eli5:What is a wave in physics?

Question

I know this seems like something that is easily googlable and that this is a dumb question but I couldn’t find anything that explained it well enough for me to understand. I saw that photons are just comprised of waves but what are these waves made of? Are they physical? How can we see waves in the form of light if they are very small?

In: Physics

Answer 1

Disclaimer: I’m going to try to explain it, but getting deep into this gets surprisingly hard.

>photons are just comprised of waves

Not exactly. Light is both particles (photons) and waves, meaning that some physical phenomena involving light are due to the light as particle aspect, others are due to the light as wave aspect. That doesn’t mean photons are made of waves.

Photons are definitely physical. They are particles, they have a physical size and speed and stuff, but they are very special since, for example, they have no mass. However, yes, they are definitely physical.

Waves can be considered a way to transport energy without transporting matter.

Mechanical waves need a physical medium to transport energy from A to B. If you think any physical object as made of molecules and atoms, a mechanical wave goes from A to B by transferring energy to the first molecule it meets, which then starts to vibrate and transfer some of that energy to the second molecule and so on. You’re not transporting matter from A to B, you’re not shooting particles to produce a wave (much like a wave in a lake doesn’t actually carry water molecules from one place to another). But you’re clearly transporting energy. Sound is a mechanical wave.

Light is an example of electromagnetic wave, like infrared, ultraviolets, microwave, X-ray. Electromagnetic waves can transport energy without transporting matter (they’re waves) AND even without a physical medium in between. Sound doesn’t propagate in vacuum (there’s no molecule to vibrate), but light does (in fact, space is pretty close to vacuum).

We can see light because our eyes are basically very sensitive receivers “tuned” to the visible part of the electromagnetic spectrum (light). Much like your phone or radio can receive radio signals from far way, we can see because our eyes can receive light from far away, and we see objects scattering (reflecting) some “colors” of light while absorbing others.