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[QUOTE]Originally posted by Sol System: [QB] I think what is being asked is along these lines: if light isn't slowed down by gravity, then what happens to light that is flying straight up? Well, consider a rocket on Earth. To leave the planet, that rocket has to accelerate to about 25,000 miles per hour. But imagine the Earth was much denser and larger than it is. Or, conversely, imagine the rocket is much less powerful. Gravity, at the surface, is pulling down at 32 feet per second squared. If you want to jump into the air, or move anything at all in that direction, you need to apply an acceleration greater than 32 f/s/s to it. So take our weak rocket. It's thrust is exactly 32 f/s/s. So what happens to the rocket? Nothing. That is, for as long as it is firing, it will not fall. But it cannot go anywhere. It is not, from the point of view of the surface of the earth, going anywhere. But it does have a speed. In the same way, a black hole, at the event horizon, has an escape velocity of exactly lightspeed. A photon, released right at this boundary, aimed straight up, will still be traveling at c. But all this does is counter the gravitational pull of the hole. The photon can't get away from it. That's why it's a black hole. Beneath the event horizon, the gravitational pull is even greater, and light, along with everything else, spirals down into the singularity. [/QB][/QUOTE]
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