# Time dilation question.

1. Jul 15, 2011

### Jaynte

The time dilation formula:
$$\Delta t'=\frac{\Delta t}{\sqrt{1-\frac{v²}{c²}}}$$
says that the closer you come to the speed of light the slower time goes (for the object in movement).

That mean if you travel to a distant star in very high speed, there will take shorter time to get there (for the traveler, not for the observers back at earth) than if you travel at lower speed.

Does that mean that it takes no time at all for light (a photon) to travel from one side of the universe to the other? (for the photon, not us the observers)

Last edited: Jul 15, 2011
2. Jul 15, 2011

### ZapperZ

Staff Emeritus
Please read the FAQ subforum in the Relativity forum. The topic on whether one can transform to the photon's frame will be relevant.

Zz.

3. Jul 15, 2011

### harrylin

Yes indeed, thanks to that effect it should be possible, in principle, to reach another star and still be alive when you get there, despite the fact that you traveled at less than the speed of light.

Now, material objects such as clocks come to a stand-still when approaching the speed of light; and we define "time" by means of such clocks. In that sense, indeed, the photon's "proper" time is frozen. But it would be a mistake to interpret this to mean that for a photon nothing happens, or other philosophical conclusions like that. It just happens that we cannot use our standard definitions and concepts at that limit.

In particular, for that same photon the distance from one end of the universe to the other is also zero. Thus we get that its speed is v=c= 0/0; and that is not very meaningful.

Cheers,
Harald

Last edited: Jul 15, 2011
4. Jul 15, 2011

### Jaynte

Now i see :) thanx