To be extremely pedantic, operations on physical systems can be performed and perfectly reversed without loss of energy, but you couldn’t ever extract anything anywhere along the way - not even direct evidence that it happened. Our models predict that this happens literally all the time in quantum mechanics.
Edit: fun fact: this prediction is actually central to what makes quantum computers work.
That’s a good point. I hadn’t considered that, as I’m a chemist approaching thermo from the stat mech/free energy POV. I was mostly just thinking that a process where ΔG<0 is spontaneous but if ΔG=0, the system is at equilibrium, so nothing happens.
Now that I type it out, even I know that’s not exactly accurate as equilibrium is a dynamic state with lots of things happening at the molecular/electronic scale, so I guess I should have added a qualifier of “at the macroscopic scale” to my original post.
To be extremely pedantic, operations on physical systems can be performed and perfectly reversed without loss of energy, but you couldn’t ever extract anything anywhere along the way - not even direct evidence that it happened. Our models predict that this happens literally all the time in quantum mechanics.
Edit: fun fact: this prediction is actually central to what makes quantum computers work.
That’s a good point. I hadn’t considered that, as I’m a chemist approaching thermo from the stat mech/free energy POV. I was mostly just thinking that a process where ΔG<0 is spontaneous but if ΔG=0, the system is at equilibrium, so nothing happens.
Now that I type it out, even I know that’s not exactly accurate as equilibrium is a dynamic state with lots of things happening at the molecular/electronic scale, so I guess I should have added a qualifier of “at the macroscopic scale” to my original post.