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Entropy itself is somewhat dubious as Carlo Rovelli gets into with the idea of relative entropy and course-graining. Entropy only exists with regard to a repres

Entropy itself is somewhat dubious as Carlo Rovelli gets into with the idea of relative entropy and course-graining. Entropy only exists with regard to a representation / set of observable operators. When you change your basis, you get a new entropy. So the cold ant, looks like it has low entropy because you've used the temperature observable. Under the structural/integrated-information observables, it would have a much higher entropy. Read more here: Is Time’s Arrow Perspectival? - Carlo Rovelli https://arxiv.org/pdf/1505.01125.pdf https://arxiv.org/pdf/1505.01125.pdf

contravariant 5y ago
Sure entropy depends partially on how you choose to describe your space but there are limits to how much two definitions can differ. In particular the set of low entropy states must be quite small, so even if two definitions don't agree they must still agree for quite a large part of the high entropy states. A cold ant is simpler because the molecules don't move in complicated ways. It's more complex if you ignore the movement of molecules, but then you're changing more than just how you define entropy you're leaving out bits of physics.
ericbarrett 5y ago
What about the entropy of a black hole, A / 4hG? (A = surface area, h = reduced Planck constant, G = gravitational constant.) That seems very well defined.
- JoBrad 5y ago
  But aren’t black holes essentially injecting large amounts of energy into their domain of influence? Entropy would decrease in the same way it would decrease for a star system.
Jensson 5y ago
This doesn't work for the ant case. Temperature is defined in terms of entropy change per energy added to the system. But if you burn it up entropy would go down in your definition, so you would have negative temperature? Doesn't make sense. So in physics the temperature view will always be correct. You can use a different basis for it, but it will always be a temperature view, since everything disintegrates into plasma if you add enough energy, so that plasma needs to have higher entropy than whatever you started with, so your "structural" interpretation of physical entropy doesn't work.
- goldenkey 5y ago
  The amount of complexity that an intelligent being can cause is far greater than the momentary temperature of that being. You are stuck on local slices of a momentum based basis. Think in broader terms, the entropy of the human race, thermodynamically, is tiny, and yet we could potentially grow to change the entire galaxy, let alone the entire universe. Entropy based on course grating of momentum states is only one possibility and is severely handicapped, especially when one realizes the universe may be cyclic -- clearly if it is, the observables we are using that lead us to believe entropy is increasing are sort of like the Shephard tones [1] https://en.wikipedia.org/wiki/Shepard_tone https://en.wikipedia.org/wiki/Shepard_tone Also, I should add, a photon of the lowest possible energy we can currently detect, still generates the same fidelity of interference and quantum effects that a high energy photon does. This is immensely applicable to low energy quantum computing. Which means that you can get a wavefunction at the final gate of one's quantum computer of enormous complexity, with almost no relation to energy magnitude. This relationship, between fidelity of the double-slit interference of low energy photons vs high energy ones was used to check for a screen-door effect to see if we might be in a discretized simulation that allocated compute based on energy magnitude. We found no such pixelation/screen-door effects. Quantum computation throws a huge wrench in classical thermodynamic entropy.

contravariant 5y ago

Sure entropy depends partially on how you choose to describe your space but there are limits to how much two definitions can differ. In particular the set of low entropy states must be quite small, so even if two definitions don't agree they must still agree for quite a large part of the high entropy states. A cold ant is simpler because the molecules don't move in complicated ways. It's more complex if you ignore the movement of molecules, but then you're changing more than just how you define entropy you're leaving out bits of physics.

ericbarrett 5y ago

What about the entropy of a black hole, A / 4hG? (A = surface area, h = reduced Planck constant, G = gravitational constant.) That seems very well defined.

JoBrad 5y ago
But aren’t black holes essentially injecting large amounts of energy into their domain of influence? Entropy would decrease in the same way it would decrease for a star system.

Jensson 5y ago

This doesn't work for the ant case. Temperature is defined in terms of entropy change per energy added to the system. But if you burn it up entropy would go down in your definition, so you would have negative temperature? Doesn't make sense. So in physics the temperature view will always be correct. You can use a different basis for it, but it will always be a temperature view, since everything disintegrates into plasma if you add enough energy, so that plasma needs to have higher entropy than whatever you started with, so your "structural" interpretation of physical entropy doesn't work.

goldenkey 5y ago
The amount of complexity that an intelligent being can cause is far greater than the momentary temperature of that being. You are stuck on local slices of a momentum based basis. Think in broader terms, the entropy of the human race, thermodynamically, is tiny, and yet we could potentially grow to change the entire galaxy, let alone the entire universe. Entropy based on course grating of momentum states is only one possibility and is severely handicapped, especially when one realizes the universe may be cyclic -- clearly if it is, the observables we are using that lead us to believe entropy is increasing are sort of like the Shephard tones [1] https://en.wikipedia.org/wiki/Shepard_tone https://en.wikipedia.org/wiki/Shepard_tone Also, I should add, a photon of the lowest possible energy we can currently detect, still generates the same fidelity of interference and quantum effects that a high energy photon does. This is immensely applicable to low energy quantum computing. Which means that you can get a wavefunction at the final gate of one's quantum computer of enormous complexity, with almost no relation to energy magnitude. This relationship, between fidelity of the double-slit interference of low energy photons vs high energy ones was used to check for a screen-door effect to see if we might be in a discretized simulation that allocated compute based on energy magnitude. We found no such pixelation/screen-door effects. Quantum computation throws a huge wrench in classical thermodynamic entropy.