4 ms·

> Why didn't God just make the universe classical and be done with it? What would've been wrong with that choice? I hear it over and over and still don't under

by stared 5y ago

> Why didn't God just make the universe classical and be done with it? What would've been wrong with that choice? I hear it over and over and still don't understand the premise. Classical mechanics is not something sacred. It is our first serious model of physics. Our first approximation is based on the scales at which we operate and our senses as humans. Furthermore, even "regular" quantum mechanics is a non-relativistic, low-energy approximation of Quantum Field Theory. It is like asking why God created clouds, not just "waters above the filament"? That said, Q2 minus Q1 is an interesting question.

platz 5y ago
It seems like you misunderstood the actual question. It attempting to get at why QM might be inevitable, not why classical mechanics is
- stared 5y ago
  Well, the very quotation treats classical mechanics as a reference. Q2 minus Q1 is much more interesting: why this specific theory (i.e. quantum mechanics), rather than anything else.
  - platz 5y ago
    Q1 answers the anything else part, not Q2 which is only limited to variations of properties of QM.
  - naasking 5y ago
    > Well, the very quotation treats classical mechanics as a reference. Yes, as a reference for an alternative possible world. Other alternatives discussed are cellular automata.
stared 5y ago
To elaborate on this a bit: One may argue that "a state" is a simpler concept than "a superposition of all state". Even in pure mathematics [1], I don't think that (say) real numbers are less fundamental than natural (unlike Kronecker in "Natural numbers were created by God, everything else is the work of men"). What's true for the set theory route, does not need to be true for any possible mathematics, including those created by other species. For me, it is perfectly conceivable that some aliens use Hilbert space, and for them natural numbers are a particular concept (finitely dimensional vector -> n=1 -> zeros of sin(𝜋z) = 0 & Γ(z+1) is finite, or something in that line). In this sense, if you understand quantization as a map between a set (e.g. {0, 1}) and a vector space over a set (e.g. |psi> = a |0> + b |1>), then it is harder within this conceptualization. For aliens, "a basis state" (i.e. |0> or |1>) might be not an object worth studying on its own. When it comes to the path from classical to quantum physics - yes, it is full of question marks. The only hints I know come from "Quantum principle of relativity" by Dragan & Ekert (previously on arXiv with a more inflammatory title, "Why devil plays dice?"). Yes, there is a contrast with cases, in physics, in which a more advanced theory could be deduced purely with the elimination of inconsistencies, or strive for mathematical beauty, e.g.: E/M -(symmetry)-> Maxwell equations -(Minkowski transformation)-> Special Relativity or non-relativistic quantum -(SR)-> Dirac equation -(Klein paradox)-> QFT At the same time, I think it is a wild hypothesis that "any physics theory point to a more advanced theory only with its own ugliness and inconsistencies". Furthermore, like almost anyone, I used to believe that it is always possible to reduce a "more advanced" theory to a "less advanced" one. Sure, for SR you take v/c << 1 and you are done. For anything dealing with emergent phenomena, well - it is (IMHO) not as straightforward as it may seem at the first glance. Decoherence is one of these cases. For even simpler ones - how to turn molecules of water into their macroscopic properties (temperature, pressure, viscosity). Yes, we can do it (well, with T and p, but still - not viscosity); but if we haven't seen any field in our life, we would not ask such questions in the first place. Even the concept of temperature would be some arbitrary, made-up quantity. Anecdote on a students' conference there were two talks after each other - one on bubbles in beer, and the other - C-star-algebras. The latter claimed that it is the more fundamental, ergo better, way of dealing with physics. Iwo Bialynicki-Birula (theoretical physics) smiled and asked the second speaker: "And how would you derive the beer bubble from C-star-algebras?") [1] Disclaimer: I believe that mathematics is created by humans, not something existing on its own. An abstraction of our language, and our sensory experiences. If we were a slime mold, maybe we wouldn't come with the idea of integers at all. Evolutionary speaking, integers are an abstraction over counting own offsprings, and perhaps - estimating strengths of groups when hunting or protecting. As a side note, it was really fun to have a longer conversation with Penrose, having very different views (also: I am Everettian, and have a naturalistic view towards consciousness, in the spirit of Dennett). After that, I got a clear idea that "the root of all misconceptions" is the assumption that mathematics exists beyond a human concept.
- kgwgk 5y ago
  > One may argue that "a state" is a simpler concept than "a superposition of all state". What would that mean in the context of QM? "A superposition" is "a state".
  - stared 5y ago
    Here by "a state" I meant "a classical state". E.g. a particle with fixed (x, p), or a binary state 0 or 1.
- VirusNewbie 5y ago
  Really interesting to read your post, despite half of it being a bit over my head. That is quite cool you got to have a long conversation with Penrose! As to your statement about platonism or mathematical realism, I'm curious about something. Surely most axiomatic systems are a choice, so I can understand why we would say they're man made (euclidean geometry, ZFC, etc). However we also know about 'meta axioms', which seem to go beyond being a choice. There are simply some axioms that don't seem optional. Do you hold those to be also man made or is that a separate phenomenon?
  - stared 5y ago
    I am not sure what is a "meta axiom". Could you give an example for one?
    - VirusNewbie 5y ago
      I'm thinking Godel's theorems or AIT.
      - stared 5y ago
        Gödel's theorem is a theorem, not an axiom.
        VirusNewbie 5y ago
l33tman 5y ago
QM/QFT is radically simpler to simulate than classical mechanics. It's infinitely more expensive though in terms of pure CPU speed though. With classical mechanics you need to timestep and integrate F=ma and all kinds of associated issues. In QFT you just generate all possible 4D configurations of all fields, assign a weight to each by a prescription, and estimate the ones you're interested in finding the probability for by adding together the weights, take their square, and normalize by the total sum of weights.
- fhars 5y ago
  That does even transcend the meaning "simple" is used with in SNMP...
CTmystery 5y ago
I don't think the author was proposing that classical mechanics is something sacred. Rather, are there prohibitive consequences to a world where our invented model of classical mechanics perfectly matches reality?
- posterboy 5y ago
  Yes, classical mechanics suggests infinity, eg. the Newtonian method and infinitesimals, which is just as problematic as a Turing Machine's infinite tape or Maxwell's Demon. Really classical, platonic geometry requiring atoms with hard bounds is also inconceivable. The uncertainty principle and stuff like Noether's theorem should nicely limit how to ask the right questions. Now I'm not sure if Noether's is a proof by contradiction that would answer the question directly, I rather doubt it. It's a valid question for the sake of didactics at least, how much can be simplified and explained in classical terms without catastrophic loss of precision. Conversely, the slit-experiments for example are a probably the most prominent display of quantum effects in the experiential domain.
anon_123g987 5y ago
> Classical mechanics is not something sacred. It is our first serious model of physics. Just a sidenote: it is at most our second serious model. Aristotle's Physics has a bad rap, but it's "a correct and non-intuitive approximation of Newtonian physics in the suitable domain (motion in fluids), in the same technical sense in which Newton theory is an approximation of Einstein's theory". See "Aristotle's Physics: a Physicist's Look" by Carlo Rovelli (https://arxiv.org/abs/1312.4057 https://arxiv.org/abs/1312.4057).
- kwhitefoot 5y ago
  You saved me the trouble of pointing out Rovelli's defence of Aristotle's physics. I think it should be required reading for anyone interested in the development of physics.
undershirt 5y ago
> waters above the filament *firmament
- Archit3ch 5y ago
  https://xkcd.com/2571/ https://xkcd.com/2571/
PaulDavisThe1st 5y ago
I consider "classical" in this context just to mean "very small things behave like very big things". That doesn't make it sacred, it just means that scale doesn't matter. The universe appears to not be that way, and SA is asking why.
IIAOPSW 5y ago
Why clouds? Sure I understand the theory of the water cycle. But the whole precipitation and evaporation thing is a complex mess. It doesn't look at all like the simplest possible form that could achieve the same job. Why not just water above the firmament? When something in nature seems needlessly complicated, one has to ask what purpose the complexity serves. Why would a hypothetical universe engineer (dare I say "god") sit down and decide to have a universe that is indistinguishable from a classical one on nearly every length scale but is still quantum at the bottom? There's only a few possibilities: 1. The complexity isn't actually needless but it is arbitrary. There are other self-consistent laws of physics that are possible, but all the alternatives are just as weird and complex as QM. 2. The complexity isn't actually needless because QM is inevitable. There's some deep logical principle that forces the hand of the hypothetical universe engineer. 3. There complexity actually is needless. Our universe is quantum because that's just how it is.

by stared 5y ago

platz 5y ago

It seems like you misunderstood the actual question. It attempting to get at why QM might be inevitable, not why classical mechanics is

stared 5y ago
Well, the very quotation treats classical mechanics as a reference. Q2 minus Q1 is much more interesting: why this specific theory (i.e. quantum mechanics), rather than anything else.
- platz 5y ago
  Q1 answers the anything else part, not Q2 which is only limited to variations of properties of QM.
- naasking 5y ago
  > Well, the very quotation treats classical mechanics as a reference. Yes, as a reference for an alternative possible world. Other alternatives discussed are cellular automata.

stared 5y ago

To elaborate on this a bit: One may argue that "a state" is a simpler concept than "a superposition of all state". Even in pure mathematics [1], I don't think that (say) real numbers are less fundamental than natural (unlike Kronecker in "Natural numbers were created by God, everything else is the work of men"). What's true for the set theory route, does not need to be true for any possible mathematics, including those created by other species. For me, it is perfectly conceivable that some aliens use Hilbert space, and for them natural numbers are a particular concept (finitely dimensional vector -> n=1 -> zeros of sin(𝜋z) = 0 & Γ(z+1) is finite, or something in that line). In this sense, if you understand quantization as a map between a set (e.g. {0, 1}) and a vector space over a set (e.g. |psi> = a |0> + b |1>), then it is harder within this conceptualization. For aliens, "a basis state" (i.e. |0> or |1>) might be not an object worth studying on its own. When it comes to the path from classical to quantum physics - yes, it is full of question marks. The only hints I know come from "Quantum principle of relativity" by Dragan & Ekert (previously on arXiv with a more inflammatory title, "Why devil plays dice?"). Yes, there is a contrast with cases, in physics, in which a more advanced theory could be deduced purely with the elimination of inconsistencies, or strive for mathematical beauty, e.g.: E/M -(symmetry)-> Maxwell equations -(Minkowski transformation)-> Special Relativity or non-relativistic quantum -(SR)-> Dirac equation -(Klein paradox)-> QFT At the same time, I think it is a wild hypothesis that "any physics theory point to a more advanced theory only with its own ugliness and inconsistencies". Furthermore, like almost anyone, I used to believe that it is always possible to reduce a "more advanced" theory to a "less advanced" one. Sure, for SR you take v/c << 1 and you are done. For anything dealing with emergent phenomena, well - it is (IMHO) not as straightforward as it may seem at the first glance. Decoherence is one of these cases. For even simpler ones - how to turn molecules of water into their macroscopic properties (temperature, pressure, viscosity). Yes, we can do it (well, with T and p, but still - not viscosity); but if we haven't seen any field in our life, we would not ask such questions in the first place. Even the concept of temperature would be some arbitrary, made-up quantity. Anecdote on a students' conference there were two talks after each other - one on bubbles in beer, and the other - C-star-algebras. The latter claimed that it is the more fundamental, ergo better, way of dealing with physics. Iwo Bialynicki-Birula (theoretical physics) smiled and asked the second speaker: "And how would you derive the beer bubble from C-star-algebras?") [1] Disclaimer: I believe that mathematics is created by humans, not something existing on its own. An abstraction of our language, and our sensory experiences. If we were a slime mold, maybe we wouldn't come with the idea of integers at all. Evolutionary speaking, integers are an abstraction over counting own offsprings, and perhaps - estimating strengths of groups when hunting or protecting. As a side note, it was really fun to have a longer conversation with Penrose, having very different views (also: I am Everettian, and have a naturalistic view towards consciousness, in the spirit of Dennett). After that, I got a clear idea that "the root of all misconceptions" is the assumption that mathematics exists beyond a human concept.

kgwgk 5y ago
> One may argue that "a state" is a simpler concept than "a superposition of all state". What would that mean in the context of QM? "A superposition" is "a state".
- stared 5y ago
  Here by "a state" I meant "a classical state". E.g. a particle with fixed (x, p), or a binary state 0 or 1.
VirusNewbie 5y ago
Really interesting to read your post, despite half of it being a bit over my head. That is quite cool you got to have a long conversation with Penrose! As to your statement about platonism or mathematical realism, I'm curious about something. Surely most axiomatic systems are a choice, so I can understand why we would say they're man made (euclidean geometry, ZFC, etc). However we also know about 'meta axioms', which seem to go beyond being a choice. There are simply some axioms that don't seem optional. Do you hold those to be also man made or is that a separate phenomenon?
- stared 5y ago
  I am not sure what is a "meta axiom". Could you give an example for one?
  - VirusNewbie 5y ago
    I'm thinking Godel's theorems or AIT.
    - stared 5y ago
      Gödel's theorem is a theorem, not an axiom.
      - VirusNewbie 5y ago

l33tman 5y ago

QM/QFT is radically simpler to simulate than classical mechanics. It's infinitely more expensive though in terms of pure CPU speed though. With classical mechanics you need to timestep and integrate F=ma and all kinds of associated issues. In QFT you just generate all possible 4D configurations of all fields, assign a weight to each by a prescription, and estimate the ones you're interested in finding the probability for by adding together the weights, take their square, and normalize by the total sum of weights.

fhars 5y ago
That does even transcend the meaning "simple" is used with in SNMP...

CTmystery 5y ago

I don't think the author was proposing that classical mechanics is something sacred. Rather, are there prohibitive consequences to a world where our invented model of classical mechanics perfectly matches reality?

posterboy 5y ago
Yes, classical mechanics suggests infinity, eg. the Newtonian method and infinitesimals, which is just as problematic as a Turing Machine's infinite tape or Maxwell's Demon. Really classical, platonic geometry requiring atoms with hard bounds is also inconceivable. The uncertainty principle and stuff like Noether's theorem should nicely limit how to ask the right questions. Now I'm not sure if Noether's is a proof by contradiction that would answer the question directly, I rather doubt it. It's a valid question for the sake of didactics at least, how much can be simplified and explained in classical terms without catastrophic loss of precision. Conversely, the slit-experiments for example are a probably the most prominent display of quantum effects in the experiential domain.

anon_123g987 5y ago

> Classical mechanics is not something sacred. It is our first serious model of physics. Just a sidenote: it is at most our second serious model. Aristotle's Physics has a bad rap, but it's "a correct and non-intuitive approximation of Newtonian physics in the suitable domain (motion in fluids), in the same technical sense in which Newton theory is an approximation of Einstein's theory". See "Aristotle's Physics: a Physicist's Look" by Carlo Rovelli (https://arxiv.org/abs/1312.4057 https://arxiv.org/abs/1312.4057).

kwhitefoot 5y ago
You saved me the trouble of pointing out Rovelli's defence of Aristotle's physics. I think it should be required reading for anyone interested in the development of physics.

undershirt 5y ago

> waters above the filament *firmament

Archit3ch 5y ago
https://xkcd.com/2571/ https://xkcd.com/2571/

PaulDavisThe1st 5y ago

I consider "classical" in this context just to mean "very small things behave like very big things". That doesn't make it sacred, it just means that scale doesn't matter. The universe appears to not be that way, and SA is asking why.

IIAOPSW 5y ago

Why clouds? Sure I understand the theory of the water cycle. But the whole precipitation and evaporation thing is a complex mess. It doesn't look at all like the simplest possible form that could achieve the same job. Why not just water above the firmament? When something in nature seems needlessly complicated, one has to ask what purpose the complexity serves. Why would a hypothetical universe engineer (dare I say "god") sit down and decide to have a universe that is indistinguishable from a classical one on nearly every length scale but is still quantum at the bottom? There's only a few possibilities: 1. The complexity isn't actually needless but it is arbitrary. There are other self-consistent laws of physics that are possible, but all the alternatives are just as weird and complex as QM. 2. The complexity isn't actually needless because QM is inevitable. There's some deep logical principle that forces the hand of the hypothetical universe engineer. 3. There complexity actually is needless. Our universe is quantum because that's just how it is.