How Does the Universe Use Temperature Differences to Create Structures?

[techmologist]

The main result of thermodynamics is that if you have a place that is hot and another place that is colder, you can operate a heat engine by absorbing heat from the hot place and dumping it in the cold place, extracting some useful work in the process. It gives you a way to calculate the maximum possible useful work per unit heat absorbed from the hot source.

Thermodynamics doesn't seem to care whether you actually do extract some useful work from the tendency of heat to flow from hot to cold. It allows for maximally irreversible processes, such as the free expansion of a perfect gas. If you start with a gas initially confined to one half of a container, and then remove the partition, it fills the whole container without doing any work. That is a squandered opportunity to extract work that the universe will never get back.

So how is it that the universe actually does use temperature differences, voltages, chemical potential gradients, and so on to do work--to create structures? What stops the universe from being maximally wasteful, letting all differences simply smear out, without generating any structures along the way?

 

[PeterDonis]

to do work--to create structures?

You're assuming that creating structures requires doing work. In the presences of gravity, that's not actually the case. The structure in our current universe--i.e., the fact that the matter is not all spread out evenly, but clumped into planets, stars, etc.--happened without requiring any work to be done, just as a result of gravitational clumping.

 

[Drakkith]

So how is it that the universe actually does use temperature differences, voltages, chemical potential gradients, and so on to do work--to create structures? What stops the universe from being maximally wasteful, letting all differences simply smear out, without generating any structures along the way?

This 'smeared out' state existed in the very early universe. It turns out that this is actually a high potential energy situation, and that the formation of structures is more favorable than no structures since it is a lower energy state.

 

[Garth]

What stops the universe from being maximally wasteful, letting all differences simply smear out, without generating any structures along the way?

One word, 'gravity'.

The effect of an attractive gravitational force is not used in your example of removing the partition in the half-filled container.

Garth

 

[Jimster41]

You're assuming that creating structures requires doing work. In the presences of gravity, that's not actually the case. The structure in our current universe--i.e., the fact that the matter is not all spread out evenly, but clumped into planets, stars, etc.--happened without requiring any work to be done, just as a result of gravitational clumping.

This 'smeared out' state existed in the very early universe. It turns out that this is actually a high potential energy situation, and that the formation of structures is more favorable than no structures since it is a lower energy state.

Are these responses in agreement? Also I'm confused by the statement that large scale structure due to gravitational clumping, is created without work being done?

 

[Jimster41]

@techmologist

That's a great question...

I think it's correct to identify a heat engine is an example of a "dissipative structure"

Check out this Nobel Prize winner, who coined that phrase.

http://en.m.wikipedia.org/wiki/Ilya_Prigogine

 

[Jimster41]

What's even more bizzare, if you narrowly define "heat engine" as a literal engine, like a reciprocating combustion engine, or combustion turbine, or a boiler+condensing steam turbine, you are talking about dissipative structures that have been intentionally created by other dissipative structures.

 

[ChrisVer]

If the matter was evenly distributed at the beginning, then our universe would be a cloud of dust.
It's the fact that the matter densities showed some perturbations that led to the creation of structure. The more dense areas became gravitational sources, and your initial soup started collapsing here and there.
Those perturbations are actually measured in the CMB spectrum. One reasonable answer for their existence is these perturbations is the quantum fluctuations that were stretched to large distances during inflation.

Then every "heating machine" is due to gravity.

 

[Jimster41]

I agree, I think with other statements, that the existence of the energy flow that "dissipative structures" dissipate is due to the low probability even mass distribution that characterizes early space-time, a situation far from equilibrium w/respect to gravity.

 

[techmologist]

Thanks for all the replies :)

Yes, I'm taking for granted the equivalence of work and structure. Or at least their inter-convertibility. Where there's smoke, there's fire. In fact I think I want to use the word "structure" very broadly, even for the temperature differences and potential differences themselves. In a reversible universe, the total amount of structure in the universe is conserved. When there are temperature differences, heat energy stored at the higher temperature has more structure than the same amount of energy at the lower temperature. So when you move energy from high temperature to low temperature in a reversible way, destroying some structure, you must be creating it somewhere else, say by lifting a weight. And then that weight can be used in turn to drive a refrigerator that pumps the heat at low temperature back up to a higher temperature. The conversion factor between the amounts of energy (heat vs work) is the Carnot efficiency.

But the universe isn't reversible. Structure is being frittered away constantly. I'm guessing this is fundamentally because the number of particles in the universe is not constant. By certain processes that I don't completely understand yet, a yellow photon can get converted into several infrared photons (without doing any work?), but the reverse doesn't happen spontaneously.

So that's why I was saying that it's not obvious why everything doesn't just smear out and wind down uniformly with nothing interesting along the way, since irreversibility doesn't seem to have any limits. If a process can generate work or structure but doesn't have to, why should it?

But yeah, you guys are right gravity has got to be a key ingredient. That makes sense now. It pulls matter together, the kinetic energy gets converted into thermal energy, the thermal energy gets radiated away into outer space and the matter settles into a clump. Structure, in the form of gravitational potential energy, has been converted into heat and radiation. But in the process matter becomes concentrated into local clumps.

I'm still not 100% convinced that having matter in clumps already represents structure. It 'looks' more structured because I'm used to thinking in terms of diffusion, smearing out, uniformity as a lack of structure. But with the attractive force of gravity it's the other way. This is what Drakkith and others are getting at.

But real structure is generated in the process of this clumping. You lose the gravitational potential but gain some temperature differences in return. Then somehow these temperature differences can be tapped into to generate other structures. Maybe I'm starting to get it, talking it out.

 

[techmologist]

What's even more bizzare, if you narrowly define "heat engine" as a literal engine, like a reciprocating combustion engine, or combustion turbine, or a boiler+condensing steam turbine, you are talking about dissipative structures that have been intentionally created by other dissipative structures.

That is exactly what I'm interested in. I am interested in organization at all levels. It is as if humans have domesticated the heat engine in much the same way that they have domesticated plants and animals. And domestication generally works both ways. It is mutual adaptation in disguise. Sheep, orange trees, and car engines have cleverly outsourced most or all of their maintenance to us by being useful. Sneaky.

Thanks for the Prigogine link, too. The library has some of his books. They have been added to the "need to read" list.

 

[PeterDonis]

Structure, in the form of gravitational potential energy

This looks to me like a very non-standard usage of the term "structure". What exactly do you mean by "structure"?

 

[Jimster41]

That is exactly what I'm interested in. I am interested in organization at all levels. It is as if humans have domesticated the heat engine in much the same way that they have domesticated plants and animals. And domestication generally works both ways. It is mutual adaptation in disguise. Sheep, orange trees, and car engines have cleverly outsourced most or all of their maintenance to us by being useful. Sneaky.

Thanks for the Prigogine link, too. The library has some of his books. They have been added to the "need to read" list.

You might be interested in this also.
http://en.m.wikipedia.org/wiki/Coevolution

 

[Jimster41]

This looks to me like a very non-standard usage of the term "structure". What exactly do you mean by "structure"?

I agree with PeterDonis that terms need to be precise. He is pretty expert in General Relativity, the technical theory of Gravity... So throwing around technical terms like Gravitational Potential Energy along with vagaries like "structure", can get you educated in a hurry on this forum! That said, I took your loose association to be referencing the the link below, as well as other posts.

http://map.gsfc.nasa.gov/universe/bb_cosmo_struct.html

 

[techmologist]

This looks to me like a very non-standard usage of the term "structure". What exactly do you mean by "structure"?

Fair enough. I'm sure it isn't standard. I needed a term that encompasses mechanical energy and everything that can be converted into mechanical energy. Gravitational potential would be structure, the way I'm using the term. So structure is in units of energy. But I wanted to take account of the fact that only part of 1 joule worth thermal energy at some temperature is convertible into work unless you have a sink at absolute zero. So that 1 joule of thermal energy is, in some sense, not a full joule of structure. You always have to deal with the 3K cosmic background, at the very least. Usually your cold sink is much hotter than that.

I am trying to stretch the heat engine concept as far as possible without it breaking. I have this impression that Darwin's natural selection mechanism is a sort of very generalized heat engine. Mutation and recombination vaguely resembles the power stroke, while natural selection resembles the exhaust stroke. Instead of turning a shaft, the engine sifts out populations of adapted genomes. These genomes and their associated organisms would be examples of what I'm calling structure. As Jimster41 pointed out, these organisms are themselves dissipative structures, which seems to be a generalization of the heat engine concept. So there are heat engines within heat engines. Admittedly this is all pretty vague, I get a kick out of thinking about it.

Does anyone know of a treatment of Benard convection cells that takes account of the thermodynamics of it? Surely each little parcel of water in the pan is acting as a tiny heat engine, doing work on its neighbors. The whole convection cell seems to be a heat engine, all of whose work output goes back into maintaining the cell. This is much different than the case of a man-made engine. We would never put up with an engine that only did enough work to keep itself together and running :).

 

[rootone]

This is much different than the case of a man-made engine. We would never put up with an engine that only did enough work to keep itself together and running :).

My fridge does that and I put up with it.

 

[PeterDonis]

I needed a term that encompasses mechanical energy and everything that can be converted into mechanical energy.

But that isn't the way you were using "structure" in your OP. There you used it to denote things that (you claimed) required work to be done to create them. Now you're using "structure" to denote the source of the work (mechanical energy) instead of the product (according to your claim) of the work. Which is it?

I am trying to stretch the heat engine concept as far as possible without it breaking.

As I noted in post #2, your original assumption, that the things you were calling "structure" in your OP required work to produce them, is false. Gravitational clumping is not a "heat engine" in any useful sense that I can see.

I have this impression that Darwin's natural selection mechanism is a sort of very generalized heat engine.

I think there is a sense in which it is, but discussing that is getting way off topic for this forum and you should open a separate thread in the appropriate forum if you want to talk about it.

These genomes and their associated organisms would be examples of what I'm calling structure.

Now you're reverting to the meaning of "structure" that you used in your OP--"structure" is the product of some "heat engine-like" process. But that's certainly not the same as "mechanical energy and everything that can be converted into mechanical energy".

Does anyone know of a treatment of Benard convection cells that takes account of the thermodynamics of it?

Same comment here as above--this is off topic for this forum and you should open a separate thread in the appropriate forum if you want to talk about it.

 

[Jimster41]

@techmologist
You would love this guy from Harvard University. I am just in a chapter on Benard Cells/structures and their role in self organizing systems.
https://www.amazon.com/dp/0674009878/?tag=pfamazon01-20

Arxiv.org. Is a library of current research going on in lots of places. There are lots on Benard cells there. They have been around a long time.

 

[Jimster41]

But that isn't the way you were using "structure" in your OP. There you used it to denote things that (you claimed) required work to be done to create them. Now you're using "structure" to denote the source of the work (mechanical energy) instead of the product (according to your claim) of the work. Which is it?
As I noted in post #2, your original assumption, that the things you were calling "structure" in your OP required work to produce them, is false. Gravitational clumping is not a "heat engine" in any useful sense that I can see.
I think there is a sense in which it is, but discussing that is getting way off topic for this forum and you should open a separate thread in the appropriate forum if you want to talk about it.
Now you're reverting to the meaning of "structure" that you used in your OP--"structure" is the product of some "heat engine-like" process. But that's certainly not the same as "mechanical energy and everything that can be converted into mechanical energy".
Same comment here as above--this is off topic for this forum and you should open a separate thread in the appropriate forum if you want to talk about it.

My understanding of the proposed cosmological theories being discussed is that Gravitational clumping, releases energy through fusion, in clumps called stars, providing the free energy that drives a whole variety of systems away from thermodynamic equilibrium, causing them to self organize to states of lower entropy, more complex structure: Life on this planet, and the planets themselves being examples.

@techmologist we can take this offline if you want, if it is considered inappropriate content... somehow.

 

[Jimster41]

In support of the mission of this forum, which seems to be to make the conversations as serious as possible. I've been searching for specific research into the detailed theoretical understanding of the principles invoked in the broader, more holistic, descriptions (that I'm familiar with), referred to here in this thread in very general and vague terms. I think it's arguably a stretch to consider this about cosmology, but I would lobby that it is, in that it is research into the theory of thermodynamics in the non-equilibrium case - relevant to the vague phenomenon of "self organization" and "dissipative structure" - which are main tenets of "Evolutionary" Cosmology.

I believe the journal is a reputable one. It's a pretty hard core paper and not very accessible to the lay person. But it's worth exposing oneself to the introduction and conclusion if nothing else, since they provide tantalizing hints of just what the heck the hard part is saying. I hope that it is not a breach of copyright protocol to link to the paper this way, showing only the abstract.

Stochastic thermodynamics, fluctuation theorems and molecular machines
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Udo Seifert

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Udo Seifert 2012 Rep. Prog. Phys. 75 126001
doi:10.1088/0034-4885/75/12/126001

© 2012 IOP Publishing Ltd
Received 18 May 2012, in final form 6 August 2012
Published 20 November 2012

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  AbstractThis article was invited by Erwin Frey.
  Stochastic thermodynamics as reviewed here systematically provides a framework for extending the notions of classical thermodynamics such as work, heat and entropy production to the level of individual trajectories of well-defined non-equilibrium ensembles. It applies whenever a non-equilibrium process is still coupled to one (or several) heat bath(s) of constant temperature. Paradigmatic systems are single colloidal particles in time-dependent laser traps, polymers in external flow, enzymes and molecular motors in single molecule assays, small biochemical networks and thermoelectric devices involving single electron transport. For such systems, a first-law like energy balance can be identified along fluctuating trajectories. For a basic Markovian dynamics implemented either on the continuum level with Langevin equations or on a discrete set of states as a master equation, thermodynamic consistency imposes a local-detailed balance constraint on noise and rates, respectively. Various integral and detailed fluctuation theorems, which are derived here in a unifying approach from one master theorem, constrain the probability distributions for work, heat and entropy production depending on the nature of the system and the choice of non-equilibrium conditions. For non-equilibrium steady states, particularly strong results hold like a generalized fluctuation–dissipation theorem involving entropy production. Ramifications and applications of these concepts include optimal driving between specified states in finite time, the role of measurement-based feedback processes and the relation between dissipation and irreversibility. Efficiency and, in particular, efficiency at maximum power can be discussed systematically beyond the linear response regime for two classes of molecular machines, isothermal ones such as molecular motors, and heat engines such as thermoelectric devices, using a common framework based on a cycle decomposition of entropy production.

 

[PeterDonis]

Gravitational clumping, releases energy through fusion, in clumps called stars

I wouldn't say that energy released by stars through fusion is due to "gravitational clumping"; a star is not converting gravitational potential energy into heat that gets radiated away. It is converting the rest mass of its fuel into heat that gets radiated away. The process of forming the star, before fusion reactions turn on, releases energy through gravitational clumping, yes. But if fusion never turns on (as with a planet, as opposed to a star), gravitational clumping can only release significant energy on a fairly short time scale, cosmologically speaking; after that, everything is clumped as much as it can be.

providing the free energy that drives a whole variety of systems away from thermodynamic equilibrium, causing them to self organize to states of lower entropy, more complex structure: Life on this planet, and the planets themselves being examples.

I don't see how a planet, by itself, in the absence of life, is an example of a "self-organizing system". It's true that a planet is not a configuration of "maximal" entropy--that would be a black hole of the same mass. But that just means a planet is a "meta-stable" state. It doesn't mean the planet itself needs a constant input of free energy to stay the way it is, as a living organism does. A planet isolated from a star, out in deep space by itself, would stay the way it is just fine; it would slowly radiate heat until it was in thermal equilibrium with the CMBR (which, in the absence of a star, would take only a few million years at most), and that's it.

Also, it's worth noting that you are using "structure" in the OP's original sense, to denote the products of a process that releases free energy, not the source of the free energy.

 

[Jimster41]

@PeterDonis Thanks for that reply. Food for thought.

When you say that "converting rest mass of it's fuel into heat that gets radiated away". Is it incorrect to say that gravitational force is responsible for the "rest mass" of that Hydrogen atom that is getting fused into helium and releasing energy? Also, would fusion ever occur without gravitational clumping?

The point you make about a planet is a good one. Your comment makes me wonder about some stuff I saw in that paper and some others, just this morning, referring to "deposits", or "development of concentrations" as part of the non-equilibrium steady state development process.

But mostly I think it invokes a theme that I have run into a number of times in trying to understand what researchers are learning about emergence and self-organization, which is the idea of there being two very different domains of behavior for non-equilibrium systems. One domain is continuous and deterministic. Over this domain dissipation occurs continuously even under an increasing dis-equilibrium (or gradient). But this domain is "puncuated" by bifurcations, or leaps of the system at "critical points" from less to more stable configuration. During those sudden events the system evolution is non-linear, stochastic. Discrete scale in-variance is a term that has come up often in stuff I've read, describing how these non-linear critical points are distributed.

My guess is that the proponents of these somewhat radical ideas would say that the the solar system formed relatively "suddenly" out of the stable but accreting planetary disk when fusion started, or some other ramp in the system gradient reached a critical point (I don't know much about planetary evolution per-se), and that this non-linear processes then "stranded" the mass of the planetary bodies in a lower entropy configuration than it would have been otherwise, and that this process is not smoothly reversible, even if the forcing function goes away.

- kind of like the housing market. This was a really good book related to this stuff. Sornette is a geo-physicist who applied the same tools of complex non-equilibrium systems used in study of earthquakes, to economic systems. Pretty spooky.

https://www.amazon.com/dp/0691118507/?tag=pfamazon01-20

 

[PeterDonis]

Is it incorrect to say that gravitational force is responsible for the "rest mass" of that Hydrogen atom that is getting fused into helium and releasing energy?

Yes.

would fusion ever occur without gravitational clumping?

If we ever figure out how to build a fusion reactor, yes. Astronomically speaking, it would have occurred in the very early universe, when the density and temperature was high enough; but since then, no, not without gravitational clumping.

 

[techmologist]

But that isn't the way you were using "structure" in your OP. There you used it to denote things that (you claimed) required work to be done to create them. Now you're using "structure" to denote the source of the work (mechanical energy) instead of the product (according to your claim) of the work. Which is it?
As I noted in post #2, your original assumption, that the things you were calling "structure" in your OP required work to produce them, is false. Gravitational clumping is not a "heat engine" in any useful sense that I can see.
I think there is a sense in which it is, but discussing that is getting way off topic for this forum and you should open a separate thread in the appropriate forum if you want to talk about it.
Now you're reverting to the meaning of "structure" that you used in your OP--"structure" is the product of some "heat engine-like" process. But that's certainly not the same as "mechanical energy and everything that can be converted into mechanical energy".
Same comment here as above--this is off topic for this forum and you should open a separate thread in the appropriate forum if you want to talk about it.

All valid points.

I don't think that using the same word to encompass a potential source of work and a result of work is automatically invalid, though. Which is more fundamental, kinetic energy or potential energy? Each is the source of the other. They can be converted into one another with no minimum loss. They are both encompassed under the general term "mechanical energy". I was attempting something like that broad enough to encompass thermal energy as well. And even the patterns that result from gradient/flow processes. I have a vague sense that these patterns themselves represent a potential to do work, even if it doesn't normally happen. Like you could reclaim the work that went into generating them, or at least some of it. To put it in a soundbite, information is physical.

In fact Jimster used a word that I should have been using all along, but didn't think of it. Free energy. That's a technically precise substitute for what I have been calling structure, although I'd prefer to have a word that applied even in non-equilibrium situations. But free energy is fine.

Right, I don't think gravitational clumping all by itself is an example of a heat engine. It is much closer to a direct loss of free energy, with no compensation. Like free expansion of a gas. Energy that used to be stored in "high quality" form (another non technical word) has been frittered away as heat and radiation. But I was thinking that the clumping would result in greater variation in temperature distribution, and that does represent a kind of "structure". Not all the original potential energy was wasted after all. Some can still be used to do work.

I do understand the usefulness of keeping the topics within a certain range. It makes it much easier to store and retrieve information. I don't mind keeping it more within the bounds of cosmology. This stuff that I'm interested in has an interdisciplinary flavor to it, so it is natural for me to try to make lots of associations, that's all.

 

[techmologist]

@techmologist
You would love this guy from Harvard University. I am just in a chapter on Benard Cells/structures and their role in self organizing systems.
https://www.amazon.com/dp/0674009878/?tag=pfamazon01-20

Arxiv.org. Is a library of current research going on in lots of places. There are lots on Benard cells there. They have been around a long time.

Awesome. I snapped up another book by Chaisson at a thrift store for like $2. Used to be in the library of the local correctional facility. I need to get around to reading it... Arxiv is a good suggestion, too.

 

[PeterDonis]

I don't think that using the same word to encompass a potential source of work and a result of work is automatically invalid. Which is more fundamental, kinetic energy or potential energy?

That's not really relevant, because both kinds of energy can be either the source of work or the result of work. If I take an object and push it up a hill, I have done work on it, and the object now has potential energy as a result of the work I did. If I then let it roll down the hill, the potential energy gets converted to kinetic energy, which can then be used to do work.

In other words, the distinction between "kinds of energy" is just different from the distinction between a source of work and a result of work. We draw distinctions between kinds of energy to help us understand various processes that convert energy from one form to another. Doing work is just one of those processes. But what you appear to be interested in is specifically free energy, not energy in general; and for that purpose, I think keeping clear the distinction between sources of work and results of work is essential. See below.

Free energy. That's a technically precise substitute for what I have been calling structure, although I'd prefer to have a word that applied even in non-equilibrium situations.

AFAIK the term "free energy" can be applied in non-equilibrium situations; in fact, one way of looking at equilibrium itself is as a condition where there is no free energy left. Anyway, if free energy is really what you're interested in, you should just use that term; the term "structure" is going to confuse people as to what you really mean--as it has in this thread.

I was thinking that the clumping would result in greater variation in temperature distribution

It can, at least temporarily, until the heat generated by the clumping process is radiated away.

that does represent a kind of "structure".

Meaning, it represents a store of free energy that, when released, can be used to do work. Yes, that's correct. (More precisely, the free energy is stored in the rest mass of hydrogen, and some of it gets released in fusion reactions, but that process would not take place without gravitational clumping.) And one of the products of that store of free energy, in our solar system, is the Earth's biosphere. But the Earth's biosphere is clearly not the same as the free energy that drives its evolution. If the free energy were taken away, the biosphere would run down; it can't sustain itself on its own. (At least, not in its current form--there are some organisms that don't depend on incoming solar energy, and humans could try to harness other energy sources to produce food, but there would have to be big changes.) So it seems important to keep distinct the free energy itself, and the things produced using it.

 

[techmologist]

AFAIK the term "free energy" can be applied in non-equilibrium situations

Didn't know that. It's settled then. I'll use free energy.

In other words, the distinction between "kinds of energy" is just different from the distinction between a source of work and a result of work.

I'm still not sure about that. But after reading your post through a couple times, I now see the importance of distinguishing between the process, work, and the things that it relates, which are the various forms of energy. But the relation seems like a two-way one. So I don't see that it makes much difference whether some free energy is the source or result of work. Typically, it will be both.

But that leads to the question in the thread title. Given that free energy can simply waste away without doing any work (or can it?), what is it about the universe that makes it much more typical for a source of free energy to do work, even organize cycles to do work, in the process of dissipating itself. Utterly wasteful processes such as the idealized free expansion of a gas seem to be atypical.

We draw distinctions between kinds of energy to help us understand various processes that convert energy from one form to another. Doing work is just one of those processes.

Exactly.

But the Earth's biosphere is clearly not the same as the free energy that drives its evolution. If the free energy were taken away, the biosphere would run down; it can't sustain itself on its own.

Absolutely true. But for a while the decaying biosphere would remain a pretty significant source of free energy. Aliens could use us for food or firewood or whatever, if they happened to be passing by. And of course it isn't nearly as much free energy as was originally put in, since life processes are irreversible.

And I agree with what you said in earlier that simply having matter clump together into a planet is not already self-organization. It doesn't need anything to sustain it. It isn't alive. But it does create a possible venue for self-organization, especially at the surface. If the sun is shining on it and a portion of the incoming yellow light goes back into space as infrared light, then something interesting is probably happening at the surface.

 

[PeterDonis]

Utterly wasteful processes such as the idealized free expansion of a gas seem to be atypical.

Atypical on our planet, maybe. But our planet is a very, very, very, very small piece of the universe. In the universe as a whole, I think "utterly wasteful processes" are the vast, vast, vast majority of all processes.

 

[techmologist]

My fridge does that and I put up with it.

You are a very tolerant person.

Seriously though, that's a good point. And on thinking about it further, that's exactly what man-made engines do, too. It's just a more indirect process than in the case of a Benard cell, in which the work produced goes immediately into overcoming viscosity. But yeah, a car engine produces enough work, directly or indirectly, to get itself assembled and maintained. And it gets us to do all of it. When it is no longer of use, it falls into disrepair. The work the car engine does might pass through amplifiers, though. It might help you get to a job nearby where you make lots and lots of money. So even if the output of the car engine in joules is not very large, it may be helping you direct lots of joules worth of other resources to yourself, making the car worth it. I'll leave it at that because this is not cosmology.

 

[techmologist]

Atypical on our planet, maybe. But our planet is a very, very, very, very small piece of the universe. In the universe as a whole, I think "utterly wasteful processes" are the vast, vast, vast majority of all processes.

Hmm. Yeah, that might be so. Kinda sad. Still, I bet there are loads of planets that have plate tectonics and weather. Maybe not most. I don't know. It wouldn't break my heart to learn that life is a very rare, special instance of self-organization. But I don't think it is a fluke either.

Speaking of cosmology...If the initial uniformity of matter is unstable because of gravity, why is it necessary for people to try to figure out initial temperature fluctuations to the nearest Kelvin. Wouldn't any fluctuation, however small, lead to the clumping of matter?

 

[PeterDonis]

If the initial uniformity of matter is unstable because of gravity, why is it necessary for people to try to figure out initial temperature fluctuations to the nearest Kelvin. Wouldn't any fluctuation, however small, lead to the clumping of matter?

Not quite, because the universe is expanding. There needs to be enough of a fluctuation to concentrate matter enough to overcome the inertia of the expansion, so that it starts clumping.

Also, the increasing precision of measurement of the fluctuations is not just to show that they were there; it is to test actual quantitative predictions of how much clumping in today's universe should have been caused by a given level of fluctuation in the early universe, by comparing those predictions with how much clumping there actually is in today's universe, vs. the level of fluctuations in the early universe.

 

[Jimster41]

https://www.quantamagazine.org/20140122-a-new-physics-theory-of-life/

This popped up on a different featured thread. honestly until like yesterday it had never occurred to me that we did not have a complete technical theory of non-equilibrium thermodynamics. Seems like a major gap.

I do think it's a bit hard to categorize this topic, because it does cross disciplines. I wanted to mention this book to you @techmologist. It is one that is still changing the way I see things w/respect to structure and emergence. I'm not recommending any of these books out of a desire to persuade. I assume it wouldn't matter if I was. I've never found people that easy to persuade. But just to be clear, I'm just another fan in the stands man.

https://www.amazon.com/dp/0262600692/?tag=pfamazon01-20

I think Jablonka is also at the edge, and somewhat controversial (maybe Lamarck was seeing something real after all...) But I found her to be a thought provoking and lucid explainer.

 

[techmologist]

Okay, that makes sense.

Not quite, because the universe is expanding. There needs to be enough of a fluctuation to concentrate matter enough to overcome the inertia of the expansion, so that it starts clumping.

Ah. I hadn't considered the effects of expansion. Thanks.

Also, the increasing precision of measurement of the fluctuations is not just to show that they were there; it is to test actual quantitative predictions of how much clumping in today's universe should have been caused by a given level of fluctuation in the early universe, by comparing those predictions with how much clumping there actually is in today's universe, vs. the level of fluctuations in the early universe.

Okay, that makes more sense now.

Does the expansion of the universe somehow represent an increasing source of free energy? I read something to that effect in an article by Stephen Frautschi once.

 

[techmologist]

https://www.quantamagazine.org/20140122-a-new-physics-theory-of-life/

This popped up on a different featured thread. honestly until like yesterday it had never occurred to me that we did not have a complete technical theory of non-equilibrium thermodynamics. Seems like a major gap.

I do think it's a bit hard to categorize this topic, because it does cross disciplines. I wanted to mention this book to you @techmologist. It is one that is still changing the way I see things w/respect to structure and emergence. I'm not recommending any of these books out of a desire to persuade. I assume it wouldn't matter if I was. I've never found people that easy to persuade. But just to be clear, I'm just another fan in the stands man.

https://www.amazon.com/dp/0262600692/?tag=pfamazon01-20

I think Jablonka is also at the edge, and somewhat controversial (maybe Lamarck was seeing something real after all...) But I found her to be a thought provoking and lucid explainer.

That article looks very interesting. I only skimmed it just now, but it makes lots of interesting connections. I will print it out later and read it carefully. Also, the Jablonka book is the kind of book I would read. I am looking for ideas. Sifting through them and keeping what fits together.

I think the next book I read will be that Chaisson book you linked to. Right now I'm reading Per Bak's How Nature Works.

 

[PeterDonis]

Does the expansion of the universe somehow represent an increasing source of free energy?

It sort of does, in the sense that, as long as the universe keeps expanding, it can never reach thermal equilibrium. Another way to put it is, if the universe keeps expanding forever, there is no such thing as a state of "maximum entropy" for the universe as a whole.

 

[techmologist]

It sort of does, in the sense that, as long as the universe keeps expanding, it can never reach thermal equilibrium. Another way to put it is, if the universe keeps expanding forever, there is no such thing as a state of "maximum entropy" for the universe as a whole.

Is the universe expanding at the expense of anything? The expansion means more gravitational potential, so is it coming from kinetic energy or something else? I am assuming that the total energy of the universe remains constant, if that is even relevant here.

The way Frautschi put it was that although entropy is still non-decreasing, as the second law requires, the maximum possible entropy is always increasing. That sounds wonderful but I don't really understand it. It also directly contradicts one of the formulations of the second law that I am accustomed to, namely that the energy available to do work is non-increasing. If what Frautschi says is true, you can have increasing entropy and increasing free energy, too.

Based on what you said above though, I do see that the universe will tend to a situation where there are many increasingly isolated systems that can't equilibrate with each other.

 

[PeterDonis]

Is the universe expanding at the expense of anything?

No.

I am assuming that the total energy of the universe remains constant

There isn't any well-defined "total energy of the universe". In general in a curved spacetime there is no way to define one; it can only be done in certain special cases. In the case of a spatially closed (i.e., finite) universe, there is a sense in which the total energy is zero (heuristically, positive energy due to matter and radiation is exactly canceled by negative gravitational potential energy); but for a spatially infinite universe, which ours is as best we can tell, even that doesn't work.

It also directly contradicts one of the formulations of the second law that I am accustomed to, namely that the energy available to do work is non-increasing.

That formulation only works in those special cases where a "total energy" can be defined.

I do see that the universe will tend to a situation where there are many increasingly isolated systems that can't equilibrate with each other.

If the universe's expansion continues to be dominated by dark energy, yes, that is what will happen.

 

[techmologist]

There isn't any well-defined "total energy of the universe". In general in a curved spacetime there is no way to define one; it can only be done in certain special cases. In the case of a spatially closed (i.e., finite) universe, there is a sense in which the total energy is zero (heuristically, positive energy due to matter and radiation is exactly canceled by negative gravitational potential energy); but for a spatially infinite universe, which ours is as best we can tell, even that doesn't work.

That is mind blowing. Why does any science based on the conservation of energy work? Is it somehow locally true that energy is conserved?

The expansion part even makes the other classical formulations of the 2nd law awkward. Can you have a cyclic process in an expanding universe?

 

[PeterDonis]

Is it somehow locally true that energy is conserved?

Yes, of course. The issue is purely with not having a well-defined notion of "total energy" for the universe.

Local energy conservation is just the law that, locally, energy cannot be created or destroyed. That is what prevents perpetual motion machines from working. But to translate this into a global law about "total energy", we have to add up the energy in all local regions of space at some instant of time. Hopefully you see the issue: "space" and "time" are relative. In a general curved spacetime, there is no well-defined, unique notion of "space" or "time". So there is no well-defined, unique way to add up all the energy in local regions to get a "total energy".

 

[techmologist]

Yes, of course. The issue is purely with not having a well-defined notion of "total energy" for the universe.

Local energy conservation is just the law that, locally, energy cannot be created or destroyed. That is what prevents perpetual motion machines from working. But to translate this into a global law about "total energy", we have to add up the energy in all local regions of space at some instant of time. Hopefully you see the issue: "space" and "time" are relative. In a general curved spacetime, there is no well-defined, unique notion of "space" or "time". So there is no well-defined, unique way to add up all the energy in local regions to get a "total energy".

Gotcha. I made an elementary logic error, transforming not (the total energy is conserved) into the total energy is not conserved without noticing it. Big difference. Heuristics work every time, except for when they don't.

So it is just because there is no way to talk about what is going on everywhere in the universe right now. Because whether or not things in different places happen at the same time depends on your reference frame.

Is it okay to talk about total energy at the galaxy level or is that too big? Then you could apply energy conservation to say that the energy of the galaxy is decreasing according to how bright it is.

 

[PeterDonis]

Is it okay to talk about total energy at the galaxy level or is that too big?

Any system that can be treated as an isolated system--a bunch of stuff surrounded by emptiness--can be given a well-defined total energy, at least as a good approximation. A planet, a star, a solar system, and a galaxy all can be treated reasonably well as isolated systems.

Then you could apply energy conservation to say that the energy of the galaxy is decreasing according to how bright it is.

Yes--the energy carried away by radiation would be equal to the decrease in energy of the galaxy.

 

[techmologist]

Any system that can be treated as an isolated system--a bunch of stuff surrounded by emptiness--can be given a well-defined total energy, at least as a good approximation. A planet, a star, a solar system, and a galaxy all can be treated reasonably well as isolated systems.

I am probably making that same logical error again, but is there a sense in which the universe is not isolated?

 

[rootone]

There is if you're inclined to take multiverses and colliding membranes in higher dimensions seriously.

 

[PeterDonis]

is there a sense in which the universe is not isolated?

More than that, there is no sense in which the universe is isolated; it is not a bunch of matter and energy surrounded by emptiness. Matter and energy is everywhere in the universe.

 

[PeterDonis]

There is if you're inclined to take multiverses and colliding memiranes in higher dimensions seriously.

This is not the sense of "isolated" I am talking about. The technical term for what I've been calling "isolated" is "asymptotically flat". The universe is not asymptotically flat. That is a statement about our 4-dimensional universe, which is valid regardless of whether or not there are multiverses, colliding branes, etc.

 

[techmologist]

More than that, there is no sense in which the universe is isolated; it is not a bunch of matter and energy surrounded by emptiness. Matter and energy is everywhere in the universe.

Ah, I was making the same error again. I need to name it so I will recognize it better. I'll call it the "Nothing-is-better-than-steak fallacy" (and hamburgers are better than nothing, so...).

 

[techmologist]

I'm going to go out on a limb and guess that the second law of thermodynamics is not directly applicable to the universe as a whole for the same reason, at least not when stated in a global form like "the total entropy is increasing". That version would only apply to parts of the universe that are approximately isolated. Perhaps the local, negative versions about what can't result from a cyclic process are the best, since they don't require that any extensive state function be defined for the universe.

 

[PeterDonis]

I'm going to go out on a limb and guess that the second law of thermodynamics is not directly applicable to the universe as a whole for the same reason, at least not when stated in a global form like "the total entropy is increasing".

Actually, it's not entirely clear that this is true. Entropy can be defined in a way that's more general than the usual way (where it's linked to the definition of energy); the more general definition is that the entropy of a given state is the logarithm of the number of states that have the same macroscopic properties as the given state. But those macroscopic properties don't have to be extensive; for example, heuristically, if we consider the universe as a whole to be homogeneous and isotropic (i.e., ignoring all local variations in energy density, etc.), then we can describe it by its energy density, pressure, and curvature, which are intensive quantities, and we could say that its entropy is just the logarithm of the number of possible universes that have the same energy density, pressure, and curvature. (This is heuristic because we don't currently have a way of counting the "possible universes", but it illustrates the sort of thing that could in principle be done.)

 

[techmologist]

for example, heuristically, if we consider the universe as a whole to be homogeneous and isotropic (i.e., ignoring all local variations in energy density, etc.), then we can describe it by its energy density, pressure, and curvature, which are intensive quantities, and we could say that its entropy is just the logarithm of the number of possible universes that have the same energy density, pressure, and curvature. (This is heuristic because we don't currently have a way of counting the "possible universes", but it illustrates the sort of thing that could in principle be done.)

That is an attractive idea. So these intensive quantities would effectively be averages over the 4-dimensional manifold, right? There would be no taking account of any gradients (and associated flows) in this picture.

Since you brought up possible universes, is there anything to the claims of fine-tuning of this particular universe? Some of the more extreme claims are obvious b.s., but the one that says some fundamental constants must be extremely precise in order for galaxies and stars to form got my attention. That is a very serious claim. Even a secular humanoid such as myself has a hard time imagining any life forms without stars and planets. But I don't know about cosmology and can't evaluate the claim.

 

[PeterDonis]

these intensive quantities would effectively be averages over the 4-dimensional manifold, right?

Correct.

There would be no taking account of any gradients (and associated flows) in this picture.

More precisely, differences in gradients/flows would be different "microstates" (detailed states of the universe) that correspond to the same "macrostate" (average values of the intensive quantities).

is there anything to the claims of fine-tuning of this particular universe?

This is still an open question, because, as I said before, we don't know how to count the "possible universes", so we don't know how to quantitatively estimate how "fine-tuned" our universe really is.