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How Space Can Expand Faster Than the Speed of Light
StartsWithABang writes You know the fundamental principle of special relativity: nothing can move faster than the speed of light. But space itself? That's not a "thing" in the conventional sense. Two years after coming up with special relativity, Einstein devised the equivalence principle, and thus began the development of general relativity, where space itself would have properties that changed over time, responding to changes in matter and energy. This includes the ability for it to expand, even faster than the speed of light, if the conditions are right.
Not exactly. The op was relatively correct in explaining general relativity (pun intended). Nothing can move through space faster than light. However during inflation, just after the Big Bang (the first 10^-34 seconds or so) space was created much faster than light could traverse. Quantum uncertainty was able to affect locations right at the Big Bang. However general relativity shows us that if you have an unbelievably dense undilutable piece of space, it will double in size extremely quickly. This doubling separated portions of the universe that only now are reconnecting due to light speed. Dark energy will move the Big Bang from beyond our perception in only 4 billion years or so through a very similar process of space creation. Quantum uncertainty is what brought our portion of inflation in reality to an end, however it is hypothesized due to the percentage of space that rolls down the density curve is so small, inflation continues eternally somewhere. Both inflation and dark energy are mechanisms that create space directly and therefore do not violate relativity because nothing is moving through it technically. Therefore both mechanisms are a way to casually disconnect space that was once connected.
No, the result of that light would be, from our point of view, going at light speed too.
Any sublight speed plus any other sublight speed must itself be sublight speed. At the limit of the speed of light, adding the speed of light to itself results in the speed of light. What happens to light is that its energy doubles, not its speed, what happens to mass is its total energy increases, but still remains finite and therefore sub light speed velocity.
This is the basic result of special relativity.
Expanding space isn't traveling in space, therefore the gap between two things can expand faster than light because nothing is moving. Those two things can themselves travel in this changed space, but their velocity will be limited to light speed no matter what they are.
The space between us and something that was 15 billion light years from us is expanding faster than the light it is emitting toward us can travel, therefore we will never see the light and that thing is beyond our light horizon of the visible universe.