# Is Gravity the only force that affects time?

1. Feb 24, 2014

### ChromeBit

Sorry I'm new to this.
There are apparently four forces in the universe: Gravity, EM, Weak and Strong.
Is gravity the only force that can cause time dilation, or can the other forces affect time too?

2. Feb 24, 2014

In special relativity (or, hypothetically far from all gravitational mass), clocks that are moving with respect to an inertial system of observation are measured to be running more slowly. This effect is described precisely by the Lorentz transformation.
So no gravity is involved.

3. Feb 24, 2014

### phinds

As far as I know, only gravity "affects" time. As measured by a distant observer, time passes more slowly for an object deep in strong gravitational well than it does for the distant observer. Note, however, that the time is NOT locally affected. That is, both the time dilation due to motion described by adjacent (which, as he said has nothing to do with gravity) and gravitational time dilation I just mentioned, are only artifacts of remote observation. A person with a clock in his hand sees that clock tick at one second per second regardless of whether he is in motion (which we all are, after all, since motion is relative) or in a gravity well.

4. Feb 24, 2014

### WannabeNewton

Quite the contrary-kinematical time dilation occurs locally in general relativity. Only gravitational time dilation is non-local.

OP, the reason only gravity affects the "flow of time" is GR models gravitation as space-time geometry itself and space-time geometry fully determines the behavior of standard clocks and rods. Within the framework of GR all other classical fields, such as the electromagnetic field, simply propagate on the dynamical curved background. Note however that the electromagnetic field generates a gravitational field because it carries energy and momentum. As a result it can induce space-time curvature and potentially lead to gravitational time dilation effects indirectly in this sense.

5. Feb 24, 2014

### PAllen

Locally, but only to 'someone else', obviously. It is never experienced by 'you'.

6. Feb 24, 2014

### A.T.

I have explained several times to phinds that calling kinematic time dilation an "artifact of remote observation" is highly misleading, if not plain wrong:

7. Feb 24, 2014

### phinds

Yes, you have and I guess I'm still confused. Aside from out disagreement about my use of the term "artifact", the more fundamental issue is that, if I understand it correctly, and it seems you are saying I don't and Pallen is saying I do, is that YOU always observe your local time as being "normal".

This, I guess, gets a bit tricky to define. If I say "your proper time is passing at one second per second" then we have the problem of how do we measure that proper time? What ever is being used to measure it is in the same frame of reference so is subject to the same effects.

Last edited: Feb 24, 2014
8. Feb 24, 2014

### pervect

Staff Emeritus
Yes, it is. Electric fields, no matter how strong, won't cause time dilation (except insofar as they may contribute to gravity - but it's the gravity that causes the time dilation, even in that case).