Chewy0087 said:
It's my understanding that gamma (the boost factor) for light is infinite which allows it to have energy (mc^2)
It's not really meaningful to talk about gamma for light, since light doesn't have its own inertial rest frame. The first postulate of relativity says that the laws of physics should be the same in all inertial frames, and obviously light cannot be at rest in any sublight inertial frame, so giving light its own rest frame would violate this.
Also, the reason light can have energy is because the full equation for energy in relativity is E = \sqrt{m^2 c^4 + p^2 c^2}. Light's rest mass m is zero, but it has a nonzero momentum p (in quantum physics its momentum is given by p = hf/c, where h is Planck's constant and f is the frequency).
Chewy0087 said:
however, this is the same factor for legnth contraction & time dilation, I'm not really concerned about time dilation as i thought photons don't experience time?
For objects moving at a speed v slower than light, the factor is \gamma = \frac{1}{\sqrt{1 - v^2/c^2}}--the ticks of a clock are expanded by \gamma, and rulers are shrunk by 1/\gamma.
Chewy0087 said:
However, there is a definite "speed limit" to time, bieng 3 x 10^8 ms, however legnth is "infiniteley" contracted, right?
No, 3 x 10^8 m/s is the limit for
speed, i.e. distance/time. There is no upper limit on the factor that a moving clock's ticks can be dilated.
Chewy0087 said:
So sureley it would have arrived already? I have a sneaky feeling this is also something to do with photons not experiencing time, but if someone could clear it up that'd be great.
We can't talk about time dilation and length contraction for light itself, but we can talk about what happens in the limit as an object gets arbitrarily close to c (relative to whatever rest frame you're using--all speeds are relative!) For example, suppose a clock moves from one end of the galaxy to another at very close to the speed of light, such that in the galaxy's rest frame its time is so dilated that it only ticks forward by one second in the ~500,000 years it takes to make the trip in the galaxy's frame. In the clock's own rest frame its own time is running normally, but in its frame the
galaxy is traveling at very close to the speed of light, so that its length is contracted down from ~500,000 light-years to just about 1 light-second, which explains why in this frame the clock only ticks 1 second between the times it passes each end.
