Relativity, time and the speed of light

[Albrecht]

wimms wrote

Why is 'clock rate' more correct?

What we physically observe is a clock rate which includes of course all periodic motions. To call this indication "time" is already a decision towards a specific physical model. So "clock rate" is more open for physical causes.

What puzzles me, is there really any chance to determine time rate of approaching relativistic body, if it has never been in same rate frame as us.

For my understanding it is in fact worse. Even if an approaching relativistic body has earlier been in the same frame as us, we do not know what it's rate at motion now is. It always depends on the physical model used.

I can imagine only one situation which makes real knowledge possible. If we can prove that we have superluminal signals and we have measurements of those signals which are precise enough, then we know that we have an inertial system at absolute rest and we are able to identify it. Related to this frame at absolute rest we can make absolute measurements of physical quantities; the clock rate of a reference clock (i.e. atomic references) could then be used as an absolute norm.

shchr wrote:

But I want to remind you the existence of
Galilean relativity in which infinite speed is allowed, at last.

So, what is your conclusion from this fact?
Galilei could live with a simple understanding of relativity in mind. He did not know about
- dilation of clocks
- contraction of physical objects.

In summary this was an interesting discussion and to some respect also shocking for me. I did not realize that there is so little knowledge about the history of relativity, it's different versions and interpretations, and the non-physical influences which caused Einstein to be the winner.

 

[Albrecht]

sdeliver645 wrote:

I am currently writing an e-mail to Prof. Selleri to clarify these issues. I will post the correspondence when I get a response.

So, what is the status of Prof. Selleri's response??

 

[pmb]

Originally posted by jby
It states that nothing can travel faster than light. But all the books that I've read on introduction to relativity use the train and light pulse to demonstrate length contraction and time dilation. And finally, they say that nothing can travel faster than light. How can this claim be made when they have just only consider light clock. What about mechanical clock, biological clock etc?

Think of it like this: The Principle of Relativity states that the laws of physics are the same in all inertial frames of referance.


Now take a look at the light clock. Just so that we're on the same page we'll use this derivation

http://www.geocities.com/physics_world/light_clock.htm

Let there be a man, a rabbit, and an atomic clock at rest in O close to the mechanical clock which are also at rest in O. The mechanical clock is designed to tick at the same rate at which the mans heart beats. Let's also assume that the rabbit's heart beats at twice the rate of the mans heart. It follows that the ratios of each of these frequencies is a constant. That ratio will not change if one measures these frequencies from anothere inertial frame. So it really doesn't matter what we use as a clock - so long as we know that the clock is reliable.

I hope that makes sense

Pete

 

[russ_watters]

Originally posted by Albrecht
On the other hand, the assumption of Einstein that time and space change at motion is also a belief as it is not necessary.

What else would explain observed time dilation? Whether Einstein assumed it or not (he had no way to verify it) it has since been verified through experimentation.

 

[Albrecht]

What else would explain observed time dilation? Whether Einstein assumed it or not (he had no way to verify it) it has since been verified through experimentation.

We have to distiguish between time and the measurement of time. Time is measured by periodic motions, some of them are used as clocks. The speed of clocks is slowed down, that is the only thing we can observe.

If we follow the relativity of Lorentz / Poincare then neither time nor space do change in any way. The "time dilation" we observe is in fact the change of clock indications, i.e. all periodic motions.

The dilation of clocks etc can be explained by today's understanding of elementary particle physics. The constituents of an elementary particle oscillate permanently with the speed of light c. (This was initially detected by Paul Dirac for the electron 1928.) If an elementary particle is moved, its rotation period has to slow down to maintain the speed limit of c. If Pythagoras is applied to this process, the result is exactly the "time dilation" given by Special Relativity.

 

[russ_watters]

Originally posted by Albrecht
We have to distiguish between time and the measurement of time. Time is measured by periodic motions, some of them are used as clocks. The speed of clocks is slowed down, that is the only thing we can observe.

If we follow the relativity of Lorentz / Poincare then neither time nor space do change in any way. The "time dilation" we observe is in fact the change of clock indications, i.e. all periodic motions.

So maybe this is just a question of semantics, but to clarify: Is there an absolute time independent of the measurement of time? If so, how can it be observed?

 

[Albrecht]

russ_watters wrote

So maybe this is just a question of semantics, but to clarify: Is there an absolute time independent of the measurement of time? If so, how can it be observed?

This question is strictly related to the existence of an absolute frame at rest. If there exists an absolute frame at rest, the time observed in this frame is the absolute time.

So, we know the absolute time as soon as we know the absolute frame. From the experiments which show superluminal signals we have to conclude, that there is an absolute frame at rest - if we trust that these experiments are true. The results are not very precise; they give the impression that our Earth conforms to the frame at rest within a margin of ca. one percent of the speed of light (i.e. 10 times the orbital speed of the Earth around the sun). That would mean that our time on Earth is quite close to the absolute time.

Anyway, we have to keep in mind that "time" is a human made entity. Nature provides us the fact that two events at the same location have a well defined sequence. We humans find it practical to put this sequencing onto a linear scale which we call "time". We use periodic motions for it, and all what we observe, when we believe to measure time, is the behaviour of periodic motion.