# The inherent symmetry of time dilation

1. Oct 23, 2008

### sanook

Please pardon this very newbie question:

I am ploughing through Mayer's "The Many Directions of Time." He seems to assume right at the outset that Relativity is correctly interpreted as meaning that BOTH observers moving in constant velocity relative motion would be entitled to claim that the other observer's clock is slower than their own. Is this universally accepted? It's been a long time since I did a very basic course in Relativity (my background is philosophy) but I seem to recall thought experiments where a space traveller would age considerably slower than someone who stayed on earth? Perhaps the two cases have nothing to do with each other?

I accept that I am out of my depth here really; should my post be inappropriate for the site I hope administrators will remove it at once. On the other hand, if anyone has time to explain this to me, I would be very grateful

2. Oct 23, 2008

### dx

Yes, both would be entitled to claim that the others clock is moving slower than their own. Also, there are no issues of interpretation in special relativity. Its meaning is crystal clear.

3. Oct 23, 2008

### sanook

ok, thank you very much. I obviously must have misuderstood the "space traveller" case

4. Oct 23, 2008

### HallsofIvy

Staff Emeritus
There is an important difference between two travelers, each moving relative to the other, and the situation where one remains in a gravity well while the other moves away.

In the first situtation, if the two travelers are at any time together, to compare ages directly, with constant relative velocity, they will never be together again so the "twin paradox" does not arise. In the second, problems of forces and accelerations, which are NOT "relative" must be dealt with.

5. Oct 23, 2008

### sanook

I see, I hadn't realized that constant relative velocity meant they would never be together again. I need to put a lot more thought and reading into this matter. Thank you both for helping me to clear up an initial doubt.

Last edited: Oct 23, 2008