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Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

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Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#91

Post by maverick_iceman »

Chinjut wrote: post #83
ThePhysicist wrote: post #34

The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consis…

This argument that the Second Law is a simple logical consequence of basic probability always seems glib to me. Why would probability demand entropy increase as one extrapolates forward in time, but probability not similarly demand entropy increase as one extrapolates backwards in time? In other words, what of Loschmidt's paradox ( https://en.wikipedia.org/wiki/Loschmidt%27s_paradox )?

You are right in that we need to assume that the universe started in an extremely small entropy state. This is basically the past hypothesis. (Which can be justified to some extent using anthropic principle and eternal inflation, however these two ideas are very controversial among physicists.)

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#92

Post by xenadu02 »

rascalpenguin wrote: post #82
ThePhysicist wrote: post #34

The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consis…

This is very true, and is the case with many 'laws'. Another example is with centre of masses: Take a hollow sphere, clearly the c.o.m. should be in the very middle, yet an object placed inside has not force whatsoever on it so it isn't attracted to the c.o.m. and the idea breaks down (NB objects outside are attracted predictably). This is because this idea is purely a tool to make calculations of large groups of par…

I don't think that's true. An object would be attracted to the inner surface of the sphere because that's where the mass actually is. The shape you're describing doesn't have a center of mass the way we traditionally think of it.

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#93

Post by maverick_iceman »

nabla9 wrote: post #89
Chinjut wrote: post #83

Earlier quoted context omitted.

This argument that the Second Law is a simple logical consequence of basic probability always seems glib to me. Why would probability demand entropy increase as one extrapolates forward in time, but probability not similarly demand entropy increase as one extrapolates backwards in time? In other words, what of Loschmidt's paradox ( https://en.wikipedia.org/wiki/Loschmidt%27s_paradox )?

Universe started from low-entropy state. From the big bang, there is nowhere go but downhill. In a microscopic level the physics can be time-symmetric (it seems not to be the case, there are T-symmetry violations), but macroscopically universe had higher entropy in the past (cosmological arrow of time) edit: CPT-symmetry -> T-symmetry .

Which experiment saw CPT violation? CPT is a straightforward consequence of QFT with minimal assumptions.

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#95

Post by dahart »

rascalpenguin wrote: post #82
ThePhysicist wrote: post #34

The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consis…

This is very true, and is the case with many 'laws'. Another example is with centre of masses: Take a hollow sphere, clearly the c.o.m. should be in the very middle, yet an object placed inside has not force whatsoever on it so it isn't attracted to the c.o.m. and the idea breaks down (NB objects outside are attracted predictably). This is because this idea is purely a tool to make calculations of large groups of par…

Which law are you thinking of? There isn't a physical law I'm aware of that claims gravitational attraction toward a center of mass, you might be conflating several laws or thinking of an approximation rule that was never intended to cover one object inside or even near another.

Newton's law of gravitation is stated in terms of a particle to particle relationship.

Center of Mass is the balance point of an object, and objects will always rotate around their center of mass unless constrained, but this doesn't relate to gravity.

You can approximate gravity at a distance from any object by using the object's center of mass, but that approximation breaks down when you're close to it.

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#96

Post by dahart »

beagle3 wrote: post #40
ThePhysicist wrote: post #34

The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consis…

The second law of thermodynamics is as fundamental as the uncertainty principle: The former is a result from markov chains and information theory, the latter is a result from fourier analysis of conjugate variables. What would you consider a "fundamental physical law"?

This list of what makes a physical law is a pretty good start: https://en.m.wikipedia.org/wiki/Physical_law#Description

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#97

Post by Florin_Andrei »

xenadu02 wrote: post #92
rascalpenguin wrote: post #82

Earlier quoted context omitted.

This is very true, and is the case with many 'laws'. Another example is with centre of masses: Take a hollow sphere, clearly the c.o.m. should be in the very middle, yet an object placed inside has not force whatsoever on it so it isn't attracted to the c.o.m. and the idea breaks down (NB objects outside are attracted predictably). This is because this idea is purely a tool to make calculations of large groups of par…

I don't think that's true. An object would be attracted to the inner surface of the sphere because that's where the mass actually is. The shape you're describing doesn't have a center of mass the way we traditionally think of it.

It's absolutely true, and it's known as the shell theorem. It's an old result actually.

https://en.wikipedia.org/wiki/Shell_theorem

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#98

Post by Florin_Andrei »

beagle3 wrote: post #40
ThePhysicist wrote: post #34

The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consis…

The second law of thermodynamics is as fundamental as the uncertainty principle: The former is a result from markov chains and information theory, the latter is a result from fourier analysis of conjugate variables. What would you consider a "fundamental physical law"?

> The second law of thermodynamics is as fundamental as the uncertainty principle: The former is a result from markov chains and information theory, the latter is a result from fourier analysis of conjugate variables.

I don't think enumerating the pedigree of a law gives it the seal of approval of validity. Newtonian physics also has pretty solid pedigree, and yet breaks down in relativistic conditions.

Please note I do not disagree with your conclusion, only with the way you present it.

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#99

Post by Russell91 »

ilyagr wrote: post #87
Chinjut wrote: post #83

Earlier quoted context omitted.

This argument that the Second Law is a simple logical consequence of basic probability always seems glib to me. Why would probability demand entropy increase as one extrapolates forward in time, but probability not similarly demand entropy increase as one extrapolates backwards in time? In other words, what of Loschmidt's paradox ( https://en.wikipedia.org/wiki/Loschmidt%27s_paradox )?

There fact that is not a consequence of statistics is that we observe the universe to not be in the state of maximal entropy. That is sufficient to explain asymmetry of time, I think. The mystery is -- why wasn't the universe in a state of maximal entropy at time 0?

Elon Musk hadn't started his simulation yet /s

Re: Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

#100

Post by nabla9 »

maverick_iceman wrote: post #93
nabla9 wrote: post #89

Earlier quoted context omitted.

Universe started from low-entropy state. From the big bang, there is nowhere go but downhill. In a microscopic level the physics can be time-symmetric (it seems not to be the case, there are T-symmetry violations), but macroscopically universe had higher entropy in the past (cosmological arrow of time) edit: CPT-symmetry -> T-symmetry .

Which experiment saw CPT violation? CPT is a straightforward consequence of QFT with minimal assumptions.

Sorry, I meant T-symmetry violation, corrected.

Kaon decay and B mesons decay break CP-symmetry and a CP-symmetry violation is equivalent T symmetry violation (CPT symmetry is preserved only if CP-violation is paired with T-symmetry violation)

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