We can't go faster than the speed of light. Can we accelerate light, then?

Question

If there's a way to artificially accelerate light, or when it's naturally faster such as around a blackhole, then in that case, would it be possible to go past the 299792458 m / s limit?

Answer 1

First of all, this question is missing something very important about the constant $c$. This only matches the speed of light (really an electromagnetic wave that satisfies Maxwell's equations) in a vacuum. Thus, when light propagates in a medium other than the vacuum, it will almost certainly not travel at $c$. The following Wikipedia article gives a fun extreme example of this phenomenon called "slow light:" https://en.wikipedia.org/wiki/Slow_light

The reason that the speed of light is a speed limit for any massive object is that the energy it takes to accelerate an object asymptotically approaches infinity as the speed of the object approaches $c$. This is a natural consequence of Einstein's special theory of relativity, whose fundamental postulate is that the constant $c$ is an invariant in every reference frame. While this might be extremely weird, it happens to produce results in remarkable agreement with our experimental observations. This idea originally came from a consideration of Maxwell's equations, which seem to produce frame invariant wave equations that propagate at the speed $c$ in every reference frame. It is almost a miracle that Maxwell was able to formulate his equations given that they pre-dated Einstein's theory!

Answer 2

The special role of the speed of light in relativity is about the speed, not about light. That is, there is one particular special speed in the universe which all observers agree on. This speed acts as a scaling factor between space and time. It so happens that light travels at that speed, and so it's called "the speed of light" for historical reasons. But it might better be called "the speed of gravity" or "the speed of causality".

Answer 3

If we assume that the speed of light is fixed, that assumption leads to models that match reality extremely well. If we throw out that assumption, we do not know how to preserve that match to reality. Since that match to reality is fundamental to reasoning about physics, we have no way to reason about a variable speed of light.

I should add that in the current state of metrology, the speed of light is a fixed quantity by definition: we calibrate distance measuring instruments using clocks and an adopted value for the speed of light. If you seek a varying speed of light, you must redefine either time or distance relative to our present understanding.

Answer 4

There is an alternative to string theory known as Loop Quantum Gravity which basically holds that space is particulate, with each particle being about 10^-30 meters in size.

While I was reading an early paper on LQG, it struck me that in a different universe, if the size of these particles was smaller or larger, then the speed of light would be faster or slower. So I developed the speculative theory of Dilating Loop Relativity which says that energy from a body leads to a dilation of these particles and thus to a slowing of time, and hence gravity.

So although LQG is still theoretical, and DLR is certainly speculative, it gives rise to thought about what is it that determines the speed of light. I can't help but wonder if c is only this speed in our universe.