How does Light have momentum without mass?

Question

My question is regarding gravity in black holes. It is said that light can’t escape the enormous gravitational force in black holes; however, is it not true that gravity is directly proportional to the object’s MASS and inversely proportional to the distance between the two objects (Newtonian, I think). If so, light has no mass. So how would light be effected by this phenomenon? Please answer with as much detail as possible

Answer 1

So that's not necessarily the best way to think about the way that light travels through a gravitational field. A better approach is to consider the following two statements:

• Very massive objects warp / curve the space around them.

• Light travels between two points along the line with the shortest length.

So ok, in space that is flat and not warped the second statement seems to make sense. If I shine a flashlight in a huge empty region of space, I shouldn't expect the light to make a 90 degree turn at Albuquerque (sorry).

However, as per the first statement, massive objects warp space. So now the definition of "straight" that we defined in flat space doesn't suffice anymore. So in reality light will still follow the most straight path, but to us it will appear curved because we're looking from the outside in at a curved space. So it will look like gravity is "bending" light, when in reality gravity is really bending space and light is still traveling in a straight line as it always does.

Hope that helps!