We don't understand them. No one has any idea how they work. We have no theory. They are unsolved problems. No one can agree on anything....
Sometimes I hear strong claims such as this.
I think they are exaggerations. They diminish/ignore/dis-respect significant progress and understanding that has been made.
Unfortunately, these claims of ignorance are often made by people who claim they are going to solve one of these problems, .... once you give them lots of money.....
Let me take one specific case: cuprate superconductors.
There are many things we know and understand that we did not when they were first discovered.
We have a phenomenological theory for all the "macroscopic" phenomena: Ginzburg-Landau!
Although not everyone agrees I think it is fair to say that the essential physics is in a one-band Hubbard model and the key physics is:
strong electronic correlations,
a doped antiferromagnetic Mott insulator,
d-wave pairing that is "mediated"/caused from some mixture/variant of "antiferromagnetic" spin fluctuations or RVB spin singlets,.....
We certainly don't understand the cuprates at the same level as elemental superconductors. But we do understand some things.
We certainly don't understand water at the same level as liquid argon. But we do understand some things.
There are still outstanding challenges and these topics should attract ongoing attention.
I don't think the topics I listed above are anything like problems such as dark energy, dark matter, quantum gravity, ... or superconductivity before BCS
and then there is consciousness....
Am I over-reacting?
Aside: the title of this post is from this music video. Some think it is hilarious. I find it a bit too close to the truth.