# Food in a microwave

1. Dec 4, 2014

### Hati

I probably have the wrong idea, but we learn by asking I guess.

I just microwaved some pizza and while doing so I remembered that microwaves are electromagnetic radiation. I then got to thinking that microwaves work by using a frequency of light that interacts with the water molecules in the food. I then started to wonder something.

Say I got bored in the middle of heating my food and zoomed off in a spaceship. In space I pass my microwave again. From the point of view of the microwave it's functioning liek it does on earth. Dielectric heating of water molecules in my pizza. Light energy going from the magnatron and being converted to thermal energy in the food. Drop in energy for the microwave, gain in energy for the pizza.

Because We're passing at near the speed of light the waves that the microwave are emitting have been doppler shifted, so I assume I'm going to see something different because of a thought experiment with a similar setup where an object emits a flash of light and from two different perspectives you see a change in mass and kinetic energy between them for the object. Problem is that I don't really understand it so I can't think whats' going on here.

What would the moving observer see?

2. Dec 4, 2014

### Staff: Mentor

The humorous answer is the observer would see someone else eating his/her pizza.

The pizza is heated by microwave radiation which is electromagnetic as you surmised. My guess is as you pass by, you'd see some photons from the microwave shifted up in frequency (ie the ones coming toward you) and some shifted down (the ones going away from you) but the net effect would be the same the pizza would be cooked although more slowly from your perspective.

3. Dec 5, 2014

### Hati

That makes sense to me. Probably a bad idea to be here in the middle of the night reading about physics while eating leftover pizza. I know there exist things that are especially receptive to certain frequencies of electromagnetic radiation, such as water molecules and microwaves. Just wondering what would happen if you shifted the frequency over with relativity so the waves are no longer within the band of frequencies that are really good at interacting with water molecules. I suppose time dilation would be the simplest answer and seems to make sense.

4. Dec 5, 2014

### nitsuj

Note it is a Doppler effect. Nothing has changed with the physical relation between the "at rest" pizza and at rest microwave.

Now if the pizza within the microwave oven was moving around that would have an impact on the heating of the pizza for the reason you thought.

But when the pizza and microwave emitter are at rest comparatively, your motion ofcourse has no impact on the physics of "Dielectric heating of water molecules in my pizza".

All frequencies would be peaks and troughs of sorts, spread along space over time....in other words regardless of the mechanism for microwaves to "heat" food, the perceived increase in microwave frequency would be in step with the perceived increase of the pizza's molecules (dipole moment?).

Now this is a great concern for my interstellar planetary travel plans, it highlights the "microwaved pizza" effect / risk. lol Perhaps a technology to dehydrate the human prior to interstellar travel, and then re-moisturize upon arrival would circumnavigate this "microwaved pizza" effect / risk.

Last edited: Dec 5, 2014