Regarding why light can't escape a black hole, this is how I always understood it (taken from wikipedia):

"As predicted by general relativity, the presence of a mass deforms spacetime in such a way that the paths taken by particles bend towards the mass.[44] At the event horizon of a black hole, this deformation becomes so strong that there are no paths that lead away from the black hole."

Aight but today our physics teacher said the reason light can't escape a black hole was because its escape velocity was too low. And if you google it some shit defines black holes as having an escape velocity greater than the speed of light.

My question is why does the speed even matter in escaping a black hole? If spacetime is curved in such a way that the particle paths lead back to the black hole, a particle could travel infinitely fast and it would just travel back on itself. So what does escape velocity have to do with it?

edit -

especially since gravity doesnt directly effect light

This post was edited by novocane on Oct 18 2011 07:49pm

different views but same ending. nothing escapes after it reaches the event horizon because of its insane gravitation force.

more detailed view on this since im lazy lol.

http://answers.yahoo.com/question/index?qid=20070227120903AAkDF2o

This post was edited by Subwoofer on Oct 18 2011 07:55pm

a good way to visualize this , is the old " sheet and ball " analogy

image you have a sheet , pulled flat , above the ground ( this represents space )
and you place a heavy ball in the middle of the sheet ( this represents mass , lol )

now , you can easily see , that the sheet now has a depression , where the ball is
if i had another ball , around the edge of the sheet , it would roll down towards the ball in the middle of the sheet
this effect is what we call " gravity "

the strength of the gravitational field , is represented by how steep the depression is
the heavier the ball in the middle , the bigger the depression , and the faster the ball on the outside will roll down the sheet

now if i wanted to get the 2nd ball that has rolled down the sheet , back out , i would need to accelerate it fast enough to climb out
the steeper the depression , the faster my ball would need to move , in order to climb out of the hole

with a black hole , it warps space so much , that the " steepness " of the sheet is so much , that even if my ball was moving at light speed , it still wouldnt be fast enough to climb out

its a rather simplified analogy , but it gives the basic gist of it


and btw , gravity most certainly does directly affect the path of light

yea, but thats not what i said is it. obviously it affects the path of light






I think you guys misunderstood my question. Im not asking how black holes keep light from escaping, if you read the second sentance of my first post it explains it.

The yahoo is answer is similar to the wikipedia one:
"A more fundamental way of viewing this (the same phenomenon) is that in a black hole, the gravitational field is so intense that it bends space and time around itself so that inside the event horizon there are literally no paths in space and time that lead to the outside of the black hole: No matter what direction you went, you would find that your path led back to the center of the black hole, where the singularity is found."

The question is if all the paths are curved back to the center of the black hole, how is escape velocity at all relavent to the black hole? Even if it was possible to travel at superluminal speeds and surpass the minimum escape velocity, you would still just loop back to the center of the black hole.

The correct answer is what Wikipedia says. The strong gravity of a black hole deforms spacetime itself. Once you pass the event horizon, every single direction you can possibly face bends back toward the center of the black hole. Even if you had a spaceship that was uncrushable and that could travel at 100 times the speed of light, you still could escape a black hole, because every single direction would be "down" or "in" so there's simply no possible way to escape "up" or "out".

this is very acnoclageable

if you were going faster than the speed of light you could avoid the event horizon(point of no return).

this more what you were looking for?

How did you come to this conclusion, and how does time become bent? Time is not a physical thing, right? So, how can it bend? Is time not a simple way for us to calculate our perception of reality?

because going faster than the speed of light is a game changer. it would fundamentally alter your interaction with the universe around you making things like black holes a non-issue.

we can only speculate what FTL travel would be like but this is just something i assume to be true.

google gravitational time dilation.

I looked up gravitational time dilation, but it goes by the principle that time is physical, thus it could be stretched or shrunk, so I cannot concur with this theory.
However, while reading about this theory, I rather enjoyed the theory that the repulsive force of dark energy will eventually come to a point in time when it overwhelms the forces of gravity and etc. so that the universe will come to an end, because it will be "ripped apart"!