Nothing Can Move Faster Than Light
Occasionally I’ll see over-zealous headlines that proclaim “Scientists send [something] faster than light!” This is completely impossible. To explain why, we have to deal with Einstein’s theory of special relativity.
The speed of light (c) is hardwired into Maxwell’s equations, the equations governing electricity and magnetism. It is the speed at which light propagates in a vacuum, 2.99792 m/s. It’s a very fundamental constant.
There are three main reasons that no massive particle can move faster than (or at) the speed of light, the first has to do with velocity addition. In relativity, velocities don’t add simply, they follow the formula:
Close inspection of this formula reveals that nothing can accelerate to the speed of light by velocity addition. C is quite literally the speed limit.
Another reason has to do with energy. In relativity, the energy of a particle is equal to:
where the factor gamma is equal to:
As v approaches c, gamma approaches infinity, and so does the energy of the particle. That means any particle that has any mass needs infinite energy to move at the speed of light, which is impossible.
The last reason that nothing can move faster than c is that it would make gamma imaginary, which would render every equation of special relativity unintelligible.
You might have noticed that everything I said above only applies to massive particles, but the story is pretty much the same for massless particles, except they can only move at the speed of light.
What’s usually going on with those headlines is that the researchers have “slowed light down”, which is misleading as well, because light always moves at the speed of light. The only way it can be slowed down is by entering a medium with an index of refraction that’s greater than one (which is why I previously said “the speed of light in a vacuum”). Slowing light down in this way is possible, and it happens all the time. It’s why things appear to bend at the water-level (which has an index of refraction of about 1.3).
I’ve read articles that claim researchers got messages to arrive before they were sent by altering the speed of light, but it’s just not possible. These usually turn out to fit the mold of the aforementioned “index of refraction” changes. Besides, there’s no good reason to believe that causality can be broken, and no current theory allows it.
In short, nothing can move faster than light, get over it.