# If nothing travels at the speed of light, except light, how can a black hole also pull light into itself?

Is it because it has super massive gravity and energy? Or is it some sort of an anti-light component in it because it used to be a star?

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Why do you say "If nothing travels at the speed of light, except light"? Any massless particle and it's associate field travels at c. It is also the speed of gravity. I think the question is based on an incorrect premise. – Jeremy Sep 25 '13 at 0:41

Gravity is a force, and it need not have a "speed"1.

A gravitational body sets up a gravitational field around itself. Note that by the time the light wave approaches the body, this field has already been set up. The gravitational force does not need to "reach out" and "catch up to the light" — it's already there.

In fact, it's not even really a force (though we can treat it as one to an approximation). Gravity bends the fabric of spacetime around it, messing with the meaning of a "straight line". From different reference frames, different lines appear straight. To the light wave, the inspiraling path seems "straight" and thus it follows that path. To an external observer, the light wave is not going straight.

1. It does, but that's the speed at which changes to the field propagate, not the speed at which it "catches up" with other things. Changes in the gravitational field propagate at lightspeed.

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What happens is that the gravity produced by a black hole is simply so great that it warps the spacetime fabric in such a way that any light which crosses the event horizon is funneled in by the fabric itself - it's a crazy notion, and one hard to get your head around. This diagram might help:

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So the light is being pulled in by gravity even though gravity can't travel as fast as light? – Timtech Sep 25 '13 at 0:10
@Timtech Gravity is a strange thing - it warps the spacetime fabric, 'funneling' the light into itself. It is changing the very path of the light. – Undo Sep 25 '13 at 0:11
Oh, so it's not exactly chasing it? – Timtech Sep 25 '13 at 0:12
No - it's changing the fabric along which the light travels, just like a ball rolling around on a blanket. It might start out going straight, but if there is a depression in the blanket and the ball passes toward it, the ball will change course. A black hole creates a 'mega-depression'. – Undo Sep 25 '13 at 0:15
@Timtech Adding to what Undo said, and an alternative explanation, "light travels in a straight line" There is no fault with this statement. Gravity simply twists the space in such a manner that straight lines lead to inside the black hole. Remember, straight lines(even if parallel) may converge for non-Euclidean geometry. I hope I made myself clear. – Cheeku Sep 25 '13 at 0:23