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Mouthwash
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14 Nov 2017 03:46

Watsisname wrote:
Mouthwash, Doc and I have been talking about this a bit and we both conclude that a universe with a reversed second law would simply be equivalent to reversing time.  

A key example is that of a black hole, which is the maximal entropy state for any system.  For entropy to decrease, the black hole must be replaced by a white hole, which is a time reversal.

The second law says that a box filled with air quickly achieves an equilibrium where the air is uniformly distributed.  If you have the air all on one side blocked by a barrier, opening the barrier quickly results in the air filling the box.  It does this because there is a vastly greater number of ways that particles can be arranged uniformly through the whole box, rather than all bunched up on one side, so the system naturally evolves to the higher entropy state.

In a universe where entropy of a closed system decreases, then this implies a box filled with air will naturally evolve to having the air bunched up into highly structured states.  This would appear very strange, as if complex things arise for no reason.  This rise of complexity does occur in our universe with time going forwards, but it is allowed by an increase in entropy elsewhere.  For instance, the complexity of life on Earth is due to the hot Sun providing energy in the form of low-entropy sunlight, and a cold dark sky acting as a sink for the high-entropy energy to flow out.  Life is like an eddy in a stream, where some water can locally move upstream while the bulk of the flow moves downward.  

Reversing the increase of entropy for the Earth system would be like having infrared energy coming in from the surrounding space, driving processes on Earth, and then being shot out as low-entropy sunlight directly into the Sun, which then flows to the core to drive fusion processes in reverse.  Very strange.

Could a universe exist where the entropy stays constant globally?  Yes.  It would have to be completely lacking in evolution of structure.  No stars, no galaxies, no life.  All "irreversible" processes increase entropy by turning useful energy into waste heat.  To avoid that requires a universe with only purely reversible processes.  The expansion of the universe itself is isentropic (does not change the entropy), but not when you include matter which can collapse under gravity and do things.  Gravitational collapse of matter into structures increases entropy.

So in a nutshell: a universe where entropy decreases requires reversing time, and a universe with no entropy change would be very boring.

Cool. However, since quantum effects seem to violate basic laws of the universe (e.g. causing matter to escape black holes, instantaneous connections), it's also conceivable for certain substances or interactions to give out more energy than they take in. Instead of positing a universe where entropy goes in reverse, how about a universe filling up with this magically produced energy?
 
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14 Nov 2017 05:22

Quantum effects do not and cannot violate any laws.  The "laws of the universe" must, by definition, include all observed phenomena. Quantum mechanics, while strange, isn't magic. :)

With black holes you are probably thinking of Hawking radiation.  But this is radiated by space itself near the event horizon, not from matter escaping the interior.  Matter cannot ever escape from within a black hole.  Once it falls through the horizon its destiny lies at the singularity.  In our frame of reference outside the hole, we say whatever falls in simply becomes the mass of the hole.

The Hawking radiation is high in entropy.  It essentially contains the completely scrambled information of whatever fell into the black hole.  The emission of this radiation comes at the expense of the mass of the black hole, so the total mass-energy is conserved.  The universe isn't getting filled with new mass-energy, it gets back the mass-energy that went into creating the black hole.  What happens to this Hawking radiation?  It spreads out isotropically, and over time is diluted and redshifted to blackness as the universe continues to expand.  And since there will come a time when the last black hole evaporates completely, the total amount of Hawking radiation will peak, and its energy density will decline toward zero.
 
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14 Nov 2017 09:58

Hey, what if you tried to reverse entropy by surrounding Earth with infra-red sensitive solar panels? (Let's assume that Earth has been teleported into the middle of a big void, because the Sun's march towards entropy is keeping entropy at bay here.) The solar panels would convert all Earth's radiated heat to usable energy, which could be stored in batteries. There would then be much lower entropy than before Earth cooled off. So, what would stop me from breaking the second law of thermodynamics?
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14 Nov 2017 10:30

Mr. Missed Her wrote:
Hey, what if you tried to reverse entropy by surrounding Earth with infra-red sensitive solar panels? (Let's assume that Earth has been teleported into the middle of a big void, because the Sun's march towards entropy is keeping entropy at bay here.) The solar panels would convert all Earth's radiated heat to usable energy, which could be stored in batteries. There would then be much lower entropy than before Earth cooled off. So, what would stop me from breaking the second law of thermodynamics?

the fact that a 100%-efficient anything doesn't exist. Today's commercially-available solar panels are considered very efficent if they reach 22-24%, and 46% is currently the record.
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14 Nov 2017 13:20

XBrain130 wrote:
Mr. Missed Her wrote:
Hey, what if you tried to reverse entropy by surrounding Earth with infra-red sensitive solar panels? (Let's assume that Earth has been teleported into the middle of a big void, because the Sun's march towards entropy is keeping entropy at bay here.) The solar panels would convert all Earth's radiated heat to usable energy, which could be stored in batteries. There would then be much lower entropy than before Earth cooled off. So, what would stop me from breaking the second law of thermodynamics?

the fact that a 100%-efficient anything doesn't exist. Today's commercially-available solar panels are considered very efficent if they reach 22-24%, and 46% is currently the record.

Of course the panels wouldn't be totally efficient. But the energy that didn't get absorbed would wind up as heat, which would be re-emitted as light, and would have another chance of being absorbed by the panels. Which are surrounding the Earth, so they're hard to miss. A lot less energy would be lost than you think. But the fact that some energy is lost still doesn't convince me, because high-entropy heat still got converted into usable energy. The question is whether this kind of energy conversion reduces entropy.
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14 Nov 2017 16:11

Mr. Missed Her, you seem to have a misunderstanding on how thermodynamics works. 

There is always a loss, because an equilibrium state cannot perform work.  To do work requires a temperature differential, so even if you had magic technology like in your example, a certain percentage of that heat energy will be radiated away and entropy will forever increase.





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Watsisname
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14 Nov 2017 17:26

Mr. Missed Her wrote:
Source of the post Of course the panels wouldn't be totally efficient. But the energy that didn't get absorbed would wind up as heat, which would be re-emitted as light, and would have another chance of being absorbed by the panels.

Ah, but how do you prevent any energy from being re-radiated from the far side of this sphere of perfectly absorbing panels, and lost to space?

If you answer with another sphere of panels, welcome to infinite recursion.  If you answer with a perfectly reflecting mirror, then you're in for a disappointment.  Even if the mirror reflects all photons, conservation of momentum requires that the atoms in the mirror gain twice the momentum of the reflected photon, which goes into thermal energy of the mirror, which will be re-radiated, again some of it outward.  End result: there is still a loss as heat is radiated away.  That radiated heat can never be brought back to do work without increasing the entropy of the whole system.  As Doc says, we cannot beat thermodynamics.

Laws of Thermodynamics in a nutshell:
1) You cannot win.
2) You cannot break even.
3) You cannot escape from the game.

There is also a more subtle problem, lurking behind the idea that the re-radiated heat can be absorbed again to do work.  The panels will not re-radiate photons of the same energy as those they initially absorbed.  The re-radiated photons must have lower energy, which are less useful for doing work in terms of generating power for the panels.  In reality a threshold exists where they will instead simply go into heating the material without producing charge.  This is because it takes some minimum energy in order to cause the charge separation -- in a silicon solar cell it's about 1.1eV which corresponds to photons of about 1.1 micrometer wavelength.  For photon energies below that, the cell cannot generate any power.  

For reference, Earth's thermal blackbody spectrum peaks at about 10 micrometers, or about 0.12eV.  Therefore most of Earth's thermal spectrum is totally useless for generating power in a solar cell.  The consequences of the increased entropy of the energy radiated by Earth are already manifest.
 
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15 Nov 2017 21:09

I'm giving up on this horrible quote system.

"Quantum effects do not and cannot violate any laws.  The "laws of the universe" must, by definition, include all observed phenomena."

But that's just semantics. How do you know that every interaction or property of the universe is going to consistently enforce the same limitations? We do not have any such assurance regarding mathematics.

"With black holes you are probably thinking of Hawking radiation.  But this is radiated by space itself near the event horizon, not from matter escaping the interior."

Again with the semantics. If I teleport out of prison, clearly I haven't "escaped," according to your definition.
 
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15 Nov 2017 23:21

Mouthwash wrote:
Source of the post But that's just semantics. How do you know that every interaction or property of the universe is going to consistently enforce the same limitations? We do not have any such assurance regarding mathematics.

I don't. :)  I only know what I can measure.  If every measurement I have is consistent with momentum being conserved, then I may consider momentum conservation to be a "universal law".  Indeed, momentum conservation is something that is verified so frequently in every conceivable situation that I have no reason to doubt that it will continue to be valid in all future experiments.  I may feel totally confident in applying it to any new situation I am likely to analyze.

Of course for all I know, someday some experiments in a particle accelerator may be found to unambiguously violate momentum conservation.  Suppose that happens.  If it does, nature has not violated its own laws.  Rather, we discover some new aspect of nature which requires modifying what we thought were its laws.  Like Einstein discovering that gravitation isn't a force at all, and "Newton's law of gravitation" is updated with Einstein's model of space-time curvature.  

So I feel it is important to understand that this is not just semantics, but a point of understanding what physical laws are.  They are models that we have created to describe what we see in nature, not the laws that nature is obligated to obey.  Nature can contradict our prior understanding of it, but it cannot contradict itself.

The second thing I want to emphasize is that the validity of the natural laws still holds in quantum mechanics.  The Schrodinger equation itself is fundamentally an energy conservation statement!  Quantum tunneling is a necessary and derivable consequence of the Schrodinger equation for matter waves.  To not have quantum tunneling would violate some laws.


Mouthwash wrote:
Source of the post Again with the semantics. If I teleport out of prison, clearly I haven't "escaped," according to your definition.

Are you a particle and your prison is a potential well?  Then your escape is nothing mysterious.

Is your prison a classical prison and you are a classical object?  Then your escape by teleportation is totally mysterious.  If well documented then you can bet a lot of physicists (and prison designers!) would be very interested in studying how you managed it.

Is your prison a black hole?  Then this implies you exceeded the speed of light.  Your escape did not violate nature, it violated our understanding of nature.  We would require updating our understanding of the dynamics of space-time.
 
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16 Nov 2017 05:55

Answer me this: there are several arbitrary values that allow the universe to have complexity, structure, and life. It seems incredibly unlikely that we stumbled upon the right ones the first time. The only alternatives are that (A) some higher entity created/simulated our universe or (B) there are enough universes that at least some of them get all the values within a range that allows it to contain observers.

With either option, it's clear that the physical laws governing our universe are *not* the ultimate laws of reality. If you then claim that "nature has not violated its own laws.  Rather, we discover some new aspect of nature which requires modifying what we thought were its laws," you are engaging in semantic diversion, since I was asking about the universe's own laws and not the ultimate ones. Moreover, you have no basis for claiming that the laws of nature can't be violated arbitrarily (any more than mathematics can be proven both complete and consistent). Only deduction can allow you to make such a statement, not induction.
 
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17 Nov 2017 00:13

I am not engaging in a semantic diversion.  I am trying to help you correct a misconception about what physics is, about what natural laws are and what they aren't.  If you truly think that I'm more interested in making pointless diversions than engaging in sincere conversation, then feel free to report me for not following the rules of the forum.


Mouthwash wrote:
Source of the post Answer me this: there are several arbitrary values that allow the universe to have complexity, structure, and life.

I'm not sure what you want to me to answer because you haven't asked a question.  You're speaking about the concept of "fine tuning", that our existence requires certain constants of nature to take very precise range of values.  Sure.  It is an open question as to why this is the case.  Maybe A is the correct explanation.  Maybe B is.  Maybe it's neither.  Maybe God did it.  Maybe it's a coincidence.  We don't know; so far we can only speculate.  For what it's worth I think B is the least crazy sounding.

What does this say about universal laws vs. ultimate laws?  It doesn't.  This is the misconception.  

We do not have access to "the universe's own laws" any more than we have access to the "ultimate laws of reality".  I have no idea what either of them are.  The best I can do is formulate models that describe what I can observe and measure.  Those models may work extraordinarily well, but they are just models.  They are something we create to describe nature, not what nature hands to us with the promise "these are the hard truths that I will obey, all the time, everywhere, exactly as written".  

Classical definitions of energy and momentum break down near the speed of light.  Newton's law of gravity breaks down near heavy masses.  General relativity breaks down close to singularities.  CP symmetry was found to be violated in kaon decay in the 1960s.  We can make an extensive list of "violations of the laws of nature", yet not once did nature contradict itself.  Nature was doing this all along; what changed was our understanding of it.  We extended and improved our models to cover a wider range of phenomena than before.

Similarly, quantum mechanics does not violate the laws of nature.  Quantum mechanics describes nature.  How is a photon less natural than a star?  What is less natural about the behavior of a photon than the behavior of a star?  If you are motivated to compile a list of laws of nature then you should include quantum mechanics in your list. :)
 
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17 Nov 2017 05:15

"I am not engaging in a semantic diversion.  I am trying to help you correct a misconception about what physics is, about what natural laws are and what they aren't.  If you truly think that I'm more interested in making pointless diversions than engaging in sincere conversation, then feel free to report me for not following the rules of the forum."

I don't think you're maliciously sabotaging a discussion, but you're confusing a word game for genuine argument.

What I asked about was the possibility that some future discovery will allow us to overcome constraints that are rooted in laws of our universe. You responded by saying "well if we discover anything like that then we were wrong about the laws to begin with, they aren't being violated." Which doesn't provide any useful answer to the question, only clarifies terms. That's what semantic quibbling is.

Anyway, I think the real discussion is about the effects of laws. Law of gravity implies that matter inside an event horizon is stuck forever, while quantum mechanics shows that isn't true.
 
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17 Nov 2017 05:52

I'm sorry, but when you ask "will allow us to overcome constraints that are rooted in laws of universe" you mean they will be violated, it seems to me that he clearly answered, and the answer is that's impossible by definition.
If you don't mean that, then there's no agreement in basic terminology and the discussion is DOA.
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17 Nov 2017 06:39

We don't know if some "laws of the universe" actually exist, but we assume that they do, and it's been a very successful assumption regardless of whether it holds or not.
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17 Nov 2017 07:35

Mouthwash, in this case I not only completely agree with  Watsisname in what he said but I would like to point out that answering you question may imply that laws of nature are something that nature has in it and not a consequence of the act of observing it and describing its behaviour with mathematical rules.

Besides that I would like to expand something:

Mouthwash wrote:
Source of the post The only alternatives are that (A) some higher entity created/simulated our universe or (B) there are enough universes that at least some of them get all the values within a range that allows it to contain observers.

Watsisname wrote:
Source of the post Maybe A is the correct explanation.  Maybe B is.  Maybe it's neither.  Maybe God did it.  Maybe it's a coincidence.  

1) There are not only two possibilities at all. Some mechanism could be involved in the fine-tunning of those universal parameters but that doesn't mean that the only mechanism possible is an intelligent superior being doing it because he want life in his universe. Why should he wanted to do in that way anyway? maybe also a superior being could want to do a universe without life and having much more complex phenomena. Why the intelligent being that simulated reality wanted it like this? It looks like he is the fine-tunned one because is, as an intelligence, particularly fine for us to exist. You just displaced the problem. Why no other mechanism is possible? Top-down cosmology for example, etc...

I mean. That was also part of the argument about life before Darwinian Theory. How perfect and suitable is the world around us to us to live in it. The air is fresh, the water can be drinked and is abundant, the sun shines and the mass of earth is the best so our bones don't degrade so much nor they get crushed by gravity. Such a perfect place. Who chosed it? No one. The thing is that life has evolved to be in concordance with the environment. The same can be said about this. Yeah those physical parameters are near perfect for us to be here but 1) The Universe is not fine-tuned to life; life is fine-tuned to the Universe it has evolved in and 2) "If the universe was designed for life, it must be said that it is a shockingly inefficient design. There are vast reaches of the universe in which life as we know it is clearly impossible: gravitational forces would be crushing, or radiation levels are too high for complex molecules to exist, or temperatures would make the formation of stable chemical bonds impossible" as Robert L. Park says.

This is very very important. Besides jokes, the universal constants are suited for life but only in the most exquisite parts of it. Life can't arise in stars, not in cold places (because of complex chemical reactions been impossible in those environments), not in objects with huge gravity, nor in objects with high doses of radiation. And that without mentioning that life can't arise or thrive in empty space (the vast majority of what there is in the universe). So yeah the universe is suited for life, but only in this tiny little patches and only during a very short time period (could life develop when the universe becomes black hole zoo without stars? could live develop when thermal equilibrium is reached? could have developed when this was a elementary particles plasma soup?). Maybe if the universal laws and constants were different then life could arise on much more places, maybe some rules allow space-time to behave in a self conscious complex dynamical way and entire light years of space are living and thinking instead of just a small dust particle suspended in a sunbeam in the void.


2) Why you even need a mechanism to explain we are here? This has to do with the anthropic principle, I mean you wouldn't be able to ask that question if you weren't here in the first place so what sense does thinking the universe is fine-tunned for you make?
You don't need other universes to explain this. Even if this is the only universe you still exist and therefore the probability is still 100% sure life is compatible with this context even if this context was nearly impossible. If we have a winning loto that doesn't mean that we have tried many, maybe just one was saled. But the difference here is that you would exist and ask this question only if the wining loto was the one that was saled.

Another thing is the fact that you seem to be very confident with the idea of the impossibility of other life forms and physical structures as complex as ours arising from another set of natural laws. If the universe had other rules that would allow for other life forms then they would think exactly the same as you. You are interpreting that only one kind of life could have the right to be and as a consequence that only one kind of parameters are suited for life ignoring all the possible values where the universe would be suited for it (even better than our current parameters).

Also there's a very important point.Not only there are other parameters that can give rise to other kind of processes that give birth to lifeformsthat could ask your same questions, but also is not true that changing a bit the current physical constants life would be impossible. The range is much wider than we usually think and we are starting to understand that now. And this is expected. Think about it; we know that life needs for chemical reactions to occur, we know that for many of those chemical reactions to occur you need electromagnetism to be very strong as to have electrons around atoms and also weak in some sense (in such a way that the nucleus of atoms don't explode because of the repulsion between protons). So since we know that, following that path we conclude that the value that describe the intensity of electromagnetic forces is quite perfect for us coincidentally. What is missing? If you didn't know life existed on this universe and you where given the laws of nature do you really think you could predict the existence of life as a consequence? I mean we are still unable to explain how can it be since we still don't know how it formed how can you predict the complexity of geologic processes, chemistry, nuclear reactions or life if I gave you another set of rules? You would have to make a lot a lot of work, more than its currently possible, in essence you would have to simulate the universe to see if this happens. Sure, there are many possibilities where you would not expect life to arise but would you have expected it in our universe? in this violent and quiet at the same time, expanding void with some impurities floating on it?

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