Magical Realist
Valued Senior Member
How can entropy exist in a universe that is expanding at an accelerating rate? Does this not suggest an infinite supply of dark energy?
Entropy is a measure of the unavailability of entry to do work or, equivalently, of the degree to which energy is spread out randomly and cannot be collected together again.How can entropy exist in a universe that is expanding at an accelerating rate? Does this not suggest an infinite supply of dark energy?
Blasted spellchecker: energy, dammit, energy, not "entry".Entropy is a measure of the unavailability of entry to do work or, equivalently, of the degree to which energy is spread out randomly and cannot be collected together again.
Why would you think an expanding universe somehow prevents energy spreading out randomly?
Exactly.I perhaps took too literally the metaphor of a watch winding down being what entropy is like. So I assumed more energy would keep the watch going forever. But apparently not. It has more to do with the distribution of energy as you point out.
Think of a glass of water and you put in a drop of dye. It's going to be distributed in the water pretty soon and it's never going to be a drop again.I perhaps took too literally the metaphor of a watch winding down being what entropy is like. So I assumed more energy would keep the watch going forever. But apparently not. It has more to do with the distribution of energy as you point out.
I’m not sure whether conversion of gravitational potential energy to kinetic energy would involve an entropy increase. But once k.e. starts being converted to heat I think the entropy would increase.If entropy is increasing because of universal expansion, why does the clumping (or contraction) of matter increase entropy?
Recall that a black hole has maximal entropy.
Yes, so entropy increases around the hot clump, while the entropy of the particles clumping together (becoming more solid) decreases, so the 2nd law holds.The hint is that a clump of matter is not a closed system, because it radiates.
Does that mean you were checking of we were bots here, then?Yes, so entropy increases around the hot clump, while the entropy of the particles clumping together (becoming more solid) decreases, so the 2nd law holds.
I tried discussing the points in my first post with ChatGPT 3, and it ended up telling me that because the universe was initially very hot, entropy was very high (!).
What do you by particles being hidden when they collapse into a regular shape?I don't know that there are any real clues in what I've posted about entropy--such as, what the hell is it--but, do you think there's an obvious connection between gravitational entropy and information?
Given that, in the theories such as Shannon's, it's about lost information or 'unavailable' information. Particles are hidden when they collapse into a 'regular' shape. Perhaps that gives you another hint. Perhaps its why a black hole's entropy is "expressed" as the sum of Planck areas on its "surface".
p.s. perhaps I should have a stab at what entropy is. It's a relation and it depends on knowing things about the state of a system. That's one thing Baez makes fairly obvious with his bacl-of-the-envelope analysis.
Because energy has different forms and because entropy is an energy-relation, entropy has different forms too. For example, thermodynamic entropy is not the same animal as gravitational entropy, or von Neumann entropy. The common thing with all forms of entropy is that they are all energy-relations.
What about information entropy, how is that an energy relation? The answer seems kind of simple but it really isn't.
I mean, take the planet we're living on. How many particles can you detect or know about, below the surface?What do you by particles being hidden when they collapse into a regular shape?
Whether you can see them or not does not affect entropy.I mean, take the planet we're living on. How many particles can you detect or know about, below the surface?
Sorry, I should have posted: when a lot of particles collapse into a clump, most of them are hidden.
So not knowing the state of particles inside an horizon, doesn't "affect" entropy? I can't really parse that.Whether you can see them or not does not affect entropy.
Well, all of them. I "detect" them by standing on a scale. It tells me - in pounds - how many there are at an distance of approximately 3860 mi below me.I mean, take the planet we're living on. How many particles can you detect or know about, below the surface?
Ok. So can you connect that number of miles, 3860, to the number in pounds the scale tells you?Well, all of them. I "detect" them by standing on a scale. It tells me - in pounds - how many there are at an distance of approximately 3860 mi below me.
A black hole of given mass, angular momentum, and charge can have a large number of different unobservable internal configurations which reflect the possible different initial configurations of the matter which collapsed to produce the hole. The logarithm of this number can be regarded as the entropy of the black hole and is a measure of the amount of information about the initial state which was lost in the formation of the black hole.