What if the second law was breakable?

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What if the second law was breakable?

Postby Pfhorrest » Thu Feb 21, 2019 6:41 pm UTC

Imagine a fictional universe exactly like ours, all of the same experiments have been run in that universe as in ours and they've had the same results, so as far as people in that universe know, their second law of thermodynamics holds as true as ours. But then, they do some new experiment, and find that in some circumstances, it can be violated. What would that experiment look like? Basically, where haven't we looked yet (there's always somewhere we haven't looked yet) where it's possible we might find falsification of the second law of thermodynamics? Not that we would expect to, but if you were to just make up a realistic scenario where against expectations we did find such an unexpected result, what would that be?
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Re: What if the second law was breakable?

Postby doogly » Thu Feb 21, 2019 6:45 pm UTC

"The law that entropy always increases, holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." - Eddington
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Re: What if the second law was breakable?

Postby Soupspoon » Thu Feb 21, 2019 8:22 pm UTC

And robots would have no reason at all to obey humans, life-threatening or not!

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Re: What if the second law was breakable?

Postby Eebster the Great » Thu Feb 21, 2019 8:33 pm UTC

The reason Eddington (and doogly) say this is that the second law is, at its most fundamental, a purely statistical law. It is not just true because we observe it to be true but because literally just counting proves that it must be true. So in this hypothetical universe, counting doesn't work either.

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Re: What if the second law was breakable?

Postby Heimhenge » Thu Feb 21, 2019 9:44 pm UTC

Well, since you said "make up" I'll feel free to speculate. Although it's true, as ETG notes, that the 2nd Law is purely statistical, that might still leave room for a Maxwell's Demon type device based on as-yet-undiscovered method of atomic manipulation (as opposed to Maxwell's "mechanical sliding shutter").

One might claim that any reduction in entropy caused by herding the fast particles from the slow particles would have to be outweighed by the energy required to do the sorting. But that claim comes from assuming the 2nd Law is always true ... not sure if it can be proven elsewise short of actually building the device.

So what about a herding mechanism with no moving parts, something using E and B fields to deflect the slower moving particles, but still allow the faster moving particles to change chambers. Of course if would have to be "one way" like a diode. I know crossed E and B fields can operate as a speed selector for moving particles, but I don't think it could work as a "diode".

You asked for speculation, so there's mine.

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Re: What if the second law was breakable?

Postby doogly » Thu Feb 21, 2019 10:04 pm UTC

The second law is derived, not an assumption. We just tend to believe it even more than the things we derived it from. But certainly it can't be violated by anything like Maxwell's equations and E and B friends.

A time machine could violate it. That kind of fucker completely fucks with your shit.
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Re: What if the second law was breakable?

Postby Eebster the Great » Fri Feb 22, 2019 7:01 am UTC

I suppose in a strict sense, superdeterminism can violate the second law. And like, if we live in a teleological universe where God has already set things up in order to play out in a specific way, then there is no law of physics saying it could not have been set up to play out in a very surprising fashion.

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Re: What if the second law was breakable?

Postby Pfhorrest » Fri Feb 22, 2019 8:20 am UTC

Superdeterminism makes me think that it seems also that if many-worlds or modal realism are true -- if every possibility is an actuality from the perspective of those living in that possibility, and the actual world is only "actual" in the sense that it's the possibility we're a part of -- then there are some very few possible timelines where entirely by chance, universal entropy does not increase. We should not expect ourselves to find ourselves living in such a timeline, and even if our timeline to date has seemed to be such a timeline, we should not expect it to continue to behave that way. But for some lucky possible people in some lucky possibly universe, just by chance they will not see universal entropy increase.

This idea seems very similar to quantum immortality. Quantum universal immortality, maybe? If it's (however slightly) possible for the universe to "not die" (of entropy), and all possibilities are actualities, then there is some actual version of the universe that never "dies".
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Re: What if the second law was breakable?

Postby Eebster the Great » Fri Feb 22, 2019 9:15 am UTC

Yeah, you can set up a system of particles to evolve into a lower entropy state. So if all possible initial conditions are real, then in some of them, entropy decreases. Like I said, it's a statistical law. But it is difficult to overstate just how unlikely this is, requiring the double exponential function to describe concisely.

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Re: What if the second law was breakable?

Postby p1t1o » Fri Feb 22, 2019 10:31 am UTC

Too fundamental a change to even start speculating.

Like asking

"How would biology work if we got rid of protons?"

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Re: What if the second law was breakable?

Postby elasto » Fri Feb 22, 2019 11:10 am UTC

p1t1o wrote:Too fundamental a change to even start speculating.

Like asking

"How would biology work if we got rid of protons?"

I'm not sure it's quite that bad.

The second law only applies to closed systems.

If scientists found a setup where entropy could reliably be lowered, my first thought would be that it somehow taps into an energy source normally inaccessible to our universe - perhaps in one of the other dimensions string theory predicts, or perhaps from a 'nearby' parallel universe.

So long as the total entropy of all of the dimensions/universes grows, our universe's entropy can go as low as you like.

(This pathway could also somehow be the source of our universe's mysterious low initial entropy, which might be how these scientists come to conduct their experiment to begin with...)

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Re: What if the second law was breakable?

Postby quantropy » Fri Feb 22, 2019 1:04 pm UTC

If the second law didn't hold then presumably we'd be able to get useful energy from a high entropy system. Since we can't do this with systems we are familiar with, the speculation is that the high entropy system is in a form that we don't understand at present. But this looks like getting energy from a mysterious source, which looks like the first law is being broken.

This means that the question is much the same as trying to imagine a universe where the first law doesn't hold. That's easy, we happen to live in one (http://www.preposterousuniverse.com/blo ... conserved/).

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Re: What if the second law was breakable?

Postby Eebster the Great » Fri Feb 22, 2019 1:09 pm UTC

Well, it's not like that, because we in fact live in a universe where energy is not conserved yet entropy is nondecreasing.

Energy is conserved locally, and entropy increases globally, always. It is possible to violate the second law of thermodynamics in principle (though not in practice), but it is not possible to violate the first law (at least locally). I think you are confusing energy with exergy.

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Re: What if the second law was breakable?

Postby p1t1o » Fri Feb 22, 2019 1:40 pm UTC

elasto wrote:
So long as the total entropy of all of the dimensions/universes grows, our universe's entropy can go as low as you like.


Wait so the universe is not a closed system, but the "multiverse" is?

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Re: What if the second law was breakable?

Postby doogly » Fri Feb 22, 2019 2:07 pm UTC

p1t1o wrote:
elasto wrote:
So long as the total entropy of all of the dimensions/universes grows, our universe's entropy can go as low as you like.


Wait so the universe is not a closed system, but the "multiverse" is?

If you're into that kind of thing.
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Re: What if the second law was breakable?

Postby Eebster the Great » Fri Feb 22, 2019 2:22 pm UTC

A system that is not closed doesn't deserve to be called a universe.

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Re: What if the second law was breakable?

Postby p1t1o » Fri Feb 22, 2019 4:40 pm UTC

quantropy wrote:That's easy, we happen to live in one (http://www.preposterousuniverse.com/blo ... conserved/).


<reads>

Brain: Ooooooohhhh noooooooo


Well look here, SOMETHING has to be conserved.

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Re: What if the second law was breakable?

Postby doogly » Fri Feb 22, 2019 4:53 pm UTC

Whoa, "observable universe" is totally a kind of universe and it's not closed.
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Re: What if the second law was breakable?

Postby Eebster the Great » Fri Feb 22, 2019 5:59 pm UTC

I disagree that the observable universe is a universe any more than an acting president is a president. It may be all we can I observe of the universe, and he may be acting as the president, but it's not the universe, and he's just a pretender.

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Re: What if the second law was breakable?

Postby ijuin » Fri Feb 22, 2019 6:09 pm UTC

p1t1o wrote:
quantropy wrote:That's easy, we happen to live in one (http://www.preposterousuniverse.com/blo ... conserved/).


<reads>

Brain: Ooooooohhhh noooooooo


Well look here, SOMETHING has to be conserved.


To give an analogy, quantum electrodynamics used to have electromagnetic charge as a conserved quantity, but then violations were observed and it was superseded by charge-parity, or CP conservation, in which certain combinations of charge and parity become the conserved quantities.

Likewise, we may be approaching a point in our understanding of physics in which the conservation of mass-energy is superseded by a more generalized underlying form of conservation.

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Re: What if the second law was breakable?

Postby Pfhorrest » Fri Feb 22, 2019 6:17 pm UTC

It occurs to me from this idea of dumping entropy into other "universes" (however applicable that term) that provided the universe (however defined) is infinite, in principle whatever finite subset of it we care about, however arbitrarily large, could be preserved against death by entropy indefinitely, because there's always somewhere else to dump the entropy from it.
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Re: What if the second law was breakable?

Postby doogly » Fri Feb 22, 2019 6:20 pm UTC

CP of course is also now known to be violated, you need CPT for the sweet goods. That one is less likely to slip away next, because you'd have to take Lorentz Invariance with it. Not impossible but we really really like both of them.
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Re: What if the second law was breakable?

Postby Heimhenge » Fri Feb 22, 2019 7:51 pm UTC

Eebster the Great wrote:Yeah, you can set up a system of particles to evolve into a lower entropy state. So if all possible initial conditions are real, then in some of them, entropy decreases. Like I said, it's a statistical law. But it is difficult to overstate just how unlikely this is, requiring the double exponential function to describe concisely.


Yep. That's what Loschmidt's paradox is all about.

https://en.wikipedia.org/wiki/Loschmidt%27s_paradox

In a nutshell, there's a finite (though vanishing small) probability that a cup of cold coffee will only be hit by the fastest particles in the air around it, and end up heating rather than cooling. But I don't think that's what the OP was asking about. What we're talking about here is a (potentially occurring) natural event totally allowed by the laws of physics. The OP was asking about "some experiment that discovers entropy reversal".

I suppose you could make it into an "experiment" by placing a cold cup of coffee (with temperature probe) in a room full of air. Then just watch the temperature monitor and wait for the coffee to get hot. :)

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Re: What if the second law was breakable?

Postby Pfhorrest » Fri Feb 22, 2019 8:30 pm UTC

Yeah, what I'm looking for is something along the lines of, say, finding that what's actually conserved in the universe is not energy, but free energy, and that as entropy increases anywhere (decreasing free energy), new free energy is created everywhere, and that new energy is what drives the metric expansion of space. So though for any finite closed system the entropy always goes up, the universe is constantly compensating for that with an influx of new energy... that could somehow in principle be harnessed to do more useful work, indefinitely. Maybe only by a ridiculously advanced civilization that can like, make cables spanning distant galaxies that get pulled by the expansion of spacetime in a way that useful energy can be extracted from them, or something.

I've no idea how plausible an idea like that could be, but it's a back-of-the-envelope kind of thing I'm looking for.
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Re: What if the second law was breakable?

Postby Eebster the Great » Sat Feb 23, 2019 2:42 pm UTC

A constant source of new free energy would violate the first law but not the second law, because as you said, entropy would still continue to increase. A constant source of free energy and a sink for energy should do the trick though, since you could just hook one end up to your refrigerator's power cord and position the other one to capture all the radiated heat in the back, giving you free cooling as desired.

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Re: What if the second law was breakable?

Postby solune » Wed Feb 27, 2019 1:48 pm UTC

Pfhorrest wrote:It occurs to me from this idea of dumping entropy into other "universes" (however applicable that term) that provided the universe (however defined) is infinite, in principle whatever finite subset of it we care about, however arbitrarily large, could be preserved against death by entropy indefinitely, because there's always somewhere else to dump the entropy from it.


Book spoiler
Spoiler:
I think you've just described the main plot point of Asimov's "The Gods Themselves"

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Re: What if the second law was breakable?

Postby elasto » Wed Feb 27, 2019 4:41 pm UTC

Solune: I absolutely loved that book! Must be 20 years since I read it though :/

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Re: What if the second law were breakable?

Postby doogly » Wed Feb 27, 2019 4:50 pm UTC

Also I have to fix the title, this has been bothering me a lot.
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Re: What if the second law was breakable?

Postby gmalivuk » Thu Feb 28, 2019 8:24 pm UTC

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Re: What if the second law was breakable?

Postby Quizatzhaderac » Fri Mar 01, 2019 10:58 pm UTC

Pfhorrest wrote:What would that experiment look like?
Two possible forums.

1) Magic. One says "Frigido" and waves a wand around, and the room gets colder. We could even keep the first law of thermodynamics by that also causing carbon dioxide and water in the air to form glucose. If a chemist actually saw this they would be very skeptical they really saw it and would look really hard for somewhere the entropy was going to, but it they could never postulate the location, the second law would need to e rewritten to say "except magic"

2) Dark matter. An experiment involving dark matter, or black holes, or PeV temperatures, or something that we just plain haven't been able to mess around with yet. We smash 2 regular iron nuclei together at 1 PeV and out comes one tellurium nucleus made out of top and bottom quarks; and let's say two photons to balance momentum and energy the rest of the way.
Eebster the Great wrote:he second law is, at its most fundamental, a purely statistical law.
That is incorrect. The second law is an empirical law that states "these statistical rules apply". There isn't (and cannot be) anything a priori that says the statistics must apply to the world.

For a simple example: Addition is on pretty solid mathematical footing, but that doesn't mean mean that 1 liter water + liter ethanol = 2L mixture, because conservation of volume isn't a thing and simple arithmetic doesn't apply.

A more direct example: In Conway's way of life in there is only one way the board can be empty, there are 2^(size/2) ways it can be 50% full, but the board is never going to evolved from 0 to 50%, and is likely to evolve from 0% to zero.
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Re: What if the second law was breakable?

Postby Eebster the Great » Sat Mar 02, 2019 5:25 am UTC

Quizatzhaderac wrote:That is incorrect. The second law is an empirical law that states "these statistical rules apply". There isn't (and cannot be) anything a priori that says the statistics must apply to the world.

Sort of. As I already pointed out, there is nothing making it impossible in principle for the world to be set up such that order evolves out of chaos naturally. It's just really unlikely that that is the case. From a naive perspective, it is just as unlikely that the laws of physics are such that this sort of thing happens as it is that it happens by chance. Things have to be very very specific in order for the second law to be violable, just as they have to be very specific for it to be violated.

Now, you can define a different entropy for every different macroscopic model. I suppose it is conceivable that if you picked an especially perverse set of variables, entropy would decrease, though that should only happen in a system that's not at equilibrium. In practice, the second law can be interpreted as saying that for any "good" macroscopic model, entropy will not decrease. This is more a function of the way we obtain information about large systems than anything fundamental to the laws of physics, i.e. it's more a question of epistemology. In a universe with different physical laws, we would also use different macroscopic descriptions. I don't think there is really any way around this.

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Re: What if the second law was breakable?

Postby Heimhenge » Sun Mar 03, 2019 12:53 am UTC

So would you say the 2nd Law is more like an "emergent property" than an actual "law" (like the 1st Law)?

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Re: What if the second law was breakable?

Postby Soupspoon » Sun Mar 03, 2019 1:20 am UTC

In some ways, I doubt any of the 'Laws' are truly what the cosmos sets itself the aim of adhering to, and that they're just what we see as emerging from the real GUT/TOE mechanism. But I don't imagine that any qualified modification of them would be totally different. Aiming much the same way as Newtonian physics has to be covered at extremes by both Relativity and Quantum Theory (remembering that we're still hunting for a good candidate successor to them that covers both their domains with another idea of What It's Reeaally All About).


So could we even be sure about where the 'emergent property' label, over at that end of hard physics?

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Re: What if the second law was breakable?

Postby Eebster the Great » Sun Mar 03, 2019 6:18 am UTC

The second law is easily laid bare. It's not like we discovered statistical mechanics first. We worked backwards from what we observed to determine a mathematical truth, which is very nice. Regardless of your ontology, it is a historical fact that the understanding of information theory came from thermodynamics rather than the other way around. I don't really expect that to happen very often, but it is a pretty persuasive argument in favor of a theory.

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Re: What if the second law was breakable?

Postby Quizatzhaderac » Mon Mar 04, 2019 5:40 pm UTC

Eebster the Great wrote:From a naive perspective, it is just as unlikely that the laws of physics are such that this sort of thing happens as it is that it happens by chance.
There's definitely truth to that, but there's two relevant issues:

First) The second law under classical thermodynamics definitions is (in principle) separable from the statistical mechanics definitions. For Pfhorrest's original question, I would consider any situation regularly breaking the classical law as valid example of the experiment he is seeking.

Furthermore, there actually is a situation where the two sets of definitions contradict: negative temperature. All things with "negative temperature" are (classically speaking) very hot things where incoming heat energy does the work of reducing entropy. But one doesn't even really need to understand those circumstances to see the contradiction, as (classically) negative temperature just means you haven't set your zero low enough.

In practice, the second law can be interpreted as saying that for any "good" macroscopic model, entropy will not decrease.
Second) That's an entirely reasonable point of view, but it now means that the definition of "Entropy" is not trivial for an arbitrary system where we understand all of it's parts (in the sense that integrating a million part polynomial equation is "trivial").

Going back to Conway's game of life, how would we define entropy? The most obvious way would be to look at the number of ways each density of the board can occur, but no all states are equal likely to evolve and some densities are systemically less likely to evolve (compare 0% and 100% densities, or 5/16ths and 11/16ths densities), one might attempt to weight the states according to how likely thy are to evolve, but that is impossible to do exactly on a infinite board (it's chaotic and Turing complete), and intractable on a finite board.
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Re: What if the second law was breakable?

Postby Heimhenge » Mon Mar 04, 2019 6:43 pm UTC

OK, how about this for an experiment. I think it meets the OP's original intent:

Take a perfectly sealed room full of air at "equilibrium" temperature (no convection). Position a slew of thermistors around the room at the same height. I'm guessing you'd need a precision of at least 0.1°C, maybe 0.01°C. You should see momentary excursions of temperature both above and below the average temperature. Basically the kinetic theory in action. Of course, the smaller the thermistors the better this would work.

Would that not suffice for an experiment demonstrating (at least local and temporary) violations of the 2nd Law?

Related question: Just how small can a thermistor get?

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Re: What if the second law was breakable?

Postby Pfhorrest » Mon Mar 04, 2019 6:54 pm UTC

I feel like I should clear up what my intent with the original question was, which I've since realized was badly worded.

The intended question was in essence "where might we possibly hope to find hope that the whole universe won't wind down to uniformly maximum entropy over a long enough time?"

An assumption built into how I actually asked the question was that any such hope would mean a repeatable, exploitable violation of the second law of thermodynamics: some way that some finite closed systems in some circumstances we have not yet observed could see their entropy decrease, in a way that could then be cleverly used to power a decrease in entropy elsewhere in the universe.

I've since realized that that assumption is false, and that infinities and non-closedness of the "universe" also offer potential answers to the real intended question, possibly allowing for some arbitrarily large finite part of the universe to be maintained against decay indefinitely, even while any completely closed portion of the universe would still decay to maximum entropy, and the infinite universe as a whole continues forever decaying toward maximal entropy.
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Re: What if the second law was breakable?

Postby Heimhenge » Mon Mar 04, 2019 7:12 pm UTC

Then the experiment I described in my previous post wouldn't scale up to what you were asking. Stray hydrogen atoms might randomly clump together to form a new star, but the time it would take for that to happen would be huge. Throw in the problem of proton decay, and I see no way entropy could be reduced over a significant portion of the cosmos ... or at least a large enough portion to make it useful for sentient beings.

Great question though. Made me think about things I hadn't since my thermo class.

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Re: What if the second law was breakable?

Postby Eebster the Great » Mon Mar 04, 2019 7:33 pm UTC

Quizatzhaderac wrote:First) The second law under classical thermodynamics definitions is (in principle) separable from the statistical mechanics definitions. For Pfhorrest's original question, I would consider any situation regularly breaking the classical law as valid example of the experiment he is seeking.

I agree with this, which is why I put in the caveat about the way we define a macrostate. The idea is that in a universe in which entropy, defined according to the same thermodynamic variables we use in our universe, can spontaneously decrease, a different definition of a macrostate would necessarily be used, since the variables that we use simply would not be macroscopic variables. I don't have a formal proof of this idea, but it seems at least intuitive. And it is a perspective in which it makes sense to say call the second law a mathematical one rather than a physical one.

Furthermore, there actually is a situation where the two sets of definitions contradict: negative temperature. All things with "negative temperature" are (classically speaking) very hot things where incoming heat energy does the work of reducing entropy. But one doesn't even really need to understand those circumstances to see the contradiction, as (classically) negative temperature just means you haven't set your zero low enough.

This is I think an example of a failure of the continuum limit. With enough available states, negative temperature is impossible. Though of course, the second law is observed in any case.

Going back to Conway's game of life, how would we define entropy? The most obvious way would be to look at the number of ways each density of the board can occur, but no all states are equal likely to evolve and some densities are systemically less likely to evolve (compare 0% and 100% densities, or 5/16ths and 11/16ths densities), one might attempt to weight the states according to how likely thy are to evolve, but that is impossible to do exactly on a infinite board (it's chaotic and Turing complete), and intractable on a finite board.

Isn't that a practical reality anyway? In most situations, we can estimate entropy by just looking at motional degrees of freedom, but sometimes we can't. There is a sense in which classical thermodynamics as a whole fails to explain the universe because the universe is not classical. And clearly the ground state is always the most probable state, even at high temperatures (though only marginally more probable than another randomly chosen microstate). So it seems like this is going to be a problem no matter what we do.

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Re: What if the second law was breakable?

Postby Quizatzhaderac » Mon Mar 04, 2019 10:32 pm UTC

Pfhorrest wrote:The intended question was in essence "where might we possibly hope to find hope that the whole universe won't wind down to uniformly maximum entropy over a long enough time?"
Both of my answers in my first post qualify, if we go further in assuming enoguh wizards or particle accelerators are recreating those exact scenarios.
Post by Eebster the Great wrote:since the variables that we use simply would not be macroscopic variables
While scientists have a tendency to define the the macro-states in terms of the micro-states, knowledge ultimately goes the other way: We know the macro system first, and we learn the micro system through careful analysis/ experimentation with the macro system. So when we find a disjoint between the two, we have to throw out the micro-system, not the macro-system. It's unlikely that statistical mechanics is wrong, it's much more ridiculous to say that classical thermodynamics is anything but close to right for common occurrences. (You put something in the oven to make it hotter? Don't you know they proved that's impossible?)
This is I think an example of a failure of the continuum limit.
I'm not sure what you mean by this. A object with negative temperature can be arbitrarily large.
Isn't that a practical reality anyway?
Not really, no. Naively counting motive degrees of freedom gets us to a good approximation; counting game of life microstates won't get you within an order of magnitude.
The thing about recursion problems is that they tend to contain other recursion problems.


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