Are time dilation experiments conclusive?

[harrylin]

First one must understand that an equation such as those in Relativity explains the result of a process, they do not and are not meant to explain a physical process. [..]

Yes indeed; this is also explained in the FAQ, you may want to have a look at it.
Consequently everyone has his/her own explanation as to the "why" (see also next).

But all the experiments say that the change is "real and permanent" and only happens to the object that changed speed. Take the cocks flown around the world. When brought back to their original location there was a difference in their time vs the "stationary" clocks time.

Well yes, only clocks that change their state of motion alter their count of elapsed time compared to clocks that do not change their state of motion (but not only compared to what you consider "stationary" clocks!).

So, if time dilation is true we can determine an absolute 0 frame of reference. [..]

Certainly not; but others already sufficiently clarified that. In a nutshell, the SR equations are based on the relativity principle, so that you cannot expect to find something else with those!

[..] It's no more mysterious than when two drivers in two cars zero their trip odometers before they leave yet find different numbers on their odometers when they arrive at their common destination - they took different routes through space, they covered a different distance in space.

In order to give that illustration physical content, can you please clarify what according to you the equivalence is with the ground that drives the odometers.

 

[Wuberdall]

It is worthwhile pointing out that in the context of physics, time is defined to be what clocks measure. Thinking of it in terms of "change" is misleading ( at best ) - you could have a system that is completely static and exhibits no change at all ( e.g. the rest frame of a free elementary particle in an otherwise completely empty region ), yet if you placed a clock into that frame it would still give you a non-zero reading.

That is entirely depending up on your philosophical believes of time; realist, non-realist, etc.

You will be correct in a realist descriotion of time.. But wrong for a non-realist on time. And i think that Boro Petrovic tendency to talk and descripe time as physical change in a system, suggest that he either is a non-realist on time or do not regard it as fundamental but instead as a derived concept (but still real).

 

[phinds]

That is entirely depending up on your philosophical believes of time; realist, non-realist, etc.

No, as Markus pointed out, in terms of physics it's a DEFINITION, not an opinion. Physicists agree that this is what time is. This forum is not about philosophy.

 

[Wuberdall]

No, as Markus pointed out, in terms of physics it's a DEFINITION, not an opinion. Physicists agree that this is what time is. This forum is not about philosophy.

Yes, as it's for now (and it has far from always been so).. But it wil be worth mentioning that there are a large amount of work and articles beeing produced by physicist on these vary topics of the nature of time; is it Real?, is it fundamental or derived ?
So it is not entirely philosophical, but 'physical' to.

I, myself is a realist on time and completely do not care whether time is fundamental or not. So I completely agress with your previus post.
I only bring this up becouse Boro Petrovic sounds like he is of a different believe of the nature of time.

 

[phinds]

I only bring this up becouse Boro Petrovic sounds like he is of a different believe of the nature of time.

And does his point of view solve problems in physics and get the right answers?

 

[Bruce Williams]

They will all 6 show exactly the same result, but all deviate from a reference clock on Earth. You can do a sub-experiment on one of the spacecraft s, again sending 6 smaller spacecraft s in all directions. Same result: the clocks on the sub- spacecraft s will all agree with each other, but they will disagree with the reference clock on the mother spacecraft . There is no "0 reference".

There is no preferred reference frame, but acceleration (as yes/no question) is frame-independent - everyone will agree that the spacecraft s changed their speed, while the Earth did not.

Are you saying this experiment has been run? If so, can you give the reference so I can read it?

 

[Bruce Williams]

There's nothing that we don't understand here - the two travelers took different paths through spacetime so covered a different amount of time.

It's no more mysterious than when two drivers in two cars zero their trip odometers before they leave yet find different numbers on their odometers when they arrive at their common destination - they took different routes through space, they covered a different distance in space.

You just said that the process was different paths through spacetime. But, both the .9999999 particle saw us go through the same spacetime as we saw the .99999999 particle go through. So, if we were both observed going through the same space time, why did the .999999999 particle change but we didn't?

 

[russ_watters]

Are you saying this experiment has been run? If so, can you give the reference so I can read it?

That experiment is run continuously by the GPS system. It's a cloud of satellites, moving in different directions. It's also a variant of what the Michelson Morley experiment does.

 

[phinds]

You just said that the process was different paths through spacetime. But, both the .9999999 particle saw us go through the same spacetime as we saw the .99999999 particle go through. So, if we were both observed going through the same space time, why did the .999999999 particle change but we didn't?

What change are you talking about?

 

[Gaz]

Pretty interesting explanation of the gps system.

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

 

[Dale]

But, both the .9999999 particle saw us go through the same spacetime as we saw the .99999999 particle go through.

This is simply not true. The only way to go through the same spacetime path is to be at the same place at the same time throughout the entire journey. If they are not colocated at all times then their spacetime path is different.

 

[Nugatory]

But, both the .9999999 particle saw us go through the same spacetime as we saw the .99999999 particle go through.

They are not the same paths through spacetime. DaleSpam's post above explains what it means to be on same path through spacetime, and you'll find a diagram in the "space-time diagram explanation" of the Twin Paradox FAQ at http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html that shows the two different paths.

 

[Bruce Williams]

That experiment is run continuously by the GPS system. It's a cloud of satellites, moving in different directions. It's also a variant of what the Michelson Morley experiment does.

The GPS satellites are influenced by the gravity of the Earth and their clocks are emitting and summing radiation in all directions at once. They rely on the transition of an electron from one shell to another to emit the radiation. And since this is strictly a random occurrence, the transition can be in any direction. The light emitted is then generally collected through mirrors to concentrate and direct it to series of items to detect its frequency. Since all there is to work with is the "summation" of many photons having been emitted in many directions they are not looking at the effect of EACH pulse, but rather the statistical sum of many. So, there is no way to accurately detect the individual photons and determine each frequency. And how one would make sure to detect only those photons emitted when the electrons were traveling in a certain direction would represent considerable technological problems. This just builds error after error into the system that would probably swamp any effect you may find.
The statistical nature of atomic clocks only says that we can average the results of many photons being emitted. Electrons traveling in an orbit around an atom are not in nice circles. As a matter of fact they are in a relatively thick cloud around the shells average size, and very few of the electron transitions are at the published frequency, on an individual basis they are quite varied and only their average is the published value.

 

[Bruce Williams]

They are not the same paths through spacetime. DaleSpam's post above explains what it means to be on same path through spacetime, and you'll find a diagram in the "space-time diagram explanation" of the Twin Paradox FAQ at http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html that shows the two different paths.

I've seen this diagram before. My question has always been - Stella's time line is different in our frame of reference, as shown. But Ours is different in her frame of reference (and no one ever draws her frame of reference). If you accept that there is only one valid frame of reference (ours) then you are saying you have chosen the 0 frame of reference, which violates the tenants of relativity.

 

[Bruce Williams]

I've seen this diagram before. My question has always been - Stella's time line is different in our frame of reference, as shown. But Ours is different in her frame of reference (and no one ever draws her frame of reference). If you accept that there is only one valid frame of reference (ours) then you are saying you have chosen the 0 frame of reference, which violates the tenants of relativity.

Forgot to add - And if you chose us as the valid frame of reference then how did the electrons/protons/neutrons, etc. know that they had to change differently from ours while our parts knew not to change any more than they may already be changing? There had to be something to tell Stellas to change differently, and whatever you call that it says you can find a true zero reference frame. You can call it spacetime, ether, space, or the universe, but if it changes Stella's "clock" from whatever we are experiencing to something new then it must have a zero reference point to start at to know how much to change Stella.

 

[Markus Hanke]

If you accept that there is only one valid frame of reference (ours) then you are saying you have chosen the 0 frame of reference, which violates the tenants of relativity.

Frames are symmetric only if they are inertial. In the scenario shown, one of the frames experiences proper acceleration, which makes it physically distinguishable from the other frame, and hence destroys the symmetry. This doesn't violate any tenants, it just means that frames with proper acceleration aren't related via Lorentz transforms.

There had to be something to tell Stellas to change differently

That "something" is the proper acceleration that she experiences - which is absent in the other frame. Remember that it is inertial frames that trace out the longest proper time between fixed events, so once you get proper acceleration involved, you get a shorter world line ( i.e. less proper time between the same two fixed events ), which is just precisely the difference in the accumulated clock times.

 

[A.T.]

(and no one ever draws her frame of reference).

This old thread addresses this:
https://www.physicsforums.com/threads/spacetime-diagram-twin-paradox.671398/page-2#post-4270375

Personally I like to use space-propertime diagrams to visualize the twins, because you see the age difference directly. In this interactive version there is both types of diagrams, and the three inertial frames of the quick-turnaround version:

http://www.adamtoons.de/physics/twins.swf

As has been mentioned: If you want to have just one rest frame of non-inertial twin, you have to smooth the acceleration to avoid discontinuities. In the simplest case the acceleration is constant, and you have a constant gravity in the rest-frame of the non-inertial twin.

In space-propertime diagrams gravity looks something like this:

http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_time.gif
From: http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html

So the twin frames would look something like this:

Keep in mind that both worldlines are supposed to have the same length in each diagram, because everything advances at the same rate in space-propertime.

Also note that this is equivalent with throwing up an object (red) from the surface of the Earth (green).

If you accept that there is only one valid frame of reference (ours)

There are infinitely many inertial frames, and they are all equivalent. But the rest frame of the non-inertial twin isn't one of them.

 

[Dale]

My question has always been - Stella's time line is different in our frame of reference, as shown.

No frame of reference is drawn.

A frame of reference would be some set of grid lines. The grid lines that you draw don't change the geometry at all. Terrence's worldline is geometrically straight and Stella's is geometrically bent in a frame invariant manner.

 

[Dale]

Forgot to add - And if you chose us as the valid frame of reference then how did the electrons/protons/neutrons, etc. know that they had to change differently from ours while our parts knew not to change any more than they may already be changing?

You seem to have a misunderstanding about geometry. Take a piece of paper and draw two points. Then draw a straight line connecting them and a bent line connecting them. All of this has been done without drawing or specifying any grid. Rotate or translate the paper how you will. Draw any grid you want. None of that changes the geometry.

 

[russ_watters]

The GPS satellites are influenced by the gravity of the Earth and their clocks are emitting and summing radiation in all directions at once. They rely on the transition of an electron from one shell to another to emit the radiation. And since this is strictly a random occurrence, the transition can be in any direction. The light emitted is then generally collected through mirrors to concentrate and direct it to series of items to detect its frequency. Since all there is to work with is the "summation" of many photons having been emitted in many directions they are not looking at the effect of EACH pulse, but rather the statistical sum of many. So, there is no way to accurately detect the individual photons and determine each frequency. And how one would make sure to detect only those photons emitted when the electrons were traveling in a certain direction would represent considerable technological problems. This just builds error after error into the system that would probably swamp any effect you may find.
The statistical nature of atomic clocks only says that we can average the results of many photons being emitted. Electrons traveling in an orbit around an atom are not in nice circles. As a matter of fact they are in a relatively thick cloud around the shells average size, and very few of the electron transitions are at the published frequency, on an individual basis they are quite varied and only their average is the published value.

I can't parse this. Is it supposed to be your understanding of how atomic clocks work? It's not very coherent, but regardless, what does it have to do with what we were discussing?

 

[mfb]

The GPS satellites are influenced by the gravity of the Earth and their clocks are emitting and summing radiation in all directions at once. They rely on the transition of an electron from one shell to another to emit the radiation. And since this is strictly a random occurrence, the transition can be in any direction. The light emitted is then generally collected through mirrors to concentrate and direct it to series of items to detect its frequency. Since all there is to work with is the "summation" of many photons having been emitted in many directions they are not looking at the effect of EACH pulse, but rather the statistical sum of many. So, there is no way to accurately detect the individual photons and determine each frequency. And how one would make sure to detect only those photons emitted when the electrons were traveling in a certain direction would represent considerable technological problems. This just builds error after error into the system that would probably swamp any effect you may find.
The statistical nature of atomic clocks only says that we can average the results of many photons being emitted. Electrons traveling in an orbit around an atom are not in nice circles. As a matter of fact they are in a relatively thick cloud around the shells average size, and very few of the electron transitions are at the published frequency, on an individual basis they are quite varied and only their average is the published value.

This is not how GPS works at all.

 

[Gaz]

how does a atomic clock work then mfb?

 

[Gaz]

ok the life span of atoms are increased by motion and gravity as there slowed down. But aren't the atoms that I am composed of going to be around long after I am dead. So my question now is what is the connection between the lifespan of a atom and my lifespan? Does a atom slowing down mean time as I am experience it is really slowing down? I highly doubt that there is any experiment ever done to prove this one but would be interested to know. Why don't they just put something like a plant (many plants) on a little satellite and blast it around in a orbit as fast as they can to see if it actually grows slower?

 

[Markus Hanke]

Does a atom slowing down mean time as I am experience it is really slowing down?

Neither an atom nor the time you experience "slows down" in any meaningful sense of the word - if you hold a clock in your hand, it will never go slower than exactly one second per second. What happens is that your relationship in space-time with respect to some far-away reference clock changes. It is crucial to understand this difference - gravitational time dilation is not something that "happens" to an isolated frame, it is a relationship between clocks at different places. Time is not an entity that "flows" like a river, or can be given mechanical attributes - time is what clocks measure, a relationship between events.

So my question now is what is the connection between the lifespan of a atom and my lifespan?

The ratio between the two is constant everywhere; like I said, an isolated clock is never seen to be dilated in its own rest frame.

 

[phinds]

The ratio between the two is constant everywhere; like I said, an isolated clock is never seen to be dilated in its own rest frame.

I agree w/ the rest of your post, but I think this part is well-intentioned but misleading. Locally, what you are saying is correct, but the fact that nothing is time dilated in its own frame does NOT mean that life-spans are identical in all cases, as is shown clearly by the "twin paradox".

 

[mfb]

how does a atomic clock work then mfb?

That was not the question.
It is also not a good description of atomic clocks, but that is a completely different topic.

 

[Markus Hanke]

Locally, what you are saying is correct

I only meant it locally. Of course, if you have two frames tracing out different world lines between the same set of events, you will get different accumulated times. Still, neither of them would notice anything special happen to their clocks, they would just find that the readings disagree once the clocks are brought back together at rest.

 

[Gaz]

That was not the question.
It is also not a good description of atomic clocks, but that is a completely different topic.

I was only asking out of interest mfb because it seemed like what Bruce was saying could have made sense.
I see you said that is not how the GPS system works not the clock sorry =).

The ratio between the two is constant everywhere; like I said, an isolated clock is never seen to be dilated in its own rest frame.

the relationship between the two is constant doesn't really answer my question Markus mate. I want to know if a atoms frequency changing with motion would really effect time as I know it. I don't see how it would like I'm thinking a atomic clock that runs by the frequency of a atom might but a mechanical clock would work the same regardless of a atoms frequency.

 

[mfb]

I want to know if a atoms frequency changing with motion would really effect time as I know it.

It is the opposite way. The motion through spacetime determines the frequency each observer will see. This is not limited to individual atoms or clocks, it is true for every system.

I was only asking out of interest mfb because it seemed like what Bruce was saying could have made sense.

Just a few points, I don't want to go into detail as this is the wrong thread:
- the emission is not in random directions, the atoms are kept in a microwave cavity. There are no "mirrors" directing radiation to whatever.
- atomic clocks rarely use transitions between shells, but transitions within a shell. The GPS satellites in particular use a hyperfine transition of caesium.
- there is no need to detect individual photons as all have the same frequency. Doppler broadening is an issue, but does not change the central value.
- the model of electrons moving around the atom is so horribly outdated that I won't comment it further.
- and all this has nothing to do with GPS and measurements of time dilation

Edit: fixed grammar

 

[Dale]

I don't see how it would like I'm thinking a atomic clock that runs by the frequency of a atom might but a mechanical clock would work the same regardless of a atoms frequency

That would violate the principle of relativity.