Gary’s Q&A

Listener question & Gary’s response · Transcript passage

TwoBuck Howie asks, All my life, I was told that there is nothing that can go faster than the speed of light. Then I heard a physicist say that galaxies are moving away from each other faster and faster until one day, they will be moving away from each other faster than the speed of light. Then I see online that a different physicist claims 4 things that are faster than the speed of light. Is there anything that moves faster than light? Is Einstein’s theory incorrect?

As far as we know, nothing can travel faster than the speed of light. As say, “as far as we know” because you always have to leave open the possibility of some future discovery.

When we say nothing can go faster than the speed of light, we are referring to a fixed starting point. If you turned on a flashlight in space, the photons from the flashlight would move at the speed of light from the flashlight.

Now, let’s say the flashlight could shoot light in opposite directions at the same time. The photons from each end would travel from the flashlight at the speed of light.

However, the photons would travel away from each other at two times the speed of light. Neither photon is traveling faster than the speed of light relative to their starting position in the flashlight.

The fastest the space between two moving objects can increase is two times the speed of light.

In the example you gave of galaxies, there is another wrinkle. In that case, space itself is expanding between the galaxies, which I confess is a very difficult thing to get your head around.

This is a much bigger subject that I can answer on a Q&A episode, but suffice it to say no object or energy can go faster than light, but that doesn’t hold for space between objects.