1. Microwaves, like other forms of electromagnetic radiation, can propagate through space (i.e. they don't require a medium like air or water to travel through). In general, when an atom or molecule absorbs energy, one or more electrons in the atom or molecule can become "excited." When the electron(s) return to what is called their "ground state energy" (the lowest energy state) the atom or molecule can produce electromagnetic radiation. It turns out that certain "transitions" to particular excited states and falling back down to lower or ground states will result in the formation of different types of electromagnetic radiation (such as microwaves, infrared, etc.).

2. The short answer to this question is that when the molecules in food absorb microwaves, they vibrate and the resulting friction between the molecules heats up the food.

3. This is a good question. I would imagine that if microwaves hit our skin, they would have a similar heating effect as they do with food. It would probably be harmful for parts of the body that can't conduct heat away quickly.

4. When you say "functioning" microwave oven, I understand that to mean that the microwave works as it is supposed to and has the appropriate screen to prevent "leakage" of microwaves from the oven. If there is no leakage from the microwave oven, then I think the chance of getting brain cancer or any other kind of cancer is pretty low. Even if there is leakage, I think the main health risk would be tissue damage from heating, and not cancer.

Microwaves are a "non-ionizing" form of radiation. What this means is that when they are absorbed by molecules, the molecules do not become ionized (they don't become charged). It is typically the ionizing forms of radiation, such as X-rays, that are associated with cancer. If you're wondering why microwaves are non- ionizing whereas X-rays are ionizing, take a look at where these kinds of radiation lie on the electromagnetic spectrum. X-rays are much higher frequency. We know from Planck's equation that frequency and energy are proportional (i.e. if we increase frequency, then we increase energy). If we think about it, radiation with higher energy has a higher chance of kicking electrons into all kinds of excited states, possibly even "ejecting/liberating" an electron and thus leaving a charge on the molecule (i.e. ionizing the molecule -- making it an ion). Something like this can be detrimental in the body, where certain molecules are supposed to be charged while others are not. But luckily for us, microwaves are non-ionizing!

5. This is a pretty controversial topic as far as I can tell. I don't think there have been enough studies to show microwaves' affects on the brain, let alone health in general. According to a study by Volcow et al., 2011, microwave radiation from cell phones increased brain glucose metabolism. But we should be careful not to jump to conclusions here. It's important to be thorough! The microwave radiation from cell phones occurs at a different frequency (i.e. have different wavelengths) than those produced in microwave ovens. Furthermore, I don't believe it's well-understood what kinds of consequences increased brain glucose metabolism could actually have. I realize this is a foggy answer to your question, but I think there's just not enough evidence out there about microwave ovens to really say anything one way or the other.

6. I am a chemistry graduate student. I earned my Bachelor of Science degrees in chemistry and biology.

1. Microwaves are light, like radio, infrared, ultraviolet, x-ray, gamma ray, and yes, the visible light that we see. All objects emit light at that frequency, but a microwave emits them by alternating electric current.

2. Microwaves are absorbed by water molecules, they cause the water molecules to heat up, and then these molecules heat up whatever the water is in. Other molecules absorb microwaves, too, but not as efficiently.

3. Microwaves cook stuff. The amount of damage they cause is because of the fact that they cook things.

4. I don't know about brain cancer, but microwaves from the oven will interact with the water in your body, which means that if you stand in front of a microwave for long enough, you will cook yourself.

5. None that I'm aware of

6. I'm currently a graduate student in Paleobotany. My undergraduate major was (essentially) a double major between ecology and geology - although I did it at UCSB, which has a special program.

1. Microwaves are a form of electromagnetic radiation, just like light and radio waves. They come from applying a large voltage to a thing called a cavity magnetron, which involves the interactions of electrons with a magnetic field.

2. The microwaves create an oscillating electric field. Polar molecules (especially water) try to move to orient themselves to the field. This molecular motion increases the kinetic energy, which is what we perceive as temperature.

3. A microwave oven has shielding (similar to a faraday cage) which reduces most all of the harmful radiation. If you were to remove this shielding, it would be very dangerous.

4. No. At least that isn't proved. Enough radiation will likely case cancer, but if the microwave is working properly, the radiation level is very low.

5. Not that I know of. You can find people who claim one way or the other.

6. I am a 3rd materials graduate student at UCSB, I was a chemistry major in college.