Tumba":3mtkk4lw said:...How can gravity bend light around a gravitational field, and not change its speed?
Edit: I'll rephrase that. Gravity causes light to no travel in a straight line, therefor changing the lenght of time it take us to see an event. :shock:
But, it is a straight line. It's "spacetime" in which the light is traveling which has been distorted by gravity. There simply isn't any other "straight line" for the light to travel. Gravity has not "bent light" as far as attracting photons like one imagines a rocketship may experience being attracted by (and attracting in exchange) the mass of the planet. The planet has simply curved the spacetime in which the photons travel. They have no other choice in the matter.
If you could make a curlicue helix out of spacetime, light would still go 'round and 'round at the speed of light. Likewise, a black hole distorts spacetime so much that light simply does not have the energy to climb out because, for illustration, the gravity well is "too steep."