Is Time Constant? Why We Assume It Is

[larrym3]

Why is it generally assumed that time is and has been constant? When a star is described as being 150 million light/years away - how do we know that the time during those years passed at the same rate as time now. Couldn't time have been faster (or slower) in the past?

 

[bcrowell]

There is a good discussion of this in the first chapter of Relativity Simply Explained, by Gardner.

 

[DLuckyE]

If time goes faster/slower everywhere then time is still going as fast everywhere, you wouldn't notice the difference.

 

[Dale]

I agree with DLuckyE, I think the question as posed is experimentally meaningless.

Let's suppose that we are some uber godlike beings watching poor humans carry out their limited measurements of time. We can tell that time has "really" slowed down by a factor of 2 since yesterday. Because the time for biological process slowed down everyone is really waking up late for their meetings, but because the time for alarm clocks slowed down nobody is rushing (any more than normal). They look out the window and because time slowed down for the solar system the day looks normal. I could go on, but I think you get the idea.