9 ms·

I've been fairly interested in pilot wave thoery, and the more I delve into it, the less I feel it's useful. My understanding is that the statistical equivalen

by rtpg 9y ago

I've been fairly interested in pilot wave thoery, and the more I delve into it, the less I feel it's useful. My understanding is that the statistical equivalent of the pilot wave theory is "when you flip a coin, there is not a 50/50 chance, but a 100% chance of getting the result, because you got the result". Hyper-determinism. The programming equivalent is "all functions are built with lookup tables, with precomputed values". Great, but I still want to predict the values of the lookup tables to describe the function. From the wiki description of the "guiding function" (basically, the universe's step function): >The main fact to notice is that this velocity field depends on the actual positions of all of the N particles in the universe. This feels totally infalsifiable! "in the exact state of the universe you get the result you get". None of the results end up being usable because there's always the "out" of "the universe has changed". You end up going into hyper-determinism, which is almost all about negating free will. Even if the pilot wave theory is the "real thing", the other model of quantum mechanics ends up being more useful because at least you can make some predictions on the state of the universe. (Would love to have someone explain to me how we can apply Pilot Wave Theory in a "local-ish" fashion, people worked hard on this stuff so I imagine there's some use)

SomeStupidPoint 9y ago
...It makes the same localized predictions as other quantum theories and has the same utility (aside from not having relativity incorporated). One just says "we fundamentally can't know, lulz random" and the other says "we could know, if we knew everything". PWT just has the local probabilistic behavior because we can't know the little fiddly bits of the rest of the universe, even if we know the dominant local forces. Copenhagen just says that it does random shit, no reason. I'm not sure why you think the other interpretation of QM gives predictive power PWT doesn't. Ed: To specifically address the stats point -- PWT says that if we had total knowledge of the universe, we could determine that the coin would always be, eg, heads under specific conditions, but due to measurement limitations we can only say that it will come up 50/50, and that the discrepancy between the theoretical ability to perfectly predict and our need to statistically approximate is related to our ability to measure (and compute). By contrast, Copenhagen says there is no coin between when it leaves your hand and when it lands, so clearly we can't do any better to predict than statistics of how often we see the coin heads on the table after it leaves our hand. You seem to fault PWT for making the same predictions as other models, just because it doesn't declare the problem of doing better fundamentally impossible.
- rtpg 9y ago
  Isn't PWT saying "well if you saw the entire state of the universe you could know the answer" the physics equivalent of "every terminating calculation is O(1) relative to the heat death of the universe"? Because the interpretation still leads to the "wave function collapse" interpretation in the expermienttal scope anyways, how does it feel less impossible? Is the theory equivalent to other quantum theories? If so, the value of that interpretation is purely philosophical right? Personally I'm not super satisfied. It's brought up as an interpretation that removes the non-determinism, but in reality it hides the non-determinism to the "practically invisible" by extending out to the entire universe. To bring back the stats thing... I could either say I have a 50/50 chance to get heads or tails on a flip, or I could say "well, if I could see through time I'd know all the results and they'd be knowable, so the results are 100% likely to be known". Sure, that's true but that's not happening. Granted, there's no local deterministic theory... but what's the value of determinism if the non-locality extends to the universe?
  - jamesrcole 9y ago
    > Granted, there's no local deterministic theory... but what's the value of determinism if the non-locality extends to the universe? This implies that "value" (some sort of utility to us) has some say in how the universe is. It's basically saying the theory could not be correct because it has less value to us.
    - rtpg 9y ago
      My understanding is that the guiding function mechanism of PWT could describe just about physical mechanism, not just quantum effects. Since the pilot wave itself is what truly encodes the results, you can mess around with this "initial data" and get whatever you want (Granted, I haven't thought too much about this, so this could be easily falsifiable). If the objective is to describe some fundamental truth, isn't it odd that the description can be applied to everything? Maybe the universe is odd and meaningless, though the Copenhagen interpretation captures that feeling pretty well ;)
amazingman 9y ago
> You end up going into hyper-determinism, which is almost all about negating free will. You seem to think this is a bad thing. Why?
- rtpg 9y ago
  It's not that I think it's a bad thing, but that it's irrelevant in the context of trying to use quantum mechanics for "practical" purposes. Sure, maybe we don't have free will but I still want to figure out how to build quantum computers.
  - zeven7 9y ago
    Some of us want to understand what the universe is really like. If that's uninteresting to you because you're more of a utilitarian, that's ok, but that's not the only way of approaching life on this blue planet.
    - alansammarone 9y ago
      It's not just about being a utilitarian. Science is supposed to make predictions. If it can't make a prediction that can be tested, it's not physics, it's philosophy.
- SCHiM 9y ago
  I've had many discussions with people who don't truly seem to grasp the concept of determinism. I think we should never accept a theory that proves everything is predetermined. If the theory is right it doesn't matter if people believe or act in accordance anyway, and everything anybody does doesn't matter. Time does not exist, nor actions and neither do people. Nothing is here or there if it is predetermined. If the theory is wrong but seems right for a while it will lead to less favourable outcomes for those who act in accordance while they actually had other options. That is if you believe in free will. I don't believe in free will (surely it's impossible) or determinism, but rather in chaos with (maybe) some reinforcement by deterministic systems (such as our brains). Our actions powered by constant rolls of the dice, at our birth, in our brains and on the surface of the sun where at this very moment photons are being released that indirectly animate all human life on earth.
roywiggins 9y ago
> This feels totally infalsifiable! This isn't too surprising, because it's a QM interpretation that's designed to be indistinguishable from the others. The MWI is unfalsifiable (you can't see the other worlds) and Copenhagen is too (you can't see wave function collapse actually happen).
- justinpombrio 9y ago
  Copenhagenism is falsifiable. It says that "large" things are classical and can't be put in superpositions. "Large" isn't well defined, but it includes at least humans. So, put a human in a superposition, and you've falsified it.
  - naasking 9y ago
    > Copenhagenism is falsifiable. It says that "large" things are classical and can't be put in superpositions. Copenhagen doesn't say that. See for instance, Schrodinger's cat.
    - akvadrako 9y ago
      The biggest problem with Copenhagen is that it doesn't say if there is a physical collapse or that there isn't one. Instead think of it as a rule of thumb; if you apply the quantum/classical cut in the appropriate spot for your experiment, it will give the right answer. But it gives no guidance where that spot is or what physically is happening.
      - justinpombrio 9y ago
        From the many worlds perspective, it's actually quite clear where the Copenhagen "collapse" occurs: it's when something enters a superposition with Earth.
        akvadrako 9y ago
        It is true that WMI gives clear guidance on the subjective collapse, but there is nothing special about Earth.
jamesrcole 9y ago
> Hyper-determinism How does "hyper-determinism" differ from "determinism"? I find that when people use adjectives like "hyper" or "ultra" for some theoretical view (like people who talk about 'ultra-darwinism') they are trying to make something appear "extreme" without making any real argument for that position. > You end up going into hyper-determinism, which is almost all about negating free will. That phrasing implies that people come up with, or want, "hyper-deterministic" views because they want to negate the idea of free will. Is that what you mean? If not, what are you trying to say?
- rtpg 9y ago
  Sorry, this might be the wrong term for a higher level concept based on determinism. If everything is deterministic, then our actions can theoretically be pre-determined. I've seen discussion around pilot wave theory that goes into details about this thought process. This is fine and good. But if I publish "A solution to the double slit experiment" and the contents are "everything is deterministic, therefore all the protons go where they go" (hidden behind a pilot wave and initial values), that's not really the right genre of paper is it? It's not that I'm demeaning it, but that I don't feel like it's in the same realm of discussion os the Copenhagen's rather pragmatic "stuff happens behind the curtain, but here's how to work with it" approach.
  - naasking 9y ago
    > It's not that I'm demeaning it, but that I don't feel like it's in the same realm of discussion os the Copenhagen's rather pragmatic "stuff happens behind the curtain, but here's how to work with it" approach. I don't get the distinction you're trying to make. The maths are all the same, so the interpretation has almost no bearing on how to work with it. Furthermore, pilot waves produce a deterministic theory because of non-locality, but it sounds like you're criticizing superdeterminism. They're not the same. 't Hooft is working on a superdeterministic theory based on cellular automata. In any case, how are pilot waves any different than any other classical theory in this regard? It's about describing the system as accurately as one can, which entails inferring the initial conditions based on how we know the system evolves, ie. this cannon ball fell here because it was launched with force X at angle Y from height Z.
jostylr 9y ago
PWT has an underlying dynamics, much like classical mechanics, that to compute the predictions exactly, one has to have perfect knowledge of the current state. Given that knowledge and a perfect computational environment, one could then determine the future for all time, at least ignoring creation and annihilation of particles. Clearly this is useless if that is all it provided. But so was classical mechanics. For example, to compute the gravitational force on my finger, technically, one needs in Newtonian theory to know the position and masses of all particles in the whole universe. Equally clearly, that's neither practical nor relevant. Instead, we use the well-defined dynamics to do a statistical analysis of the theory. What happens when we do that is that we get a quantum thermodynamics equivalent which is what the Copenhagen interpretation is. But Copenhagen suffers from being vague and undefined (what the heck is a macroscopic measurement?) It is very imprecise and not a theory at all. And yet, when it appears as a statistical framework from an underlying well-define theory, the measurement problem completely recedes. And it is important to understand that it is the theory that ought to tell us what a measurement actually means. The next point to raise is, what is the point if we just derive Copenhagen? Well, the point is that it allows to both understand the setup and thus extend it. If all questions were known and answered, it would be largely philosophical. But we have not resolved the problems (QM + relativity) in standard quantum theory after many decades of research. What are a few things that PWT explain? 1) Identical particles. By having configurations of particles, one can investigate what a configuration is. And, after a moment's thought, identical particles are not labelled by nature. Choosing a configuration space of unlabelled particles, we end up with the identical particle choices of symmetric or antisymmetric wave functions. It gets more complicated with spin, but it turns out spin is best represented as a value of the wave function located at a spatial point, not an intrinsic part of the particle. And then the problems just disappear from that. 2) Arrival times. There is a time of arrival naturally enough in a theory with particles actually moving about. In most theories, the collapse or splitting of the universe, etc., does not really fit in with experiments of time arrival. That doesn't stop physicists from coming up with answers, of course, but a theoretical framework is conceptually trivial based on this. 3) Collapse of the wave function. This collapse is central to the whole business. There is no collapse in the fundamental theory. But in suitable situations (measurements), the environment can be conditioned on to get a local wave function for the system in question. When a measurement happens with the environment registering it, the environmental conditioning changes that local wave function and that appears as a collapse. This also helps deal with the murkiness of a position measurement which is never some precise state to collapse into. It is all a bit wishy-washy which is a problem for a theory such as Copenhagen in which that is all there is. It is trivial shrug in PWT. 4) Creation and annihilation of particles. There are particles that exist and they can be born or destroyed. There are formulas that give a probabilistic form for the creation of particles. This makes the theory no longer deterministic, but that was never the point of PWT. The point was to be an actual theory, one which was well-defined. There is nothing wrong with randomness. So the creation and annihilation of particles is perfectly consistent with PWT. It requires wave functions defined on a disjoint union of configuration spaces of different number of particles. This is exactly what quantum field theory does. 5) Well-defined quantum field theory. It is legendary that QFT is not well-defined mathematically. Recent work, inspired by PWT, looks promising in finding a well-defined path in QFT. Essentially, the perturbation from a free evolution cannot work. Instead, one has to work with functions in which the different number of particles spaces are linked in such a way as to preserve the probability. Once that is done, divergences fade away. The mathematical work is still quite difficult and it is early days, but it has had successes in toy theories that were not workable before. 6) Relativity. This is the big one. By having a clear theory to work with, one can understand the nonlocality that is present in reality (Bell's theorem) [unless you deny the results of experiments when they happen as in MWI]. There are explorations of natural foliations of space-time which provides the kind of nonlocality needed. In terms of something that works mathematically, that exists. A theory that is philosophically satisfactory is still being pursued. Essentially, the foliation is needed but is not detectable which is kind of what is needed, but it is unsatisfactory. PWT is not a return to determinism. It is a return to clearly defined theories, whether they are deterministic or not. PWT is a theory that one could envision a computer being fed data and then computing out without further intervention. Copenhagen is not like that. One needs to know what experiments and measurements are to be done which, of course, can't really be specified in advance since what experiments are done may rely on what happened in the past.
snarfy 9y ago
It's no more or less useful than any other interpretation of quantum mechanics. Is a many worlds interpretation more useful? They all have the same mathematics.
Mendenhall 9y ago
Interesting, since I dont see a coin flip as random at all. There are just more "factors" than we can take into account.
- neom 9y ago
  Data from Star Trek likely nails it every single time.
root_axis 9y ago
"Free will" negates itself as a useful concept whether you embrace or reject determinism (either one's will is a function of body and environment or its not in which case it is arbitrary), so I don't think it's a relevant consideration to the veracity of determinism or PWT in general.

by rtpg 9y ago

SomeStupidPoint 9y ago

...It makes the same localized predictions as other quantum theories and has the same utility (aside from not having relativity incorporated). One just says "we fundamentally can't know, lulz random" and the other says "we could know, if we knew everything". PWT just has the local probabilistic behavior because we can't know the little fiddly bits of the rest of the universe, even if we know the dominant local forces. Copenhagen just says that it does random shit, no reason. I'm not sure why you think the other interpretation of QM gives predictive power PWT doesn't. Ed: To specifically address the stats point -- PWT says that if we had total knowledge of the universe, we could determine that the coin would always be, eg, heads under specific conditions, but due to measurement limitations we can only say that it will come up 50/50, and that the discrepancy between the theoretical ability to perfectly predict and our need to statistically approximate is related to our ability to measure (and compute). By contrast, Copenhagen says there is no coin between when it leaves your hand and when it lands, so clearly we can't do any better to predict than statistics of how often we see the coin heads on the table after it leaves our hand. You seem to fault PWT for making the same predictions as other models, just because it doesn't declare the problem of doing better fundamentally impossible.

rtpg 9y ago
Isn't PWT saying "well if you saw the entire state of the universe you could know the answer" the physics equivalent of "every terminating calculation is O(1) relative to the heat death of the universe"? Because the interpretation still leads to the "wave function collapse" interpretation in the expermienttal scope anyways, how does it feel less impossible? Is the theory equivalent to other quantum theories? If so, the value of that interpretation is purely philosophical right? Personally I'm not super satisfied. It's brought up as an interpretation that removes the non-determinism, but in reality it hides the non-determinism to the "practically invisible" by extending out to the entire universe. To bring back the stats thing... I could either say I have a 50/50 chance to get heads or tails on a flip, or I could say "well, if I could see through time I'd know all the results and they'd be knowable, so the results are 100% likely to be known". Sure, that's true but that's not happening. Granted, there's no local deterministic theory... but what's the value of determinism if the non-locality extends to the universe?
- jamesrcole 9y ago
  > Granted, there's no local deterministic theory... but what's the value of determinism if the non-locality extends to the universe? This implies that "value" (some sort of utility to us) has some say in how the universe is. It's basically saying the theory could not be correct because it has less value to us.
  - rtpg 9y ago
    My understanding is that the guiding function mechanism of PWT could describe just about physical mechanism, not just quantum effects. Since the pilot wave itself is what truly encodes the results, you can mess around with this "initial data" and get whatever you want (Granted, I haven't thought too much about this, so this could be easily falsifiable). If the objective is to describe some fundamental truth, isn't it odd that the description can be applied to everything? Maybe the universe is odd and meaningless, though the Copenhagen interpretation captures that feeling pretty well ;)

amazingman 9y ago

> You end up going into hyper-determinism, which is almost all about negating free will. You seem to think this is a bad thing. Why?

rtpg 9y ago
It's not that I think it's a bad thing, but that it's irrelevant in the context of trying to use quantum mechanics for "practical" purposes. Sure, maybe we don't have free will but I still want to figure out how to build quantum computers.
- zeven7 9y ago
  Some of us want to understand what the universe is really like. If that's uninteresting to you because you're more of a utilitarian, that's ok, but that's not the only way of approaching life on this blue planet.
  - alansammarone 9y ago
    It's not just about being a utilitarian. Science is supposed to make predictions. If it can't make a prediction that can be tested, it's not physics, it's philosophy.
SCHiM 9y ago
I've had many discussions with people who don't truly seem to grasp the concept of determinism. I think we should never accept a theory that proves everything is predetermined. If the theory is right it doesn't matter if people believe or act in accordance anyway, and everything anybody does doesn't matter. Time does not exist, nor actions and neither do people. Nothing is here or there if it is predetermined. If the theory is wrong but seems right for a while it will lead to less favourable outcomes for those who act in accordance while they actually had other options. That is if you believe in free will. I don't believe in free will (surely it's impossible) or determinism, but rather in chaos with (maybe) some reinforcement by deterministic systems (such as our brains). Our actions powered by constant rolls of the dice, at our birth, in our brains and on the surface of the sun where at this very moment photons are being released that indirectly animate all human life on earth.

roywiggins 9y ago

> This feels totally infalsifiable! This isn't too surprising, because it's a QM interpretation that's designed to be indistinguishable from the others. The MWI is unfalsifiable (you can't see the other worlds) and Copenhagen is too (you can't see wave function collapse actually happen).

justinpombrio 9y ago
Copenhagenism is falsifiable. It says that "large" things are classical and can't be put in superpositions. "Large" isn't well defined, but it includes at least humans. So, put a human in a superposition, and you've falsified it.
- naasking 9y ago
  > Copenhagenism is falsifiable. It says that "large" things are classical and can't be put in superpositions. Copenhagen doesn't say that. See for instance, Schrodinger's cat.
  - akvadrako 9y ago
    The biggest problem with Copenhagen is that it doesn't say if there is a physical collapse or that there isn't one. Instead think of it as a rule of thumb; if you apply the quantum/classical cut in the appropriate spot for your experiment, it will give the right answer. But it gives no guidance where that spot is or what physically is happening.
    - justinpombrio 9y ago
      From the many worlds perspective, it's actually quite clear where the Copenhagen "collapse" occurs: it's when something enters a superposition with Earth.
      - akvadrako 9y ago
        It is true that WMI gives clear guidance on the subjective collapse, but there is nothing special about Earth.

jamesrcole 9y ago

> Hyper-determinism How does "hyper-determinism" differ from "determinism"? I find that when people use adjectives like "hyper" or "ultra" for some theoretical view (like people who talk about 'ultra-darwinism') they are trying to make something appear "extreme" without making any real argument for that position. > You end up going into hyper-determinism, which is almost all about negating free will. That phrasing implies that people come up with, or want, "hyper-deterministic" views because they want to negate the idea of free will. Is that what you mean? If not, what are you trying to say?

rtpg 9y ago
Sorry, this might be the wrong term for a higher level concept based on determinism. If everything is deterministic, then our actions can theoretically be pre-determined. I've seen discussion around pilot wave theory that goes into details about this thought process. This is fine and good. But if I publish "A solution to the double slit experiment" and the contents are "everything is deterministic, therefore all the protons go where they go" (hidden behind a pilot wave and initial values), that's not really the right genre of paper is it? It's not that I'm demeaning it, but that I don't feel like it's in the same realm of discussion os the Copenhagen's rather pragmatic "stuff happens behind the curtain, but here's how to work with it" approach.
- naasking 9y ago
  > It's not that I'm demeaning it, but that I don't feel like it's in the same realm of discussion os the Copenhagen's rather pragmatic "stuff happens behind the curtain, but here's how to work with it" approach. I don't get the distinction you're trying to make. The maths are all the same, so the interpretation has almost no bearing on how to work with it. Furthermore, pilot waves produce a deterministic theory because of non-locality, but it sounds like you're criticizing superdeterminism. They're not the same. 't Hooft is working on a superdeterministic theory based on cellular automata. In any case, how are pilot waves any different than any other classical theory in this regard? It's about describing the system as accurately as one can, which entails inferring the initial conditions based on how we know the system evolves, ie. this cannon ball fell here because it was launched with force X at angle Y from height Z.

jostylr 9y ago

PWT has an underlying dynamics, much like classical mechanics, that to compute the predictions exactly, one has to have perfect knowledge of the current state. Given that knowledge and a perfect computational environment, one could then determine the future for all time, at least ignoring creation and annihilation of particles. Clearly this is useless if that is all it provided. But so was classical mechanics. For example, to compute the gravitational force on my finger, technically, one needs in Newtonian theory to know the position and masses of all particles in the whole universe. Equally clearly, that's neither practical nor relevant. Instead, we use the well-defined dynamics to do a statistical analysis of the theory. What happens when we do that is that we get a quantum thermodynamics equivalent which is what the Copenhagen interpretation is. But Copenhagen suffers from being vague and undefined (what the heck is a macroscopic measurement?) It is very imprecise and not a theory at all. And yet, when it appears as a statistical framework from an underlying well-define theory, the measurement problem completely recedes. And it is important to understand that it is the theory that ought to tell us what a measurement actually means. The next point to raise is, what is the point if we just derive Copenhagen? Well, the point is that it allows to both understand the setup and thus extend it. If all questions were known and answered, it would be largely philosophical. But we have not resolved the problems (QM + relativity) in standard quantum theory after many decades of research. What are a few things that PWT explain? 1) Identical particles. By having configurations of particles, one can investigate what a configuration is. And, after a moment's thought, identical particles are not labelled by nature. Choosing a configuration space of unlabelled particles, we end up with the identical particle choices of symmetric or antisymmetric wave functions. It gets more complicated with spin, but it turns out spin is best represented as a value of the wave function located at a spatial point, not an intrinsic part of the particle. And then the problems just disappear from that. 2) Arrival times. There is a time of arrival naturally enough in a theory with particles actually moving about. In most theories, the collapse or splitting of the universe, etc., does not really fit in with experiments of time arrival. That doesn't stop physicists from coming up with answers, of course, but a theoretical framework is conceptually trivial based on this. 3) Collapse of the wave function. This collapse is central to the whole business. There is no collapse in the fundamental theory. But in suitable situations (measurements), the environment can be conditioned on to get a local wave function for the system in question. When a measurement happens with the environment registering it, the environmental conditioning changes that local wave function and that appears as a collapse. This also helps deal with the murkiness of a position measurement which is never some precise state to collapse into. It is all a bit wishy-washy which is a problem for a theory such as Copenhagen in which that is all there is. It is trivial shrug in PWT. 4) Creation and annihilation of particles. There are particles that exist and they can be born or destroyed. There are formulas that give a probabilistic form for the creation of particles. This makes the theory no longer deterministic, but that was never the point of PWT. The point was to be an actual theory, one which was well-defined. There is nothing wrong with randomness. So the creation and annihilation of particles is perfectly consistent with PWT. It requires wave functions defined on a disjoint union of configuration spaces of different number of particles. This is exactly what quantum field theory does. 5) Well-defined quantum field theory. It is legendary that QFT is not well-defined mathematically. Recent work, inspired by PWT, looks promising in finding a well-defined path in QFT. Essentially, the perturbation from a free evolution cannot work. Instead, one has to work with functions in which the different number of particles spaces are linked in such a way as to preserve the probability. Once that is done, divergences fade away. The mathematical work is still quite difficult and it is early days, but it has had successes in toy theories that were not workable before. 6) Relativity. This is the big one. By having a clear theory to work with, one can understand the nonlocality that is present in reality (Bell's theorem) [unless you deny the results of experiments when they happen as in MWI]. There are explorations of natural foliations of space-time which provides the kind of nonlocality needed. In terms of something that works mathematically, that exists. A theory that is philosophically satisfactory is still being pursued. Essentially, the foliation is needed but is not detectable which is kind of what is needed, but it is unsatisfactory. PWT is not a return to determinism. It is a return to clearly defined theories, whether they are deterministic or not. PWT is a theory that one could envision a computer being fed data and then computing out without further intervention. Copenhagen is not like that. One needs to know what experiments and measurements are to be done which, of course, can't really be specified in advance since what experiments are done may rely on what happened in the past.

snarfy 9y ago

It's no more or less useful than any other interpretation of quantum mechanics. Is a many worlds interpretation more useful? They all have the same mathematics.

Mendenhall 9y ago

Interesting, since I dont see a coin flip as random at all. There are just more "factors" than we can take into account.

neom 9y ago
Data from Star Trek likely nails it every single time.

root_axis 9y ago

"Free will" negates itself as a useful concept whether you embrace or reject determinism (either one's will is a function of body and environment or its not in which case it is arbitrary), so I don't think it's a relevant consideration to the veracity of determinism or PWT in general.