# Recent content by RNA

1. ### Osmosis, osmotic pressure, vapour pressure

All the above explanations are fine but do not, I think, get to the heart of the OP's first question, which was "Why does osmosis happen?" I.e., yes, dissolving a solute in water lowers the water's chemical potential. But this leaves unanswered the question of why this happens. The answer is...
2. ### Do electron energies (in atoms) have fixed values, or only fixed expectation values?

SpectraCat: Ah, yes, of course (this indicates the dangers of trying to think about QM long after you last studied it). Thanks for your detailed reply (I also appreciated the pedagogy of guiding me to figure it out for myself). So the resolution is that, as in a quantum harmonic oscillator...
3. ### Do electron energies (in atoms) have fixed values, or only fixed expectation values?

Hi. First post. I'm trying to understand if electronic energy levels have fixed values, or merely fixed expectation values (in the latter case, orbital electrons could have any energy and it's only the average that would be fixed). Here's my argument for the latter. If it's incorrect, could...