Quantum randomness may not be random

[n2doc]

22 March 2008
From New Scientist Print Edition.
Mark Buchanan
AT ITS deepest level, nature is random and unpredictable. That, most physicists would say, is the unavoidable lesson of quantum
theory. Try to track the location of an electron and you'll find only a probability that it is here or there. Measure the spin of an
atom and all you get is a 50:50 chance that it is up or down. Watch a photon hit a glass plate and it will either pass through or be
reflected, but it's impossible to know which without measuring it.

Where does this randomness come from? Before quantum theory, physicists could believe in determinism, the idea of a world unfolding
with precise mathematical certainty. Since then, however, the weird probabilistic behaviour of the quantum world has rudely
intruded, and the mainstream view is that this uncertainty is a fundamental feature of everything from alpha particles to Z bosons.
Indeed, most quantum researchers celebrate the notion that pure chance lies at the foundations of the universe.

However, a sizeable minority of physicists have long been pushing entirely the opposite view. They remain unconvinced that quantum
theory depends on pure chance, and they shun the philosophical contortions of quantum weirdness. The world is not inherently random,
they say, it only appears that way. Their response has been to develop quantum models that are deterministic, and that describe a
world that has "objective" properties, whether or not we measure them. The problem is that such models have had flaws that many
physicists consider fatal, such as inconsistencies with established theories.

Until now, that is. A series of recent papers show that the idea of a deterministic and objective universe is alive and kicking. At
the very least, the notion that quantum theory put the nail in the coffin of determinism has been wildly overstated, says physicist
Sheldon Goldstein of Rutgers University in New Jersey. He and a cadre of like-minded physicists have been pursuing an alternative
quantum theory known as Bohmian mechanics, in which particles follow precise trajectories or paths through space and time, and the
future is perfectly predictable from the past. "It's a reformulation of quantum theory that is not at all congenial to supposedly
deep quantum philosophy," says Goldstein. "It's precise and objective - and deterministic."

If these researchers can convince their peers, most of whom remain sceptical, it would be a big step towards rebuilding the universe
as Einstein wanted, one in which "God does not play dice". It could also trigger a search for evidence of physics beyond quantum
theory, paving the way for a better and more intuitive theory of how the universe works. Nearly a century after the discovery of
quantum weirdness, it seems determinism may be back.

more:

http://groups.google.com/group/alt.philosophy/browse_thread/thread/31b8c1658e7c4e7a/ebfdbc782e24ea7d

[RUMMYisFROSTED]

1. This reply to your post randomly appeared in this thread...

Interesting.

[GoesTo11]

2. I'm no physicist but

If it may be random, may not be random, why don't we flip a coin and decide?

[selador]

3. to some extent

it depends on what you mean by random. this is really old news and old ideas

generally when people say random, they mean that there is no way to predict the result.

quantum physics could be unpredictable because

1) it IS truly unpredictable. (the orthodox TRUE random school)
2) it is not within our MEANS to predict (the it's Functionally or Practically Random)

see: a dice roll

there is nothing random about a dice roll. if you could roll the dice EXACTLY the same way, with the exact same controlled environment as well (air current, etc.) you WOULD get the same result

but as a matter of practicality, it's impossible. it's random in outcome because we DON'T throw them exactly the same each time. it's random practically speaking because we can't.

but there is no (that i am aware of) quantum element to dice physics.

[RUMMYisFROSTED]

4. #2, I would guess. nt

[Fredda Weinberg]

5. You are correct. Quantum effects only take place @ the atomic scale

But there are interesting analogues in our world. When I watch a pot boil, for example, I know I'm seeing discontinuities in a brane. Lower the heat and the surface appears smooth again ... studying physics was fun.

[VWolf]

6. I originally read it as "Bohemian mechanics"

That got me thinking about my old "Night at the Opera" album.

I'm more-or-less in camp #1. I believe that quantum randomness is indeed fundamental. But I could be wrong. I'd give it about a 50% chance.

[napoleon_in_rags]

7. I don't think this is going anywhere.

Mostly intuition...but first of all, this does't make sense:

The trick, Goldstein says, is that measuring one variable stirs up uncertainty in the other due to interactions between the measuring device
and the particle, in a way that matches the uncertainty principle.

I read that measuring it doesn't collapse the wave function if the result is not recorded, but collapses it if it does. This kind of thing is very spooky and doesn't fit into a classical model at all. The second problem I have is very intuitive, and its that there is too much information(in an information theory sense) in a quantum system to express classically. You can see it in the q-bits of quantum computers, the way they can solve intractable problems because q-bits can represent more information than bits by a profound degree. It seems like there are too many states in a quantum system to be represented by a classical theory, just as there are more real numbers than the naturals, though there are infinite naturals.

But that's just feeling. If there is a deterministic solution I hope they find it, and lead us out of the quantum madness.

[eppur_se_muova]

8. I should have guessed this had to do w/David Bohm, but didn't.

I've got his book around somewhere -- still packed in a box with lots of other interesting books -- but never got a chance to get started on it.

[caraher]

9. Bohmian mechanics is indeed not new

I can't say I've investigated Bohm's interpretation in any detail, but from what little I do know I wonder how a Bohmian physicist talks about Bell inequality experiments. The genius of Bell is that the details of how one accounts for unmeasured properties being "real" and merely uncertain do not matter. If there is such a thing as a "fact of the matter" before measurement there must be a different set of correlations among results of certain experiments than if it is "purely" random. A more precise statement is that Bell inequality measurements pretty much rule out "local realism" (or at least "loophole free" experiments would; I'm not sure which (if any) loopholes are still not closed).

So we need to unpack the term "local realism." "Realism" is what I think Bohm's mechanics seek to preserve. And if you're willing to concede that quantum mechanics is not local, there's no experimental evidence I'm aware of to rule out the kind of "realism" (in this case, a deterministic account of the evolution of a "particle's" properties). The price of preserving this kind of determinism is abandoning the notion that everything you need to know to describe what a field or particle does is "encoded" in the immediate environment of the particle.

Alternatively, one can insist that all interactions are local -- that there are no "spooky" instantaneous long-distance connections -- but certain properties of "individual" particles never have well-defined values except when those properties are measured. The photon doesn't have a polarization until it is "measured."

Two nice non-technical articles exploring the meaning of Bell inequality measurements are Mermin's "Is the moon there when nobody looks? and Kwiat & Hardy's "mystery of the quantum cakes".

Finally, I'm not sure I'd point to the success of quantum computing in solving otherwise intractable problems as evidence against Bohm. For one thing, I don't think there has yet been a single result obtained experimentally via quantum computing that is too hard for conventional computing. That cannot happen until the state of the art allows a significant scale-up from the small systems built to date. Certain algorithms based on quantum theory (such as Shor's algorithm for factoring integers) do result in computational demands that scale much more favorably with the size of the problem than they do for any conventional computer, but if you look at the state of the experimental art you're still way ahead simulating the algorithm on a conventional computer than by using any physical realization of a quantum computer created so far. In addition, Bohm proposes a new interpretation of quantum theory. The Bohmian agrees with everyone else on the experimental predictions; it's just the "back story" of what is "really happening" that is different. Quantum computers should work equally well with the Bohm interpretation; what changes is the story you tell about what the theory "means."

Hence, the popularity of the "shut up and calculate" stance on interpreting quantum mechanics...

[Orsino]

10. I cannot believe that God plays darts with the universe. n/t