Assume we have two identical clocks made on the earth. One of them is sent to other corner of universe (I mean very far). The clock starts to tick simultaneously (Maybe it is not practical in practice, but lets assume it is possible for now). Then, are both of them measure same value of time or there is possibility that one of them measure slowly or faster than other? Let assume that these two clocks are stationary relative to each other and space-time for both of them are flat not curved.
@ Vahid Dabbagh ;;;
my dear Vahid Dabbagh ............
identical clocks are made on the earth!!
1) how do you one of them is sent to other corner of the universe (I mean very far)?
2) where the clock starts to tick simultaneously? on the Earth itself or after sending it to the other corner of the universe?
you clarify this question then you will get proper answer for your question....
VD: The clock starts to tick simultaneously (Maybe it is not practical in practice, but lets assume it is possible for now).
That is the key problem, there is no physical meaning for "simultaneous" so you have to define exactly the procedure you wish to apply to define what you mean by the word in this case. Once yo do that, you apply it twice, some time apart. You can set one clock so that they are synchronised for the first pair of readings, then if they are also synchronised for the second pair of readings, they are ticking at the same rate.
Typically, for any sensible definition of simultaneous, the answer will be no because of cosmological redshift.
@ Maria Krikeli....
my dear Maria Krikeli......
do you have proofs of your assumptions or you have confidence that your assumption works practically?
I think the US Military already did this experiment whre they had one stationary clock, and one mounted in a fast moving jet that went around the Earth. They were the same at the beginning of the test, and different at the end of the test.
MK: But assuming that the other clock is somewhere in our local universe, the cosmological redshift is negligible thus our clocks measure the same distance of time. Right?
Well you have to then take account of local effects. Gravitational time dilation exists between GPS satellites and ground clocks for example. Clocks in the Milky Way and Andromeda galaxies would remain synchronised provided each was sufficiently far from the centre that their respective gravitational potentials were the same and there was negligible relative motion.
My previous comments assumed that the locations were co-moving and sufficiently far apart that cosmological redshift dominated over local effects because the question specifically asked about "clocks located in two far places in the universe".
Thanks for you guys answering the question. If laws of physics and their constants changed even slightly, speed of light should be changed. How we know, that in all part of our universe, the same laws with same constant are working right now?
The onus is on anyone claiming they have changed to prove their claim.
Is it correct scientifically, that we accept the uniform physical properties of space all over the universe? without rigorous proofs!
Yes, the approach is based on "Ockham's Razor" or "Russell's Teapot". The saying is "any scientific theory should be as simple as possible but no simpler". We therefore start with the assumption that properties are universal as being the simplest version, then if that is wrong, discrepancies should be found between theory and experiment. The nature of those discrepancies then drives an adjustment to the theory. Without those differences, (a) any significant changes introduced would cause theory to depart from observation, and (b) there is no way to know how the theory should be altered to make it a better match if any errors are smaller than can be measured.
There is also the point that you cannot ever prove any theory true, by experiment theories can only be shown to be false or not false.
https://en.wikipedia.org/wiki/Occam's_razor
https://en.wikipedia.org/wiki/Russell's_teapot
Thank you George, for your comprehensive answer. I think now I know my answer.
Two identical clocks show the same times between two different points jf the Universe only by the condition that its space does not rotates and the gravitational field is absent. See Hafele-Keating's experiments, where they investigated the behaviour of two clocks in the gravitational field of the rotating Earth.
Everything in this universe have no absolute motion or stillness so the two clocks will never show the same time at the same moments.
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