26 Mar 11
Originally posted by DeepThoughtBell's inequality rules out hidden variable theories, but that does not imply that the universe is fundamentally non-deterministic. The Schrödinger equation is deterministic; non-deterministic phenomena (at least those related to the Born rule) emerge when you don't have a full quantum mechanical description of the "measurement" process. Since there is no adequate description of the Born rule in terms of deterministic rules (yet?), quantum mechanics is inconclusive about whether or not the universe is deterministic.
Hidden variable theories were ruled out. Bell's inequality provides a way of distinguishing between the predictions of quantum theory (the theory assumes complete randomness) and hidden variable theories, which is what you described. The experiment was done by someone called Alain Aspect and the experiment ruled out hidden variable theories. The unive ...[text shortened]... but that's no different to conventional farming), it doesn't require soil detoxification.
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26 Mar 11
1 edit
Originally posted by vivifyWrong. The media are a terrible source of science all the time.
Man, the media's such a terrible source of science sometimes.
Seriously. The only requirement for a "science journalist" is the same as that for other journalists: being able to come up with a catchy headline. Not even being able to hack together a sound article to go beneath the headline is necessary, since nobody worth anything (read: no politician, and no industry mogul) reads science articles anyway. Hell, in most cases, the capability to write a grammatical sentence nine times out of ten is super to requirements.
(And yeah, I know what I'm talking about. I used to work with these guys. Nice colleagues, mostly, but 95% dumb as a brick.)
Richard
26 Mar 11
1 edit
Originally posted by KazetNagorraMore accurately it's local hidden variable theories that are ruled out. Global hidden variable theories are not, but they amount to cosmological conspiracy theories so you can more or less use Occam's Razor. The Schrodinger equation is deterministic, but the thing that is evolving is a distribution which isn't directly measurable (you can't measure absolute phase). The set of possible results of a measurement is predictable, but quantum theory states that the actual outcome is completely random. The theory is more than just the evolution equation for the wave-function. As far as quantum theory is concerned the universe is not deterministic in an absolute sense. If you are suggesting that we may discover new physics then you could be right, but then the theory has changed.
Bell's inequality rules out hidden variable theories, but that does not imply that the universe is fundamentally non-deterministic. The Schrödinger equation is deterministic; non-deterministic phenomena (at least those related to the Born rule) emerge when you don't have a full quantum mechanical description of the "measurement" process. Since there is ...[text shortened]... yet?), quantum mechanics is inconclusive about whether or not the universe is deterministic.
I think there are some problems with the quantum theory of measurement. For one thing it talks about measurements you can't actually make. If you measure the position of an electron what you are actually doing is detecting an interaction - the electron you observe exchanges a virtual photon with an electron in the detector,but quantum electro-dynamics says there's a non-zero amplitude for an electron which is a significant distance from the detector to trigger the detection event. What is actually being detected is an event in the detector and it's not clear to me that that is the same as measuring the position of a particle.
26 Mar 11
3 edits
Originally posted by DeepThought“....You are right about chaos theory not being a theory of non-deterministic systems, But the behaviour is effectively random as predictions depend on measuring initial conditions on scales smaller than any scale you can make measurements on (similar to the notion of pseudo-random numbers in computer science). ….”
You are right about chaos theory not being a theory of non-deterministic systems, But the behaviour is effectively random as predictions depend on measuring initial conditions on scales smaller than any scale you can make measurements on (similar to the notion of pseudo-random numbers in computer science). In fact you can make a case for true ran never found any significant benefit, and have found harms (e.g. beta-carotene for smokers).
I know, and I ought to! I have done a course at university on this.
“....In fact you can make a case for true randomness because at very short distance scales the physics is determined by quantum mechanics which is random. ...”
that would depend on which interpretation of the equations in quantum mechanics are correct for although they all predict unpredictability, they don't all predict true randomness.
“...But the use of pesticides and overuse of antibiotics and hormones, especially in high intensity farming do present a health hazard. ...”
not much generally -especially with most modern pesticides that, unlike in the bad old days when they often were so toxic you would drop dead from just touching them ( literally: some could go straight through unbroken skin! ) , are very selective and which do NOT persist in the environment and are not much more toxic to humans than soap!
I should know for I have got a C&G in horticulture and used to be a grower until my health problem.
“...I'd like a reference on the carbon footprint of organic farming. ...”
http://www.independent.co.uk/environment/green-living/organic-farming-no-better-for-the-environment-436949.html
-OK, that may be not a very convincing source. So try:
http://www.scribd.com/doc/17356325/Carbon-Footprint-of-Organic-Fertilizer
you have to read from about a third down in the above link before you see one reason why the idea of organic farming having less carbon footprint is too simplistic -it just depends.
Also, consider this: organic farming generally results in less food per hector than non-organic farming. “So what?” you may ask. Well, that can by itself, with all else being equal, makes its carbon footprint higher PER given amount of food produced. This is because one hector of land would need the same amount of ploughing and tilling etc regardless of the actual yield and all that ploughing and tilling will require machinery that burns up the SAME amount of diesel -think about that!
Also:
http://www.scribd.com/doc/14079717/The-Seven-Most-Dangerous-Myths-About-Organic
scroll down three quarters down and read what it says under:
“... Myth 6: Organic production could be the answer to concerns
about global climate change because it has a lower carbon
footprint ...”
27 Mar 11
Originally posted by Andrew HamiltonI don't know enough about the arguments surrounding organic farming, I'm just left wondering what they think happens to all this animal manure which is going to return to nature one way or another if it's not composted...
“....You are right about chaos theory not being a theory of non-deterministic systems, But the behaviour is effectively random as predictions depend on measuring initial conditions on scales smaller than any scale you can make measurements on (similar to the notion of pseudo-random numbers in computer science). ….”
I know, and I ought to! I have d ...[text shortened]... answer to concerns
about global climate change because it has a lower carbon
footprint ...”
I'm having the same argument with Kazet about quantum theory. I don't see how a non-random interpretation of quantum theory can avoid being a hidden variable theory; they violate Bell's inequality which was verified in an experiment and so non-random interpretations have pretty much been ruled out.
27 Mar 11
Originally posted by DeepThoughtI'm certainly not an expert, but if I understand hidden variable theories correctly, they posit that e.g. an electron does have a "true" position, but you simply don't know it. Assuming an electron has a "true" position violates Bell's inequality. However, if you don't assume an electron has a "true" position the theory may still be deterministic and you don't necessarily need a nonlocal hidden variable theory.
I don't know enough about the arguments surrounding organic farming, I'm just left wondering what they think happens to all this animal manure which is going to return to nature one way or another if it's not composted...
I'm having the same argument with Kazet about quantum theory. I don't see how a non-random interpretation of quantum theory can av ...[text shortened]... rified in an experiment and so non-random interpretations have pretty much been ruled out.
27 Mar 11
1 edit
Originally posted by DeepThoughtNon-locality is not just "cosmological conspiracy theories". In general, isn't Bell's inequality used to rule out local hidden variable theories by precisely using the non-local properties of quantum entanglement?
More accurately it's local hidden variable theories that are ruled out. Global hidden variable theories are not, but they amount to cosmological conspiracy theories so you can more or less use Occam's Razor. The Schrodinger equation is deterministic, but the thing that is evolving is a distribution which isn't directly measurable (you can't meas r and it's not clear to me that that is the same as measuring the position of a particle.
As a layman, it always seemed to me it's much more a refutation of locality than of hidden variable theories. Describing then to non-locality as cosmological conspiracy theories seems strange to me.
27 Mar 11
Originally posted by PalynkaThe point is that in Quantum Theory the information about whatever variable you are measuring doesn't exist before you make the measurement. In a hidden variable theory it does and if you knew the hidden variable in advance you could predict the outcomes of individual experiments, This is why one theory is regarded as deterministic and the other isn't.
Non-locality is not just "cosmological conspiracy theories". In general, isn't Bell's inequality used to rule out local hidden variable theories by precisely using the non-local properties of quantum entanglement?
As a layman, it always seemed to me it's much more a refutation of locality than of hidden variable theories. Describing then to non-locality as cosmological conspiracy theories seems strange to me.
I've never seen a global hidden variable theory, but they almost certainly have problems avoiding faster than light signaling. I'm basing this on a comment by a lecturer from 20 years ago so it's possible they've managed to construct one in the meantime that doesn't have these problems. All non-local theories mix badly with relativity (including the classical mechanics of rigid bodies, you don't need anything exotic).
The EPR experiment probes this strange situation where a measurement of a particle whose wave-function is entangled with that of another one predicts the outcome of an experiment on the second particle, which Einstein objected to because it seemed to require faster than light signaling. However it's not regarded as action-at-a-distance as no useful information (or energy) can ever be transferred that way, you can't use it to send signals. The outcomes are not selected before the measurement (which they are in a hidden variable theory) and that's the important difference between deterministic theories and quantum theory.
For a theory to be deterministic I'd expect to be able to calculate the results of an experiment based on initial conditions and some parameters. The parameters are the hidden variables. So any deterministic theory is either a local hidden variable theory, which is ruled out by experiment, or a global hidden variable theory which tend to have undesirable properties.
27 Mar 11
Originally posted by DeepThoughtSuppose I put a particle in an infinite well in some state. The Schrödinger equation will predict the behaviour of the particle deterministically. Where do you need a hidden variable theory?
The point is that in Quantum Theory the information about whatever variable you are measuring doesn't exist before you make the measurement. In a hidden variable theory it does and if you knew the hidden variable in advance you could predict the outcomes of individual experiments, This is why one theory is regarded as deterministic and the other isn't. ...[text shortened]... iment, or a global hidden variable theory which tend to have undesirable properties.
27 Mar 11
Originally posted by KazetNagorraIt predicts the wave-function deterministically, but the wave-function only gives you the distribution of outcomes, it doesn't tell you which one you are going to get. In a hidden variable theory things like the momentum and position have simultaneously well defined values.
Suppose I put a particle in an infinite well in some state. The Schrödinger equation will predict the behaviour of the particle deterministically. Where do you need a hidden variable theory?
The non-deterministic features of quantum mechanics do not appear until you try to measure something. The wave-function is a distribution and that it evolves deterministically (between measurements), but this is not enough to make quantum mechanics deterministic as the results of any experiment depend randomly on the distribution.
28 Mar 11
Originally posted by DeepThoughtIt doesn't tell you which one you get, but that could be because an adequate quantum mechanical description of "measurement" is lacking. Put multiple particles in an infinite well and you still get a deterministic description of the time evolution of the system.
It predicts the wave-function deterministically, but the wave-function only gives you the distribution of outcomes, it doesn't tell you which one you are going to get. In a hidden variable theory things like the momentum and position have simultaneously well defined values.
The non-deterministic features of quantum mechanics do not appear until you t ...[text shortened]... m mechanics deterministic as the results of any experiment depend randomly on the distribution.
29 Mar 11
Originally posted by KazetNagorraNo this is independent of the details of the process of measurement. Essentially any theory of quantum measurement that has the result pre-determined, except for pure eigenstates, is a hidden variable theory and is ruled out, unless you are going to admit global hidden variable theories which are problematic.
It doesn't tell you which one you get, but that could be because an adequate quantum mechanical description of "measurement" is lacking. Put multiple particles in an infinite well and you still get a deterministic description of the time evolution of the system.
The number of particles present doesn't really change the argument. Between measurements the wave-function of the system might evolve in a deterministic fashion, but a quantum measurement is like pressing a reset button, the system starts evolving from the last state you measured it to be in.
29 Mar 11
On the organic farming thing, someone told me veggies and such have something like only 1/3 of the nutrients of the same plants say, 50 years ago. Anyone hear this one?
With the forced growing and intensive fertilization today, I tend to believe it but has anyone else come across this? Urban myth or fact?
29 Mar 11
Originally posted by sonhouseI would guess that it is an urban myth. Most of the nutrients in plants are required for the plant to grow. To have 2/3 missing just doesn't seem possible.
On the organic farming thing, someone told me veggies and such have something like only 1/3 of the nutrients of the same plants say, 50 years ago. Anyone hear this one?
With the forced growing and intensive fertilization today, I tend to believe it but has anyone else come across this? Urban myth or fact?
I can understand cases where plants that grow faster or larger through selective breeding have a different composition, but not to that extent.
29 Mar 11
Originally posted by DeepThoughtCould you enlighten me as to why a deterministic quantum measurement is necessarily a hidden variable theory (you don't have to hold back on the mathematics if required)? It was my impression that quantum measurements were simply not well-understood and might be an emergent phenomenon from more fundamental quantum theory (i.e. interactions between few particles rather than a macroscopic interaction).
No this is independent of the details of the process of measurement. Essentially any theory of quantum measurement that has the result pre-determined, except for pure eigenstates, is a hidden variable theory and is ruled out, unless you are going to admit global hidden variable theories which are problematic.
The number of particles present doesn't r ...[text shortened]... essing a reset button, the system starts evolving from the last state you measured it to be in.