Theory of Relativity

[MASTERASTRONOMER]

I have herad about Einstien's theories which states that if an object travels at the speed of light then 'time' stops flowing for it and if it travels faster than light then it goes back into time. Is it true? What positive proofs did Einstien give? I think that it is never possible.

 

[yevaud]

Well, that's not correct.

In General Relativity, C can be looked upon as a physical barrier, so to speak. No object with mass can be accelerated to a close fraction of C, without the energy requirements to do so exceeding the energetic output of the entire universe. It is simply forbidden, a word you will hear physicists and astronomers use periodically.

However...while it's impossible to accelerate an object to a velocity faster than light, it is possible for the object to have a velocity greater than c. For example, it's been shown that the group velocity of electromagnetic propagation can exceed C. Quantum tunneling is another example, where the apparent velocity is superluminal.

The rub here is that no useful information may be transferred, as it would violate causality.

 

[origin]

I have herad about Einstien's theories which states that if an object travels at the speed of light then 'time' stops flowing for it and if it travels faster than light then it goes back into time. Is it true? What positive proofs did Einstien give? I think that it is never possible.

If you think it is impossible to travel faster than the speed of light and travel back in time then you are correct. However it is true that time slows down for an object relative to you when it has been accelerated to some velocity. The higher the velocity the slower time goes. Time would stop (relative to you) if the speed of light could be reached, which is not possible. This effect of slowing time with increased velocity has been tested and is measurable.

 

[mental_avenger]

If you think it is impossible to travel faster than the speed of light and travel back in time then you are correct. However it is true that time slows down for an object relative to you when it has been accelerated to some velocity. The higher the velocity the slower time goes. Time would stop (relative to you) if the speed of light could be reached, which is not possible. This effect of slowing time with increased velocity has been tested and is measurable.

There is no proof that time slows down for an object as it is accelerated. Perhaps the only thing that is really happening is that the atoms of the object simply interact more slowly due to the acceleration. AFAIK, there is no way to tell the difference.

 

[drwayne]

A point of clarification. There seems to be a use of acceleration in this discussion that is confusing
to at least me. Time dialation for example does not require acceleration to happen.

I am not sure if that is the point you are making here MA:

"There is no proof that time slows down for an object as it is accelerated"

This presentation includes a discussion on time measurements made by plane - which might
be of interest.

http://spiff.rit.edu/classes/phys314/le ... _long.html

 

[mental_avenger]

This presentation includes a discussion on time measurements made by plane - which might be of interest.

Time measurements which are made by clocks that depend upon the interaction of atoms. At rest it appears that those atoms interact predictably, and therefore those interactions are used as a time base. But what if the rate at which those interactions occur slows down with acceleration or relative velocity? The clocks would still run slower, even though time itself did not change for the object.

 

[Saiph]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

 

[ArcCentral]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

There is an important distinction between time slowing down, and the rate of interaction of entities. A whole different ballgame.

 

[drwayne]

This presentation includes a discussion on time measurements made by plane - which might be of interest.

Time measurements which are made by clocks that depend upon the interaction of atoms. At rest it appears that those atoms interact predictably, and therefore those interactions are used as a time base. But what if the rate at which those interactions occur slows down with acceleration or relative velocity? The clocks would still run slower, even though time itself did not change for the object.

This is argument is a bit of a reach to me because

(1) I find it unlikely that clocks, operating on different mechanisms, would slow down in exactly the same
way, in the magnitude predicted by theory

and

(2) Since time effect show up in constant velocity frames of reference - in the words of a country scientist I knew,
"how do they know"?

Wayne

 

[drwayne]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

There is an important distinction between time slowing down, and the rate of interaction of entities. A whole different ballgame.

Can you propose an experiment that will tell the difference between a scenario in which time slows, or a process
in which all* interactions slow?

Wayne

*Given that clocks relying on varying meachanisms show the same effect, one must assume all includes *all* i.e.
mechanical, chemical, biological, nuclear etc.

 

[Mee_n_Mac]

Would radioactive decay be considered an "interaction" ? If not then the lifetime of certain particles would be an independant measure. And it's already been done I believe.

 

[bowman316]

I think the doubters are using this line of logic:
Water molecules slow down as they begin to freeze, and speed up as they boil. But time is not affected. So maybe speed effects molecules just like temperature does, but there is no effect on time itself. Just like temperature does not effect time.
That being said, I believe if an atomic clock slows down at speed, that proves time dilation. The atom decays slower, and the only explination can be the higher velocity.

 

[drwayne]

"I think the doubters are using this line of logic:"

I know, I have seen variations of this posted on a number of physics boards by folks that
seek to come with alternative explanations to state that time dilation has not been proved.
"Everything slows down, but time remains the same"* is the hypothesis.

The problem is this. If one constructs an hypothesis like this, you have now constructed something
whose behavior is indistinguishable from special relativity.

Wayne

*in the simulation world, we might call this something like "scaled real-time"

 

[SpeedFreek]

This presentation includes a discussion on time measurements made by plane - which might be of interest.

Time measurements which are made by clocks that depend upon the interaction of atoms. At rest it appears that those atoms interact predictably, and therefore those interactions are used as a time base. But what if the rate at which those interactions occur slows down with acceleration or relative velocity? The clocks would still run slower, even though time itself did not change for the object.

Would the rate at which your hair grows depend on the interaction of atoms? Would the rate at which you age depend on the interaction of atoms? Would the duration of any event in the whole universe depend on the interaction of atoms?

If the answer is yes, then we can use the interaction of atoms to measure time.

Is a clock at the top of a mountain accelerating more or less than a clock at sea level? Does a clock at the top of a mountain have a relative velocity to a clock at the base of that mountain? What are your thoughts on gravitational time dilation? Does the clock at the top of the mountain tick "faster" or "slower" than a clock at sea level, and why?

 

[mental_avenger]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

On the contrary, the point is quite significant. Considering the concept of space-time, and the theory of time dilation, whether or not time actually slows down is a very important distinction.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

Theory of Relativity.

 

[mental_avenger]

(1) I find it unlikely that clocks, operating on different mechanisms, would slow down in exactly the same
way, in the magnitude predicted by theory

I would be surprised if atomic interactions, subjected to the same forces, did not react in the same way.

 

[mental_avenger]

Would the rate at which your hair grows depend on the interaction of atoms? Would the rate at which you age depend on the interaction of atoms? Would the duration of any event in the whole universe depend on the interaction of atoms?

If the answer is yes, then we can use the interaction of atoms to measure time.

Not necessarily. The atoms in a Bose-Einstein Condensate are deliberately slowed down, but time continues to proceed unchanged. We could only use the interactions of atoms to measure time is we could know for certain exactly how those atoms are affected by different conditions.

Is a clock at the top of a mountain accelerating more or less than a clock at sea level? Does a clock at the top of a mountain have a relative velocity to a clock at the base of that mountain? What are your thoughts on gravitational time dilation? Does the clock at the top of the mountain tick "faster" or "slower" than a clock at sea level, and why?

I’m not sure that a test for the comparison of a clock on the top of a mountain with one at sea level can be devised that is able to accurately predict or compensate for all of the variables. That is especially true if we don’t know exactly how any of the variables or combination of variables are going to affect the working of the clocks.

 

[SpeedFreek]

Would the rate at which your hair grows depend on the interaction of atoms? Would the rate at which you age depend on the interaction of atoms? Would the duration of any event in the whole universe depend on the interaction of atoms?

If the answer is yes, then we can use the interaction of atoms to measure time.

Not necessarily. The atoms in a Bose-Einstein Condensate are deliberately slowed down, but time continues to proceed unchanged. We could only use the interactions of atoms to measure time is we could know for certain exactly how those atoms are affected by different conditions.

But we do know for certain how atoms are affected by different conditions - we have measured it by flying atomic clocks around the world in both directions and then comparing them to a clock on the ground that they were originally synchronised with. We have also tested it using satellites in orbit and both work as relativity predicts time should work.

Is a clock at the top of a mountain accelerating more or less than a clock at sea level? Does a clock at the top of a mountain have a relative velocity to a clock at the base of that mountain? What are your thoughts on gravitational time dilation? Does the clock at the top of the mountain tick "faster" or "slower" than a clock at sea level, and why?

I’m not sure that a test for the comparison of a clock on the top of a mountain with one at sea level can be devised that is able to accurately predict or compensate for all of the variables. That is especially true if we don’t know exactly how any of the variables or combination of variables are going to affect the working of the clocks.

Relativity tells us that time dilation is not just due to relative speed, it is also due to a difference in relative gravitational potential. Two clocks at different distances from the centre of the Earth will show time dilation relative to each other. The clock that is higher above sea level will show time running at a faster rate than a clock at sea level. A clock down a mineshaft ticks even slower, relatively. I stress the term relatively, as for each clock, a second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

A second always lasts a second, in any valid frame of reference. Time dilation shows that different frames of reference will measure different elapsed times for the same event, but the difference only becomes apparent if they can meaningfully compare their results. Nobody experiences time speeding up or slowing down, they only find that they have experienced different amounts of elapsed time, depending on what they were doing, relative to the other.

The energy that runs around the microchips on a GPS satellite seems to cycle at a different rate up there when compared to the rate it cycles down here. We had to set the chips to run slow by the amount predicted by relativity, for us down here to measure that clock up there as running at the same rate as our own.

We have also measured the decay rates of muons from cosmic rays to be time dilated as predicted by relativity. In fact, every chance we get to measure something that might be time-dilated by the amount predicted by relativity (which happens a lot in particle accelerators), we find it is! The logical assumption is that we are indeed seeing that time is actually relative, rather than absolute.

If we ever manage to send someone away on a long relativistic journey and they return having aged noticeably less than the people that stayed behind, that will be the absolute clincher for non-absolute time, by any definition of the term. Is that what takes (not that we will get that in our lifetimes), or would that still not be enough proof?

 

[drwayne]

(1) I find it unlikely that clocks, operating on different mechanisms, would slow down in exactly the same
way, in the magnitude predicted by theory

I would be surprised if atomic interactions, subjected to the same forces, did not react in the same way.

An object in a constant velocity frame of reference is experiencing no net force.

Wayne

 

[ArcCentral]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

There is an important distinction between time slowing down, and the rate of interaction of entities. A whole different ballgame.

Can you propose an experiment that will tell the difference between a scenario in which time slows, or a process
in which all* interactions slow?

Wayne

*Given that clocks relying on varying meachanisms show the same effect, one must assume all includes *all* i.e.
mechanical, chemical, biological, nuclear etc.

Can't say I could propose an experiment to tell the difference, but a distinction between the two choices discussed is an important one and certainly not meaningless.

 

[yevaud]

God.

The experiment is simple. Run anything up to even a modest acceleration. The observer onboard will see 1) atoms interacting exactly as they should, and 2) time-dilation effects taking place wrt the outside universe.

 

[Saiph]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

On the contrary, the point is quite significant. Considering the concept of space-time, and the theory of time dilation, whether or not time actually slows down is a very important distinction.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

Theory of Relativity.

MA, I think you missed my point. It is indeed very important to ascertain if time itself is slowing down, or it's just the mechanisms. But experiments with time dilation use all sorts of different mechanisms to measure time, from vibrating atoms, light travel times, frequency shifts, mechanical oscillations, all using different sets of forces and principles to count out a time interval. And in each case, for any mechanism tested, using any set of forces and properties, we find the same answer, the time intervals measured are identically altered and concur with theoretical predictions.

If every mechanism we use to measure time gives us a result that indicates time for them is slowed (and they all agree!)...what other conclusion can we draw?

 

[Floridian]

What you describe, to me, makes it a moot point. If all the motion, vibrations, and processes of observable reality are slowed in identical fashions (i.e. any mechanism we use to measure time) it is the same in all respects as time itself being slowed. Since there is no way to tell the difference, it doesn't matter.

I can't think of any instance where it would matter. If I did, then we'd be able to tell the difference which means it matters!

There is an important distinction between time slowing down, and the rate of interaction of entities. A whole different ballgame.

I think it does matter if time exists. The same molecules and energies exist in the universe that existed 5 minutes ago, but something has changed, I would say that it is the passage of time.

I think gravity slows the passage of time, since space-time is a fabric it bends it. You could test this by going out into intergalactic space, or just outside our solar system really, and create an environment exactly the same as an environment on earth, meanwhile keeping clocks going in both places, after x time had passed you would head back and compare.

Also, I think that spacetime had a beginning, how could it just create itself, and you think it just goes back forever, I kind of think thats a copout argument. I think ultimately time had to be created, either through whatever theory or random event you want to believe or God. Whatever insanely powerful force that was outside of time that started the universe/big bang, whatever it is, I think it is pretty similar to God either way.

 

[mental_avenger]

But we do know for certain how atoms are affected by different conditions - we have measured it by flying atomic clocks around the world in both directions and then comparing them to a clock on the ground that they were originally synchronised with. We have also tested it using satellites in orbit and both work as relativity predicts time should work.

The fact that they work as TOR predicts does not mean that TOR is correct. Remember, the theory was developed to explain observed phenomena, not the other way around. Since AFAIK, there would be no way to tell the difference between time dilation and the slowing down of atomic interactions, the observed results would be the same regardless of which is taking place.

Relativity tells us that time dilation is not just due to relative speed, it is also due to a difference in relative gravitational potential. Two clocks at different distances from the centre of the Earth will show time dilation relative to each other. The clock that is higher above sea level will show time running at a faster rate than a clock at sea level. A clock down a mineshaft ticks even slower, relatively. I stress the term relatively, as for each clock, a second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

At different altitudes, the clocks are being subjected to different rates of acceleration due to rotation of the Earth. The only way to test for gravitational differentiation would be on a non-rotating body. And again, there may be no way to tell if the atomic transitions of the cesium atoms are slowing down, or if time is slowing down.

A second always lasts a second, in any valid frame of reference. Time dilation shows that different frames of reference will measure different elapsed times for the same event, but the difference only becomes apparent if they can meaningfully compare their results. Nobody experiences time speeding up or slowing down, they only find that they have experienced different amounts of elapsed time, depending on what they were doing, relative to the other.

That statement contradicts the concept of time dilation.

The energy that runs around the microchips on a GPS satellite seems to cycle at a different rate up there when compared to the rate it cycles down here. We had to set the chips to run slow by the amount predicted by relativity, for us down here to measure that clock up there as running at the same rate as our own.

And that agrees with what I said might be happening, that is, the atomic interactions may change as opposed to time actually changing. BTW, did you get the slowing down reversed in your example?

If we ever manage to send someone away on a long relativistic journey and they return having aged noticeably less than the people that stayed behind, that will be the absolute clincher for non-absolute time, by any definition of the term. Is that what takes (not that we will get that in our lifetimes), or would that still not be enough proof?

That would not necessarily be proof of time dilation or confirm TOR. It might only confirm that atomic interactions slow down under acceleration. Of course the relativistic journey could not take place without a great deal of acceleration.

 

[mental_avenger]

An object in a constant velocity frame of reference is experiencing no net force.
Wayne

An object in orbit is experiencing constant acceleration. That is countered by the force of gravity between the object and the whatever it is orbiting. The fact that the two forces are in balance to keep the object in orbit does not mean that the object is not under constant acceleration. While gravity may counteract the affect acceleration has on orbiting, it may not counteract the affect that acceleration has on atomic interactions.