The direction of entropy

Apr 28, 2021
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Would the direction of entropy run in reverse in a contracting universe? To me it seems that the whole reason entropy is increasing is because our universe is expanding. The reason for this is because particles have more places to go than previously. In a contracting universe the opposite would be true. Also a contracting universe would lead to a singularity which has zero entropy.
 
Would the direction of entropy run in reverse in a contracting universe? To me it seems that the whole reason entropy is increasing is because our universe is expanding. The reason for this is because particles have more places to go than previously. In a contracting universe the opposite would be true. Also a contracting universe would lead to a singularity which has zero entropy.
Only when the universe is crunched into 100% energy, or just before, is there much of an argument for regaining entropy. I think more cosmologists would suggest full restoration would be unlikely, which is one reason against a cyclic universe. But physics can’t reach into this near zero time period. Energies after the first trillionth second are studied in the LHC, however.
 
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Entropy is the amount of heat, in a closed system, that is not available to do work. Work can only be done by moving heat from a hotter area to a cooler area. Once thoroughly mixed, there is no heat available to do work thus the entropy is at 100%. Whether the universe is expanding, static or contracting is irrelevant.
When the universe is at a singularity, entropy is undefined since heat cannot move since a singularity has but one dimension. Once the universe expanded to a finite size, quantum fluctuations gave some areas more heat then others and the amount of entropy became defined. It has increased ever since and will reach 100% when all matter has finally disappeared, which happens somewhere around 10^100 years.
 
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It is hard to get a wholistic definition of "entropy" that can be used in all possible states of the universe for cosmology. In general, I don't see any reason to expect something like a gravitational collapse of the matter in the universe to make entropy decrease by some manner like "time running backwards" during the collapse. But, once you get inside an event horizon of a black hole, there can be some disputes about how to decide if some of the potential mathematical solutions are real or not, including the direction of time. So, I am not going to speculate about that. And, I also note that gravitational collapse in astronomy is one way to convert matter into energy via fusion. So, the diffuse matter, theorized to have been made diffuse by the expansion of space itself, doe not need much non-uniformity to eventually lead to gravitational collapse. Whether all matter can be converted to energy in some ultimate form of collapse, such as the state theorized for the initial moments of the Big Bang, is not clear either. Assuming that all matter can be converted to energy, and that it can then somehow rebound into space or make space itself expand, the issue is whether that could be so uniform that it would not create any differences in energy distribution that could then be used to "do work". I don't think that the collapse would necessarily be so uniform that the following rebound must be uniform, even if the minimum size is greater than the Plank size. We at least theorize about "isentropic" processes where there is no loss in process that turns useable forms of energy into unusable forms, such as friction turning motion energy into heat energy. It is not clear to me that the sum total of all the processes happening in the universe cannot be isentropic. But, somebody had probably claimed that it is not. However, with the BBT theorizing that what we are able to observe makes up only about 5% of all the energy and matter in the universe, it seems to me that any proof about how that is affected by the law of entropy could be missing a lot about the effects of dark matter and dark energy on total entropy.
 
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If the apparent expansion of the universe from any local point is never ending, toward infinity, the apparent energy expansion of the universe from any local point is never ending, toward infinity, and the equivalent mass expansion of the universe from any local point is never ending, toward infinity. The view is timelessly entropic to the maximum of entropy like infinite layers, levels, of chaos will reduce, flatten out, to being timelessly entropic to the maximum of entropy.
 
Apr 28, 2021
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But isn’t the increase in entropy in our universe linked to the expansion of our universe? At the beginning of the universe there was more energy in a smaller amount of space and therefore had lower entropy. If the universe continues on its current course we will get to the big freeze which would have minimal energy in a larger space and will have maximum entropy. Dark energy increases hand in hand with entropy. Almost as if energy is being converted into spacetime. I mean if energy is never created or destroyed then where is the increase in dark energy coming from?
 
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Nov 19, 2021
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Entropy is the amount of heat in a closed system that is not available to do work.
Say you have a tank with two one kg glasses of water sitting in it. One is at zero degrees C and one is at 100 degrees C. Define zero degrees as the base and the cold glass has no heat in it. The entire amount of heat in the hot glass, 100 kilocalories, is available to do work. Entropy of the system is zero.
Now mix them together and you have two kg of water at 50 degrees C. There is still 100 kilocalories but none of it is available to do work. Entropy is thus 100 kilocalories.
Entropy went up. In a closed system, eventually the two glasses would reach the same temperature. This no matter how well you try to insulate them. It is unavoidable. Heat flows from hot to cold and there is no way to stop it. Thus entropy always increases. To make it decrease you would have to violate the second law of thermodynamics which says heat flows from hot to cold. Another way would be to make time go backwards but this is not possible.

The universe is no different, it started with a certain amount of heat difference from place to place due to quantum effects. Eventually the entire universe will be at the same temperature and entropy will be at a maximum. There is no way to stop this from happening.

Dark energy is created as new volume of space is created by the expansion of space. This positive energy is a property of space and continually appears. It is exactly balanced out by the negative potential energy of the expansion of gravitationally bound galaxies thus the conservation of energy is maintained.
 
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Apr 28, 2021
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Thanks for that last paragraph. Very informative. Surprised that isn’t more talked about to the general public. Can you explain a bit more about the negative potential energy?
So our expanding universe is going from hot to cold. So then a contracting universe it would go from cold to hot therefore entropy would be reversed?
 
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I don't understand the energy balance very well myself. I have read up on it and all I can say is that when two objects with mass move farther apart against their gravity this is considered to be gravitational potential energy and has a negative sign attached to it.

Going from hot to cold has nothing to do with whether the universe is expanding or contracting. Heat moves from hot regions to cold regions and this cannot be stopped. We can slow it down with insulation but not stop it. Over time, everything will be the same temperature. This is unavoidable. It is called the "Heat Death" of the universe.
 
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There is more to it than going from cold to hot. Entropy would not be reversed unless and until there was a larger difference between the hots and the almost as hots at some point in time. Not clear how that would happen.

On the other hand, Bill sort of glossed over the assumed reason that there was ever any difference in temperature (or other energy forms) in the materials that comprise the universe. Cosmologists like to think of the universe as being uniform (except for "small" differences like galaxies and voids), and assume that the universe started as a tiny uniform spec that "inflated" to billions of light years. The tiny spec was so small that "quantum fluctuation" created even tinier non-uniformities, which then got "inflated" to enormous dimensions, so that was how the energy got separated into different regions and could be used to "do work" as it tries to become uniformly distributed, again.

But, it really is much more difficult to think about when you realize that the BBT starts with pure energy and somehow there is spontaneous development of order in the form of 6 types of quarks and various other forms of "sub-atomic matter" coming into existence, which then organized themselves into atomic matter, which then underwent fusion in stars to produce more complex atoms, which then combined chemically to produce, ultimately, life and us.

Another way of describing entropy is to relate it to order and disorder. But, when you look at the spontaneous development of all of that order in matter, starting from pure energy, it certainly looks like entropy must have decreased with that definition.

So, once we get out of the physical conditions of our experience with glasses of hot and cold water, and start trying to use the theory that entropy must always increase in anything the universe ever did or could ever do in the future, it seems to me that we should not be ruling out anything on the basis that it would require a decrease in entropy.

In particular, I do not believe that entropy should be used to rule out the possibility of a cyclic universe. Clearly, if the universe could gravitationally "crunch" back into a tiny spec like the BBT theorizes its beginning, then quantum fluctuations should be able to restore whatever entropy condition that existed when it was a tiny spec experiencing those fluctuations in the Big Bang, and then bang back to a new universe with nothing by hydrogen and energy (plus whatever dark matter and dark energy are, if they really exist).
 
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Right, it is not clear how you could increase the difference between the hots and the colds once things have evened out. It would require us to violate the second law of thermodynamics or run time backwards.
I am not well versed on the beginning of the universe other than to know that quantum fluctuations were calculated to be so great as compared to the differences found today that inflation was introduced in order to even them out to match what we see.
A cyclic universe is at odds with our current observation of increased acceleration at the far reaches of the universe.
 
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I agree that we don't see any indications of a cycle in what we can observe. But, that doesn't mean there cannot be a cycle in progress, with only a tiny fraction of the cycle period being observable from here, for now.

One of the things that amuses me about the BBT is when people claim that the conservation of energy is not applicable, but then insist on never decreasing entropy and even insist on conserving "information". Conservation of energy is a much more fundamental law than conservation of information, and is actually implied in the law requiring the increase of entropy.
 
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The problem is that the outer edges of the universe are accelerating faster and faster away from us. What would make those objects start slowing down and eventually causing a Big Crunch?
 
Bill, I don't know what would make the universe's expansion stop and go into contraction.

But, we don't understand why it is expanding in the first place, so I am not going to just assume it must keep doing so. Just naming some unknown mechanism "dark energy" doesn't really tell us anything about how and why. So, I am just not willing to accept "always" without understanding the "how" and "why".

That is my main problem with the BBT. It just keeps extrapolating current observations, backward to a singularity, or at least to the dimension that we say we cannot understand anything smaller. Just because theorists think they have a description of the early events that seems to fit theories derive from quantum mechanics experiments, that is really no guarantee that the universe actually did that. I am open to other possibilities, even though many of the BBT proponents are not.
 
It’s frustrating how often the extrapolations of BBT occur.

Perhaps there should be a BBTc, where the “c” stands for “core”. The “core” limits BBT to objective-based science. No wild event suppositions at t=0, or to any time less than where particle colliders can go. And it would limit, or ignore all together, the suppositions extending the cosmos’ conditions much beyond our current time. It’s clear no one knows the future behavior of DE.
 

JMF

Jan 4, 2023
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I have always felt disappointed/cheated with the idea of the "Heat Death of the Universe" so I have been thinking of alternative possibilities. My ideal scenario would be for the 2nd law of thermodynamics to be a local effect in a universe where the entropy of different regions oscillated about an average value. Obviously this would require a mechanism for reversing entropy in some situations so I considered a known example of entropy reversal.

There are filters (think Maxwell demons) in an organic cell wall that enable entry of nutrients and exit of waste. Cells die but are capable of reproduction - hence are an example of entropy reduction. You may argue, that in a closed system, waste products would overtake nutrients and kill all the cells but is that true in all possible open systems?

I hope that there are structures in our universe capable of converting waste products back into nutrients. Maybe black holes are doing the job (i.e. acting as entropy batteries).

Other thoughts:-
Maybe galactic centres are regions of reducing entropy
Maybe the Universe is an organism with its galactic parts each containing the seed of the whole
Maybe dark energy is galactic cellular wall material
 
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A cell is not a closed system, it has a supply of energy available to it.

Entropy is simply a measure of how much heat in a closed system is not available for work.

Take two glasses of water, one hot and one cold. The difference in temperature is available to do work. Thus only a portion of the total energy is not available. The entropy is low in this case.

Since there is no perfect insulation, it is inevitable that the two glasses will eventually assume the same temperature. Once this happens there is no energy available to do work. All the energy is unavailable. Entropy is at its maximum.

There are only two ways to decrease the entropy of a system:
- Make heat travel from the cold area to the hot area
- Make time go backwards

Not only is it impossible to make entropy go down, it is also impossible for it to stay the same (until the point in time where it reaches its maximum.)
 
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If our universe reverses course and started to collapse would time run in reverse and therefore so would entropy?
 
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No, I am afraid not. If universe started collapsing time would still go forward.
However, Roger Penrose thinks that in 10^100 years from now, all particles will decay and without particles there can be no heat. Heat is vibration of particles. Also there can be no time without particles to create events. At that instant entropy will reset to zero and a new universe will begin. Don't ask for details, that's all I can remember. The good news is, we have plenty of time to mull it over.
 
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Seems awfully speculative about what creates time and how entropy could "reset".

I agree that a collapsing universe would not look like time had changed direction, and more that would a rocket shot into the air and falling back to Earth. If gravity can win the contest and turn around the expansion of the universe, time would still be going in the same direction.

What I thinkk would probably reset entropy would be something like the universe collapsing into a dense state such that elementary particles are all that there is. Some theorists believe that somehow, "information" is always conserved (even though they don't believe that energy is conserved). So they believe that entropy can never be reset no matter what happens.

But, they have no proof for that belief, and I don't believe it with them.

On the other hand, if there was some way to actually reverse time, as in making results be the cause and the causes be the results, then that would seems like it make entropy decrease. So far as we can tell, that doesn't happen.
 
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Yes, there is much speculation involved in the purported "Death of the Universe". It would require protons to decay, which I believe has never been observed. Also electrons I suppose. Free electrons don't decay, right? But then, 10^100 years is a long time, a lot can happen.

As best I understand, the quantum fluctuations present at the moment of creation are the source of the hot and cold areas we currently have. It is the presence of hot and cold areas that allow work to be done and entropy to increase.

If the universe collapsed into a point then I presume those fluctuations would reoccur and prevent an entirely uniform universe from arising. Such uniformity would be at a maximum entropy condition.
 
FWIW, I recently read that most of the entropy of the universe likely took place during the time when baryons formed. [per P.J.E. Peebles] I had not heard that before, but perhaps it's mainstream.
 
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I believe that in the future the concept of entropy will change. It will be realized that a simple radio transmission can adjust an electron or a proton to any quantum level we want. At room temperatures and pressures. With the right induction rate and angle, electrons can be charged up(shrunk down) to the proton level....which is an anti-proton. A long runway is not necessary. A short pulse at the right angle will suffice. Matter-anti-matter reactions will give all the energy we could possibly ever want or need. Without waste products. With simple EM induction principles. All mass and matter will be available for energy extraction.

And of course will demonstrate that electrons and protons are the same thing. One has a low energy personality(left handed, not negative) and one has a high energy personality(right handed, not positive). CERN will eventually be shut down, because it only produces charge fragments that dissolve quickly and have no use. And expose's no secrets....about mass and matter. It only adds useless confusion. And a false standard model.

The only physical entity in this universe is electrons and protons.....and all other structures and objects are made from them. Including neutrons. A neutron is a over dampened dipole. It does not oscillate like a normal dipole. It is locked.....with the proton placed in the center of an electron. The proton lays co-planar inside the electron. A locked oscillation. This is very necessary for any nucleus that contains more than 2 protons. Because of the weak point of a nuclear structure. This is easy to see and understand when you see the structure of a dipole, and the structure of a nucleus.

But many believe that structure and motion as we know it, does not exist at sub atomic levels. But the laws we observe and know, come from those sub atomic structures. Handedness comes from those structures. Mass and the dynamic of inertia comes from these structures. All the laws and proportions we know, come from these structures.
 
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There is no infinite non-local without finite locals to infinity. Infinity, though, cannot be observed. The horizon of all local universes collapse. The collapsed horizon of infinity is an eternal Big Bang Horizon to every local universe. There is no "heat death" of any universe. The other end to that singularity of eternal Big Bang Horizon is numberless singularities of black hole horizons linking back to it like wormholes. There being many different dimensions, many different levels, no immortal traveler traveling galaxies to galaxies, universes to universes, would ever even begin to approach the Big Bang Horizon without having entered a black hole horizon as the door to it. Universes would seem to come from it evolving and expanding toward him as he traveled toward the Big Bang Horizon (that Horizon maintaining itself as Horizon to his rear and side in the universe). Stephen Hawking essentially presented this view of forever travel, forever migration, to mean the existence always of an arriving and arrived steady state infinity of 'frontier', in his Brief History of Time.
 
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