## Recommended Posts

"Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics. This puts the time reversal symmetry of (almost) all known low-level fundamental physical processes at odds with any attempt to infer from them the second law of thermodynamics which describes the behaviour of macroscopic systems. Both of these are well-accepted principles in physics, with sound observational and theoretical support, yet they seem to be in conflict; hence the paradox. "

All physical laws except of the 2nd law of thermodynamics are reversible in time. Which is a paradox, because it should not be possible to deduce an irriversible law (2nd law of td) from reversible ones (all other physical laws are T-Symmetrical).

The paradox is: it should not be possible to deduce an object absent of the properties of the objects from which it is deduced.

One possible sollution to the paradox is: the 2nd law is not a physical law, but rather an overwhelming probbability, thus we are not likely to see the reversal of it, but it shouldnt be impossible. (the consequence is that in all probabbility, eventualy somewhere such a process should be observed. Or to 'feed' from phylosophy, perhapse it is not observed precisely because the subject is signified by the observed object - is the reversal of the 2nd law,...).

a)You are welcome to develop your sollutions!

b)This is not a thread in which you say "2nd law is irreversible, everybody knows that", because that would mean you havent read or understood the original problematic,

c) or say "there is no proof it is not a law", (same reason)

d) if b or c please read the definition of the paradox one more time and go to a)

Note of inspiration: persisting at b) or c) puts physicists at an awkward situation: to do it, it is to claim physics is a paradox.

Resources:

http://en.wikipedia....wiki/T-symmetry

http://en.wikipedia....tion_to_entropy

http://www.sidis.net/ANIM3.htm

Edited by wucko
##### Share on other sites

Wucko - just a quick note. Is there any reason that the natural world must follow our very human ideas of logic and avoid what to us seems to be a paradox?

Note of inspiration: persisting at b) or c) puts physicists at an awkward situation: to do it, it is to claim physics is a paradox.

Awkward and spooky perhaps - but not necessarily incorrect

##### Share on other sites

"Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics. This puts the time reversal symmetry of (almost) all known low-level fundamental physical processes at odds with any attempt to infer from them the second law of thermodynamics which describes the behaviour of macroscopic systems. Both of these are well-accepted principles in physics, with sound observational and theoretical support, yet they seem to be in conflict; hence the paradox. "

All physical laws except of the 2nd law of thermodynamics are reversible in time. Which is a paradox, because it should not be possible to deduce an irriversible law (2nd law of td) from reversible ones (all other physical laws are T-Symmetrical).

The paradox is: it should not be possible to deduce an object absent of the properties of the objects from which it is deduced.

One possible sollution to the paradox is: the 2nd law is not a physical law, but rather an overwhelming probbability, thus we are not likely to see the reversal of it, but it shouldnt be impossible. (the consequence is that in all probabbility, eventualy somewhere such a process should be observed. Or to 'feed' from phylosophy, perhapse it is not observed precisely because the subject is signified by the observed object - is the reversal of the 2nd law,...).

a)You are welcome to develop your sollutions!

b)This is not a thread in which you say "2nd law is irreversible, everybody knows that", because that would mean you havent read or understood the original problematic,

c) or say "there is no proof it is not a law", (same reason)

d) if b or c please read the definition of the paradox one more time and go to a)

Note of inspiration: persisting at b) or c) puts physicists at an awkward situation: to do it, it is to claim physics is a paradox.

Resources:

http://en.wikipedia....wiki/T-symmetry

http://en.wikipedia....tion_to_entropy

http://www.sidis.net/ANIM3.htm

Bolded mine.

the bolded part must be wrong. Simple mecanisms can provoke irreversibility even if irreversibility is not a fundamental feature of space and geometry.

The statement "it should not be possible to deduce an object absent of the properties of the objects from which it is deduced" is like stating that there cannot exist properties C made of the sum of other properties A and B, although IMHO to world we are observing is exactly that: a construction of complex properties made of simple ones.

Edited by michel123456
##### Share on other sites

Bolded mine.

the bolded part must be wrong. Simple mecanisms can provoke irreversibility even if irreversibility is not a fundamental feature of space and geometry.

The statement "it should not be possible to deduce an object absent of the properties of the objects from which it is deduced" is like stating that there cannot exist properties C made of the sum of other properties A and B, although IMHO to world we are observing is exactly that: a construction of complex properties made of simple ones.

we are looking for a particular reversibility: of the 2nd law od thermodynamics. The problem is it is derrived from reversible laws, but itself isnt reversible.

the reversal of the 2nd law for your example: all the causual relations in universe have been exactly so arranged, that the clicquet opens while at the same time the 'roue' turns clockwise. I can do that. Or you.

yes c can be c = a+b, but you cant have C=c from -c or b

Wucko - just a quick note. Is there any reason that the natural world must follow our very human ideas of logic and avoid what to us seems to be a paradox?

Awkward and spooky perhaps - but not necessarily incorrect

@ Is there any reason that the natural world must follow our very human ideas of logic and avoid what to us seems to be a paradox?

No. But nature is simple and consistent, meaning any paradoxes in physics are not flaws of nature , but flaws of human reasoning or pure error.

Edited by swansont
fix quote tag
##### Share on other sites

/snipped...

No. But nature is simple and consistent, meaning any paradoxes in physics are not flaws of nature , but flaws of human reasoning or pure error.

Nature is not bound to be simple and consistent - that is a human prejudice that is being projected upon it. We hope and assume that nature does not involve paradox - but to assume that our knowledge of the underpinning axiomata of nature is sufficiently well-formed to judge certain theories as paradoxical is dangerous.

##### Share on other sites

we are looking for a particular reversibility: of the 2nd law od thermodynamics. The problem is it is derrived from reversible laws, but itself isnt reversible.

the reversal of the 2nd law for your example: all the causual relations in universe have been exactly so arranged, that the clicquet opens while at the same time the 'roue' turns clockwise. I can do that. Or you.

How do you mean derived in this context?

I don't see any mention of the effect of Heisenberg's uncertainty principle on reversibility. Also, what of random events?

##### Share on other sites

Ya, the "laws" of physics are time-symmetric -- they do not show a direction of time. But the 2nd law of thermodynamics is a different kind of law. It is a deduction based on probability. This is because the odds of a number of constituents being highly ordered gets dramatically lower as the number gets larger.

For example, if you have three cards -- Ace, two, three -and you shuffle them, the odds of drawing them in order are one in six. (3! = 3x2x1) But if you have four cards -- Ace, two, three, four, the odds of drawing them in order grows to 24 (4! = 4x3x2x1). With 10 cards, its 3,628,800. The odds very quickly become astronomical.

So the increase in entropy or disorder we see as a indicating an arrow of time is just a probability-based argument, due to the very large number of constituents in the macro world. It is not a physical "law" in the same sense as other physical laws.

I don't think there is anything new in these arguments.So I think the "possible solution" to the "paradox" is interesting but nothing new.

Edited by IM Egdall
##### Share on other sites

Ya, the "laws" of physics are time-symmetric -- they do not show a direction of time. But the 2nd law of thermodynamics is a different kind of law. It is a deduction based on probability. This is because the odds of a number of constituents being highly ordered gets dramatically lower as the number gets larger.

For example, if you have three cards -- Ace, two, three -and you shuffle them, the odds of drawing them in order are one in six. (3! = 3x2x1) But if you have four cards -- Ace, two, three, four, the odds of drawing them in order grows to 24 (4! = 4x3x2x1). With 10 cards, its 3,628,800. The odds very quickly become astronomical.

So the increase in entropy or disorder we see as a indicating an arrow of time is just a probability-based argument, due to the very large number of constituents in the macro world. It is not a physical "law" in the same sense as other physical laws.

I don't think there is anything new in these arguments.So I think the "possible solution" to the "paradox" is interesting but nothing new.

would you vote that there could be a 'breach' of the 2nd law in nature or not? what do you think?

How do you mean derived in this context?

I don't see any mention of the effect of Heisenberg's uncertainty principle on reversibility. Also, what of random events?

@ How do you mean derived in this context?

http://www.sidis.net/ANIM4.htm

"The second law of thermodynamics is, as we have seen, an irreversible physical law, and seems to be the one distinguishing characteristic between the real universe and the reverse universe. At the same time, that law is of such a nature, that, for the ultimate particles of matter, it does not exist; it is essentially a law concerning transformations of energy of large masses. And yet all large bodies are made up of countless numbers of the ultimate particles of matter, the laws of whose motion are all perfectly reversible. All phenomena of the reverse universe, however strange they may look, are perfectly explicable in terms of the ordinary physical laws as applied to the smallest material particles. It would seem, then, as though there must be some reason in terms of the reversible physical laws why the second law of thermodynamics must be true; that is, the second law of thermodynamics, if true, should be a consequence of the reversible physical laws applicable to ultimate particles. We are, then, confronted with the paradox of having to deduce an irreversible law from perfectly reversible ones."

or from: "Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics"

Nature is not bound to be simple and consistent - that is a human prejudice that is being projected upon it. We hope and assume that nature does not involve paradox - but to assume that our knowledge of the underpinning axiomata of nature is sufficiently well-formed to judge certain theories as paradoxical is dangerous.

i dont understand this, but if you could make it sound more natural i might seriously, studying developpment of physical discourse from antient times to today (from the Earth on a collosal Turtle to quantuum physics) we get a very strong pattern in argumentation:

conservative physicists vs (usualy theoretical) progressive ones: the first will support accepted +thruths+ to the point of correcting those truths to the point of complete incomprihensibility, while the new theorists usualy come up with radically simple theories.

An example par exellance are the geocentrical arguments vs heliocentrical arguments. And in this grand battle of old-accepted vs new challenging ideas in physics the pattern is: the most simple (beautiful even) theories are right most of the time.

Nature is simple in this manner.

Edited by wucko
##### Share on other sites

the second law of thermodynamics, if true, should be a consequence of the reversible physical laws applicable to ultimate particles. We are, then, confronted with the paradox of having to deduce an irreversible law from perfectly reversible ones."

or from: "Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics"

Why does the 2nd Law have to be deduced from the other laws? Are they deduced from each other?

##### Share on other sites

Why does the 2nd Law have to be deduced from the other laws? Are they deduced from each other?

the second law of thermodynamics, if true, should be a consequence of the reversible physical laws applicable to ultimate particles.

##### Share on other sites

the second law of thermodynamics, if true, should be a consequence of the reversible physical laws applicable to ultimate particles.

Why?

Why does it need to be a consequence rather than an additional law? Conservation of energy, for example, is not a consequence of conservation of charge.

##### Share on other sites

"Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics. This puts the time reversal symmetry of (almost) all known low-level fundamental physical processes at odds with any attempt to infer from them the second law of thermodynamics which describes the behaviour of macroscopic systems. Both of these are well-accepted principles in physics, with sound observational and theoretical support, yet they seem to be in conflict; hence the paradox. "

All physical laws except of the 2nd law of thermodynamics are reversible in time. Which is a paradox, because it should not be possible to deduce an irriversible law (2nd law of td) from reversible ones (all other physical laws are T-Symmetrical).

The paradox is: it should not be possible to deduce an object absent of the properties of the objects from which it is deduced.

One possible sollution to the paradox is: the 2nd law is not a physical law, but rather an overwhelming probbability, thus we are not likely to see the reversal of it, but it shouldnt be impossible. (the consequence is that in all probabbility, eventualy somewhere such a process should be observed. Or to 'feed' from phylosophy, perhapse it is not observed precisely because the subject is signified by the observed object - is the reversal of the 2nd law,...).

a)You are welcome to develop your sollutions!

b)This is not a thread in which you say "2nd law is irreversible, everybody knows that", because that would mean you havent read or understood the original problematic,

c) or say "there is no proof it is not a law", (same reason)

d) if b or c please read the definition of the paradox one more time and go to a)

Note of inspiration: persisting at b) or c) puts physicists at an awkward situation: to do it, it is to claim physics is a paradox.

Resources:

http://en.wikipedia....wiki/T-symmetry

http://en.wikipedia....tion_to_entropy

http://www.sidis.net/ANIM3.htm

Loschmidt's paradox is not the only reason which the second law of thermodynamics is in conflict with the time-reversibility of mechanics.

The solution to this paradox is that the time symmetry of mechanics is an approximated symmetry valid only for certain simple situations. Universe is not described by a group, but by a semigroup with a well-defined arrow of time. Time-symmetry is recovered only under certain approximations.

A non-technical explanation is given in the well-known book The End of Certainty, which summarizes recent research advances. A set of references can be found in Prigogine webpage. Complementary non-technical presentations about recent advances in understanding irreversibility are given here and here.

Edited by juanrga

## Create an account

Register a new account