# How do waves travel in a vacuum?

1. Jan 15, 2010

### MrPickle

Today in class we started talking about waves.

I understand waves to be energy. This makes sense to me when thinking about sound waves, because the energy can travel from one particle to the next to travel; but I don't understand how things like electromagnetic waves can travel through a vacuum. The wave's energy can't be passed from one particle to the next because there are no particles in a vacuum and I don't understand how the energy could move because well, it's energy. I accept that it travels because otherwise we wouldn't be able to see the planets and Martians and what-not.

Is this something to do with E=mc2? Do we even know the answer?

This isn't a homework question, just me questioning things, but it's still related to school so I'm sorry if this is the wrong place.

2. Jan 15, 2010

### mgb_phys

Thats where thinking of light as a wave isn't useful.
Think of a photon as a little bullet that is vibrating with a certain frequency, the wavelength is then just this frequency * the speed of the bullet.

One good analogy is to think of a police car with a flashing light driving along a street. The light flashes with a certain frequency and the car goes at a fixed speed.
If you mark on the road the position of the car everytime the light flashes - this gives a wavelength, but it doesn't mean the car is this long.

3. Jan 15, 2010

### Bob S

At one time, physicists thought that empty space was filled with "aether", and there was a preferential reference frame where the speed of light was constant. The Michelson Morley experiment disproved this, and verified that the speed of light was indeed constant = c in every inertial frame. See
http://en.wikipedia.org/wiki/Michelsonâ€“Morley_experiment

So light propagates in empty space without any medium (aether or particles) to propagate it..

Bob S

4. Jan 15, 2010

### cragar

I think it is weird that they thought they wan an aether because if there was it would have slowed the earth down to a stop , the earth wouldn't have been able to go around the sun . , the electromagnetic field is doing the waving

5. Jan 15, 2010

### Redbelly98

Staff Emeritus
This is a little like asking, how can two masses that are separated by a vacuum attract each other gravitationally? Or more on topic, how can two charges that are separated by a vacuum attract or repel each other?