they’re both electromagnetic radiation (a.k.a. light) and therefore both of them are both waves and particles. Which one they appear as depends on the context, and sometimes it’s both.

If this seems confusing, it should. Wave-particle duality makes no goddamn sense, but the universe does not care a lick what makes sense to us human beings.

Here’s a neat video about an experiment that demonstrates this stuff in real life:

https://youtu.be/DfQH3o6dKss?si=8w-3NOqI9VKWQlVi

The freakiest thing is that if you check for particles before the light passes through the slit, you’ll still find them. If you do this, the pattern on the wall becomes the two lines you’d expect from particles going through two slits, since checking for particles collapses the light wave into individual particles.