TIME DILATION. WHY do clocks that are

[sisoev]

Ah, so you're perfectly happy with General Relativity, just not special relativity? GPS, satellite experiments, even aiplane experiments on Earth must take account of general relativity (which includes special relativity as an exact special case: exact on the tangent plan to any spacetime point; asymptotically true in any small region of spacetime). The demand for testing special relativity without any (even very small) gravitational corrections would require doing only experiments in an empty universe with mass-less equipment. Have fun with that.

Note that current generation of most accurate clocks must use GR+SR corrections to account for differences when they are raised from the floor to a table top.

Ha-ha
I wouldn't say "perfectly happy", but definitely happier with GR.
And no, we don't need mass-less equipment in an empty universe; just identical equipment and relatively empty region of space.
Then we can compare the difference in the time between those two spacecraft s and the difference we get between our satellite and ground clocks.

 

[PAllen]

Ha-ha
I wouldn't say "perfectly happy", but definitely happier with GR.
And no, we don't need mass-less equipment in an empty universe; just identical equipment and relatively empty region of space.
Then we can compare the difference in the time between those two spacecraft s and the difference we get between our satellite and ground clocks.

Do you understand that every aspect of SR is included in GR? And the GPS tests both?

 

[A.T.]

Let's say your "correct" clock is placed right next to a light clock, and synchronized so they both tick in sync in their common rest frame. Wouldn't then all observers have to agree that they tick in sync?

Of course.

So here you a agree that a light clock at rest to your Earth clock will always be observed in sync with the Earth clock, reagrdless how the observer moves relative to them.

If the clocks stay synchronized in every frame,

Obviously, it will not stay synchronized when you start to move.

And now you say the opposite of what you agreed to above.

Note that this is not the same as how someone observes a rotation of the earth,

So now we cannot use the observation of the Earth to measure the "correct" time anymore? Well then again: How do you measure it?

 

[Ernst Jan]

So here you a agree that a light clock at rest to your Earth clock will always be observed in sync with the Earth clock, reagrdless how the observer moves relative to them.

This is correct.

And now you say the opposite of what you agreed to above.

No, I'm saying there is a difference between the clock moving away from the observer and the observer moving away from the clock. Only the Doppler effect will be the same in both cases.

So now we cannot use the observation of the Earth to measure the "correct" time anymore?

We've only been discussing the animation in a way that all observers know what the situation is, not how they would actually see the clocks.

Well then again: How do you measure it?

Obviously we can use any clock to measure time. For it to make sense they should all run the same for a "universal observer". Just like the atomic clocks in our GPS satelites, if the satelite moves to a higher or lower orbit they'd have to be adjusted again.

 

[Ernst Jan]

Two reasons. First, and most importantly, because of the experimental evidence cited above. Second, because the mathematical forms of all of the currently known fundamental laws of physics are invariant under boosts.

Sorry, I thought you meant this postulate:
The speed of light in vacuum has the same constant value c in all inertial systems.
since it was the one I was questioning.

No, your view does not explain that atomic clocks will slow down with high speed. The idea that clocks slow down with high speed could be added as an ad-hoc patch to your idea, but it certainly would not explain it.

This is strange, because according to me the ONLY thing different is the reason why clocks slow down. Other than that I'm using the axact same numbers.

I've taken a look at the experiments in your link and I think they are all about frequencies. Is this correct?

 

[Dale]

Sorry, I thought you meant this postulate:
The speed of light in vacuum has the same constant value c in all inertial systems.
since it was the one I was questioning.

The idea of a universal observer directly contradicts the principle of relativity, and would only indirectly impact the postulate of the invariance of c if at all. However, that postulate is also tested in the list I sent.

This is strange, because according to me the ONLY thing different is the reason why clocks slow down. Other than that I'm using the axact same numbers.

Exactly, and that reason must be added as an ad-hoc assumption if you are using a preferred observer.

I've taken a look at the experiments in your link and I think they are all about frequencies. Is this correct?

Not all of them, no. The interferometer ones are about length or phase. The speed tests are generally about either speed or mass. There are also many that are about decay times, including ones that decay based on the weak and based on the strong interaction.

One of the reasons that the evidence is so overwhelming is that there is such a wide variety of different mechanisms that are tested.

 

[Dale]

DaleSpam, we have evidence that the clocks slow down on satellites, but they move in a gravitational field.
Do we have proof that clocks slow down in non-gravitational field?
If the energy and the mass depend on the speed, can we say that those clocks are identical with the ground clocks?

[EDIT] I started to stress from my English :D Should I say "related with" instead of "depend on"?

I am not interested in discussing GR with you at this time. IMO, it doesn't make any sense to try to tackle GR when you still don't understand SR since SR is the simplest possible case of GR. In fact, since you struggle with Newtonian mechanics even discussing SR is challenging.

 

[A.T.]

I'm saying there is a difference between the clock moving away from the observer and the observer moving away from the clock.

What difference?

Obviously we can use any clock to measure time. For it to make sense they should all run the same for a "universal observer".

Define "make sense".

 

[HallsofIvy]

And define "universal observer"!

 

[Ernst Jan]

The idea of a universal observer directly contradicts the principle of relativity, and would only indirectly impact the postulate of the invariance of c if at all. However, that postulate is also tested in the list I sent.

Again... just saying that the principle of relativity is TRUE doesn't make it so.

Exactly, and that reason must be added as an ad-hoc assumption if you are using a preferred observer.

I'm not sure what you mean. I'm simply exploring 2 possible ways of looking at the animation. In order to find out which is the right one I'm asking questions.

Let me describe the difference between SR and my view.

Suppose we have an observer in rest in a train.
This is an observer in any FoR in SR, and in my view it's an observer who's in rest for the "universal observer". Let's say the observer is in a FoR where both views apply.

Now the observer points a laserpen at a spot on the wall.
The train starts to accelerate to 0.8c and holds this speed.
Now SR predicts that the observer is still pointing at the same spot on the wall without having to adjust his aim, where in my view he would have to adjust his aim.

Let's say this train accelerates further to c.
Now SR predicts time stops and in my view there no longer is an angle that will allow the observer to point towards the spot on the wall.
With time stopped it seems difficult to move, but in my view nothing changes.

Since both views differ a lot, I'll be pretty easilly convinced SR is the right view. All I need is one experiment or reason that my view is false. Until then my view seems the most logical.

Not all of them, no. The interferometer ones are about length or phase. The speed tests are generally about either speed or mass. There are also many that are about decay times, including ones that decay based on the weak and based on the strong interaction.

One of the reasons that the evidence is so overwhelming is that there is such a wide variety of different mechanisms that are tested.

Thanks, it seems you're not able or willing to give me one experiment that will certainly proof my view is false, so I'll just try The Michelson-Morley Experiment. I'll start a new thread if it won't convince me.

 

[Ernst Jan]

What difference?

In my view all velocities are absolute, in SR they are relative.
In my view the change of velocity is absolute in SR it's absolute too.

[/QUOTE]
Define "make sense". [/QUOTE]
If someone says "it took me a day to do something", it would make sense if the one listening knows how long it took without having to ask at what relative speed to how we're moving now.

And define "universal observer"!

GOD (if you believe such an entity is all knowing and sees everything)

 

[A.T.]

In my view all velocities are absolute,

How do you measure the absolute velocity of something?

If someone says "it took me a day to do something", it would make sense if the one listening knows how long it took without having to ask at what relative speed to how we're moving now.

Define "knowing how long it took".

GOD

That's quite an exclusive measurement device. If that is the only thing that can measure your "correct time" and "absolute velocities", than those concepts are pretty useless to us humans. But maybe you can get GOD interested in them, next time you both have a chat.

 

[Dale]

Again... just saying that the principle of relativity is TRUE doesn't make it so.

Obviously not. The mountain of evidence does.

All I need is one experiment or reason that my view is false. ...
Thanks, it seems you're not able or willing to give me one experiment that will certainly proof my view is false

I gave you dozens of experiments. Your view is incompatible with a mountain of evidence.

If you think that your view is also compatible with the same evidence, then it is up to you to not only explain one experiment, but all of them. It is not our job to prove your theory wrong, but your job to prove your theory right. But not here, the proper place for that is a peer reviewed mainstream scientific journal. This forum is for learning relativity, not debunking alternatives.

 

[Denius1704]

Define "make sense".

If someone says "it took me a day to do something", it would make sense if the one listening knows how long it took without having to ask at what relative speed to how we're moving now.

I don't know if the intent Ernst Jan put into this sentence is the understanding i got from it, but this is actually a very good example of why SR is weird. Because at the end of the day, even if you are moving at 80% the speed of light and then a buddy is in rest, and you are having a conversation, when that above sentence is said it will not need clarification, because one day for a moving object is still measured the same way as one day for a stationary object.

 

[Dale]

this is actually a very good example of why SR is weird.

Sure, SR is weird. But it is the way the universe works. Weird stuff happens.

 

[Agerhell]

I don't know if the intent Ernst Jan put into this sentence is the understanding i got from it, but this is actually a very good example of why SR is weird. Because at the end of the day, even if you are moving at 80% the speed of light and then a buddy is in rest, and you are having a conversation, when that above sentence is said it will not need clarification, because one day for a moving object is still measured the same way as one day for a stationary object.

This is getting interesting. Now if we live on one of the poles of a spinning planet and take the spinning planet to be our local clock. We also have an atomic clock. They are synchronized at some time. Let us imagine that the planet has a very elliptic orbit, sometimes the planet is very close to the sun and sometimes it is very far away. Would our spinning planet clock and our atomic clock stay synchronized at all times? We let the planet be so small that we can ignore tidal effects.

 

[Buckleymanor]

g is the gravitational field, or more precisely, the proper acceleration.

I don't get your point. You could smash it with a hammer too. Once it is broken it is no longer an identically constructed clock.

That was never the point trying to be made it was purely the effect of G.
I imagined that the dependence on gravity and acceleration was made quite clear with regards atomic clocks.
Ok. the event horizon of a black hole is an extreme example but your formulated reply that there is no dependence with regards gravity or acceleration is false.
I insist that all clocks are effected by gravity and acceleration it is not possible to discriminate between relativistic, gravitational, or those caused by accelerational effects.

 

[sisoev]

I am not interested in discussing GR with you at this time. IMO, it doesn't make any sense to try to tackle GR when you still don't understand SR since SR is the simplest possible case of GR. In fact, since you struggle with Newtonian mechanics even discussing SR is challenging.

You could at least answer the question for those who understand GR and SR more than me :)

 

[ghwellsjr]

Let me describe the difference between SR and my view.

Suppose we have an observer in rest in a train.
This is an observer in any FoR in SR, and in my view it's an observer who's in rest for the "universal observer". Let's say the observer is in a FoR where both views apply.

Now the observer points a laserpen at a spot on the wall.
The train starts to accelerate to 0.8c and holds this speed.
Now SR predicts that the observer is still pointing at the same spot on the wall without having to adjust his aim, where in my view he would have to adjust his aim.

While the train is accelerating, the spot of laser light on the wall will move to a different place but after the train holds its speed, it will move back to its original location and everything in the train will be the same as it was before the train started moving. The train could repeat this sequence any number of times with the same result. The train will never get any closer to the speed of light than it was before it started.

Let's say this train accelerates further to c.
Now SR predicts time stops and in my view there no longer is an angle that will allow the observer to point towards the spot on the wall.
With time stopped it seems difficult to move, but in my view nothing changes.

No train can ever accelerate to c, so the rest of your comments are meaningless.

Since both views differ a lot, I'll be pretty easilly convinced SR is the right view. All I need is one experiment or reason that my view is false. Until then my view seems the most logical.

Is the fact that your view of SR is incorrect enough to convince you that your comparisons are invalid and maybe you should learn what SR really means?

 

[Dale]

You could at least answer the question for those who understand GR and SR more than me :)

If one of them asks I will.

 

[Dale]

That was never the point trying to be made it was purely the effect of G.

Did you mean to make that a capital G (the universal gravitational constant) or did you mean lower case g (the local gravitational field). Either way it doesn't have an effect to my knowledge, unless you have such strong tidal forces (changes in g) that the atoms are spaghettified.

I insist that all clocks are effected by gravity and acceleration it is not possible to discriminate between relativistic, gravitational, or those caused by accelerational effects.

It should be pretty easy to discriminate. Simply attach an accelerometer to your clock. Then you can tell if the acceleration is entirely due to gravity (accelerometer reads 0) or not.

 

[Janus]

I insist that all clocks are effected by gravity and acceleration it is not possible to discriminate between relativistic, gravitational, or those caused by accelerational effects.

Except that it has been shown experimentally that acceleration has no effect on time measurement.

The set up is fairly simple" you put radioactive samples on a centrifuge, spin it up to high speed and then see how fast they decay.

Now here's the trick. By varying the angular velocity and length of the centrifuge arm, you can set the experiment up so that the sample travels at different speeds but experiences the same acceleration or travels at the same speed but experiences different accelerations.

Such experiments have shown that the resulting time dilation depends only on the speed at which the sample moves and is independent of the acceleration it undergoes.

 

[Ernst Jan]

While the train is accelerating, the spot of laser light on the wall will move to a different place but after the train holds its speed, it will move back to its original location and everything in the train will be the same as it was before the train started moving. The train could repeat this sequence any number of times with the same result. The train will never get any closer to the speed of light than it was before it started.

That's indeed what I said where SR and my view disagree.

No train can ever accelerate to c, so the rest of your comments are meaningless.

Even though I also said this is where SR and my view disagree. Light goes with the speed of light in SR, so the "problem" of movement stays. (In GR you get the same problem at the event horizon of a black hole.)

Is the fact that your view of SR is incorrect enough to convince you that your comparisons are invalid and maybe you should learn what SR really means?

I'm unaware my view of SR is incorrect. Please explain.

 

[Agerhell]

Except that it has been shown experimentally that acceleration has no effect on time measurement.

The set up is fairly simple" you put radioactive samples on a centrifuge, spin it up to high speed and then see how fast they decay.

Now here's the trick. By varying the angular velocity and length of the centrifuge arm, you can set the experiment up so that the sample travels at different speeds but experiences the same acceleration or travels at the same speed but experiences different accelerations.

Such experiments have shown that the resulting time dilation depends only on the speed at which the sample moves and is independent of the acceleration it undergoes.

I completely agree. However, the FAQ in this forum refers to a web site:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Twin_paradox
which states that:

"The so-called “twin paradox” occurs when two clocks are synchronized, separated, and rejoined. If one clock remains in an inertial frame, then the other must be accelerated sometime during its journey, and it displays less elapsed proper time than the inertial clock. This is a “paradox” only in that it appears to be inconsistent but is not. "

Now if people keep saying acceleration has anything to do with the elapsed time, it will confuse people... I do not know if this is the case this time... The link is actually referencing to jour example:

"“Measurements of relativistic time dilation for positive and negative muons in a circular orbit,” "

 

[Dale]

The acceleration does not directly affect time dilation. It only breaks the symmetry between the twins. There is nothing wrong with mentioning acceleration, because the broken symmetry is important (even though by itself it does not affect time dilation).

 

[PAllen]

Except that it has been shown experimentally that acceleration has no effect on time measurement.

The set up is fairly simple" you put radioactive samples on a centrifuge, spin it up to high speed and then see how fast they decay.

Now here's the trick. By varying the angular velocity and length of the centrifuge arm, you can set the experiment up so that the sample travels at different speeds but experiences the same acceleration or travels at the same speed but experiences different accelerations.

Such experiments have shown that the resulting time dilation depends only on the speed at which the sample moves and is independent of the acceleration it undergoes.

But, in defense of EP arguments, it is worth noting that differences in 'pseudo-gravity potential' due to acceleration produce clock rate differences. I'm sure you're very familiar with the setup:

Two clocks set up to accelerate uniformly such from the view of the (e.g.) the back clock the distance between the clocks remains constant. There will be a clock rate difference proportional to the distance between the clocks and the acceleration, as if in a uniform gravitational field.

However, in an inertial frame, the above requirements lead to observation that the clocks get closer together, do not have identical acceleration or velocity, and that the velocity difference accounts for the difference in clock rate.

 

[Agerhell]

Two clocks set up to accelerate uniformly such from the view of the (e.g.) the back clock the distance between the clocks remains constant. There will be a clock rate difference proportional to the distance between the clocks and the acceleration, as if in a uniform gravitational field.

However, in an inertial frame, the above requirements lead to observation that the clocks get closer together, do not have identical acceleration or velocity, and that the velocity difference accounts for the difference in clock rate.

How do you mean? The back clock is sending light towards a mirror next to the front clock and he measures the time it takes for the light to come back? Are you assuming that the light speed is c in the inertial frame and by somehow regulating the distance between the clock to accout for this and the time dilation, the measured round trip time of light will always be the same for the guy at the back clock?

 

[PAllen]

How do you mean? The back clock is sending light towards a mirror next to the front clock and he measures the time it takes for the light to come back? Are you assuming that the light speed is c in the inertial frame and by somehow regulating the distance between the clock to accout for this and the time dilation, the measured round trip time of light will always be the same for the guy at the back clock?

Look up the Bell spaceship paradox. This is a variant of it, and any discussion of that will explain my other points. I don't have time to write up the details now. I'm sure Janus is completely familiar with all of this, just emphasizing different points. And there is no contradiction between what he said and what I said.

One key point is that if the distance remains constant from the point of view of the back clock, then length contraction demands that the two clocks get closer and closer in the inertial frame (as the back clock goes faster and faster). This requires that their speeds cannot be identical in the inertial frame. Thus two different explanations of the same observations: (pseudo)gravitational potential difference in the accelerating frame, simple difference in speed in the inertial frame.

 

[ghwellsjr]

Light goes with the speed of light in SR, so the "problem" of movement stays.

"Problem"? What problem? What are you talking about?

I'm unaware my view of SR is incorrect. Please explain.

Well, you stated:

"Let's say this train accelerates further to c.
Now SR predicts time stops and in my view there no longer is an angle that will allow the observer to point towards the spot on the wall.
With time stopped it seems difficult to move, but in my view nothing changes."

This is an incorrect understanding of SR. As I said earlier, no matter how much the train has accelerated, it still is just as far from c as before it started. SR makes no prediction that there is any condition in which time stops. Rather, it states that time will be completely normal for any train, it never slows down or speeds up or stops, no matter how it has accelerated in the past.

 

[Ernst Jan]

According to my starting FoR, which I didn't change, you are wrong.

 

[ghwellsjr]

According to my starting FoR, which I didn't change, you are wrong.

I made a lot of statements, which one(s) do you think I'm wrong about?

 

[Buckleymanor]

Did you mean to make that a capital G (the universal gravitational constant) or did you mean lower case g (the local gravitational field). Either way it doesn't have an effect to my knowledge, unless you have such strong tidal forces (changes in g) that the atoms are spaghettified.

Yes I did but it ain't absolute.
Well where do you draw the line, at which point do you decide where tidal(spagetiffication) forces and gravitational effects are distinct and apart.

 

[Buckleymanor]

Except that it has been shown experimentally that acceleration has no effect on time measurement.

The set up is fairly simple" you put radioactive samples on a centrifuge, spin it up to high speed and then see how fast they decay.

Now here's the trick. By varying the angular velocity and length of the centrifuge arm, you can set the experiment up so that the sample travels at different speeds but experiences the same acceleration or travels at the same speed but experiences different accelerations.

Such experiments have shown that the resulting time dilation depends only on the speed at which the sample moves and is independent of the acceleration it undergoes.

I am clueless to how they can do that.
How do accelerate a sample without making it move.

 

[Agerhell]

I am clueless to how they can do that.
How do accelerate a sample without making it move.

An object moving in a circle is always accelerating towards the center of that circle. Otherwise it would be moving in a straight line and not in a circle.
The acceleration goes as (v^2)/r.

 

[Dale]

Yes I did but it ain't absolute.

Huh? So was it the universal gravitational constant or the local gravitational field?

Well where do you draw the line, at which point do you decide where tidal(spagetiffication) forces and gravitational effects are distinct and apart.

That's easy. Gravitational effects can be removed through a coordinate transform and are not felt at all by a free-falling object, regardless of the strength of the gravitational field. Tidal effects cannot be removed through a coordinate transform and are still felt by a free-falling object.