stormsewer (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
stormsewer) wrote2013-06-13 06:12 pm
stormsewer) wrote2013-06-13 06:12 pm
Entry tags:
Public Service Announcement: Obeying the Second Law of Thermodynamics is Not Optional
So, I subscribe to a mailing list about peak oil. Sometimes the people on there annoy me. Most of the time these days I just ignore that. But recently people on there were arguing about entropy and the second law of thermodynamics and how that plays out in the context of biological systems, which seem to go against the Law. However, no one there really seemed to know what they were talking about, and I find a lot of people generally have misunderstandings where this is concerned. But as a molecular biologist and as a human it's something I think about a lot. It's foundational to how the universe operates. For your edification, I present my involvement (thus far) in the conversation.
It started when Person A brought up the second law of thermodynamics as a limiting factor in considering energy regimes. (A very valid point when discussed in the right way, though it wasn't.)
Person B responded, "The 2nd law only applies to isolated systems, which do not exist in nature" as a way to brush off this concern, as if to say that we therefore don't have to worry about it. I just rolled my eyes at that point and moved on to the next email. (Though I will now point out that, yes, the 2nd law only applies to isolated systems, but it is not true that they don't exist in nature. You're in one right now. It's called "the universe.")
The argument continued, with Person A not making a very good case. ("There’s nothing I like less than bad arguments for a view I hold dear." -Daniel Dennett) Then Person B started trotting out Schrödinger quotes from What is Life? about a concept Schrödinger called "negative entropy" (which was his popular term for "free energy," though probably a bad choice given how it's misinterpreted) to support Person B's assertion that "life is proof that nature can reverse entropy." That was it for me, and I decided to enter the fray. My first missive-
[missive ON]
I think the best way to understand entropy is like so: the entropy of the universe as a whole must always increase.
That doesn't mean that there can't be pockets of order. But they have to be "paid for" with an increased amount of entropy for the universe as a whole. Our bodies, for instance, are exquisitely well ordered, and some might think that goes against the second law. It doesn't, because we pay the entropic price of destroying (i.e., eating) numerous other ordered systems in exchange. On the level of the solar system, the sun is a massive entropy generator, and life on Earth can ride coattails on that to create our smidgens of order.
Any time you use energy, you're increasing entropy, since somehow disorder must be increased to do so. This is why there is no such thing as 100% energy efficiency or perpetual motion machines. You will always get out less than you put in (usually a lot less), because entropy is always skimming off the top. If entropy doesn't get its take, it ain't gonna happen. This knowledge is useful for picking out certain ridiculous schemes for generating energy.
"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." –Sir Arthur Eddington
It's also important to note that when we say, "the entropy of the universe always increases," that doesn't mean the entropy increase takes place somewhere far removed. Usually the disorder (often in the form of heat) is vented directly into the immediate environment. This is why, for instance, you can't use a refrigerator as an air conditioner- in order to cool something, it must heat something else even more. It also goes a long way in explaining global warming and the other environmental problems we've caused. That increase in entropy is the cost for the order we create. It's also why the alternative energy sources that would cause the fewest problems long-term, such as wind and solar, are those that make use of entropy flows that are already in place, rather than pulling stuff up out of the ground and destroying it at a pace many orders of magnitude faster than would have occurred naturally.
[missive OFF]
I would have thought that would settle it, but no. Person C then emerged from the muck to try and argue with me. I've had some rather involved arguments with Person C before about his plan for the future. The plan basically involves two parts (A) a completely planned economy to ensure sustainability, and (B) a strict eugenics program to select for people that happily adhere to the system. For (A) I should think it obvious by now that planned economies don't work. I think that hypothesis has been tested enough times. I didn't spend much time on that, since it's not really my area of expertise, anyway. As for the eugenics... I touched on the fact that it's not very nice, to say the least, but that was never going to get through the guy's "desperate times call for desperate measures" mindset. So I tried to focus on the fact that it wouldn't even yield the desired results, because
But it was futile. Spent a lot of time, never got anywhere with him. He was convinced he's the lone genius that's got it all figured out, frustrated that all the idiots don't realize that fact.
And now he's going to argue with me about thermodynamics. Okay. In the following science rant, lines containing his words are preceded with ">" and what I said is the rest. (Part of the reason it's so long is that I'm trying to anticipate arguments and cut them off pre-emptively. Not that that has an amazing chance of working.)
[science rant ON]
> I don't think so.
You're really going to argue with me about whether the second law of thermodynamics applies to biology? That's kind of impressive. Given our past interactions I have no expectation of you changing your mind, but I just can't let statements like that fly by without comment, so what the hey, let's get into it. (I'll say the peak-oil relevance is that if you want to design a new energy economy, you really ought to understand how energy works.)
>Does a highly ordered tree "pay the price" for
>its ordered existence by destroying other highly ordered systems?
>If ordered systems can only exist by destroying other ordered
>systems, where does this "food" come from in the first place?
>This makes no sense.
The simple answer is yes, the tree does pay the price by breaking apart water molecules (which, while you might not call them "highly ordered," are certainly more ordered before the tree gets done with them), and the "food" comes from water, carbon dioxide, and sunlight. It doesn't matter if it makes sense to you; that's how it works.
As for the more complicated answer... The sun is in the process of destroying itself on a grand scale, and generating massive amounts of energy in the process. It is possible to capture some of that energy and use it to build an ordered system. Two points are important to understand here.
(1) You will never convert all of that energy into order. Some of it will always be lost as heat, increasing disorder. The theoretical maximum efficiency of photosynthesis is 29%, and I know some textbooks claim that 25% has been achieved in controlled laboratory settings (though I've never found an actual reference in the primary literature for that second number). The highest reported efficiency for algae in a bioreactor is about 9%; the highest reported for plants is about 4%. The global average has been estimated to be 0.3%. (References available upon request.) The rest is dissipated as heat. (Essentially by definition, heating something up increases its entropy, as temperature is a measure of how much things are moving around at the atomic/molecular level. This is something most people can intuitively understand.) So the vast majority of that energy flow goes to increasing disorder, not increasing order.
(2) Even what energy you do convert into order is only temporary. Any molecule you build will eventually be broken apart. You can keep repairing and rebuilding it, but too bad. Entropy always collects on its debts, sooner or later. The end result, speaking in terms of energy flows in cosmic time frames, will be the same as if those pockets of order never existed at all.
And heat release isn't even the full story when it comes to plants increasing the entropy of their surroundings in exchange for existing. To build a complex molecule like starch or fat, you need two things: a carbon source (CO2 in the case of photosynthetic organisms) and what are called "reducing equivalents," which are basically electrons. These act as energy carriers and as something like a "glue" for bonding atoms into molecules and holding them there.
Plants use high energy electrons to bond CO2 into more complicated molecules. The energy comes from the sun, but the electrons actually come from water. Photosynthetic organisms have a molecular machine called the water-splitting complex that takes two molecules of H2O and breaks them apart into four electrons, four H+ ions (acid), and one molecule of O2.
So the tree increases disorder immediately by breaking what was in two pieces into nine, allowing that destructive process to happen much faster than would have occurred without the tree's intervention. Besides that, it turns out that O2 is a highly destructive molecule. In order to burn something, you need heat and O2. Burning is basically just a reaction with oxygen; the heat is needed to overcome the "activation energy" necessary to get it started. Without O2 these complicated biomolecules would last a long, long time before entropy got around to taking them apart, but oxygen destroys them in a relative eye-blink. Oxygen is also what causes rust, and oxygen is ultimately responsible for most of the oxidative damage implicated in aging and other medical "disorders." That's how plants "pay" for their order.
Oxygen's immense destructive power does have its benefits, since it creates a powerful entropy-increasing energy flow that we can skim off of to build the molecules that constitute our bodies. In exchange for burning huge amounts of biomass, of course. This is why we breathe in O2 molecules (generated by the water-splitting complex) and breathe them out as CO2- the "C" atoms in CO2 are the fragments of the biomolecules we let O2 destroy in exchange for staying alive. (Plants also use O2 in exactly the same way, mostly at night.)
Maybe it's ironic that the source of plants' success is also their downfall (it turns out humans are not particularly special in that regard). They get the electrons they need to grow from splitting water, but the oxygen produced is directly responsible for how they usually meet their demise, whether it be from burning or from being eaten or just from oxidative damage. But that's just the way the universe works.
> Order can be observed to increase as energy dissipates from a
> system. And I'm not talking about some vague notion of what order
> is, but looking at it as something mathematically defined, which is
> necessary if you are going to talk about it scientifically in
> conjunction with energy and other such measures.
Yes, order requires energy flows to exist. (Though to be nitpicky, energy flows are necessary but not sufficient for ordered systems to arise.) But the dissipation of energy is by definition an increase in entropy. The amount of order that may come out as a result is always less than the amount of disorder ultimately created, and can in fact only occur in exchange for accelerating the destruction of something else. Plants destroy water molecules, and we destroy plants. Heat is generated in the process.
This is overwhelmingly well established, and in mathematical terms. And it can be used to predict whether any given chemical reaction will actually occur or not. You ask, does this reaction release heat into the environment and/or increase the entropy of the reactants? If not, it just ain't gonna happen. In terms of "open systems," the entropy of the system itself and/or the entropy of whatever is outside the system must increase (heat release is the increase in external entropy). One or the other can decrease, but the mathematical sum of both must be an increase in entropy in order for ANYTHING to occur. That sum is called the "free energy," and it is basic thermodynamics.
Every chemical reaction known to occur, including all those we know of that organisms use to build their complicated molecules, follows this rule. People have also done all kinds of studies on, for example, the heat released by single leaves during photosynthesis. Guess what? Leaves follow the second law. Every properly performed study on energy flows has shown this to be the case. The entropy of the universe always increases. In theory the best you can ever do is leave the entropy of the universe unchanged (it's called a "reversible process"), but in reality you can never quite achieve even that.
If you want to deny this, you are denying the very foundations of everything we know about physics and chemistry. While your mileage may vary as to whether you like the metaphors I chose, the second law of thermodynamics is not a matter of opinion. Though everything in science is a model and not a "fact" per se, the second law comes as close as anything in science to being ironclad just-the-way-it-is reality.
There is always an entropic cost to using energy. You will never get it for free. If you don't understand this, you don't understand energy, and you don't understand biology, either.
This does mean that life, and all forms of order, will eventually come to an end. Sooner or later the stars will burn out, the molten cores of rocky planets will cease to emit heat, and then ordered systems will also die out because there is no more energy to pay off their entropic debts. Entropy will win. Such is life.
"It’s an unpleasant thing to bring people into the basic laws of physics." –Steven Weinberg
[science rant OFF]
Again, I'd like to think that settles it, but knowing this guy, probably not. I may post further iterations here later, if I bother to continue to discuss it with him.
It started when Person A brought up the second law of thermodynamics as a limiting factor in considering energy regimes. (A very valid point when discussed in the right way, though it wasn't.)
Person B responded, "The 2nd law only applies to isolated systems, which do not exist in nature" as a way to brush off this concern, as if to say that we therefore don't have to worry about it. I just rolled my eyes at that point and moved on to the next email. (Though I will now point out that, yes, the 2nd law only applies to isolated systems, but it is not true that they don't exist in nature. You're in one right now. It's called "the universe.")
The argument continued, with Person A not making a very good case. ("There’s nothing I like less than bad arguments for a view I hold dear." -Daniel Dennett) Then Person B started trotting out Schrödinger quotes from What is Life? about a concept Schrödinger called "negative entropy" (which was his popular term for "free energy," though probably a bad choice given how it's misinterpreted) to support Person B's assertion that "life is proof that nature can reverse entropy." That was it for me, and I decided to enter the fray. My first missive-
[missive ON]
I think the best way to understand entropy is like so: the entropy of the universe as a whole must always increase.
That doesn't mean that there can't be pockets of order. But they have to be "paid for" with an increased amount of entropy for the universe as a whole. Our bodies, for instance, are exquisitely well ordered, and some might think that goes against the second law. It doesn't, because we pay the entropic price of destroying (i.e., eating) numerous other ordered systems in exchange. On the level of the solar system, the sun is a massive entropy generator, and life on Earth can ride coattails on that to create our smidgens of order.
Any time you use energy, you're increasing entropy, since somehow disorder must be increased to do so. This is why there is no such thing as 100% energy efficiency or perpetual motion machines. You will always get out less than you put in (usually a lot less), because entropy is always skimming off the top. If entropy doesn't get its take, it ain't gonna happen. This knowledge is useful for picking out certain ridiculous schemes for generating energy.
"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." –Sir Arthur Eddington
It's also important to note that when we say, "the entropy of the universe always increases," that doesn't mean the entropy increase takes place somewhere far removed. Usually the disorder (often in the form of heat) is vented directly into the immediate environment. This is why, for instance, you can't use a refrigerator as an air conditioner- in order to cool something, it must heat something else even more. It also goes a long way in explaining global warming and the other environmental problems we've caused. That increase in entropy is the cost for the order we create. It's also why the alternative energy sources that would cause the fewest problems long-term, such as wind and solar, are those that make use of entropy flows that are already in place, rather than pulling stuff up out of the ground and destroying it at a pace many orders of magnitude faster than would have occurred naturally.
[missive OFF]
I would have thought that would settle it, but no. Person C then emerged from the muck to try and argue with me. I've had some rather involved arguments with Person C before about his plan for the future. The plan basically involves two parts (A) a completely planned economy to ensure sustainability, and (B) a strict eugenics program to select for people that happily adhere to the system. For (A) I should think it obvious by now that planned economies don't work. I think that hypothesis has been tested enough times. I didn't spend much time on that, since it's not really my area of expertise, anyway. As for the eugenics... I touched on the fact that it's not very nice, to say the least, but that was never going to get through the guy's "desperate times call for desperate measures" mindset. So I tried to focus on the fact that it wouldn't even yield the desired results, because
But it was futile. Spent a lot of time, never got anywhere with him. He was convinced he's the lone genius that's got it all figured out, frustrated that all the idiots don't realize that fact.
And now he's going to argue with me about thermodynamics. Okay. In the following science rant, lines containing his words are preceded with ">" and what I said is the rest. (Part of the reason it's so long is that I'm trying to anticipate arguments and cut them off pre-emptively. Not that that has an amazing chance of working.)
[science rant ON]
> I don't think so.
You're really going to argue with me about whether the second law of thermodynamics applies to biology? That's kind of impressive. Given our past interactions I have no expectation of you changing your mind, but I just can't let statements like that fly by without comment, so what the hey, let's get into it. (I'll say the peak-oil relevance is that if you want to design a new energy economy, you really ought to understand how energy works.)
>Does a highly ordered tree "pay the price" for
>its ordered existence by destroying other highly ordered systems?
>If ordered systems can only exist by destroying other ordered
>systems, where does this "food" come from in the first place?
>This makes no sense.
The simple answer is yes, the tree does pay the price by breaking apart water molecules (which, while you might not call them "highly ordered," are certainly more ordered before the tree gets done with them), and the "food" comes from water, carbon dioxide, and sunlight. It doesn't matter if it makes sense to you; that's how it works.
As for the more complicated answer... The sun is in the process of destroying itself on a grand scale, and generating massive amounts of energy in the process. It is possible to capture some of that energy and use it to build an ordered system. Two points are important to understand here.
(1) You will never convert all of that energy into order. Some of it will always be lost as heat, increasing disorder. The theoretical maximum efficiency of photosynthesis is 29%, and I know some textbooks claim that 25% has been achieved in controlled laboratory settings (though I've never found an actual reference in the primary literature for that second number). The highest reported efficiency for algae in a bioreactor is about 9%; the highest reported for plants is about 4%. The global average has been estimated to be 0.3%. (References available upon request.) The rest is dissipated as heat. (Essentially by definition, heating something up increases its entropy, as temperature is a measure of how much things are moving around at the atomic/molecular level. This is something most people can intuitively understand.) So the vast majority of that energy flow goes to increasing disorder, not increasing order.
(2) Even what energy you do convert into order is only temporary. Any molecule you build will eventually be broken apart. You can keep repairing and rebuilding it, but too bad. Entropy always collects on its debts, sooner or later. The end result, speaking in terms of energy flows in cosmic time frames, will be the same as if those pockets of order never existed at all.
And heat release isn't even the full story when it comes to plants increasing the entropy of their surroundings in exchange for existing. To build a complex molecule like starch or fat, you need two things: a carbon source (CO2 in the case of photosynthetic organisms) and what are called "reducing equivalents," which are basically electrons. These act as energy carriers and as something like a "glue" for bonding atoms into molecules and holding them there.
Plants use high energy electrons to bond CO2 into more complicated molecules. The energy comes from the sun, but the electrons actually come from water. Photosynthetic organisms have a molecular machine called the water-splitting complex that takes two molecules of H2O and breaks them apart into four electrons, four H+ ions (acid), and one molecule of O2.
So the tree increases disorder immediately by breaking what was in two pieces into nine, allowing that destructive process to happen much faster than would have occurred without the tree's intervention. Besides that, it turns out that O2 is a highly destructive molecule. In order to burn something, you need heat and O2. Burning is basically just a reaction with oxygen; the heat is needed to overcome the "activation energy" necessary to get it started. Without O2 these complicated biomolecules would last a long, long time before entropy got around to taking them apart, but oxygen destroys them in a relative eye-blink. Oxygen is also what causes rust, and oxygen is ultimately responsible for most of the oxidative damage implicated in aging and other medical "disorders." That's how plants "pay" for their order.
Oxygen's immense destructive power does have its benefits, since it creates a powerful entropy-increasing energy flow that we can skim off of to build the molecules that constitute our bodies. In exchange for burning huge amounts of biomass, of course. This is why we breathe in O2 molecules (generated by the water-splitting complex) and breathe them out as CO2- the "C" atoms in CO2 are the fragments of the biomolecules we let O2 destroy in exchange for staying alive. (Plants also use O2 in exactly the same way, mostly at night.)
Maybe it's ironic that the source of plants' success is also their downfall (it turns out humans are not particularly special in that regard). They get the electrons they need to grow from splitting water, but the oxygen produced is directly responsible for how they usually meet their demise, whether it be from burning or from being eaten or just from oxidative damage. But that's just the way the universe works.
> Order can be observed to increase as energy dissipates from a
> system. And I'm not talking about some vague notion of what order
> is, but looking at it as something mathematically defined, which is
> necessary if you are going to talk about it scientifically in
> conjunction with energy and other such measures.
Yes, order requires energy flows to exist. (Though to be nitpicky, energy flows are necessary but not sufficient for ordered systems to arise.) But the dissipation of energy is by definition an increase in entropy. The amount of order that may come out as a result is always less than the amount of disorder ultimately created, and can in fact only occur in exchange for accelerating the destruction of something else. Plants destroy water molecules, and we destroy plants. Heat is generated in the process.
This is overwhelmingly well established, and in mathematical terms. And it can be used to predict whether any given chemical reaction will actually occur or not. You ask, does this reaction release heat into the environment and/or increase the entropy of the reactants? If not, it just ain't gonna happen. In terms of "open systems," the entropy of the system itself and/or the entropy of whatever is outside the system must increase (heat release is the increase in external entropy). One or the other can decrease, but the mathematical sum of both must be an increase in entropy in order for ANYTHING to occur. That sum is called the "free energy," and it is basic thermodynamics.
Every chemical reaction known to occur, including all those we know of that organisms use to build their complicated molecules, follows this rule. People have also done all kinds of studies on, for example, the heat released by single leaves during photosynthesis. Guess what? Leaves follow the second law. Every properly performed study on energy flows has shown this to be the case. The entropy of the universe always increases. In theory the best you can ever do is leave the entropy of the universe unchanged (it's called a "reversible process"), but in reality you can never quite achieve even that.
If you want to deny this, you are denying the very foundations of everything we know about physics and chemistry. While your mileage may vary as to whether you like the metaphors I chose, the second law of thermodynamics is not a matter of opinion. Though everything in science is a model and not a "fact" per se, the second law comes as close as anything in science to being ironclad just-the-way-it-is reality.
There is always an entropic cost to using energy. You will never get it for free. If you don't understand this, you don't understand energy, and you don't understand biology, either.
This does mean that life, and all forms of order, will eventually come to an end. Sooner or later the stars will burn out, the molten cores of rocky planets will cease to emit heat, and then ordered systems will also die out because there is no more energy to pay off their entropic debts. Entropy will win. Such is life.
"It’s an unpleasant thing to bring people into the basic laws of physics." –Steven Weinberg
[science rant OFF]
Again, I'd like to think that settles it, but knowing this guy, probably not. I may post further iterations here later, if I bother to continue to discuss it with him.