TIME DILATION. WHY do clocks that are

[A.T.]

If a light source moves from back to front it has no effect on the speed of the light, but if a light source moves sideways there suddenly is some mysterious sideways velocity of the light.

You are comparing apples with oranges here. Look at the animation again:

[URL]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/length_con2.gif[/URL]

- The "speed" (magnitude of velocity vector) is the same for all 4 photons, regardless how they where emitted.

- The individual velocity vector components of the two "vertically" emitted photons are different. But that has nothing to do with "source velocity affecting the light". It is simply a consequence of the fact that direction of a velocity vector is frame dependent (even in Newtonian mechanics).

After all, all observers must agree that the photon hit the mirror. Otherwise you get contradictions.

 

[Dale]

In my view there can be a "universal observer" ... Note that if SR is true, such an observer is no longer possible.

Your view is not consistent with experimental evidence:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

 

[Ernst Jan]

You are comparing apples with oranges here. Look at the animation again:

[URL]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/length_con2.gif[/URL]

- The "speed" (magnitude of velocity vector) is the same for all 4 photons, regardless how they where emitted.

- The individual velocity vector components of the two "vertically" emitted photons are different. But that has nothing to do with "source velocity affecting the light". It is simply a consequence of the fact that direction of a velocity vector is frame dependent (even in Newtonian mechanics).

After all, all observers must agree that the photon hit the mirror. Otherwise you get contradictions.

This animation is exactly what I mean, it proves my point doesn't it?
In the stationary frame you follow the photon going straight down and in the moving frame you follow the photon going in an angle, exactly like I said.

If you're suggesting that in both frames the observer would see the photons hit the mirror after exactly the same time then we disagree and your animation shows I'm right?

 

[Ernst Jan]

Your view is not consistent with experimental evidence:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

Thanks, this was the answer I was hoping for. Too bad there are a lot of experiments in the link, could you say which of them contradict my view please, or did you mean all of them?

 

[Ernst Jan]

I don't think so; SR makes no claims about what "really is" and merely pretends that we cannot identify such an observer. Please show me wrong.

With time dilation and length contraction it seems no longer possible to see what a 3 dimensional space looks like for a "universal observer", these are real physical effects right?

 

[A.T.]

This animation is exactly what I mean, it proves my point doesn't it?

No idea what your point is. But you seemed to compare "speed"(for photons the same in every frame) and "velocity components"(can vary between frames). The velocity of the source doesn't come in here.

In the stationary frame you follow the photon going straight down and in the moving frame you follow the photon going in an angle, exactly like I said.

What do you mean by "follow a photon in some frame"?

If you're suggesting that in both frames the observer would see the photons hit the mirror after exactly the same time ...

No, I never suggested that.

 

[Ernst Jan]

No idea what your point is. But you seemed to compare "speed"(for photons the same in every frame) and "velocity components"(can vary between frames). The velocity of the source doesn't come in here.

I said that the animation in my original post compared 2 different photons, exactly like in your animation.

What do you mean by "follow a photon in some frame"?

I mean the photon going between two mirrors. With stationary frame I mean the mirrors that are stationary and with moving frame I mean the mirrors that are moving.

No, I never suggested that.

Good, but why do you think there are any contradiction?
To me it seems we're saying exactly the same thing.

 

[harrylin]

This animation is exactly what I mean, it proves my point doesn't it?
In the stationary frame you follow the photon going straight down and in the moving frame you follow the photon going in an angle, exactly like I said.

If you're suggesting that in both frames the observer would see the photons hit the mirror after exactly the same time then we disagree and your animation shows I'm right?

I still don't see of what you should be convinced; but you seem to mean with such jargon something else as the others! In such cases it's better to abstain from jargon and to spell everything completely out. Thus:

Let's call S1 the "stationary" system because we choose it for our reference, and S2 the "moving" system system.

Then:
- as measured with S1, we observe the one light pulse going straight down wrt our system S1.
- also as measured with S1, we observe the other light pulse going under an angle wrt our system S1, but straight down wrt S2 (the y coordinates of that light pulse and the mirror are at every time the same).
- consequently, as measured with S2, one will observe that other light pulse also to go straight down wrt S2.

- We can measure "time" with for example such oscillators; as a result, according to our perception (measurements), the clocks that are at rest with S2 run at half the speed as the ones that are at rest with our system.

Note that due to the different reference standards in which the same situation is measured with S2, observers using S2 will conclude just the opposite, that is, that clocks that are at rest with S1 run at half the speed as the ones that are at rest with S2; that's however another topic which has also been discussed many times because it's at first sight mind-boggling or even paradoxical ("mutual" or "symmetric" time dilation). It's a direct requirement of the relativity principle.

 

[A.T.]

Good, but why do you think there are any contradiction?

I think it is misleading to the bring movement of the light source into it, like you do here;

but if a light source moves sideways there suddenly is some mysterious sideways velocity of the light.

To see the the movement of the light source is irrelevant, you can change the experiment: Instead of two vertical light clocks in relative horizontal movement, you have two long parallel mirrors, with two photons jumping between them:

FRAME A (rest frame of the mirrors):
- photon A is going vertically up & down
- photon B is zig-zaging at 45° to the right

FRAME B (moving to the right relative to the mirrors):
- photon A is zig-zaging at 45° to the left
- photon B is going vertically up & down

As you see the movement of the photons it perfectly symmetrical, between the two frames, despite the fact that in one frame the mirrors are static while moving in the other frame. So the movement of the source doesn't affect how the light propagates.

This is easier to see when you consider a 360° light pulse, instead of single photon.

 

[harrylin]

With time dilation and length contraction it seems no longer possible to see what a 3 dimensional space looks like for a "universal observer", these are real physical effects right?

Perhaps you mean that if we assume the existence of an "absolute" reference, according to SR we cannot know which point of view corresponds to it? Indeed, at least not by measurements. However, I think that according to cosmology it makes sense to postulate that the centre of mass of the universe corresponds to the origin of such a frame (maybe someone else here knows of that?).

In any case, the point of Newtonian physics was that observers who use instead an inertial system will observe exactly the same laws of nature as such such an universal observer - that's the PoR, that any inertial frame is equally suited for using the laws of physics. And this is the same in SR.

 

[harrylin]

commenting on:
"if a light source moves sideways there suddenly is some mysterious sideways velocity of the light."

I think it is misleading to the bring movement of the light source into it, like you do here;

To see the the movement of the light source is irrelevant, you can change the experiment: Instead of two vertical light clocks in relative horizontal movement, you have two long parallel mirrors, with two photons jumping between them:

FRAME A (rest frame of the mirrors):
- photon A is going vertically up & down
- photon B is zig-zaging at 45° to the right

FRAME B (moving to the right relative to the mirrors):
- photon A is zig-zaging at 45° to the left
- photon B is going vertically up & down

As you see the movement of the photons it perfectly symmetrical, between the two frames, despite the fact that in one frame the mirrors are static while moving in the other frame. So the movement of the source doesn't affect how the light propagates.

This is easier to see when you consider a 360° light pulse, instead of single photon.

Not completely correct: the motion of the source does affect the direction of light rays, even for uniform light sources (but that is nothing mysterious, it's conservation of momentum). A moving uniform light source will show a "head light" effect. I thought it was mentioned in the physics FAQ but now I can't find it back... so I'll hopefully not link to crank site by giving a link from Google here:
http://www.adamauton.com/warp/lesson5.html

 

[Dale]

Thanks, this was the answer I was hoping for. Too bad there are a lot of experiments in the link, could you say which of them contradict my view please, or did you mean all of them?

The idea of a privileged observer violates the first postulate, which is the specific subject of the tests in sections 3.1, 3.2, 3.5, and 3.6. However, in a broader sense you recognized the incompatibility of your idea with SR, and all of the tests confirm SR.

 

[Ernst Jan]

I still don't see of what you should be convinced; but you seem to mean with such jargon something else as the others! In such cases it's better to abstain from jargon and to spell everything completely out. Thus:

Let's call S1 the "stationary" system because we choose it for our reference, and S2 the "moving" system system.

Then:
- as measured with S1, we observe the one light pulse going straight down wrt our system S1.
- also as measured with S1, we observe the other light pulse going under an angle wrt our system S1, but straight down wrt S2 (the y coordinates of that light pulse and the mirror are at every time the same).
- consequently, as measured with S2, one will observe that other light pulse also to go straight down wrt S2.

I think this is how everyone interprets the animation.

- We can measure "time" with for example such oscillators;

According to my "universal observer" you can't do this. The reason seems obvious; the photons do not hit the mirrors at the same time.

as a result, according to our perception (measurements), the clocks that are at rest with S2 run at half the speed as the ones that are at rest with our system.

Under the premisse that you can measure "time" with for example such oscillators, you will get no argument from me.

My question I started with is why you would assume you can measure time like that.
Like I explained earlier is stating that you can, doesn't seem like much of an explanation.

 

[Ernst Jan]

The idea of a privileged observer violates the first postulate,

I know, my question is why would you think the first postulate is true.

which is the specific subject of the tests in sections 3.1, 3.2, 3.5, and 3.6.

Thanks, I hope to find my answer there then :)

However, in a broader sense you recognized the incompatibility of your idea with SR, and all of the tests confirm SR.

Yeah, we can agree to that, but I was hoping you'd tell me which of those test disagree with my view. Since my view also explains that atomic clocks will slow down with high speed.

 

[A.T.]

My question I started with is why you would assume you can measure time like that.

How would you measure time? What kind of clock would you use?

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? Otherwise you could easily create paradoxes.

If the clocks stay synchronized in every frame, what difference does it make, if we use your "correct" clock or a light clock to measure time?

 

[ghwellsjr]

Since my view also explains that atomic clocks will slow down with high speed.

I have been following this thread since you made your first post and I cannot tell what your view is. Could you express it again, one more time, with no reference to previous explanations so that hopefully, I, and possibly others will understand what you are promoting, please?

And one more question: does your view explain how slowed down atomic clocks moving at high speed will measure the stationary atomic clocks as being slowed down by the same amount? In other words, do you understand that time dilation is reciprocal?

 

[Ernst Jan]

How would you measure time? What kind of clock would you use?

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? Otherwise you could easily create paradoxes.

If the clocks stay synchronized in every frame, what difference does it make, if we use your clock or a light clock?

A "correct" clock would be a clock that would show a "universal observer" that one second has passed when the Earth has made (1/24 * 1/60 * 1/60=) 1/86400 of a rotation.

Let's agree that I can't stop time by smashing a clock, so that a clock does not necesarrily tell the "correct" time.

 

[Ernst Jan]

does your view explain how slowed down atomic clocks moving at high speed will measure the stationary atomic clocks as being slowed down by the same amount? In other words, do you understand that time dilation is reciprocal?

Your question is a bit strange, since measuring implies actually looking at the clock. It brings up all kinda new problems like the Doppler effect. Let's just keep looking at it as if an observer just knows what's happening.

Obviously, in my view only the clock moving at high speed will slow down. If you would bring those clocks together you could check that this is indeed the case.

 

[ghwellsjr]

does your view explain how slowed down atomic clocks moving at high speed will measure the stationary atomic clocks as being slowed down by the same amount? In other words, do you understand that time dilation is reciprocal?

Your question is a bit strange, since measuring implies actually looking at the clock. It brings up all kinda new problems like the Doppler effect.

Well, yes, measuring does imply actually looking at the clock. But the Relativistic Doppler effect is a solution (not a problem) to how each clock, moving in relation to each other, sees and measures what the other clock is doing. Do you deny that Relativistic Doppler comports with reality?

Let's just keep looking at it as if an observer just knows what's happening.

If you believe in an absolute ether rest state in which there is a single absolute definition of time and space, you need to tell us how to identify it. Otherwise, it's your opinion against everyone else's as to what's happening.

Obviously, in my view only the clock moving at high speed will slow down. If you would bring those clocks together you could check that this is indeed the case.

And which is the clock that is moving at high speed? And there is more than one way to bring those two clocks together and depending on how you do it, you can determine that either one is the one that was slowed down.

 

[A.T.]

A "correct" clock would be a clock that would show a "universal observer" that one second has passed when the Earth has made (1/24 * 1/60 * 1/60=) 1/86400 of a rotation.

So you want to use the Earth's rotation as a clock. Well anything I said still applies:

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? Otherwise you could easily create paradoxes. If the clocks stay synchronized in every frame, what difference does it make, if we use your clock or a light clock?

Let's agree that I can't stop time by smashing a clock,.

But by smashing the Earth?

so that a clock does not necesarrily tell the "correct" time.

So who does tell the "correct" time? How do you measure it?

 

[Ernst Jan]

Well, yes, measuring does imply actually looking at the clock. But the Relativistic Doppler effect is a solution (not a problem) to how each clock, moving in relation to each other, sees and measures what the other clock is doing. Do you deny that Relativistic Doppler comports with reality?

No, the Doppler effect only depends on the difference in velocity, so it makes no difference if speed is relative or absolute. For a "universal observer" it will look different though, but the effect is the same.

If you believe in an absolute ether rest state in which there is a single absolute definition of time and space, you need to tell us how to identify it. Otherwise, it's your opinion against everyone else's as to what's happening.

Actually, the easiest solution should always be preferred over a more complex one.
I'm convinced my solution is not right though, but still trying to find out why it's false.

And which is the clock that is moving at high speed?

It's the clock that runs slower.

And there is more than one way to bring those two clocks together and depending on how you do it, you can determine that either one is the one that was slowed down.

That's ONLY true for SR and frankly you have a lot of trouble explaining the following with it.
You put an atomic clock on a plane and you keep one on the ground. You then let the plane circle the Earth and you bring the clock from the ground up to the plane. If you check the clocks you'll notice that the one that was in the plane first will have a time indicating it has run slower.

 

[Ernst Jan]

So you want to use the Earth's rotation as a clock. Well anything I said still applies:

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.

Otherwise you could easily create paradoxes.

You can proof everything with 0=1 indeed.

If the clocks stay synchronized in every frame, what difference does it make, if we use your clock or a light clock?

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

So who does tell the "correct" time? How do you measure it?

Well, "correct" time can only be a question of definition. Measuring should be done by something that's the same for everyone. Like calling one rotation of the Earth a day.
(I'm aware that it means each day has a different length, but it doesn't matter as long as it's the same for everyone. Note that this is not the same as how someone observes a rotation of the earth, because for someone moving away it will seem like the Earth is rotating slower than it is.)

 

[Dale]

I know, my question is why would you think the first postulate is true.

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.

Yeah, we can agree to that, but I was hoping you'd tell me which of those test disagree with my view.

Again, all of those supporting the first postulate disagree with your view (3.1, 3.2, 3.5, 3.6).

Since my view also explains that atomic clocks will slow down with high speed.

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. In other words, from the two postulates you can derive time dilation. The same is not true if you replace the first postulate with a preferred observer.

 

[sisoev]

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. In other words, from the two postulates you can derive time dilation. The same is not true if you replace the first postulate with a preferred observer.

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"?

 

[PAllen]

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"?

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.

 

[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?