"Nothing can travel faster than the speed of light."
Have you heard these statements before? They are often
quoted as results of Einstein's theory of relativity. Unfortunately, these
statements are somewhat misleading. Let's add a few words to them to clarify:
"Nothing can travel faster than the speed of light in a vacuum."
|Those additional three words in a vacuum are very
important. A vacuum is a region with no matter in it. So a vacuum would
not contain any dust particles (unlike the vacuum cleaner shown to the
left, which is generally full of dust particles).
Light traveling through anything other than a perfect vacuum will scatter off of whatever particles exist. This scattering slows light down when light travels through any medium other than the empty space of a vacuum, as illustrated below.
This illustration is by necessity a simplification of the interaction between
light and matter. It is meant to help the reader remember that light
in a non-vacuum medium slows down due to scattering, but it is not intended
to represent an exact model of that scattering.
Continue to the next page to find out!
Copyright © 1999-2004 Doris Jeanne Wagner and Rensselaer Polytechnic Institute. All Rights Reserved.