Question

In terms of physical structure of the ear, why do some musical notes sound dissonant together and others nice together?

Answer 1

I'd guess that'd be almost entirely a mental thing rather than a physical thing. It's kind of like asking why some colors look ugly on a physical level in terms of rods, cones, and electromagnetic waves.

Answer 2

I suppose. On the other hand, it could be an evolved mental thing due to physical properties of the sound.