# Light speed; time dialation theory and its age

1. Jul 20, 2012

### rgprasannakum

Hi All..
I have a basic doubt in time dialation theory. As per time dialation theory, when an object moves with the velocity of light, then relatively its time becomes zero. In that case, light is travelling at 'velocity of light'. So for light, there is no age? Or I misconcepted time dialation theory?

2. Jul 20, 2012

### ZapperZ

Staff Emeritus
You are asking for an unphysical situation. We don't have the ability to transform and know what laws work in the frame moving with velocity c.

I suggest you read the Relativity FAQ

https://www.physicsforums.com/forumdisplay.php?f=210 [Broken]

....especially the entry on the rest frame of a photon.

Zz.

Last edited by a moderator: May 6, 2017
3. Jul 20, 2012

### Saeide

When you look at an someone moving with the velocity near to that of light, in your rest frame, you see that he gets older more slowly than if he was in your inertial frame, and obviously it doesn't mean that he is younger in his inertial frame too. The fact is that you are talking about the worldtime while his age, which is defined by himself, is according to the propertime (time in his rest frame). It is clear that matter never reach to c and your question is about light, but it seems the approach to it the same, for measuring the light's age you should go to its rest frame that is impossible while we can never reach to c.

4. Jul 20, 2012

### rgprasannakum

@ Saeide: As you said, we're not potential enough to reach velocity of light to measure its age. Maybe in light's frame; it might have some ages. But What I'm talking about is the intertial frame where the light does exist.

5. Jul 21, 2012

### Saeide

The inertial frame where the light exists and the light's frame are the same, while the light velocity is constant and as a result we can say that the frame is inertial. Of course our physics laws are applicable only for velocities less than c, just like singularities in GR that we are not aware of what is going on in them.

6. Jul 21, 2012

### ghwellsjr

In Special Relativity, light is defined to propagate at c in any inertial frame you choose. When we talk about an object's inertial frame, we mean one in which the object is at rest. Therefore, it is meaningless to talk about light's frame. This isn't just a semantic issue, the mathematics won't support one inertial frame moving at c relative to another inertial frame so we can safely conclude that no object can move at c in any inertial frame.