[treeman79]

Gravity. Still the biggest unknown.

[billti]

Do we even have a total understanding of light, or electricity? (I may be wrong, but I thought there were still some pretty fundamental unknowns)

[XCSme]

It depends on what you mean by "understanding". We can explain using a specific set of rules how something works. It doesn't mean that those rules are the best way to explain it or that they are even correct.

For example, we could explain that electricity works because of how electrons move, which would be correct from our point of view, but if we find out that we were living in a simulation, then the explanation would be that this is how "electricity" was coded to behave.

Also, usually in physics a formula is thought to be correct until some new laws/rules are found, then the formula is updated by adding some extra terms and then again thought to be correct.

[z3t4]

To summarize: we know how to smash two particles together, but not much about what they are made of. Replace particles with stones and bones. 10000 years of science progress and we are still smashing things. With the occasional lab accident like discovering that mold kills bacteria.

[whimsicalism]

Maybe at a certain point "what they are made of" ceases to be a meaningful question.

[gmadsen]

Quantum electrodynamics is the most precise and accurate theory ever created. So not sure what you mean exactly by understand.