Originally Posted by Gingerbread Man
Here's the problem I have. Apparently black holes can ingest light because they are so powerful. For this to happen, the light must have some mass, otherwise surely the gravity could not act on it. If the light has mass, it can't travel at the speed of light. Which bit is wrong? I always thought that the black hole would just be absorbing anything that reflected light, which is why they would appear black, but physicists have told me otherwise.
Ginger
Light has mass - but not rest mass. Which is why it always travels at the speed of light.
Another view as to why you cannot exceed the speed of light is to note that the speed of light is in a sense still infinite. As you accelerate towards the speed of light there is the "slowing down" of clocks, and Lorentz contraction. If you measure the distance covered in outside world, with nonmoving ruler, and divide it by time passed for an outside, non-moving and non-slowed clock, the speed is finite and slower than light. But if you divide the distance covered for outside ruler with the time measured by a clock that moves along and is thereby slowed, the result can be however big. So, accelerating towards the speed of light looks like accelerating to an infinite speed.