## Entropy can be reset to a previous or to an initial state

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If matter has existed from infinite past, then entropy is such that it can be reset to a previous state.

If this was not true, the world would be approaching much closer to a fully entropic state than what we experience right now. Or else perhaps we'd be in a fully entropic state.
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then entropy is such that it can be reset to a previous state

It can, but it won’t. That’s sort of the whole point. Statistically speaking, it is almost impossible for entropy to decrease in a complicated system
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If time is a closed circle, then we can get to a stage where the entropy reaches the maximum value possible and suddenly it becomes ordered. The question deals with the arrow of time. Is time a linear line or a circular path
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Entropy increases with time but if time is a circular path, does that cause entropy to decrease at the starting point.
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but if time is a circular path

This is almost impossible. It will mean the world has to keep returning to an initial state over and over again. That makes you think our world works this way?
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I won't talk about possibility as that is clearly beyond our scope here. We are nor physicists. Time being a circular path is possible
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'Entropy' is a human concept linked to their other concepts 'time', and 'events'. Without considering human requirements in defining 'order of events' relative to their reference frames, all talk of 'the world' tends to be meaningless.
NB 'What works' equates to 'what is predictable for humans', nothing more more and nothing less.
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or it isn't.

When we say something is possible, in these kinds of situations, it can have two meanings which often get conflated.

One is a factual understanding: It is possible to have the light switch on 'on' or on 'off'. Those are real possibilities, which we can in fact test. There can be all sorts of this type of possibility.

The other possibility has to do with our limited knowledge: it means, more of less, for all we know X is possible. Or 'we cannot rule out X' given our limited knowledge.

I think saying Time being a circular path is possible is of the latter kind of assertion. IOW it may not be possible, in the first sense at all. But perhaps, for all we know it might be the case. The nature of reality might utterly rule out this 'possibility'. And some might be able to make a case we already know that.
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If the universe existed eternally, and if all events have a finite duration, then everything that could have happened, would have finished already.
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Can you expand on this? I'm not sure it follows. Could it not be that there are infinitely many finite events.
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I would say entropy is a physical event recognized by humans as such. Not merely a human concept divorced entirely from reality.
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If the universe existed eternally, and if all events have a finite duration, then everything that could have happened, would have finished already.

Yes, and then the events would repeat again and again and again.

Everything possible not only has happened, but has happened an infinite number of times.

And that would be impossible if entropy was not something that could be reset to an earlier state.
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It can, but it won’t. That’s sort of the whole point. Statistically speaking, it is almost impossible for entropy to decrease in a complicated system

I thought that it couldn't. It turns out that it not only can, but it does. Much smarter men and women figured this out. I researched the topic because I wanted to publish my idea, and it turns out the physicists have already figured out the time span at the end of which entropy resets. Don't ask me, I forgot the value, it's some huge number of picaseconds. And I have no clue why, how, and in what process entropy gets reset.
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Can you expand on this? I'm not sure it follows. Could it not be that there are infinitely many finite events.

I think Wayfarer meant that there are two cosmic clocks: one gets reset every so often, and that is the clock, so to speak to the time that it shows the world's events are tied to, on a one-to-one bases, accountably to every infinitely small or finitely large moment or span of time; and there is another clock, that keeps on ticking and not getting reset every time the circular clock does. The clock that keeps on ticking conceptually can measure the time elapsed between many circular time-universes.

Think of it as years. In each year we have the months repeating from january to december inclusive. Then this repeats. But we have years, also. The repeating months would be the circular modus operandi, and the years, the straight-line counter. The entropy would be tied to the circular time, and on the straight scale, it would appear to reset itself, while on the circular clock it would not be noticable how and when it resets itself.
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Only closed systems are statistically required to increase in entropy. According to our current understanding, our universe is not a closed system: there is a continuous (but not constant; currently it is accelerating) influx of dark energy. The theory of eternal inflation holds that it was a runaway acceleration of this energy of space itself, or rather a local sudden stopping of such a runaway acceleration that is otherwise continuously ongoing everywhere, that gave rise to the "initial" energy-dense state of the universe as we know it; and the currently accelerating expansion is our local universe gradually returning to the eternally-inflating state of the rest of it.

I have hopes that some day we will figure out a way to harness that energy of the expansion of space itself as a way of providing unlimited energy with which to maintain life forever. There's something like 2000% as much dark energy as there is energy of ordinary matter as we know it, so if we could manage to capture even around 5% of that, we could literally recreate the entire universe of ordinary matter that we know, over and over and over again, as long as we wanted. No need to worry about even protons decaying over unfathomably long periods of time, if we can always make more.
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Only closed systems are statistically required to increase in entropy

It's not a statistical reality. Energy levels equalize, via heat transfer. They can't unequalize. This leads to the depletion of useful energy, as work (change) can only be attained by using the energy between two unequal energy states.

I think your concept of entropy is way different from mine. I don't know what yours is; I just described mine. It would be helpful for me to know what you mean by entropy.
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The expanding universe model has many, many theoretical explanations, and none defy the continuing event of entropy.
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The second law of thermodynamics happens as a result of statistical mechanics: more-entropic states are definitionally more likely than less-entropic ones, so over time dynamical systems will tend to evolve toward more-entropic states. See here for further explanation. It's the same law you're talking about, just understood at a deeper level.

That's not the point though; "statistically" was just me being pedantic, because in principle it is possible for entropy to randomly decrease, it's just unbelievably unlikely, so it felt wrong to just write "required" without the "statistically" qualifier.

The point is that the second law of thermodynamics doesn't require that an open system with more energy pouring into it eventually wind down to maximal entropy. The Earth, for example, doesn't wind down to maximal entropy because we have the sun pumping new energy into our ecosystem all the time. The second law still applies on Earth, things do wind down, but so long as there is a constant influx of new energy they can keep winding down without ever hitting bottom.

Dark energy is precisely such a new influx into the universe as a whole. The second law still applies, things do keep winding down, but with a constant influx of new energy they don't have to ever hit bottom.
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Dark energy is precisely such a new influx into the universe as a whole.

Okay, I get it. Thanks.

The problem with this is that the entire universe, in its infinite expanse, whether it contains finite or infinite amount of matter, is a closed system. You restrict your observation to the observable universe, the universe we call known or seen or observed universe. But space is infinitely large, and together it is a closed system.

To take your analogy of Earth and Sun: sure nuff, Earth gets an influx of useful energy from the sun, but the sun has its own process of entropy, so the closed system of Earth, will deplete the open system too, which includes (in this example) only the sun as the 'outside' part of the closed system.

The entire infinite space with infinite matter, the whole system is a closed system.
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Can you expand on this? I'm not sure it follows. Could it not be that there are infinitely many finite events.

Not sure that I can. It’s a one-sentence paraphrase of an argument I read about but I don’t have enough information to elaborate on it. But it makes intuitive sense to me.

According to our current understanding, our universe is not a closed system:

Do you think that has any bearing on the ‘causal closure’ principle beloved by materialist philosophers? (Which is that every physical event has a physical cause.) Science doesn’t know what ‘dark energy’ (or dark matter) are, so how can they say they’re physical, when they’re not even described by current physics?
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Science doesn’t know what ‘dark energy’ (or dark matter) are, so how can they say they’re physical, when they’re not even described by current physics?

I think this is a misunderstanding. Current physics do describe "dark matter" and "dark energy". These names describe physical phenomena that have been observed. The name implies that these phenomena are different from other phenomena in that they interact only in very specific ways, not that they're outside of physics.

The entire infinite space with infinite matter, the whole system is a closed system.

Well we don't really know that, do we? It seems logical on its face, but we can only establish the laws of physics for the observable universe. In a way the observable universe is just a visualisation of the laws of physics. Beyond the observable, all bets are off.
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Current physics do describe "dark matter" and "dark energy". These names describe physical phenomena that have been observed.

They have *never* been observed. There's an inference that they must exist because of their effect, but nobody has a clue about their nature. Dark matter is said to be non-baryonic, that is, doesn't consist of the same types of particles that regular matter does, but nobody knows what it might be.
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Can it be a too difficult process though? Perhaps entropy cannot.

Will it all just fade away some day? Is this permenant?
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The problem with this is that the entire universe, in its infinite expanse, whether it contains finite or infinite amount of matter, is a closed system.

Not according to current theories of physics. "Closed system" means no energy enters the system or leaves it. But according to current physics, new energy is constantly being created everywhere; and if eternal inflation is correct, then in most places it is being created far faster than it is in our observable universe, and it's only a temporary pause in it that allowed the structure we see in that observable universe to form.

Do you think that has any bearing on the ‘causal closure’ principle beloved by materialist philosophers? (Which is that every physical event has a physical cause.) Science doesn’t know what ‘dark energy’ (or dark matter) are, so how can they say they’re physical, when they’re not even described by current physics?

The principle of causal closure is about what counts as physical. Anything that has a physical effect counts as a physical thing. We observe physical effects (galaxies rotating faster than we would otherwise expect should be possible without flying apart, and galaxies accelerating away from each other faster that we would otherwise expect), and we don't yet know what is causing them, so we give whatever those things are placeholder names, "dark matter" and "dark energy". But since they have physical effects, whatever those things turn out to be count as physical things.

They have *never* been observed. There's an inference that they must exist because of their effect

Almost everything we have learned about the universe in the past few hundred years has been learned through indirect observation. We see effects on things we can directly observe, posit something we can't directly observe as the cause of those effects, and then check if other effects we would expect from such a thing are also observed or not. That's how basically all of science works.
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new energy is constantly being created everywhere

Coming into existence, then. Hard to imagine how this could be observed, isn't it? Or what kind of physical theory could account for that?

They [dark matter/energy] have *never* been observed. There's an inference that they must exist because of their effect
— Wayfarer

Almost everything we have learned about the universe in the past few hundred years has been learned through indirect observation

I think that's too broad a generalization. There's been an enormous amount of direct observation in astronomy. I understand where the dark matter conjecture comes from - that according to current physics, galaxies ought to fly apart, something must be preventing that from happening. As physics is basically physicalist, then the placeholder for that 'something' is named 'dark matter', but we ought to make it clear, that nobody knows what 'dark matter' is or even if it is real.
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Coming into existence, then. Hard to imagine how this could be observed, isn't it? Or what kind of physical theory could account for that?

No? We observe it happening. We just don’t have an account of why yet.
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As physics is basically physicalist, then the placeholder for that 'something' is named 'dark matter', but we ought to make it clear, that nobody knows what 'dark matter' is or even if it is real.

We know it is real, we just don’t have much of account of what it’s like besides the basic stuff we observe about it (weakly interacting, massive, about how much there is and how it’s distributed in the universe).

Also, looking through a telescope is an indirect observation. Especially a non-visible-light telescope.
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Also, looking through a telescope is an indirect observation. Especially a non-visible-light telescope.

Data collected from radio-telescopes of distant stellar objects is direct - you're seeing the light waves or radio waves emitted by the object. It's no less direct than looking at anything. But if you see the effects of something about which you have no concept, that's inferential - you're inferring that some unknown substance - dark matter, say - is exerting gravitational pull on galaxies.

And 'we' don't know it's real at all. There are astronomers who believe that physics is inaccurate or problematical at those scales, for example. Other physicists say they're wrong, but nobody has direct empirical evidence of the existence of dark matter. As of now, it's metaphysics.
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We can’t see radio waves. We can build machines that interact with those radio waves and do things in response that we can see, and so infer what kind of radio waves are coming from where indirectly that way.

We can’t see wind, but we can see leaves moving and infer the existence of wind from that. (Disregarding other senses for this example).

We can’t see asteroids in the asteroid belt, or single-celled organisms, but we can build arrangements of lenses and mirrors that project images of them that we can see.

I’m surprised you didn’t comment on this in my thread Against Transcendentalism as it’s a pretty important part of establishing a what “natural” means. Without it, germs are as “metaphysical” as you say dark matter is.
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I’m surprised you didn’t comment on this in my thread Against Transcendentalism as it’s a pretty important part of establishing a what “natural” means. Without it, germs are as “metaphysical” as you say dark matter is.

Mistaken. In the case of radio waves, wind, and germs, we have a precise physical description of these, even if they're not visible to the naked eye. They're certainly visible to the eye augmented by radio telescopes, wind-socks and microscopes, respectively. But these aren't indirect means of detection; we can see and measure the phenomenon that is the cause of the observed effect.

Whereas there is no theory of what dark matter is at all. Something not being detectable by unaided vision doesn't make it metaphysical. What makes dark matter a metaphysical conjecture, is precisely that it is beyond - "meta" - known physics. Likewise, questions about whether there are parallel universes or the multiverses predicted by string theory.

I'm surprised by your apparent naivety in this matter ;-)
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we have a precise physical description of these

There is a difference between not having a complete explanation of a pheonomenon, and that phenomenon being "metaphysical" or somehow not physical. And that has nothing to do with direct vs indirect detection. Radio waves, wind, germs, etc, are things that we have done enough indirect observation of and enough theorizing about to come up with thorough explanations of them in the same terms as the things we have direct observation of.

But, for example, we had such detection of radio waves long before we had physical theories that framed them as the same kind of thing as light. Dark matter is currently in that stage: we have observed that it is, even though we don't yet have a complete theoretical explanation of what it is. We can "see" dark matter in exactly the same way you can "see" a transparent glass orb: by the distortion of light from behind it, via gravitational lensing in the case of dark matter. We know for sure that there is a certain amount of mass in a certain place and that it doesn't interact strongly with certain forces, and we don't yet know a lot more about what is there, but we know for sure that there is something there.

You have this weird thing where you don't differentiate between things that we don't currently have a full explanation of and things that are beyond explanation, like when you conflate the paranormal with the supernatural. Supernatural things have no physical effects to be observed at all. Paranormal things supposedly do, but the occurrence of the claimed phenomena has not yet been confirmed. Something like dark matter is a step further still away from that: we know that a phenomenon is for sure occurring, we just can't completely explain it yet. And then there are the familiar well-known topics that we can explain. But lack of an explanation doesn't mean it's unexplainable, just that it's unexplained. Being physical isn't the same thing as being fully explained by current theories of physics, it's just being the kind of thing that we can learn about through the methods of physics.
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