« on: 14/08/2016 00:26:57 »
I don't think it's a very useful concept. As I understand it, any object moves through spacetime at the speed of light.
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Sure, but irrespective of what units we apply to it, light still has a maximum speed of a certain value. Why is it that value, 300 million metres per second?I think this is the same as asking why the speed of light is finite at all, since any numerical value we assign to it is purely arbitrary, depending on our perception of whatever time is. Other than that I like AI42's answer, that it can't go any faster because there's no fuel left to push it.
I think you've said it yourself - "no material thing is moving faster than light". Your inference depends on the 'image' of the light on the shell being a physical object when it is nothing of the sort. The only reality of that image is that it is a product of your brain's interpretation of photons hitting your retina having bounced back from the shell.
"If you wave a flashlight across the night sky, then, in principle, its image can travel faster than light speed (since the beam of light is going from one part of the Universe to another part on the opposite side, which is, in principle, many light years away). The problem here is that no material object is actually moving faster than light. (Imagine that you are surrounded by a giant sphere one light year across. The image from the light beam will eventually hit the sphere one year later. This image that hits the sphere then races across the entire sphere within a matter of seconds, although the sphere is one light year across.) Just the image of the beam as it races across the night sky is moving faster than light, but there is no message, no net information, no material object that actually moves along this image."
my point is light is not like a ball that you throw upwards, then it slows down and falls back to the ground. It always travels at the speed of light. Are we suggesting that when a photon leaves a body with sufficient gravity it travels upwards for a bit, and then slows down and falls back to the body? Cause that's what it means when an object is under the escape velocity.Correct, the light doesn't slow down at all, which is a common misconception. However, if you watch from a distance it might appear to.
Light doesn't travel slower when it exits a body with larger gravity, so how can gravity be responsible for stopping light in its' tracks?