same paradox would happen; Earth would see the spaceship at high speed, the spaceship would see Earth at a high speed.

Which one would time be slower to?

I have seen other topics where the answer is that both points-of-view are valid, but one of them must happen while the other one not, because the implications are very different for each perpective. Or they both occur at the same time, but being so would make it impossible to detect time dilation.
You have to think of time dilation as related to a Frame of Reference and you need to quit thinking that a Frame of Reference is the same as a point-of-view or that it is tied only to an observer in your scenario. There is no preferred Frame of Reference. The observers/objects/clocks can move at different speeds in each Frame of Reference and therefore have different time dilations in each Frame of Reference.

And there are not just two Frames of Reference because there are only two observers. You can have a Frame of Reference that is "midway" between the two observers such that both observers are traveling at the same speed but in opposite directions in which case their clocks would be ticking at the same rate.

Think about the question of speed. Do you have confusion over the concept of speed? Isn't it fairly obvious that if in your chosen Frame of Reference, the Earth is at rest and the spaceship is in motion, this in no way creates any conflict or confusion with another Frame of Reference in which the spaceship is at rest and the Earth is in motion? Do you concern yourself with the "paradox" of how both of these Frames of Reference can be valid? Or if I bring up the "midway" Frame of Reference in which the spaceship and Earth are moving in opposite directions at the same speed, does that cause you to wonder about its validity?

If you have no problem with speed being defined by a Frame of Reference, then you shouldn't have any problem with time dilation being defined by a Frame of Reference since time dilation is a function of speed.
 

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