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Any sufficiently complex system that has a sufficiently large number of known/unknown parameters whose interactions are unknown/partially known/not measurable a

by msravi 12y ago

Any sufficiently complex system that has a sufficiently large number of known/unknown parameters whose interactions are unknown/partially known/not measurable appears random. For example, while the path of a piece of paper as it drops to the ground can be modeled exactly based on several parameters such as gravity, air currents (and its parameters), etc. the number of parameters are so large and their interactions so complex, that the only useful approach is to model it statistically. The same goes for the weather. Or the economy. Or the stock market. It appears that the current quantum mechanical view of the world is simply an acknowledgement of this complexity and the associated unknowns. While it presents a statistical "model" that works for our purposes, it must be acknowledged as a model and not confused with reality. The push for figuring out what drives the statistics needs to continue beyond the building of a model.

amluto 12y ago
> It appears that the current quantum mechanical view of the world is simply an acknowledgement of this complexity and the associated unknowns. While it presents a statistical "model" that works for our purposes, it must be acknowledged as a model and not confused with reality. The push for figuring out what drives the statistics needs to continue beyond the building of a model. This is not a accurate representation of quantum mechanics. If you were to write down a classical description of the state of all the particles in a piece of paper and the state of all the particles that they might interact with over the course of a few seconds, and you solved the equations for what happens, you would get an exact description of the result. This description would be wrong if you look closely enough because classical mechanism doesn't correctly describe the universe we live in. If you did the same thing with a quantum description of the initial state of the paper, you would also get an exact description of the result. That description would be very strange -- if try to deduce what you would see if you looked at the piece of paper (remember, you're just a bunch more particles interacting with that paper), you learn the bizarre answer that you would seem to have some chance of seeing the paper in one configuration and some chance of seeing the paper in a different configuration. But there's no respect in which quantum mechanics is an acknowledgement of some kind of complexity that is beyond our computational ability to describe exactly. To the contrary, quantum mechanics is our attempt to describe things exactly, and it works amazingly well. It's certainly true that a full quantum description of all but the smallest systems is far beyond our ability to compute directly. That's when we switch to statistical mechanics or similar techniques to try to deal with the complexity in a manageable way. To the pedants: if you're trying to model a piece of paper with quantum mechanics, then you'll have to approximate the very small-scale high-energy bits, because we don't know the laws of physics at those scales. But there is so far no compelling reason to believe that those laws will not fit perfectly in the framework of quantum mechanics once we figure them out.
- msravi 12y ago
  > you learn the bizarre answer that you would seem to have some chance of seeing the paper in one configuration and some chance of seeing the paper in a different configuration And so why couldn't there be an underlying parameter that determines that chance of which configuration you will see the paper in? > But there's no respect in which quantum mechanics is an acknowledgement of some kind of complexity that is beyond our computational ability to describe exactly. I certainly didn't mean that we are limited by our computational ability. What I meant (if it wasn't clear) was that we currently lack the understanding of these unknown parameters and their interactions
  - 4ad 12y ago
    > And so why couldn't there be an underlying parameter that determines that chance of which configuration you will see the paper in? http://en.wikipedia.org/wiki/Bell's_theorem http://en.wikipedia.org/wiki/Bell's_theorem
    - deleted 12y ago
      [deleted]
    - matt_kantor 12y ago
      msravi didn't mention anything about this hypothetical parameter being local. Bell's theorem does not rule out nonlocal hidden variables. See also http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experime.... Many of these are practical matters and have been overcome in one experiment or another, but some issues (like the possibility of superdeterminism) are more fundamental. And the article explicitly mentions how pilot waves through superfluids could give rise to nonlocal yet deterministic effects.
- pmoriarty 12y ago
  "remember, you're just a bunch more particles interacting with that paper" Very controversial statement.
jessriedel 12y ago
No. Quantum mechanics is fundamentally different than all those examples you gave, because they all admit reasonable hidden variable models (i.e. unknown or intractable degrees of freedom which we can nevertheless assume to exist and explain our ignorance). Bell's theorem shows that this is impossible in QM.
- msravi 12y ago
  And yet, Bohm's hidden variable theory showed that "it was possible to attribute properties to an underlying reality, in contrast to the conventional approach to quantum mechanics" http://en.wikipedia.org/wiki/Hidden_variable_theory#Bohm.27s_hidden_variable_theory http://en.wikipedia.org/wiki/Hidden_variable_theory#Bohm.27s...
  - 4ad 12y ago
    De Broglie–Bohm theory does not have local hidden variables, it has global hidden variables. The difference is quite fundamental. Paper falling is influenced by local hidden variables, because all interactions are described by Euler-Lagrange equations which being differential equations are by their very nature local. Global hidden variables are no different than modelling quantum mechanics on a computer (using traditional quantum field theory) and saying that the seed you use for your random number generator value is a global hidden variable. There's nothing deep in that.
Rapzid 12y ago
I noticed a few of the quotes in the article from physicists who, while not outright dismissive, couldn't be bothered about pursuing something that could lead to a more fundamental understanding of reality.
- inclemnet 12y ago
  > couldn't be bothered about pursuing something that could lead to a more fundamental understanding of reality. This seems like a bit of an insult based on a misconception. There are many things that could lead to a more fundamental understanding of reality, and many different people working on different options. There is no real reason for people to jump on this one, especially since it isn't clear what insight it could actually give.
- deleted 12y ago
  [deleted]
- scottlocklin 12y ago
  Unfortunately this was written by a science reporter, and so, it was written with an angle by someone who doesn't know what he is talking about. Their dismissiveness is well justified. I was a big fan of exploring the alternative ideas in quantum mechanics, and I tried to like Bohmian pilot waves. They are very philosophically appealing. Then I saw some results in quantum optics which pretty much convinced me it was a silly idea. Walther's ideas on Surrealistic Bohm trajectories should have been enough. I'd be curious if these oil droplets exhibit the surrealistic trajectory behavior. It would be neat if they did, but I doubt it. While the fluid mechanical experiments are pretty damn neat, the modern revival of Bohmian mechanics is a symptom of the disease that afflicts today's physics community: there are many people who call themselves physicists who insist on working on things which have no physical consequences. If you can't do an experiment, you're a philosopher, armed with math. People who claim they might be able to make an experiment in 20-40 years (after they have tenure and have retired) are arguably worse: yes, I am looking at you, entire field of quantum information snake oil salesman: build something or shut up. All this is a sign of decadence and decay, and it is extremely sad to see so many clever people being so stupid. FWIIW, I was exposed to Bohm mechanics in my junior year QM course; it's not like nobody has heard of it. It is actually quite ubiquitous in certain kinds of gutter popular literature; the kinds of popular QM books people who believe in psychic powers read. I've met strippers in gothic nightclubs who knew who David Bohm is. As in, more than one.

by msravi 12y ago

amluto 12y ago

> It appears that the current quantum mechanical view of the world is simply an acknowledgement of this complexity and the associated unknowns. While it presents a statistical "model" that works for our purposes, it must be acknowledged as a model and not confused with reality. The push for figuring out what drives the statistics needs to continue beyond the building of a model. This is not a accurate representation of quantum mechanics. If you were to write down a classical description of the state of all the particles in a piece of paper and the state of all the particles that they might interact with over the course of a few seconds, and you solved the equations for what happens, you would get an exact description of the result. This description would be wrong if you look closely enough because classical mechanism doesn't correctly describe the universe we live in. If you did the same thing with a quantum description of the initial state of the paper, you would also get an exact description of the result. That description would be very strange -- if try to deduce what you would see if you looked at the piece of paper (remember, you're just a bunch more particles interacting with that paper), you learn the bizarre answer that you would seem to have some chance of seeing the paper in one configuration and some chance of seeing the paper in a different configuration. But there's no respect in which quantum mechanics is an acknowledgement of some kind of complexity that is beyond our computational ability to describe exactly. To the contrary, quantum mechanics is our attempt to describe things exactly, and it works amazingly well. It's certainly true that a full quantum description of all but the smallest systems is far beyond our ability to compute directly. That's when we switch to statistical mechanics or similar techniques to try to deal with the complexity in a manageable way. To the pedants: if you're trying to model a piece of paper with quantum mechanics, then you'll have to approximate the very small-scale high-energy bits, because we don't know the laws of physics at those scales. But there is so far no compelling reason to believe that those laws will not fit perfectly in the framework of quantum mechanics once we figure them out.

msravi 12y ago
> you learn the bizarre answer that you would seem to have some chance of seeing the paper in one configuration and some chance of seeing the paper in a different configuration And so why couldn't there be an underlying parameter that determines that chance of which configuration you will see the paper in? > But there's no respect in which quantum mechanics is an acknowledgement of some kind of complexity that is beyond our computational ability to describe exactly. I certainly didn't mean that we are limited by our computational ability. What I meant (if it wasn't clear) was that we currently lack the understanding of these unknown parameters and their interactions
- 4ad 12y ago
  > And so why couldn't there be an underlying parameter that determines that chance of which configuration you will see the paper in? http://en.wikipedia.org/wiki/Bell's_theorem http://en.wikipedia.org/wiki/Bell's_theorem
  - deleted 12y ago
    [deleted]
  - matt_kantor 12y ago
    msravi didn't mention anything about this hypothetical parameter being local. Bell's theorem does not rule out nonlocal hidden variables. See also http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experime.... Many of these are practical matters and have been overcome in one experiment or another, but some issues (like the possibility of superdeterminism) are more fundamental. And the article explicitly mentions how pilot waves through superfluids could give rise to nonlocal yet deterministic effects.
pmoriarty 12y ago
"remember, you're just a bunch more particles interacting with that paper" Very controversial statement.

jessriedel 12y ago

No. Quantum mechanics is fundamentally different than all those examples you gave, because they all admit reasonable hidden variable models (i.e. unknown or intractable degrees of freedom which we can nevertheless assume to exist and explain our ignorance). Bell's theorem shows that this is impossible in QM.

msravi 12y ago
And yet, Bohm's hidden variable theory showed that "it was possible to attribute properties to an underlying reality, in contrast to the conventional approach to quantum mechanics" http://en.wikipedia.org/wiki/Hidden_variable_theory#Bohm.27s_hidden_variable_theory http://en.wikipedia.org/wiki/Hidden_variable_theory#Bohm.27s...
- 4ad 12y ago
  De Broglie–Bohm theory does not have local hidden variables, it has global hidden variables. The difference is quite fundamental. Paper falling is influenced by local hidden variables, because all interactions are described by Euler-Lagrange equations which being differential equations are by their very nature local. Global hidden variables are no different than modelling quantum mechanics on a computer (using traditional quantum field theory) and saying that the seed you use for your random number generator value is a global hidden variable. There's nothing deep in that.

Rapzid 12y ago

I noticed a few of the quotes in the article from physicists who, while not outright dismissive, couldn't be bothered about pursuing something that could lead to a more fundamental understanding of reality.

inclemnet 12y ago
> couldn't be bothered about pursuing something that could lead to a more fundamental understanding of reality. This seems like a bit of an insult based on a misconception. There are many things that could lead to a more fundamental understanding of reality, and many different people working on different options. There is no real reason for people to jump on this one, especially since it isn't clear what insight it could actually give.
deleted 12y ago
[deleted]
scottlocklin 12y ago
Unfortunately this was written by a science reporter, and so, it was written with an angle by someone who doesn't know what he is talking about. Their dismissiveness is well justified. I was a big fan of exploring the alternative ideas in quantum mechanics, and I tried to like Bohmian pilot waves. They are very philosophically appealing. Then I saw some results in quantum optics which pretty much convinced me it was a silly idea. Walther's ideas on Surrealistic Bohm trajectories should have been enough. I'd be curious if these oil droplets exhibit the surrealistic trajectory behavior. It would be neat if they did, but I doubt it. While the fluid mechanical experiments are pretty damn neat, the modern revival of Bohmian mechanics is a symptom of the disease that afflicts today's physics community: there are many people who call themselves physicists who insist on working on things which have no physical consequences. If you can't do an experiment, you're a philosopher, armed with math. People who claim they might be able to make an experiment in 20-40 years (after they have tenure and have retired) are arguably worse: yes, I am looking at you, entire field of quantum information snake oil salesman: build something or shut up. All this is a sign of decadence and decay, and it is extremely sad to see so many clever people being so stupid. FWIIW, I was exposed to Bohm mechanics in my junior year QM course; it's not like nobody has heard of it. It is actually quite ubiquitous in certain kinds of gutter popular literature; the kinds of popular QM books people who believe in psychic powers read. I've met strippers in gothic nightclubs who knew who David Bohm is. As in, more than one.