Light as Wave/particle and Speed

Most recent answer: 10/22/2007

Q:
I know that light is kind of special because of its wave-particle duality. So does the speed of light change in a vacuum? (or in different temperatures?)
- Damon (age 15)
Mason High School, MI
A:
Actually, the wave-particle duality turns out to be about the least special thing about light. So far as we know, all objects share this property, which becomes important for all small objects. Those include electrons, protons, neutrons, atoms, and even small molecules. There are more modern ways to think about the quantum effects shown by small things, so you actually can avoid using the wave-particle duality idea. We can describe more about that if you’re interested.

The speed of light in a vacuum appears to be constant. Light slows down a little in a medium, like water, due to the effects of the light waves emitted by the water molecules’ responses to the incoming light. In a vacuum, the temperature doesn’t affect the speed of light, but it does affect how much thermal light is present.(That’s the glow you see from anything hot.)

At very extreme temperatures, such as in the Big Bang, temperature might affect light. In fact, we don’t even know if anything like ordinary space and time would exist at very high temperatures. But for the entire range we understand, the speed of light in a vacuum is constant.

Mike W.

(published on 10/22/2007)