11 ms·

Physicists rewrite the fundamental law that leads to disorder

136 points by theafh 4y ago

edgyquant 4y ago
Sigh. There is no link to a peer reviewed paper in there, just describing entropy and a few scientists working on describing thermodynamics via quantum theory.
- civilized 4y ago
  It would be nice, but I think this is a survey of an evolving field and there probably isn't any one pivotal paper. Plugging some key names (Marletto, Halpern) and key terms (constructor theory, resource theory) from the article into Google Scholar, or visiting the linked researchers' websites, will probably get you what you're looking for.
  - drallison 4y ago
    David Deutsch as well. Chiara Marleto has a nice recent book, The Science of Can and Can't, which discusses briefly the Second Law in the context of constructor theory.
- boole1854 4y ago
  The key papers are as follows: This paper introduced constructor theory: Deutsch, D. Constructor theory. Synthese 190, 4331–4359 (2013). https://doi.org/10.1007/s11229-013-0279-z https://doi.org/10.1007/s11229-013-0279-z (Download preprint version: https://arxiv.org/abs/1210.7439 https://arxiv.org/abs/1210.7439) Then this paper applied constructor theory to form a constructor theory of information: Deutsch David and Marletto Chiara 2015 Constructor theory of information Proc. R. Soc. A.4712014054020140540 (Download: https://royalsocietypublishing.org/doi/10.1098/rspa.2014.0540 https://royalsocietypublishing.org/doi/10.1098/rspa.2014.054...) Then this paper applied the constructor theory of information to probability: Marletto Chiara 2016 Constructor theory of probabilityProc. R. Soc. A.4722015088320150883 http://doi.org/10.1098/rspa.2015.0883 http://doi.org/10.1098/rspa.2015.0883 (Download: https://royalsocietypublishing.org/doi/10.1098/rspa.2015.0883 https://royalsocietypublishing.org/doi/10.1098/rspa.2015.088...) Finally, this paper applied the constructor theories of information and probability to thermodynamics: https://arxiv.org/pdf/1608.02625.pdf https://arxiv.org/pdf/1608.02625.pdf (not yet published in a journal, to my knowledge)
- mindcrime 4y ago
  It appears that the first occurrence of the the name of each of the researchers mentioned in the article links through to their respective home-page. At a quick glance, most of them appear to publish lists of their publications, some with direct links to the actual papers. Of course it might be hard to tease out which papers they've contributed to that pertain to this specific topic, but it would probably be worth the effort for someone who was really interested. For what it's worth, the Deutsch "Constructor Theory" stuff has its own homepage at https://www.constructortheory.org/ https://www.constructortheory.org/ There is also a Wikipedia page that has a list of references and external links. https://en.wikipedia.org/wiki/Constructor_theory https://en.wikipedia.org/wiki/Constructor_theory
- photochemsyn 4y ago
  A little digging turns up this, which discusses their experimental work: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080401 https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080... "(2022) Emergence of Constructor-Based Irreversibility in Quantum Systems: Theory and Experiment, Marletto & Vedral" That's related to this quote from the article: > "But crucially, the theory also predicts that the row becomes even less able to do the reverse transformation from B2 to B1. The researchers have confirmed this prediction experimentally using photons for B and a fiber optic circuit to simulate a row of three qubits." The experiment is rather complex, and would take a long time to analyze and understand in depth. They appear to be claiming that microscopic reversibility, a cornerstone of atomic-molecular kinetic theory, is being violated in their setup? Seems like a rather extraordinary claim but it passed peer review in a major journal so, worth digging into probably. For those who want an introductory overview of the issue, this is a good one: https://www.thoughtco.com/laws-of-thermodynamics-p3-2699420 https://www.thoughtco.com/laws-of-thermodynamics-p3-2699420 > "Kinetic Theory & the Laws of Thermodynamics The laws of thermodynamics do not particularly concern themselves with the specific how and why of heat transfer, which makes sense for laws that were formulated before the atomic theory was fully adopted. They deal with the sum total of energy and heat transitions within a system and do not take into account the specific nature of heat transference on the atomic or molecular level." In practice the second law is not all that useful although it's philosophically important I suppose. For example, a redwood tree growing from a redwood seed plus simple inputs (CO2, H2O, photons, NH3 etc.) is clearly a local decrease in entropy, as opposed to the dispersal of those elements when a redwood tree burns or falls and is digested by fungi, but since solar fusion is creating a much greater increase in entropy, there are no second law violations. Similarly the creation of heavy elements in a supernova would seem to be a decrease in entropy but the release of all that energy to the surrounding universe ensures no second law violations take place. In practice it's very difficult to do all the accounting for even moderately complex systems.
  - edgyquant 4y ago
    Thank you for taking the time to dive into this
- deleted 4y ago
  [deleted]
atx42 4y ago
I've wondered why we don't just assume the arrow of time was reversed in the past? We know that in the past the universe was more organized (had less entropy), so it doesn't seem like much of a stretch from believing entropy started out that way. Wouldn't that make it easier things like life to form, etc. and simpler than reaching for alien life / multiverse theories? Or does it make it just as difficult? Just a lazy armchair physicist here, but maybe evening TO morning was the first day?
- leephillips 4y ago
  I can’t grasp the meaning of all of your comment, but I think it’s worth pointing out that there’s nothing in the Second Law that prevents life from evolving. We certainly don’t need to invoke multiverses for that. For systems out of thermal equilibrium, such as a planet embedded in a flux of energy from its star, entropy can and does decrease all the time. An air conditioner (heat pump), for example, causes heat to flow opposite to the temperature gradient, pushing heat from your house into the outside, and increasing the temperature difference, thereby decreasing the entropy in your area. But you have to expend energy to do so, hence your electricity bill.
  - atx42 4y ago
    Does reversing time makes it "easier" to get life, than the current direction?
    - leephillips 4y ago
      The direction of time is just a convention, and the laws of physics are (still, as far as I know) time-reversible, so this is really irrelevant. You need an energy source to make anything, including life.
      - pfortuny 4y ago
        All except for (precisely) the heat equation, which is not time-reversible (there is a “loss of information” as time passes, very badly and roughly speaking). See https://math.stackexchange.com/questions/628720/why-heat-equation-is-not-time-reversible-time-arrow-in-mathematics https://math.stackexchange.com/questions/628720/why-heat-equ...
dgellow 4y ago
I know very little about actual physics, but generally speaking the more grandiose headlines sound the less I pay attention… Could someone who knows the topic tell us (and by “us” I mean layman like me) if there is something to keep from this article? It brings so much context that after reading it I still have no idea what this “rewrite of fundamental law” is about.
- boole1854 4y ago
  My summary: There has always been something unsatisfactory about the second law of thermodynamics. Unlike many other laws in physics, which precisely state both what kinds of structures exist in reality and how they behave, the second law has a built-in lack of precision. Specifically, there are multiple statements of what the second law says, but they all suffer from referencing some concept which is inherently fuzzy at some scale. For example, they may refer to "heat" as part of the law, but the physical definition of "heat" is fuzzy at the microscale -- it only has a clear meaning for "large systems". However, using a new physio-mathematical formalism called "constructor theory" the researchers have now found a way to state the second law of thermodynamics which is precise at all scales.
  - namero999 4y ago
    A tiny adjustment to an otherwise ok summary: physics state how nature behaves, and not what structures exist in and of themselves. All structures posed by physics are metaphorical proxies stemming from our perception, not real structures.
    - boole1854 4y ago
      I suppose I should say that I am using the understanding of "physical explanations" promoted by David Deutsch, among others. (Deutsch is the creator of constructor theory which is the subject of this thread): "A scientific explanation is a statement of what is there in reality, and how it behaves and how that accounts for the explicanda." (emphasis added) [1] Deutsch argues strongly against the view of physics which says that physical explanations are just about predictions of behaviors and not about what is really out there. See also his 1997 book The Fabric of Reality. [1] https://www.sciencedirect.com/science/article/pii/S135521981530023X https://www.sciencedirect.com/science/article/pii/S135521981...
ThePhysicist 4y ago
The article is of course oversimplifying, but if I understand correctly the irreversibility in the qubit system comes from the fact that they assume you don't know the states of the qubit chain that transforms the first qubit from B_1 to B_2. If you'd know that the state would be pure and it would be easy to reverse the entanglement, it's just that if you look at the state of the first qubit alone that it's mixed. I actually envisioned a similar thought experiment that could be done with a very complex quantum computer (say millions of qubits) to test whether the universe is actually keeping tabs of all these states or if it gives up at some point and produces irreversibility. But I guess if you'd formulate it like that the academic community wouldn't take you very seriously anymore. I'd wager Deutsch's actual motivation might be along this line, as he seemed very interested to find a way to test the many worlds interpretation against other interpretations of quantum mechanics.
- boole1854 4y ago
  Deutsch's position is actually that the many worlds interpretation has already been tested and has passed the tests so far, whereas rival theories have been refuted. See https://www.sciencedirect.com/science/article/pii/S135521981530023X https://www.sciencedirect.com/science/article/pii/S135521981...
  - lisper 4y ago
    Deutsch is wrong. http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...
    - boole1854 4y ago
      To summarize the argument that the blog post makes: The multiverse interpretation accounts for cases where the probabilities of each distinct observable outcome are equal according to the Born rule. But it cannot account for cases where the Born rule says there are non-equal probabilities for the possible outcomes. This is a fairly common problem which critics of the multiverse interpretation raise. See [1] for another example where a critic raises that problem in more detail (with examples). Deutsch and others have responded. In short, the reply is that the mathematics of the Schrodinger equation describes a density of universes in the continuum which is the multiverse, not a finite set of distinct, interacting single universes. This undercuts the critics' argument. See [2] for an example of this kind of response. [1] https://arxiv.org/pdf/0810.2657.pdf https://arxiv.org/pdf/0810.2657.pdf [2] https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111 https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111
photochemsyn 4y ago
Here's the apparent important source paper, Feb 2022 in Physical Review Letters: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080401 https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080... Figs 1 and 2 show the setup. Here's the conclusion: > "This gives a clear proof of the compatibility of constructor-based irreversibility with unitary quantum theory, providing a frame for the emergence of thermodynamical irreversibility in quantum mechanics." It seems like an extraordinary claim, but is very interesting. The theoretical framework (constructors) is a bit confusing. Hopefully this will be replicated. I recall someone talking about something rather similar once, related to so-called chaos theory (now more generally called 'sensitive dependence on initial conditions'), which describes how deterministic systems can give rise mostly unpredictable phenomena (strange attractors etc.), in which indeterminate quantum states at the atomic level are the ultimate cause of the phenomenon.
- leephillips 4y ago
  Since all these phenomena of chaos are inherent in the differential equations, how can they possibly have anything to do with quantum states? The sensitive dependence on initial conditions is a mathematical property of the description of the chaotic systems. It’s a closed mathematical system that makes no reference to any physical reality.
  - photochemsyn 4y ago
    Here's the quote, it was in some talk he gave: The chaos can act as a magnifier of quantum fluctuations so that they can produce sizable effects in the world around us. But we know that that can happen often. - Murray Gell-Mann I guess the idea is that if you have a collection of particles in a system that displays sensitive initial dependence, then any quantum jiggling gets rapidly amplified. [edit] As you note this doesn't explain the chaos phenomena, because a stable dynamic system would squelch any quantum weirdness rather than amplify it.
    - clairity 4y ago
      yes, chaos theory, including strange attractors, is still deterministic. it acts at a level where the tiny probabalistic effects of a multitude of tiny particles cancel out in ways to miraculously make the larger subjects of interest predictable. it's the same phenomenon underlying the wisdom of crowds (and the pricing function in fair markets): each individual can be wildly incorrect in an observation, but averaging many (independent) observations together reveals stable insight.
derbOac 4y ago
It's hard to tell from the Quanta article, but without meaning to sound dismissive, a lot of this seemed like reexpressing some of the same ideas in different ways. The constructor and resource theories seemed very similar to me, for instance. I was also extremely puzzled by the dismissal of probabilistic or statistical models as being fuzzy or something. Probability has always been the domain of possibility -- this is basically the Jaynesian-style account of probability. It's always seemed to me to be the case that at some level statistics is about selective loss of information -- that is, as you go from descriptions at the particle level to group-level statistical accounts, you summarize (in a coding sense) the ensemble of particles' behavior to shed information required to maintain complete information about the ensemble. To make an analogy, if you wanted to know people's heights, at some point storing information about 1 million person's heights would become burdensome, so you'd replace it with a single number (e.g., the mean) instead. That's not to say what's being discussed in the article isn't interesting, but it just seems like a different level of analysis or something? There's also different ways of representing amount of information in the quantum realm vs classical realm, so there's that, but it's also the case that a chamber of gas will generally involve a lot of molecules in many classical cases. I also had the sense that there was probably something more fundamental that you could invoke that would integrate a lot of this, at the level of logic or computational theory or something. But maybe at this level the difference is sort of moot.
- thingification 4y ago
  > I was also extremely puzzled by the dismissal of probabilistic or statistical models as being fuzzy or something. Probability has always been the domain of possibility Perhaps you're just saying that probability is useful in some practical ways? Deutsch agrees (see video below). But if that's not all you're saying: If the "domain of possibility" (which I interpret to refer to quantum mechanics and thermodynamics) can be described without the whole concept of probability, why not eliminate it? Why eliminate it, though? As Deutsch says "We don't need a reason: Physics likes to do without things"? [1] You may say constructor theory adds new fundamental concepts. I don't know constructor theory so I don't know whether that's true. In cany case, what's not to like about probability concepts? In what way are they "fuzzy or something", as you put it? Deutsch points out here [2] (few minutes later in the same talk as the other link) a sense in which probability statements don't describe physical facts: for example "drawing to an inside straight is very risky" is logically consistent with any sequence of cards in a poker game. I think that's the "fuzziness" they want to eliminate from Physics. He then goes on to deal with some objections to that idea such as "in the long run, probability statements describe physical facts". If the game of Physics is describing physical reality, and we don't need that specific kind of fuzziness, success would seem to me an advance in Physics. [1] https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=13m12s https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=13m12s [2] https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=14m18s https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=14m18s
RandomWorker 4y ago
Laws in physics are written based on testable hypotheses and measurements to confirm. This is a constant process as the hypotheses improve and the measurements improve laws will change. This is the way.
mc4ndr3 4y ago
Both conventional probability and quantum mechanics are worrisome: On a long enough timeline, the universe will (repeatedly) reset itself to precisely the original state at the time of the big bang. It is difficult to avoid a universe where time is not cyclical. Especially if space turns out to be finite. Or if indeed parallel worlds do exist. Or if a big crunch happens.

136 points by theafh 4y ago

Sigh. There is no link to a peer reviewed paper in there, just describing entropy and a few scientists working on describing thermodynamics via quantum theory.

civilized 4y ago
It would be nice, but I think this is a survey of an evolving field and there probably isn't any one pivotal paper. Plugging some key names (Marletto, Halpern) and key terms (constructor theory, resource theory) from the article into Google Scholar, or visiting the linked researchers' websites, will probably get you what you're looking for.
- drallison 4y ago
  David Deutsch as well. Chiara Marleto has a nice recent book, The Science of Can and Can't, which discusses briefly the Second Law in the context of constructor theory.
boole1854 4y ago
The key papers are as follows: This paper introduced constructor theory: Deutsch, D. Constructor theory. Synthese 190, 4331–4359 (2013). https://doi.org/10.1007/s11229-013-0279-z https://doi.org/10.1007/s11229-013-0279-z (Download preprint version: https://arxiv.org/abs/1210.7439 https://arxiv.org/abs/1210.7439) Then this paper applied constructor theory to form a constructor theory of information: Deutsch David and Marletto Chiara 2015 Constructor theory of information Proc. R. Soc. A.4712014054020140540 (Download: https://royalsocietypublishing.org/doi/10.1098/rspa.2014.0540 https://royalsocietypublishing.org/doi/10.1098/rspa.2014.054...) Then this paper applied the constructor theory of information to probability: Marletto Chiara 2016 Constructor theory of probabilityProc. R. Soc. A.4722015088320150883 http://doi.org/10.1098/rspa.2015.0883 http://doi.org/10.1098/rspa.2015.0883 (Download: https://royalsocietypublishing.org/doi/10.1098/rspa.2015.0883 https://royalsocietypublishing.org/doi/10.1098/rspa.2015.088...) Finally, this paper applied the constructor theories of information and probability to thermodynamics: https://arxiv.org/pdf/1608.02625.pdf https://arxiv.org/pdf/1608.02625.pdf (not yet published in a journal, to my knowledge)
mindcrime 4y ago
It appears that the first occurrence of the the name of each of the researchers mentioned in the article links through to their respective home-page. At a quick glance, most of them appear to publish lists of their publications, some with direct links to the actual papers. Of course it might be hard to tease out which papers they've contributed to that pertain to this specific topic, but it would probably be worth the effort for someone who was really interested. For what it's worth, the Deutsch "Constructor Theory" stuff has its own homepage at https://www.constructortheory.org/ https://www.constructortheory.org/ There is also a Wikipedia page that has a list of references and external links. https://en.wikipedia.org/wiki/Constructor_theory https://en.wikipedia.org/wiki/Constructor_theory
photochemsyn 4y ago
A little digging turns up this, which discusses their experimental work: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080401 https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080... "(2022) Emergence of Constructor-Based Irreversibility in Quantum Systems: Theory and Experiment, Marletto & Vedral" That's related to this quote from the article: > "But crucially, the theory also predicts that the row becomes even less able to do the reverse transformation from B2 to B1. The researchers have confirmed this prediction experimentally using photons for B and a fiber optic circuit to simulate a row of three qubits." The experiment is rather complex, and would take a long time to analyze and understand in depth. They appear to be claiming that microscopic reversibility, a cornerstone of atomic-molecular kinetic theory, is being violated in their setup? Seems like a rather extraordinary claim but it passed peer review in a major journal so, worth digging into probably. For those who want an introductory overview of the issue, this is a good one: https://www.thoughtco.com/laws-of-thermodynamics-p3-2699420 https://www.thoughtco.com/laws-of-thermodynamics-p3-2699420 > "Kinetic Theory & the Laws of Thermodynamics The laws of thermodynamics do not particularly concern themselves with the specific how and why of heat transfer, which makes sense for laws that were formulated before the atomic theory was fully adopted. They deal with the sum total of energy and heat transitions within a system and do not take into account the specific nature of heat transference on the atomic or molecular level." In practice the second law is not all that useful although it's philosophically important I suppose. For example, a redwood tree growing from a redwood seed plus simple inputs (CO2, H2O, photons, NH3 etc.) is clearly a local decrease in entropy, as opposed to the dispersal of those elements when a redwood tree burns or falls and is digested by fungi, but since solar fusion is creating a much greater increase in entropy, there are no second law violations. Similarly the creation of heavy elements in a supernova would seem to be a decrease in entropy but the release of all that energy to the surrounding universe ensures no second law violations take place. In practice it's very difficult to do all the accounting for even moderately complex systems.
- edgyquant 4y ago
  Thank you for taking the time to dive into this
deleted 4y ago
[deleted]

atx42 4y ago

I've wondered why we don't just assume the arrow of time was reversed in the past? We know that in the past the universe was more organized (had less entropy), so it doesn't seem like much of a stretch from believing entropy started out that way. Wouldn't that make it easier things like life to form, etc. and simpler than reaching for alien life / multiverse theories? Or does it make it just as difficult? Just a lazy armchair physicist here, but maybe evening TO morning was the first day?

leephillips 4y ago
I can’t grasp the meaning of all of your comment, but I think it’s worth pointing out that there’s nothing in the Second Law that prevents life from evolving. We certainly don’t need to invoke multiverses for that. For systems out of thermal equilibrium, such as a planet embedded in a flux of energy from its star, entropy can and does decrease all the time. An air conditioner (heat pump), for example, causes heat to flow opposite to the temperature gradient, pushing heat from your house into the outside, and increasing the temperature difference, thereby decreasing the entropy in your area. But you have to expend energy to do so, hence your electricity bill.
- atx42 4y ago
  Does reversing time makes it "easier" to get life, than the current direction?
  - leephillips 4y ago
    The direction of time is just a convention, and the laws of physics are (still, as far as I know) time-reversible, so this is really irrelevant. You need an energy source to make anything, including life.
    - pfortuny 4y ago
      All except for (precisely) the heat equation, which is not time-reversible (there is a “loss of information” as time passes, very badly and roughly speaking). See https://math.stackexchange.com/questions/628720/why-heat-equation-is-not-time-reversible-time-arrow-in-mathematics https://math.stackexchange.com/questions/628720/why-heat-equ...

dgellow 4y ago

I know very little about actual physics, but generally speaking the more grandiose headlines sound the less I pay attention… Could someone who knows the topic tell us (and by “us” I mean layman like me) if there is something to keep from this article? It brings so much context that after reading it I still have no idea what this “rewrite of fundamental law” is about.

boole1854 4y ago
My summary: There has always been something unsatisfactory about the second law of thermodynamics. Unlike many other laws in physics, which precisely state both what kinds of structures exist in reality and how they behave, the second law has a built-in lack of precision. Specifically, there are multiple statements of what the second law says, but they all suffer from referencing some concept which is inherently fuzzy at some scale. For example, they may refer to "heat" as part of the law, but the physical definition of "heat" is fuzzy at the microscale -- it only has a clear meaning for "large systems". However, using a new physio-mathematical formalism called "constructor theory" the researchers have now found a way to state the second law of thermodynamics which is precise at all scales.
- namero999 4y ago
  A tiny adjustment to an otherwise ok summary: physics state how nature behaves, and not what structures exist in and of themselves. All structures posed by physics are metaphorical proxies stemming from our perception, not real structures.
  - boole1854 4y ago
    I suppose I should say that I am using the understanding of "physical explanations" promoted by David Deutsch, among others. (Deutsch is the creator of constructor theory which is the subject of this thread): "A scientific explanation is a statement of what is there in reality, and how it behaves and how that accounts for the explicanda." (emphasis added) [1] Deutsch argues strongly against the view of physics which says that physical explanations are just about predictions of behaviors and not about what is really out there. See also his 1997 book The Fabric of Reality. [1] https://www.sciencedirect.com/science/article/pii/S135521981530023X https://www.sciencedirect.com/science/article/pii/S135521981...

ThePhysicist 4y ago

The article is of course oversimplifying, but if I understand correctly the irreversibility in the qubit system comes from the fact that they assume you don't know the states of the qubit chain that transforms the first qubit from B_1 to B_2. If you'd know that the state would be pure and it would be easy to reverse the entanglement, it's just that if you look at the state of the first qubit alone that it's mixed. I actually envisioned a similar thought experiment that could be done with a very complex quantum computer (say millions of qubits) to test whether the universe is actually keeping tabs of all these states or if it gives up at some point and produces irreversibility. But I guess if you'd formulate it like that the academic community wouldn't take you very seriously anymore. I'd wager Deutsch's actual motivation might be along this line, as he seemed very interested to find a way to test the many worlds interpretation against other interpretations of quantum mechanics.

boole1854 4y ago
Deutsch's position is actually that the many worlds interpretation has already been tested and has passed the tests so far, whereas rival theories have been refuted. See https://www.sciencedirect.com/science/article/pii/S135521981530023X https://www.sciencedirect.com/science/article/pii/S135521981...
- lisper 4y ago
  Deutsch is wrong. http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...
  - boole1854 4y ago
    To summarize the argument that the blog post makes: The multiverse interpretation accounts for cases where the probabilities of each distinct observable outcome are equal according to the Born rule. But it cannot account for cases where the Born rule says there are non-equal probabilities for the possible outcomes. This is a fairly common problem which critics of the multiverse interpretation raise. See [1] for another example where a critic raises that problem in more detail (with examples). Deutsch and others have responded. In short, the reply is that the mathematics of the Schrodinger equation describes a density of universes in the continuum which is the multiverse, not a finite set of distinct, interacting single universes. This undercuts the critics' argument. See [2] for an example of this kind of response. [1] https://arxiv.org/pdf/0810.2657.pdf https://arxiv.org/pdf/0810.2657.pdf [2] https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111 https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111

photochemsyn 4y ago

Here's the apparent important source paper, Feb 2022 in Physical Review Letters: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080401 https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.128.080... Figs 1 and 2 show the setup. Here's the conclusion: > "This gives a clear proof of the compatibility of constructor-based irreversibility with unitary quantum theory, providing a frame for the emergence of thermodynamical irreversibility in quantum mechanics." It seems like an extraordinary claim, but is very interesting. The theoretical framework (constructors) is a bit confusing. Hopefully this will be replicated. I recall someone talking about something rather similar once, related to so-called chaos theory (now more generally called 'sensitive dependence on initial conditions'), which describes how deterministic systems can give rise mostly unpredictable phenomena (strange attractors etc.), in which indeterminate quantum states at the atomic level are the ultimate cause of the phenomenon.

leephillips 4y ago
Since all these phenomena of chaos are inherent in the differential equations, how can they possibly have anything to do with quantum states? The sensitive dependence on initial conditions is a mathematical property of the description of the chaotic systems. It’s a closed mathematical system that makes no reference to any physical reality.
- photochemsyn 4y ago
  Here's the quote, it was in some talk he gave: The chaos can act as a magnifier of quantum fluctuations so that they can produce sizable effects in the world around us. But we know that that can happen often. - Murray Gell-Mann I guess the idea is that if you have a collection of particles in a system that displays sensitive initial dependence, then any quantum jiggling gets rapidly amplified. [edit] As you note this doesn't explain the chaos phenomena, because a stable dynamic system would squelch any quantum weirdness rather than amplify it.
  - clairity 4y ago
    yes, chaos theory, including strange attractors, is still deterministic. it acts at a level where the tiny probabalistic effects of a multitude of tiny particles cancel out in ways to miraculously make the larger subjects of interest predictable. it's the same phenomenon underlying the wisdom of crowds (and the pricing function in fair markets): each individual can be wildly incorrect in an observation, but averaging many (independent) observations together reveals stable insight.

derbOac 4y ago

It's hard to tell from the Quanta article, but without meaning to sound dismissive, a lot of this seemed like reexpressing some of the same ideas in different ways. The constructor and resource theories seemed very similar to me, for instance. I was also extremely puzzled by the dismissal of probabilistic or statistical models as being fuzzy or something. Probability has always been the domain of possibility -- this is basically the Jaynesian-style account of probability. It's always seemed to me to be the case that at some level statistics is about selective loss of information -- that is, as you go from descriptions at the particle level to group-level statistical accounts, you summarize (in a coding sense) the ensemble of particles' behavior to shed information required to maintain complete information about the ensemble. To make an analogy, if you wanted to know people's heights, at some point storing information about 1 million person's heights would become burdensome, so you'd replace it with a single number (e.g., the mean) instead. That's not to say what's being discussed in the article isn't interesting, but it just seems like a different level of analysis or something? There's also different ways of representing amount of information in the quantum realm vs classical realm, so there's that, but it's also the case that a chamber of gas will generally involve a lot of molecules in many classical cases. I also had the sense that there was probably something more fundamental that you could invoke that would integrate a lot of this, at the level of logic or computational theory or something. But maybe at this level the difference is sort of moot.

thingification 4y ago
> I was also extremely puzzled by the dismissal of probabilistic or statistical models as being fuzzy or something. Probability has always been the domain of possibility Perhaps you're just saying that probability is useful in some practical ways? Deutsch agrees (see video below). But if that's not all you're saying: If the "domain of possibility" (which I interpret to refer to quantum mechanics and thermodynamics) can be described without the whole concept of probability, why not eliminate it? Why eliminate it, though? As Deutsch says "We don't need a reason: Physics likes to do without things"? [1] You may say constructor theory adds new fundamental concepts. I don't know constructor theory so I don't know whether that's true. In cany case, what's not to like about probability concepts? In what way are they "fuzzy or something", as you put it? Deutsch points out here [2] (few minutes later in the same talk as the other link) a sense in which probability statements don't describe physical facts: for example "drawing to an inside straight is very risky" is logically consistent with any sequence of cards in a poker game. I think that's the "fuzziness" they want to eliminate from Physics. He then goes on to deal with some objections to that idea such as "in the long run, probability statements describe physical facts". If the game of Physics is describing physical reality, and we don't need that specific kind of fuzziness, success would seem to me an advance in Physics. [1] https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=13m12s https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=13m12s [2] https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=14m18s https://invidious.namazso.eu/watch?v=wfzSE4Hoxbc&t=14m18s

RandomWorker 4y ago

Laws in physics are written based on testable hypotheses and measurements to confirm. This is a constant process as the hypotheses improve and the measurements improve laws will change. This is the way.

mc4ndr3 4y ago

Both conventional probability and quantum mechanics are worrisome: On a long enough timeline, the universe will (repeatedly) reset itself to precisely the original state at the time of the big bang. It is difficult to avoid a universe where time is not cyclical. Especially if space turns out to be finite. Or if indeed parallel worlds do exist. Or if a big crunch happens.