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### Re: What if the second law was breakable?

Posted: Tue Mar 05, 2019 7:01 pm UTC
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?)

What are you talking about? On the one hand, you say we throw out the microstate, not the macrostate. On the other hand, you say that because of the UV catastrophe, classical thermodynamics is useless. I don't get it. Can you be more specific abut what you mean?

Classical thermodynamics actually does make extremely good predictions within its domain of validity. It's just that high frequency radiation isn't in that domain. It can still explain why your oven heats your food, and it can even do it to a high degree of accuracy, as long as you only integrate up through visible light.

As for "throwing out the microstate," well you don't know the microstate, so there is nothing to throw out. Microstates are not observable, only macrostates. My contention was that in a universe in which the set of variables we use to define our macrostate would result in a definition of entropy that could decrease, such a universe would not use our variables, because they would not define a macrostate according to subjective experience.

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.

But it cannot have arbitrarily many available energy levels. It is a fundamentally quantum phenomenon.

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 game of life is discrete and doesn't really have macrostates. It is also not random. Most states are impossible, at least after a single generation. But of the states that are possible, how do you know that at the largest scales they don't all seem essentially uniform and random? It is only when you look at the finer details of just exactly how all the persistent elements work together to maintain their shape that you can distinguish between one microstate and another.

### Re: What if the second law was breakable?

Posted: Tue Mar 05, 2019 9:44 pm UTC
Eebster the Great wrote:On the other hand, you say that because of the UV catastrophe, classical thermodynamics is useless.
I have not mentioned the UV catastrophe, or EM radiation. I said the classical and statistical thermodynamics aren't perfectly consistent, but I didn't say either was useless.

But it cannot have arbitrarily many available energy levels. It is a fundamentally quantum phenomenon.
Well, it can't have arbitrary small energy levels, but it can have arbitrarily many energy quanta. But let me back up, because I think we're talking past each other.

Under statistical mechanics, "temperature" is defined as the multiplicative inverse of the thermodynamic beta. The thermodynamic beta is the derivative of entropy with respect to heat. Both entropy and heat energy are extensive quantities, meaning a larger sample will have both more entropy and more heat energy.

Dealing with the "derivative" of discrete quantities can produce artifacts, but large values relative to the quanta tend to trivialize these artifacts; which is why I thought you were talking about the continuum limit. A sample with negative temperature can be arbitrarily large, and as such can have arbitrarily large values of entropy and heat, and therefore any quantization artifacts would be trivial in a large enough sample.

The game of life is discrete and doesn't really have macrostates. It is also not random. Most states are impossible, at least after a single generation.
I brought up the game of life precisely because it's not like the real world, but it is conceivable. Also a world where we see regular and frequent violations of the second law isn't like our world (as we understand it) .

I don't challenge the notion that, (among the infinite consistent ways to define "entropy") there probably exists one that works the way you say it should for the game of life; what I challenge is the ability to find it. Until we have that definition in hand, talking about the second law with respect to the game of life is meaningless since we don't know what entropy looks like.

Likewise with the real world, once we see we've made major mistakes with thermodynamics, it's in principle possible to redefine "entropy" so we have have a second law again. However, however until we have that new definition of "entropy" it's meaningless to talk about there being a second law.

### Re: What if the second law was breakable?

Posted: Wed Mar 06, 2019 3:22 am UTC
Eebster the Great wrote:On the other hand, you say that because of the UV catastrophe, classical thermodynamics is useless.
I have not mentioned the UV catastrophe, or EM radiation. I said the classical and statistical thermodynamics aren't perfectly consistent, but I didn't say either was useless.

You said that they proved it was impossible to heat something in an oven. If that isn't a reference to the UV catastrophe, what is it? Convective heating is perfectly well explained by classical thermodynamics.

Dealing with the "derivative" of discrete quantities can produce artifacts, but large values relative to the quanta tend to trivialize these artifacts; which is why I thought you were talking about the continuum limit. A sample with negative temperature can be arbitrarily large, and as such can have arbitrarily large values of entropy and heat, and therefore any quantization artifacts would be trivial in a large enough sample.

I don't see how this makes any sense. It can have arbitrarily large internal energy, but it can't have an arbitrarily high temperature. For a population inversion to occur, you need large gaps in energy quanta. It is impossible to explain classically. Your explanation sounds to my ears like saying that stimulated emission is a classical phenomenon because it can produce a powerful laser.

The game of life is discrete and doesn't really have macrostates. It is also not random. Most states are impossible, at least after a single generation.
I brought up the game of life precisely because it's not like the real world, but it is conceivable. Also a world where we see regular and frequent violations of the second law isn't like our world (as we understand it) .

I don't challenge the notion that, (among the infinite consistent ways to define "entropy") there probably exists one that works the way you say it should for the game of life; what I challenge is the ability to find it. Until we have that definition in hand, talking about the second law with respect to the game of life is meaningless since we don't know what entropy looks like.

Likewise with the real world, once we see we've made major mistakes with thermodynamics, it's in principle possible to redefine "entropy" so we have have a second law again. However, however until we have that new definition of "entropy" it's meaningless to talk about there being a second law.

A problem with this is that I'm trying to talk about what an observer within the universe would use to define a macrostate, which you can't really do with the game of life, among other reasons because it can't contain any observers. But in any case, you said yourself what the definition of entropy is, and pointed out that simply weighting the sum of all microstates by their probability is the obvious solution (and what is the correct equation that actually is used for statistical entropy). Your concern is that this would be hard to calculate in practice. And it is, in some universes. But I don't see the problem with this. Plenty of things are hard to calculate but easy to define.

### Re: What if the second law was breakable?

Posted: Thu Mar 07, 2019 2:53 pm UTC
What sort of matter would make up a universe of total entropy?

Presumably, there's no electro-magnetic activity of any kind? Just (statistically) undifferentiated mass?

Is such a universe consistent with an ever-expanding universe?

Is it consistent with a contracting one?

### Re: What if the second law was breakable?

Posted: Thu Mar 07, 2019 7:24 pm UTC
tomandlu wrote:What sort of matter would make up a universe of total entropy?
A little of everything, but mostly a lot of the simplest, lowest energy thing like photons and neutrinos.
Presumably, there's no electro-magnetic activity of any kind? Just (statistically) undifferentiated mass?
Electromagnetic activity of every kind, but overwhelming of the small kind, and an equal balance of "does x" and "does the opposite of x". Although an external macro-scale observer would almost certainly see nothing but an undifferentiated mass.
Is such a universe consistent with an ever-expanding universe?
Not quite. "Maximum entropy" changes with the geometry of the universe. Slowly and smoothly expanding a universe with maximum entropy will keep you pretty close to maximum entropy. A rapid increase in the universe's size will take it out of being at maximum entropy.
Is it consistent with a contracting one?
Same as above.

Eebster the Great wrote:You said that they proved it was impossible to heat something in an oven. If that isn't a reference to the UV catastrophe, what is it? Convective heating is perfectly well explained by classical thermodynamics.
I'm saying that any model of thermodynamics that does not allow heating an object in an oven should be rejected. Or more generally, any model that doesn't allow commonly observed macro scale phenomena should be rejected. Since classical thermodynamics does a good job of explaining commonly observed macro scale phenomena, the only acceptable micro-scale models are ones that predict similar things under common circumstances.

Going back a bit further in the conversation, you said "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 was saying that, just as we'd need to keep something roughly like classical thermodynamics, we'd need to keep something like the macro variables defined.

Since we're postulate some extraordinary evidence of something breaking the second law, our most detailed model (statistical mechanics) will need to be changed. If we're keeping the rough model, but changing the precise model, we can't guarantee aspects of the relationship between the detailed model and the rough model will survive.

I don't see how this makes any sense. It can have arbitrarily large internal energy, but it can't have an arbitrarily high temperature. For a population inversion to occur, you need large gaps in energy quanta. It is impossible to explain classically. Your explanation sounds to my ears like saying that stimulated emission is a classical phenomenon because it can produce a powerful laser.
Okay, I see where we went awry. I have exclusively been using "classical" to mean "classical thermodynamics" as opposed to "statistical thermodynamics", and have not been referring to anything to do with quantum mechanics. "Statistical thermodynamics" predates quantum mechanics, and as such can work in the classicalnon quantum limit.

Negative temperatures do require a finite range of allowed energy states (because they have to be above the middle, therefore the middle must exist), but the number of intermediate steps don't need to be finite. It just so happens that the steps are quantiziaed because quantum mechanics also happens to be true.

A problem with this is that I'm trying to talk about what an observer within the universe would use to define a macrostate, which you can't really do with the game of life, among other reasons because it can't contain any observers. But in any case, you said yourself what the definition of entropy is, and pointed out that simply weighting the sum of all microstates by their probability is the obvious solution (and what is the correct equation that actually is used for statistical entropy). Your concern is that this would be hard to calculate in practice. And it is, in some universes. But I don't see the problem with this. Plenty of things are hard to calculate but easy to define.
The game of life is Turing complete and can contain an observer.

Let me clarify about "hard to calculate but easy to define". I have not defined "entropy" in the game of life, I have provided the outline of an algorithm to find the definition. This algorithm is not merely "hard to calculate", is it (mathematically) impossible to calculate to exactly, and (computationally) impossible to calculate approximately. (This is because the basic actions of our universe are linear and the game of life isn't). Under such circumstances "entropy" describes nothing and the second law predicts nothing.

### Re: What if the second law was breakable?

Posted: Thu Mar 07, 2019 10:00 pm UTC
Quizatzhaderac wrote:Slowly and smoothly expanding a universe with maximum entropy will keep you pretty close to maximum entropy.

Close to, but not exactly at. Any expansion at all will pull the universe proportionally out of equilibrium, creating proportionally large energy gradients that can then cause useful work to be done. If you then have systems in that universe that exploit energy gradients to do the work of pumping entropy out of themselves -- which is how I would define "life" -- then in principle all you need is enough time (inversely proportional to the rate of expansion) to gradually build up and indefinitely maintain arbitrarily much low-entropy structure in that universe. And the more space you have roped into this life-process, the greater advantage you can take of the expansion of that space to power that life.

### Re: What if the second law was breakable?

Posted: Fri Mar 08, 2019 2:12 am UTC
It just occurred to me that there is a test, of sorts, of my earlier hypothesis(-ish) that perhaps the metric expansion of space is necessarily proportional to the increase in entropy of the universe, such that total universal entropy actually stays constant thanks to the decrease in entropy caused by the expansion of space exactly offsetting the otherwise-increasing entropy. I don't have enough information myself to check this, but maybe others here do. Basically I'm wondering if it's known, or could be reasonable to conclude, that the total entropy of the universe increased more rapidly at the start of time as we know it than it is increasing today, and if that early rapid increase in entropy (if that happened) would then coincide with the inflationary period (presuming that that happened too).

### Re: What if the second law was breakable?

Posted: Fri Mar 08, 2019 8:21 am UTC
Okay, I'm going to have to keep asking/saying stupid things...

Would the following statements be true? Presumably not, but why not?

1. Max entropy is not consistent with either an expanding or contracting universe, since both of those scenarios still contain useful energy
2. However, a static universe at max entropy would still be subject to its own mass, and would necessarily contract
3. Since a contracting universe is not at max entropy, max entropy is therefore not possible

Also, Quizatzhaderac said that a universe at max entropy would have "a little bit of everything", which implies atoms? Don't atoms still have useful energy?

### Re: What if the second law was breakable?

Posted: Fri Mar 08, 2019 7:28 pm UTC
So just as a caveat, I've been using a definition of entropy that works basically like "In the given space, configuration A of matter and energy has an entropy of x". Cosmologists are working on definitions that treat space as variable, and those might give different answers, bt I'll continue t give my answers because 1) I don't fully understand those 2) They're not (as far as I know) a settled matter and 3) THey still have to account for the details I'm talking about.
tomandlu wrote:Don't atoms still have useful energy?

Okay, so an analogy first. Pour a bunch of sand into a container and shake it around. You would expect it to be flat-ish, but not completely flat, yes? With a careful error you could make it perfectly flat, but you can only get perfect by trying for the specific perfect thing.

A system at maximum entropy is like that flat-ish sand. Energy is not perfectly even, but it is even-ish. The size and shape of the bumps follow a statistical distribution the basically comes out to probability = boring-ness. How this differs from intuition is that the math tells us that with a large enough bucket of sand, eventually a sand castle would likely be in the bucket.

So in a universe that is mostly plasma there would still have "bumps" in the form of atoms and chemicals.
Since a contracting universe is not at max entropy, max entropy is therefore not possible
Yes, unless maybe if one is using one of the new fancy cosmological definitions.
Pfhorrest wrote:...such that total universal entropy actually stays constant thanks to the decrease in entropy caused by the expansion of space exactly offsetting the otherwise-increasing entropy.
Interesting idea. First point of terminology: entropy isn't decreasing because the universe is expanding, the maximum possible entropy is increasing and the existent entropy is starting from the old max and increasing.

To articulate your idea, I'd define a cosmological variable: entropy of the observable universe/ maximum entropy for a fixed universe of those dimensions. Has this number remained constant? I have no idea, but it seems like something a team of PhDs could definitely figure out.

### Re: What if the second law were breakable?

Posted: Fri Mar 08, 2019 9:38 pm UTC
You definitely want an entropy density. A total entropy would require an integral that is not.

### Re: What if the second law was breakable?

Posted: Fri Mar 08, 2019 10:31 pm UTC
Pfhorrest wrote:Since a contracting universe is not at max entropy, max entropy is therefore not possible

that wasn't me

### Re: What if the second law was breakable?

Posted: Sat Mar 09, 2019 5:49 am UTC
[thanks for editing, I hadn't realized you'd even actually replied to me before]

Quizatzhaderac wrote:To articulate your idea, I'd define a cosmological variable: entropy of the observable universe/ maximum entropy for a fixed universe of those dimensions.

The number I'm really interested is sort of the inverse of that; I've heard terms like "negentropy" (ugh that's an awful word) and "extropy" and "free energy" used in a way that sounds like one of them might be the thing I'm actually interested in. A number that in a universe at maximal entropy would be zero, and that increases as universal entropy decreases.

### Re: What if the second law was breakable?

Posted: Sat Mar 09, 2019 9:58 am UTC
Drifting into the realms of SF here, but if we assume one intelligent species, wouldn't they keep reducing all matter to a state where no useful work remained in the universe?

### Re: What if the second law was breakable?

Posted: Sat Mar 09, 2019 6:43 pm UTC
That's precisely why it's important that there be some way to have an unending amount of useful work to do in the universe.

When I started this thread, I thought that that required some way for a closed system to go from a state of not being able to do any useful work, back to a state of being able to do useful work, and I was looking for where exactly we weren't absolutely 100% certain that that wouldn't happen.

I've since realized thanks to this thread that an infinite universe is effectively not a closed system for practical purposes (however big of a finite closed system you're concerned about preserving, there's always more beyond it that you can move on to burning through), and an expanding universe is explicitly not a closed system.

### Re: What if the second law was breakable?

Posted: Sat Mar 09, 2019 6:52 pm UTC
tomandlu wrote:Drifting into the realms of SF here, but if we assume one intelligent species, wouldn't they keep reducing all matter to a state where no useful work remained in the universe?

Given sufficient time, yes. However, the necessary span of time may be long enough for most stars to die of old age in the meantime.

### Re: What if the second law was breakable?

Posted: Mon Mar 11, 2019 11:35 am UTC
ijuin wrote:
tomandlu wrote:Drifting into the realms of SF here, but if we assume one intelligent species, wouldn't they keep reducing all matter to a state where no useful work remained in the universe?

Given sufficient time, yes. However, the necessary span of time may be long enough for most stars to die of old age in the meantime.

Would the death of all stars stop them?

If we assumed that this species kept extracting any available energy until there was nothing to extract, what would the final composition of the universe be?

### Re: What if the second law was breakable?

Posted: Mon Mar 11, 2019 12:00 pm UTC
Some tricky wording being thrown around - To be clear, all of the stars have to die in order to reduce all matter to a state where no more work can be done.

So the question of whether or not the death of the stars could stop them is moot.

The aliens themselves have to die too.

The final composition of the universe, if it went ahead, depends on whether or not protons decay. If they dont, then 100% protons is the final recipe I think, IIRC. If they do, its what ever they decay into.

### Re: What if the second law was breakable?

Posted: Mon Mar 11, 2019 1:08 pm UTC
p1t1o wrote:Some tricky wording being thrown around - To be clear, all of the stars have to die in order to reduce all matter to a state where no more work can be done.

So the question of whether or not the death of the stars could stop them is moot.

The aliens themselves have to die too.

The final composition of the universe, if it went ahead, depends on whether or not protons decay. If they dont, then 100% protons is the final recipe I think, IIRC. If they do, its what ever they decay into.

Yes - I thought that the implication was that the aliens couldn't go on extracting energy after the stars died - not that stars dying marks max entropy.

### Re: What if the second law was breakable?

Posted: Mon Mar 11, 2019 1:12 pm UTC
Well, my point was that, even if there was a Kardashev Type IV civilization out there already disassembling things now, it would still take them much longer than the current age of the universe before they would be finished.

### Re: What if the second law was breakable?

Posted: Mon Mar 11, 2019 4:50 pm UTC
ijuin wrote:Well, my point was that, even if there was a Kardashev Type IV civilization out there already disassembling things now, it would still take them much longer than the current age of the universe before they would be finished.

Agreed.
But I still jar at the language.
If there is anyone left to be aware, then you cant be finished.
In fact awareness will not be possible long before the finish, so nobody could survive to the end.
So "how long it takes someone to do this" is a weird question.
Tying deliberate action to the heat death of the universe feels like nails on a chalkboard to my brain.

### Re: What if the second law was breakable?

Posted: Mon Mar 11, 2019 9:33 pm UTC
Even if protons don't decay, a bunch of protons doesn't seem like an accurate description of the end state of universal heat death, because black holes are a thing, and will gobble up those protons in due time, and then slowly, slowly, slowly transform into photons via Hawking radiation over unimaginable lengths of time. A sea of photons is more like it.

Also, even if protons do decay, the date that all the currently existing protons will have most likely decayed doesn't have to mark any special occasion, since surely with enough energy at our disposal, we can keep making new protons as needed.

So really all that matters is that there be an unending supply of usable energy. Even a trickle of it. Which an expanding universe gives us. The rest is just engineering, and patience.

### Re: What if the second law was breakable?

Posted: Tue Mar 12, 2019 2:56 am UTC
Nickel-62 has the most binding energy per nucleon, so if your future species can somehow get all the nuclei to fuse or fission into those, they could probably extract a little more energy than the expected process of iron star formation I think. (Assuming protons do not decay.)

### Re: What if the second law was breakable?

Posted: Tue Mar 12, 2019 2:22 pm UTC
Pfhorrest wrote:So really all that matters is that there be an unending supply of usable energy. Even a trickle of it. Which an expanding universe gives us. The rest is just engineering, and patience.

I have recently heard of the expansion of space "violating" conservation of energy (or it may just come from somewhere else, but still).

But is it really *usable*?

Does the expansion of space also alter entropy?

If space expanding marks an increase in energy, is it not balanced by the seperation of particles spontaneously increasing?

I dunno, I still feel like we live in a universe of finite resource and even if expansion provide a source of energy, that still has to come from somewhere. Infinite energy still makes no sense to me - especially using the expansion of the universe to halt/reverse heat-death.

### Re: What if the second law was breakable?

Posted: Tue Mar 12, 2019 5:38 pm UTC
As we've been discussing upthread, the expansion of space reduces the... apparently not "total entropy", but "ratio of current entropy to maximum entropy", or something to that effect, creating room for entropy to fall further than it could have before, and so useful work to be done along the way. Small but transient energy gradients constantly exist all over the place in a state of maximal entropy, but if you blow up all of space, you blow up those energy gradients too, and then as those gradients collapse back to equilibrium, useful work can be done. The faster your space is expanding, the greater the effect, but even a little bit of expansion creates some continuous potential for doing some kind of useful work.

For a simplified illustration, picture an image of old TV static "snow", which is a high-entropy image, and then enlarge it to the point that what had been four pixels now fills the whole screen. Instead of a uniform rough grey-white picture, you've probably now got a picture where one side of the screen is noticeable lighter than the other, which is low-entropy.

### Re: What if the second law was breakable?

Posted: Wed Mar 13, 2019 9:44 am UTC
So what impact does that have on the contraction of space?

Im not sure what the current state-of-the-art is, whether a "big crunch" has now been ruled out, but would it have the reverse effect? Would it suck energy out of systems? I cant quite get my imagination to work.

### Re: What if the second law was breakable?

Posted: Wed Mar 13, 2019 6:42 pm UTC
Reducing space would also reduce the energy of the universe, the same way as reducing the hieght of the ball from the ground reduces i's potential energy.

It would destroy entropy because a lot of things that were in one of n locations would now be in one of n/2 locations. How this works with quantum affects is unknown to be, and I suspect unknown to physicists with any certainty.

Negentropy would be created. Imagine each of the sets of particle fields as bucket somewhat filled with energy: a photon bucket, an electron bucket, a neutrino bucket and a quark bucket. As we change the width of space, the width of the buckets changes unequally, as such the height of energy in each bucket changes unequally; this enables work to be done as energy can flow of buckets of lower energy.

### Re: What if the second law was breakable?

Posted: Thu Mar 14, 2019 8:46 am UTC
It sounds as though you could get a nice SF story about intelligent races struggling to extract enough energy to keep going at the end of the universe, seeking out the boundaries and resources, and scavenging each other.

Not a million miles, I suppose, from the end of the cities in flight stories.

### Re: What if the second law was breakable?

Posted: Thu Mar 14, 2019 10:00 am UTC
tomandlu wrote:It sounds as though you could get a nice SF story about intelligent races struggling to extract enough energy to keep going at the end of the universe, seeking out the boundaries and resources, and scavenging each other.

Not a million miles, I suppose, from the end of the cities in flight stories.

"The Last Question" by Isaac Asimov

### Re: What if the second law was breakable?

Posted: Thu Mar 14, 2019 1:04 pm UTC
For a more combative story*, there was an old, wishy-washy sci-fi story I recall merely the broad plot of where rival planet-bound nations/groups on Earth engaged in the ultimate Cold War, delving deep into the Earth's mass to extract from increasingly rarified and cooled hot spots discoverable within the largely extinct core (including heat-pumping away from their adversary's installations, as a 'cold strike') in an attempt to survive and 'dominate' against the whims of their counterparts and/or whatever disaster and end-of-times may have forced them to do this thing.

Spoiler-alert: Somehow they were so good/desperate at this that they end up taking the temperature down to a negative absolute temperature (it was not Hard SF, probably more a pulp/Amazing Stories kind of writing, I'm guessing it was '60s or earlier in origin) which stopped being life-threatening to the main protagonists of the tale (having survived the low-absolute temperatures somehow!) and may have conferred immortality in the process, if that wasn't a different story altogether, by dint of now having all temperature vibrations vibrating backwards.

Yeah, negentropy is the least of the issues with that model of physics.

* Throughout Asimov's essentially ur-story, it all seems to be considerably egalitarian. Neither the forward-looking pioneers of various kinds nor the hold-outs who seem to be late-adopters at each development/exploration/ascension look unkindly upon their counterparts.

Conflict has largely been avoided (at least for the snapshot periods depicted, whatever hints there are about the intervening times) and obviously destruction and (avoidable) death would act against the concept of concentrating usefully packaged information into furthering The Last Answer.

### Re: What if the second law was breakable?

Posted: Thu Mar 14, 2019 10:56 pm UTC
I have been brainstorming ideas recently for a short story about a child prodigy genius who at a very young age, while voraciously devouring encyclopedias and such, realizes just how many existential threats to his life, human life, and life generally there are, and dedicates himself wholeheartedly to the task of averting them. All of them. Preserving all life forever. Starting with creating a self-improving friendly general AI, because he realizes no human, even himself, is smart enough to solve all of that fast enough; ending unfathomably far in the future with the creation of a massive construct made of everything in, and spanning the size of, the observable universe, a kind of pantheistic-god machine, that harnesses the metric expansion of space and uses it to preserve everything that was of interest (like human life) in the universe that it was built out of, forever.

I'm tentatively titling it "...And The Pale Horse You Rode In On!"

### Re: What if the second law was breakable?

Posted: Fri Mar 15, 2019 10:39 am UTC
Pfhorrest wrote:I have been brainstorming ideas recently for a short story about a child prodigy genius who at a very young age, while voraciously devouring encyclopedias and such, realizes just how many existential threats to his life, human life, and life generally there are, and dedicates himself wholeheartedly to the task of averting them. All of them. Preserving all life forever. Starting with creating a self-improving friendly general AI, because he realizes no human, even himself, is smart enough to solve all of that fast enough; ending unfathomably far in the future with the creation of a massive construct made of everything in, and spanning the size of, the observable universe, a kind of pantheistic-god machine, that harnesses the metric expansion of space and uses it to preserve everything that was of interest (like human life) in the universe that it was built out of, forever.

I'm tentatively titling it "...And The Pale Horse You Rode In On!"

Sounds very interesting, I like it. Reminds me of the "BLAME" manga.

**
Anyone read any of the "Revelation Space" series?
In it it has a concept called a "cryo-arithmatic engine". In their universe someone discovers an obscure and esoteric set of mathematic operations, which if performed, through some strange twist of quantum mechanics and information theory (so it goes....not hard sci-fi either) results in a net loss of energy. So a supercomputer running these calculations endlessly "destroys" heat (for various uses, mainly stealth-in-space).

A fun concept I thought.

### Re: What if the second law was breakable?

Posted: Sat Mar 16, 2019 5:08 pm UTC
My understanding of entropy currently derives from five concepts: Non-cyclic time, physics in which the universe's next state can be determined by its current state, the pigeonhole principle, entropy as information, and the Bekenstein Bound. To start off, let's say time is linear rather than cyclic: If it was the latter, I presume breaking out of that cycle would be at least as much a concern as defeating entropy, for comparable reasons. So, the universe at each time-step is going to have some kind of state, and one that's not identical to that of the universe at a previous time-step. Via the pigeonhole principle, we can tell that infinite time steps occurring without re-using a universe state requires infinite universe states.

These states need to be distinguished in some way: At the very least, they need to be counted, so at this point we know that the information content (which I'm taking as also being the entropy content) of the universe must at the very least be allowed to grow logarithmically, so as to contain the value of the number denoting which time-step the universe is currently at. Not sure why entropy growth is faster than that, but I don't see how it really changes the big picture view of what we're dealing with. Then, with the Bekenstein Bound, we have the entropy of the universe being proportional to the magnitude of the spatial dimensions times the mass/energy within that space. So really, it looks like the second law isn't necessarily the problem at all, but the first: Energy density as a constant would be much more suitable for maintaining habitability to known life than total energy.

Now, my first thought here might be to consider ways that we could get around this by looking for a situation where the only way to conserve the first law of thermodynamics would be to break the second. However, it seems that the expansion of space over time can itself disregard conservation of energy, for instance by stretching out electromagnetic waves. As an aside, this could itself drive further expansion of space: As energy is lost due to space's expansion, even more space must emerge just to stop entropy from decreasing as a result. Anyway, if there was a way to create energy via space expansion, maybe via large devices that somehow harness the acceleration of themselves away from each other due to space expansion to split quark pairs and thus produce more quarks, then we can maintain energy density. If not, we might need to instead continually adapt by observing what types of physical patterns will persist into the future and re-encoding our physical forms in terms of those patterns.

### Re: What if the second law was breakable?

Posted: Mon May 20, 2019 11:02 pm UTC
ijuin wrote: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.

That's not true.

Electric charge most certainly is conserved in QED.

The "C" in CP does not mean electric charge. It means "charge conjugation" which is something completely different: C-symmetry means that replacing every particle with its anti-particle in a valid physical process, will yield an equally valid process.

For example, a neutron decays to a proton, an electron and a right-handed anti-neutrino.

If C were conserved, an anti-neutron would decay to an anti-proton, anti-electron and a right-handed neutrino. But there's no such thing as a right-handed neutrino, so neutron decay violates C-symmetry. The net electric charge, of course, did not change. These are two completely different quantum numbers.

### Re: What if the second law was breakable?

Posted: Tue Jun 25, 2019 4:31 pm UTC
Perhaps there is a chance that as the universe approaches absolute zero, some sort of symmetry break will occur.