MadSci Network: Astronomy

Re: What happens when something travel faster than the speed of light?

Area: Astronomy
Posted By: Philip Plait, Astronomer/Programmer
Date: Fri Jun 13 08:29:35 1997
Area of science: Astronomy
ID: 864456900.As

Like most things in science, there are two ways to answer your question!

The first way is to say that as far as we know, nothing can travel faster than light. Back near the beginning of the 20th century, Albert Einstein started working out his theory of relativity. Part of that theory shows that as you get very near the speed of light, it takes more and more energy to make you go even a little bit faster. The equations work out in such a way that it literally takes infinite energy to travel at the speed of light! That means that moving faster than light is impossible.

The second way to answer your question is a bit trickier. What Einstein showed is that nothing can travel faster than the speed at whioch light can travel in a vacuum. That speed is about 300,000 kilometers a second. However, light doesn't travel quite as quickly through anything other than a vacuum, like, say, air or water. It moves a tiny bit slower than it would through a vacuum, so an object can actually travel faster than light in a particular medium. This happens in our own atmosphere; particles from space can be moving just under the speed of light in a vacuum, but still be moving faster than light can travel in our atmosphere. When these particles impact the atmosphere, they create something very much like a shock wave, except they give off light and not a sonic boom. This light is called Cerenkov radiation, and is an eerie blue glow. Sometimes you can see it in nuclear reactors as well.

But when most people say "speed of light", they mean speed in a vacuum. As far as we know, it is not possible to travel faster than that speed.

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