time dilation

Can someone patiently explain time dilation to me?

d = 5 396 264 244 000 or 5.4 billion kilometers

takes light 5 hours from our perspective to travel that distance

from the perspective of the light, it happens in less than a minute

If a clock were mounted to a particle of light, the mechanism of the clock - each atomic component of the clock - would register less than a minute passing as the light traveled that distance.

Why?

>>8
Time dilation and the like refers to the speed of light in a vacuum, or 299,792,458 metres per second. It may be sloppy to omit it, but everyone who isn't a total dumbass (or getting their physics from Star Trek) understands that.
There are plenty of examples of particles moving faster in a given medium than light does in that medium (most famously, Cherenkov radiation), but that's completely irrelevant, since the speed of light in that medium refers to the light beam as a whole, not individual photons, which do still move at 299,792,458 metres per second (as anything with 0 rest mass must). The effective slowing down of light beams in other media than vacuum is due to scattering.

Basically, the observed speed of a beam of light isn't necessarily constant, but the observed speed of individual photons is. Neither is particularly relevant to backward time travel.

Oh, and >>9 is a moron.