Thread by @inftoe

The idea for this thread came from this short dialogue with @Elisabe09456260 in the thread about @elonmusk's attempt to save humanity:

https://twitter.com/Elisabe09456260/status/1405042960421502978

Colleague expresses the opinion that increasing entropy will eventually eliminate everything in the universe.
1 ᐅ

This is a very interesting opinion indeed.
And first of all, it is interesting in attitude to this problem in modern physics. Modern physics is little shy about this topic.
Because it is very inconvenient not to have a clear answer to a such simple question.
2 ᐅ

This question sounds like this: "Will the heat death of the universe occur: yes or no?"
If you ask physicist, he will do everything not to answer. He will discourse a lot, deeply explain, refer to the history and latest research, but you shouldn't expect neither yes nor no.
3 ᐅ

It is all the more embarrassing for physicists that this question is so simple that, unlike many other physical concepts, it is quite accessible for understanding (and, therefore, asking) any person who has ever touched an iron with his finger.
4 ᐅ

Everyone knows from personal experience that a hot iron will cool down "by itself" after a while, slightly heating the air in the room, but "by itself" will never be able to heat up. To make it hot again, it needs to be heated with something, such as electricity.
5 ᐅ

This behavior is typical for all hot objects around us, from which it is easy to conclude that all hot bodies in the universe behave in the same way, including our Sun and all the stars, that make the universe what we know it: existing actively.
6 ᐅ

So, by the time thermodynamics was created in the 19th century, the idea of the inevitable death of the universe due to the equalization of temperature had long been in circulation.
Scientists have not come up with anything better how to scientifically confirm these fears.
7 ᐅ

They (Clausius and Kelvin are to blame most of all) introduced the concept of entropy, and irrefutably proved that it always increases in one way or another until it reaches a maximum at which any useful work becomes impossible.
8 ᐅ

This reckless act led to quite tragic consequences (the usual story with science): the population was seized by the sin of despondency. E.g., it is said that the son of "the pioneer of Soviet cosmonautics" Konstantin Tsiolkovsky, a talented young man, even committed suicide.
9 ᐅ

Since then, scientists, realizing what they had done (the usual story with science), have done a lot to confuse this problem so that people decide that they do not understand anything, return to a comfortable state of ignorance and stop sinning.
10 ᐅ

When a physicist will try not to answer your question, you will hear a lot of muddy and contradictory things, which will make you wave your hand in bewilderment, they say, sort it out yourself. This is what he wants from you. And knowing this, he is embarrassed.
11 ᐅ

He will first of all say (following Max Planck) that the universe is not a thermodynamic system, therefore the concept of entropy is inapplicable to it. When you give the definition of a thermodynamic system, he will ask you not to mention Wikipedia with him.
12 ᐅ

He will also embark on philosophical discussions about what the universe is, hoping to lead you eventually to the fashionable idea of a multiverse, so that you are amazed at its beauty and grandeur and do not bother with silly little things.
13 ᐅ

He will certainly operate with the concept of infinity, but so, that you do not understand whether he considers the universe to be finite or infinite, but also so that you understand that in the presence of infinity it is tactless to ask so finite questions.
14 ᐅ

He will argue that the universe is expanding adiabatically, like a banal bubble of warm gas, serenely ignoring that in other sections of his own physics, this same universe is capable of miracles are far from thermal effects: inflation, dark energy.
15 ᐅ

He will also hint that the magical power of gravity dispels all your doubts about entropy. Do not try to figure out how, otherwise you will be led into the region of black holes, the universal picklock of modern cosmology, and there you will fall beyond the event horizon.
16 ᐅ

But if you are a lucky and you hit off a renegade physicist, he can, carefully looking around and turning on the water, whisp that the universe, or rather life present in it, demonstrates the ability to reduce entropy. But this is no my wage, will cut he with relief.
17 ᐅ

If you still want to get the opinion most relevant to today's mainstream views, ask Ethan Siegel @StartsWithABang. He usually expounds and firmly defends the canonical picture of the world for modern physics.
18 ᐅ

In his extensive blog, Ethan pays a lot of attention to this question, as anxious people ask it quite often: google.com/search?q=site%…
19 ᐅ

In the article forbes.com/sites/startswi… Ethan describes the scenario of heat death of the universe over the next 10¹²⁰ years, but how it is customary, accompanies it with such a set of reservations that you will have a feeling that everything may be somehow not so.
20 ᐅ

So, now we will finally figure out how it will be, i.e. whether the thermal death of the Universe will occur: yes or no.
(Spoiler: if you've seen a long boring thread about the sad @elonmusk

https://twitter.com/inftoe/status/1402233954070007811

, you already know that no.)
21 ᐅ

For now, in order not to annoy the adherents of the fictive Big Bang Theory, which today are a little more than almost everyone who is in the subject, we will adhere to its system of concepts.
22 ᐅ

And in this fictive system of concepts, let's immediately agree that the universe is, of course, a closed thermodynamic system, at least from the moment when a lot of what can be called interacting particles moving in space and time appeared in it and carrying energy.
23 ᐅ

Many particles, their movements in space and time, energy and interactions, the absence of an external environment – all that is needed for the system to be closed thermodynamic. And this is exactly what the universe is from at least 10⁻⁴³ (or so) seconds of Big Bang.
24 ᐅ

If you have a desire to refute this ferroconcrete statement (definition, not chronology) with the fictive idea of the multiverse, just stop calling the multiverse multiverse, call it the universe in accordance with the semantics of this term, and we continue.
25 ᐅ

Well, since we agreed that the universe is a closed thermodynamic system, then it must fulfill the second law of thermodynamics. Whatever happens in it, its entropy increases. And, therefore, it leads us to its inevitable heat death, right?
26 ᐅ

And here is where let's start to understand.
First, remember what entropy is. Everyone who said that this is a measure of useless energy, you can go and pour yourself some coffee for now. Let's continue with those who said it is a measure of disorder.
27 ᐅ

It so happened since the steampunk 19th century with its cylinders and pistons that we imagine a closed system with maximum entropy approximately like a room evenly filled with an ideal gas, whose particle energies obey the Maxwell distribution:
28 ᐅ

(For reference: this is a 2d projection onto the screen of a model of a 3d room filled with ideal gas. Yellow flashes indicate collisions of particles with walls, including front and rear, blue flashes - collisions of particles with each other.)
29 ᐅ

Yes, indeed, it looks very (more precisely, absolutely) disorderly. Such a universe is a bit pity: it is dead. No work is possible in it.
But let's put this room on the surface of the Earth, which, as we know, has gravity:
30 ᐅ

It is clear that the emergence of a new factor – attraction to the Earth – makes the system unbalanced. We observe a short transition period, during which the initial equiprobable placement of particles in the room is replaced by a gradient in height.
31 ᐅ

During the transition period, we could get the particles to do useful work. But after its completion, the system comes to equilibrium, entropy reaches its maximum, and no useful work becomes possible again.
But this system looks a little less disorder, right?
32 ᐅ

The density of particles in the lower part of the room is noticeably higher. It turns out that the school stereotype, that maximum entropy means complete disorder, is at least not entirely accurate: here the entropy is maximum, but some "order" is present.
33 ᐅ

Well, according to the tradition introduced by Maxwell, let's take the poor little demon and make him not let the particles fly from the right side of the room to the left:
34 ᐅ

The result of his work is a system that no longer looks disorder: particles are collected on the right side of the room, and the left is empty (although Twitter, with its 2:20 limit for video, does not allow waiting for this).
35 ᐅ

We know from school what the trick is. In fact, the demon was secretly doing the job: installing the baffle. Placing an elastic reflective baffle for particle flying from right to left is equivalent to colliding it with exactly the same particle flying from left to right.
36 ᐅ

So if we remove the partition from the room, we can get from the returning particles the work no more that the demon spent on installing the baffle.
37 ᐅ

And he spent energy on determining the direction of particles, so that the total entropy in the room (particles + demon), as a result of his labors, undoubtedly increased.
However, the growth of this entropy was accompanied by the establishment of order, not destruction!
38 ᐅ

So thermodynamic entropy is a measure of useless energy. But to consider it a measure of disorder, as the delightful Victorian era habitually dictated to us, let's no longer. Not so simple.
Those who drank coffee can return.
39 ᐅ

Yes, the threat of heat death does not seem so obvious to us now, but it has not completely receded yet.
Well, let's move our modeling closer to reality.
40 ᐅ

In reality, as we know, particles can not only collide elastically, but also enter into other interactions. Let's add the simplest: mutual attraction.
41 ᐅ

As we can see, after a transition period, a thermodynamic equilibrium is established. The particles are pulled into a some area with a common center of attraction (quite dynamic), around which they describe complex smooth trajectories until collide with someone.
42 ᐅ

The redistribution of energy as a result of collisions (and now also mutual attraction) leads to the fact that some of the particles sometimes become too fast, and fly away from friends, so that they even collide with the walls of the room, spoiling the picture.
43 ᐅ

To reduce the effect of the presence of walls, let's take a larger room. Yes, after the establishment of an equilibrium state, the system reached its maximum entropy, we observe the thermal chaos usual for this state with a complete impossibility of performing work.
44 ᐅ

But this chaos has a well-defined form: particles are stably distributed in some variable region of space, and leave it only if acquiring very high energy, obviously due to other particles, which are fall into the depth of the region, full of collisions.
45 ᐅ

As we see, entropy is not the absolute enemy of order. Yes, a real complex system, in which many factors act, moves in accordance with the second law of thermodynamics to the increasing entropy, but at the same time it does not lose, but, on the contrary, takes shape.
46 ᐅ

And since we started talking about factors, let's remember that in reality we are not dealing with the simplest particles of the model – balls that can only collide elastically and attract – but with much more complex physical phenomena.
47 ᐅ

If we consider quark-gluon plasma, then against the background of an increase in its entropy (synthesis releases energy), strong interaction will combine quarks, creating hadrons, which, naturally, are more ordered than plasma. The result is baryonic gas.
48 ᐅ

In a baryonic gas, under the same strong interaction, primary nucleosynthesis will occur. Yes, entropy is still increasing, but the atomic nuclei of hydrogen and helium are certainly more ordered than baryonic gas.
49 ᐅ

Atomic nuclei will begin, under the electromagnetism, to combine with electrons that have appeared as a result of the decay of neutrons, and the universe will be filled with hydrogen and helium atoms. And again, the increased entropy will not prevent the higher ordering.
50 ᐅ

Then gravity will come into play: it will compress gas clouds, and stars, more ordered objects, will light up in them. And entropy, meanwhile, is increasing.
51 ᐅ

Gravity will pull the stars into entirely ordered galaxies. Supernovae flashing in them, according to Carl Sagan, fill galaxies with clouds of heavy chemical elements, from which stars form their planetary systems.
Entropy continues to increase, so does the order.
52 ᐅ

Once on the one planet, many different conditions will converge in such a way that a cyclically self-copying chemical complex will arise. Variations of its copies will give a start to the evolution of living nature, parasitizing on the continuing increase in entropy.
53 ᐅ

And one day, as a result of all this 14 billion years of irreversible progress, people will appear who, having admired the puffing steam engine, will declare that all this was the continuous destruction of everything by increasing entropy, and it goes to the heat death.
54 ᐅ

But then they will think a little and decide that something is wrong with this universe, the observed reality is somehow very different from that dictated by an irrefutable law. Let's better let it be foggy on this simple and unambiguous question.
55 ᐅ

Well, this is the way.
And we will commit the achieved clarity:
56 ᐅ

1. The Universe, of course, is a closed thermodynamic system at all stages of its existence (in the chronology of the fictive Big Bang Theory) since the time particles appeared in it.
57 ᐅ

2. The second law of thermodynamics is fully related to the universe: entropy in it consistently increases. At no stages of its existence (in the chronology of the fictive Big Bang Theory) did the entropy decrease.
58 ᐅ

3. It is wrong to consider thermodynamic entropy as a measure of disorder. With an increase in entropy, the order in a thermodynamic system can increase. It is correct to think of entropy as a measure of useless energy, unsuitable for doing work.
59 ᐅ

4. The process of increasing entropy in the universe is the background for the process of successive complication of the universe's beings, which began with the appearance of elementary particles, and has led to the present time to the most complex being: humanity.
60 ᐅ

OK. In order not to retell the story of the universe every time, let's briefly call it the progress of the universe. It would not be a mistake to use the term "evolution", but it is traditionally used for protein life, there is a risk of unnecessary associations.
61 ᐅ

That is, what we used to call the Darwinian evolution of living (protein) nature is a natural stage in the overall progress of the universe. And it is not the last stage. More on this here:

https://twitter.com/inftoe/status/1405228128423792641

62 ᐅ

So, after all, why is the universe progressing, despite the inexorable opposition of the second law of thermodynamics, which seeks to deprive it of the energy capable of doing work, on the basis of which this progress can only occur?
63 ᐅ

We are sure that by this time the answer to this fundamental question is already obvious to you. Of course, the more complex a being, the relatively less energy is required to perform work on its further complication. Definitely less than the increasing entropy takes away.
64 ᐅ

Why so? Because as the complexity increases, the need for energy increases additively, and the achievable complexity increases combinatorially. 4 things of something can form 6 combinations of 2; 5 things – 10; 6 things – already 15, etc.
65 ᐅ

That is why it took such a huge energetically saturated and rather simple universe to create in its center a small island of an extremely complex and extremely economical being: humanity.
66 ᐅ

The history of the universe is not a history of increasing entropy leading to heat death. This is a completely different story.
67 ᐅ

This is a history of progress, consistent complication, leading to the creation of more and more organized beings, the result of which will not be death, but, on the contrary, the creation of the universe. We have already said something about this:

https://twitter.com/inftoe/status/1404258270668378121

68 ᐅ

So, we have dealt with the heat death of the universe: it will not be. This is the time to end the reasoning in terms of the fictitious Big Bang Theory. Let's hope that someday it will be possible to have dealt what it really was.
69.
And thanks, @Elisabe09456260, for this theme.

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