Is time relative for each observer in motion?

[pervect]

What if I change my question as, "the two ships start from very distant points but are getting closer at a constant velocity"?

Years and years later the ships come across each other; at that point Astra and Cosmo go to a window in their respective ships and smile and wave at each other.

Who looks older? And why?

There's still not enough information to answer the question, but the question makes more sense because Astra and Cosmo can wave to each other when their ships are close, and compare ages.

If you time-reverse the question, though, you'll see that you still have to deal with the relativity of simultaneity. The age comparison operation has a unique answer when the space-ships are close, but it does not have a unique answer when the space-ships are far apart, it depends very much on the details, which were not specified in the problem statement.

 

[Juan R.]

A moment, special relativity does not say that one "see" that other's time is runing slowers. It says that time runs slower for systems in motion than for systems at rest, independently if one observes or no the other system.

A moment Aer! don't "modify" my posts and, please, attempt to interpret them correctly.

If somebody says that one "see" (note i used "") that time is runing slower, then it appears that time dilation is an kind of "optical" effect, but it is not.

This problem of interpretation is rather usual in both time dilation and length contraction. In his textbook on relativity

The length contraction is a velocity perception effect due to the motion of the reference frame relative to the rigid body. However, note that the length contraction is not an optical illusion; it is a real effect originating from the Lorentz transformation

I did a similar claim for saving some people for obtainin an incorrect understandin of time dilation that you obviously misread.

In fact, this relativistic effect is called the retardation of moving clocks (Check section 2.6 of Moller). It is a real effect asociated to motion, no some kind of illusion that we "see".

According to standard knowledge, the time of a clock in motion run slower that clock at rest and that is independent of i am observing the system or not as said. The mean life of unstable Mesons IS larger when are moving at high velocities independently if am observing the next CERN experiment or not.

 

[paul_abbotts]

Hi
I have unfortunately spelt reciprocity wrong in a previous thread a few weeks ago! Sorry for that. The point here is there should be a principle of reciprocity to explain why observers at different velocities disagree with each other about which one of them experiences the true time dilation and length contraction. In the real universe only one observer experiences time dilation and length contraction, the other observer experiences time contraction and length dilation. The universe picks out one observer as being correct and the other as being incorrect with regards to special relativity. Gravity ineffect violates the principle of reciprocity! Can this be used as a definition of gravity?

 

[pervect]

Hi
I have unfortunately spelt reciprocity wrong in a previous thread a few weeks ago! Sorry for that. The point here is there should be a principle of reciprocity to explain why observers at different velocities disagree with each other about which one of them experiences the true time dilation and length contraction. ?

I know of no principle by that name, and I think that you're getting onto a wrong track here.

What relativity does have is not "reciprocity" but "the relativity of simultaneity".

The point is that there are multiple equally valid ways of comparing the times of two spatially separated clocks, thus there is no paradox in each observer thinking the other observer is aging slowly. They are using different notions of simultaneity.

 

[JesseM]

Hi
I have unfortunately spelt reciprocity wrong in a previous thread a few weeks ago! Sorry for that. The point here is there should be a principle of reciprocity to explain why observers at different velocities disagree with each other about which one of them experiences the true time dilation and length contraction. In the real universe only one observer experiences time dilation and length contraction, the other observer experiences time contraction and length dilation. The universe picks out one observer as being correct and the other as being incorrect with regards to special relativity.

Not true, as long as they are both moving at constant velocity there will be no physical reason to prefer one point of view over the other, both will make the same predictions about all physical events like what two other clocks read at the moment they cross paths. Check out my post An illustration of relativity with rulers and clocks for help visualizing this.

 

[paul_abbotts]

The Principal of reciprocity in Special Relativity

Hi
I agree that there is no Principal of reciprocity in special relativity, but I think there should be one as it is so important. The point with reciprocity is that both observers, reference frames or perspectives disagree with each other when there is a velocity difference between them, the twin paradox. In Generalized relativity this disagreement is converted into an agreement between differing observers. This agreement process is known as gravity state vector reduction. The big question is how does the universe or our brains do this? Is it an instantaneous jump from disagreement to generalized agreement or generalized Consentience or more of a gradual process in which both disagreeing observers come to a general understanding of each others perspective over time, resulting in them both agreeing with each other! The concept of entropy or randomness can be associated with disagreement or fermion like characteristices whereas agreement or mutual information can be likened to boson like characteristics. This links the 2nd law of thermodynamics with General relativity, entropy is being converted into order or mutual information(brains) and vice-versa using gravity state vector reduction.