What is Radiation?
Very smart people say very dumb things about radiation. I have been in many conversations where I see people completely talk past each other because neither really understands exactly what the other means by "radiation". I think this is reflective of a particular cognitive bias, where even though you know a variety of disparate concepts are associated with a particular label, you have never had them presented as all falling under a single shared class. There are three things people usually mean when they say radiation: "electromagnetic radiation", "particle radiation", and "thermal radiation".
electromagnetic radiation
Electromagnetic radiation travels in waves. Light, radio, infrared, x-rays, microwaves, and gamma rays are all types of electromagnetic radiation. In certain contexts, when people say "radiation" they mean "heat". This type of radiation is actually a subset of electromagnetic radiation. When we feel warmth from the sun or a heater, that's infrared radiation. Radiation is just one form of heating. There is also conduction (cold thing touching hot thing) and convection (fluid carrying heat from hot thing to cold thing). These are not radiation.
particle radiation
Particle radiation is what comes from radioactive materials. These are physical particles that launch off from a radioactive material and physically interact with the things they hit. They are small particles. When you hear "alpha" and "beta" radiation, that is referring to this type of radiation.
ionizing vs. non-ionizing
Once last thing you may hear is "ionizing" and "non-ionizing" radiation. This can be either particle or electromagnetic radiation. This refers to whether radiation can impact the composition of an atom.
things that are not radiation
- magnetism
- electrostatic fields
- contact heat
- smells
- sounds waves
- pressure