Good question! The answer doesn't have to do
with whether or not light is "bright" inside a
black hole; instead, it has to do with the way
light travels near a black hole.
As you may know, a black hole is an object
which has a huge mass packed into a small volume,
so its gravity is very strong. But according
to Einstein's theory of general relativity, this
strong gravity means that the spacetime around the
black hole is very strongly curved (imagine
putting a heavy object on a trampoline - the mass
of the object bends the surface of the
trampoline). Now, what role does light
play? Well, because the spacetime is
curved, beams of light travel in curves rather
than straight lines. It turns out that the
spacetime around a black hole is so strongly bent
that a light beam that's shot out from the surface
of the black hole gets pulled back into the black
hole, so it can't escape. That means that if
someone was on the surface (or even inside) the
black hole and pointed a flashlight out towards
you, none of the light from the flashlight would
be able to escape! That makes the black hole
look black to you - no light comes out of it.
Your friend inside the black hole, however,
will still see light coming out of the flashlight
- the light doesn't get any dimmer or black. It's
just that the light (and your friend!) can never
escape from the black hole to reach you.
I hope this helps!
Black holes have such powerful gravity that the
escape velocity - that is, the speed needed to get
out - is faster than light. Because not even
light travels fast enough to get out, it's not
possible to see anything outside of a black hole
from outside. Thus, they look black.
There is no reason why you could not see things
inside of a black hole if you were yourself
already inside, however. That said, you wouldn't
be seeing anything for long, because black holes
have other properties that would kill you rather
quickly (you would be pulled apart).
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