Quantum mechanics and randomness [Archive]

SeventhSigma

Sep24-10, 08:58 AM

Hello, all --

I feel as if I've only really been exposed to classical physics thus far, and I want to educate myself a bit further.

What really puzzles me the most is the concept of randomness, which I've always attributed to an inability to measure all variables involved with the outcome. The more information we know about a system's properties/variables at a given point in time, the more we know about that system at a given point in a future based on various laws of physics. I'm familiar with the Heisenberg Uncertainty Principle but I feel like it's an "older" view. My current understanding is that trying to find the position of something is like searching for a blimp in a dark room -- by the time you find it, you've already touched/moved it. But I suspect the Principle is something far more fundamental than "interfering" via observation.

I do not understand how QM is thought to somehow be "truly random" at some level or if there are simply other variables we haven't found yet. I know that the "hidden variables" argument is rendered very unlikely by other rules, but I have never really seen the full argument. Simply speaking, I want to know what is *known* in QM and what is still debatable/up to speculation.

Apologies if my questions make no sense. Simply put, I'm here to learn and would love some guidance in the right direction. I want to erase any misconceptions I have and replace them with more up-to-date ones.

arkajad

Sep24-10, 12:12 PM

"I want to know what is *known* in QM and what is still debatable/up to speculation."

Well, if you will read the papers in arxiv.org, then you will see that there is no one idea that is not debatable. What is not debatable is the necessity of getting a good agreement with the experiment, at least as good as the standard textbook QM allows us to get.

But even the standard textbook quantum mechanics is being rendered with different philosophies - depending on the particular author.

SeventhSigma

Sep24-10, 12:26 PM

So what of the "hidden variables" theory?

My initial response to the notion that QM is fundamentally random was that there were possibly other variables influencing the outcomes that we are somehow not noticing/able to measure. What is the general response to this?

arkajad

Sep24-10, 01:24 PM

As an intro I suggest reading Beyond the Quantum (http://arxiv.org/abs/1001.2758). You may find it controversial, nevertheless it represents an active research area.

ThomasT

Sep26-10, 01:01 AM

SeventhSigma, welcome -- type 'randomness' into a thread search and you'll get lots (I got 248 different threads) of discussions in lots of different forums at PF.

So what of the "hidden variables" theory?

My initial response to the notion that QM is fundamentally random was that there were possibly other variables influencing the outcomes that we are somehow not noticing/able to measure. What is the general response to this?That's everybody's initial response. But it's a question that's complicated by semantics and logic. Again, a thread search on 'hidden variable theories' or 'local realistic theories' or something similar, should result in more than enough discussions to satisfy your curiosity. You can also consult the Stanford Encyclopedia of Philosophy, Wikipedia, etc. I don't think anybody in the qm forum wants to get into a protracted discussion of this stuff anytime in the foreseeable future.

SeventhSigma

Sep29-10, 03:33 PM

DrChinese

Sep29-10, 03:53 PM

I've done a lot of reading but I am still unconvinced. I feel like the general consensus is "We can't explain the randomness yet -- but local variables are essentially impossible, and you'd have to bend over backwards to explain the randomness with non-local variables. It's possible, but currently without any evidence."

What confuses me is how people seem to say that the randomness is fundamentally uncaused/random (an ontologically positive statement). Is it more accurate to say that "So far, QM appears random"?

OK: So far, nature appears random.

We don't know the underlying mechanisms at work. Maybe there is a causal explanation. But if there is, it does not lie in the past light cone: it must exist in the future, the present (non-local) or in other worlds.

SeventhSigma

Sep29-10, 03:55 PM

Thanks for the reply!

How might an "underlying" mechanism be fundamentally non-local? Maybe my definition of "local" is off. I assume "local" means that if we have a closed system, we can say every variable involved is "local" to that system, whereas "non-local" is really just another way of saying "it's a variable local to your experiment but it's interfering in a way from afar that makes one think it is non-local, but it's outside the system," where a non-local variable that has influence is technically "local."

arkajad

Sep29-10, 04:32 PM

"But if there is, it does not lie in the past light cone: it must exist in the future, the present (non-local) or in other worlds. "

Plus complexity.

apeiron

Sep29-10, 05:41 PM

I do not understand how QM is thought to somehow be "truly random" at some level or if there are simply other variables we haven't found yet. I know that the "hidden variables" argument is rendered very unlikely by other rules, but I have never really seen the full argument.

You are asking an interesting question. And there is always almost constantly a thread going on this, so you could just browse the archives.

Anyway, you are taking a classical view of probability modelling. One that has some key hidden assumptions.

The basic idea is that you have a bag of numbered balls and you chose blindly. So an ensemble of microstates exists - they are a crisp or concrete reality - but the chosing process, the observation or act of measurement, is random.

Now already, you can see here that the "randomness" is not really fundamental to the balls, the microstates, but is saying something fundamental about the selection process. A blind choice is an undetermined one, as opposed to a "determinstic" choice where we peek, have a rummage, and pick out a ball with some particular number.

But QM goes further. It shows via evidence for nonlocality that something more than this is going on. Because the balls in the bag are mysteriously entangled in ways that chosing one somehow does something to the state of the others.

If you are indeed chosing balls blindly, and in your mind randomly, then you won't even notice this. It is only if you decided you want to sneak a peek, chose one ball deterministically and "know" that all the other balls remain in the bag, unchanged, that you would run into problems.

There isn't a general agreement about how to model this kind of "randomness", but I like approaches that are based on true indeterminancy - where the initial state of things is vague (a state of simple unformed potential) rather than crisp (definite, actual, already in existence).

So now, we may have a bag. But there is nothing yet inside it apart from a general propensity to generate "numbered ballishness". And reaching inside becomes an act of global constraint that produces some actual ball from this state of indeterminate potential - simultaneously ruling out the many other outcomes that might have been the case.

Of course, this is a qualitative description, not a quantitative one. Probability models based on ensembles of crisp microstates have a highly developed mathematical description that allows us to actually calculate stuff. This other approach based on vagueness, on true indeterminancy, is more philosophical. Though there is work being done that could make it properly mathematical one day.

But anyway, the first question to ask here is "where is the randomness"? In standard probability modelling, the microstates just are. They exist crisply. Their state has already been "determined". (Someone made the balls, numbered them so they could be told apart, and stuffed them in a bag). So at the local level, we are not modelling any random action.

The randomness lies instead at the global level, in the hand of the chooser. It describes the process - was it a blind or a deliberate choice? And if a blind choice, then certain probablistic patterns will emerge with high certainty.

QM must be more than this because the balls no longer behave themselves. They seem to change state for reasons we do not appear to control. Their individual, local, state is not crisply determinate but now in some respects undetermined.

So some kind of larger model will now be needed to see all the action, all the causality.

SeventhSigma

Sep30-10, 10:19 AM

arkajad

Sep30-10, 10:57 AM

Quantum randomness may be not so random after all. Do we know for sure? How sure?

ThomasT

Oct1-10, 02:49 AM

I'm not following. Even if we reach into the bag, there is still a choice involved. How do we know the choosing process is truly random? How do I know the balls are random versus the choosing process being random? How do I know that the states of the balls change only when I look at them versus not looking at them?

If I peek at quantum balls and then choose, is the result the same as peeking/choosing macro-level balls? How is it different when I don't peek? Where is the difference in the type of randomness?SeventhSigma, I'm supposing that you're having difficulty seeing the difference between quantum randomness and classical randomness. Ok, there's no essential difference, even while there is some meaning and truth wrt statements that quantum phenomena are truly random.

The attribution of essential randomness to certain experimental phenomena simply results from their being quantum experimental phenomena -- because this is the deepest physical theory. Unfortunately, the deepest physical theory isn't really a deep physical theory. It's a theory of quantum experimental phenomena. That is, it's a theory that has to do with material and instrumental preparations, and the behavior of detectors. Since the behavior of detectors is random, that is it can't be precisely predicted, and since qm, the theory of these detectors, is the deepest theory there is, then this behavior is deemed truly random. But truly random wrt qm and qm phenomena doesn't mean anything other/different than random in the ordinary sense. That is, it doesn't mean anything other than unpredictable. Just as, say, superdeterminism doesn't mean anything other/different than determinism.

So, the bottom line is that quantum experimental phenomena are random in the same sense that a fair deal of cards or a roll of fair dice are random. They're unpredictable. That's all that can be said about it, because that's all that's known about it.

To reiterate, quantum experimental phenomena are called truly random simply because qm quantitatively accounts for things that classical mechanics doesn't and is therefore considered a more fundamental theory. But, as has been mentioned, qm isn't a theory of fundamental reality. It's a very precise probabilistic accounting of instrumental behavior. No more, no less. The correspondence that the various mathematical models incorporated within the general qm algorithm have with an underlying reality is unknown. The correspondence that the Schroedinger equation has with an underlying reality is unknown. The bottom line is that the qm formalism cannot, generally, precisely predict quantum experimental phenomena. But it's the deepest theory. So we call these phenomena truly random to differentiate them from the results of, say, dice rolls. But, really, there's no difference regarding their randomness. Random means unpredictable. Random is random. Randomness is evidence of our ignorance, assuming that reality is evolving lawfully -- and if we want to assume that it isn't evolving lawfully, then what need, what use, is there for fundamental science?

I should add that I will defer to whatever apeiron and arkajad have to say on this, as they are much more qualified to comment -- even though I think that what I said was essentially correct (but I'm certainly open to corrections, etc.).

arkajad

Oct1-10, 02:58 AM

Random means unpredictable. Random is random.
But what is unpredictable today can be predictable tomorrow. So, perhaps, random is not necessarily random?

wuliheron

Oct1-10, 03:31 AM

But what is unpredictable today can be predictable tomorrow. So, perhaps, random is not necessarily random?

Perhaps, but since random and orderly define each other it is pretty meaningless to say everything is random or orderly. I hear the same thing about energy all the time. People say everything is made of energy, but mass and energy define each other so it is a pretty meaningless and useless statement. The only way to make such a statement meaningful and useful is to place it in a specific context and life, the universe, and everything is not a specific context.

ThomasT

Oct1-10, 04:38 AM

But what is unpredictable today can be predictable tomorrow. So, perhaps, random is not necessarily random?Random means unpredictable. If you can predict an event today that you couldn't yesterday, then today that event isn't random, while yesterday it was.

I don't know what you want the word, random, to mean. Please tell me.

Would you agree that the attribution of "truly random" to quantum phenomena has to do with those phenomena not being quantitatively accounted for via classical mechanics? But quantum phenomena are accounted for, approximately/probabilistically via qm. The reason we call qm phenomena "truly random" is because qm is fundamental to (ie., it approximately quantitatively accounts for certain experimental phenomena more accurately than) classical mechanics. This is the only reason. So, I submit to you that the term "truly random" has no essentially different referents than the term "random" wrt dice rolls or card draws or any other classically "random" stuff. And that popularisations that present quantum phenomena as being "truly random", as differentiated from just "random", are basically bullsh*t.

Then again, reconsidering your statement, I think I have to agree with you, more or less.

arkajad

Oct1-10, 05:09 AM

wuliheron

Oct1-10, 05:35 AM

@ThomasT
What I know is that quantum randomness can be modeled by pseudo-random number generators used by our software. The only difference is the speed of generation. So I do not see any reason whatsoever for calling quantum randomness "truly random". Moreover nowadays we know that what we thought not so long ago to be beyond any control (like radioactive decay rates), can be, possibly, influenced by unknown factors. So, I do not exclude the possibility that some important discovery about what we call "quantum randomness" is in the air.

The difference is that you can predict one and not the other, ergo, we call one truly random and the other pseudo-random. It doesn't have to mean anything metaphysical, merely that at this time no one can predict the outcome. If you can't predict it, then for all practical purposes it is truly random. This is precisely the kind of specific context I was talking about that is necessary for the words random and orderly to have any demonstrable meaning.

arkajad

Oct1-10, 05:57 AM

The difference is that you can predict one and not the other.
You can't predict the outcome of a complex deterministic machine when it it goes through a certain number of iterations. There is absolutely nothing particular about quantum randomness that would distinguish it, by objective tests, form sufficiently complex deterministic schemes. What is amazing in quantum theory is its apparent nonlocality of computation, not its "randomness".

ThomasT

Oct1-10, 06:39 AM

ThomasT

Oct1-10, 06:56 AM

The difference is that you can predict one and not the other, ergo, we call one truly random and the other pseudo-random. It doesn't have to mean anything metaphysical, merely that at this time no one can predict the outcome. If you can't predict it, then for all practical purposes it is truly random. This is precisely the kind of specific context I was talking about that is necessary for the words random and orderly to have any demonstrable meaning.Thanks for your contributions wuliheron. I think I can learn from you also.

ThomasT

Oct1-10, 07:06 AM

What is amazing in quantum theory is its apparent nonlocality of computation, not its "randomness".Ok, I don't think that this is so amazing. It's based on empirically established optical principles for the most part. The problem is that a local mechanistic model (using the same qualitative conceptualizations that the qm stuff is based on) doesn't seem to be possible.

arkajad

Oct1-10, 07:10 AM

The problem is that a local mechanistic model (using the same qualitative conceptualizations that the qm stuff is based on) doesn't seem to be possible.

I would say that the problem is that a non-local mechanistic model is possible. So, I am asking, why are we so attached to local models? Is it just our inertia of thinking and nothing more? If non-local works - then why don't we use it without any hesitation whatsoever? Why don't we go full speed an efficient non-local physics?

ThomasT

Oct1-10, 07:43 AM

I would say that the problem is that a non-local mechanistic model is possible. So, I am asking, why are we so attached to local models? Is it just our inertia of thinking and nothing more? If non-local works - then why don't we use it without any hesitation whatsoever? Why don't we go full speed an efficient non-local physics?A nonlocal model is possible, and extant (dBB). But it isn't a mechanistic model. It's as nonrealistic as standard qm is.

Why are we attached to local models? Because the physical evidence suggests that our universe is evolving in accordance with the principle of local causality.

SeventhSigma

Oct1-10, 07:56 AM

The problem is that I seem to hear that "quantum" randomness has nothing to do with our ignorance of the variables involved (hence Bell's Theorem and the impossibility of local hidden variables), but this may be incorrect on some level, perhaps?

At any rate, I feel like on a classical scale, even if we have a really complex deterministic process, we can always take those processes and their properties/attributes and figure out some probability/expected value from them and be able to predict the outcomes with some degree of certainty (even if it's very low). But if we are able to accurately measure those processes and simulate them, we may even be able to predict the outcomes of a complex machine with even higher certainty.

I suspect that quantum mechanics differs from this because we don't have any other variables to measure when it comes to explaining quantum randomness. I also suspect there is a difference in the speed of convergence to the expected value of a distribution on average?

arkajad

Oct1-10, 08:31 AM

@Thomas
I do not necessarily agree that physical evidence suggests anything by itself. It suggests what we want it to suggest. The same evidence can suggest different things to different people - depending on their knowledge and understanding.
I agree that so far dBB is not yet realistic, but do we care about a given model being realistic or not? I think what we should really care about is the predictive and explanatory power.

@SeventhSigma
"But if we are able to accurately measure those processes and simulate them, we may even be able to predict the outcomes of a complex machine with even higher certainty."

It does not quite work this way. Because "even higher certainty" may well mean "essentially a complete uncertainty". We have only that much of a computing power under our our control in our macroscopic world. There may well be some ultimate limits. So what can we hope for? I think we can hope for discovering new ways of thinking about what "understanding Nature" may mean. If, suppose, Nature is nonlocal - perhaps we should learn how to think in these categories too?

SeventhSigma

Oct1-10, 08:39 AM

Some certainty is better than no certainty at all, though, is my point -- if there's any certainty, it isn't fully random if we can predict/explain some of the variance. I am assuming we can't explain any of the variance on a quantum scale.

nismaratwork

Oct1-10, 08:54 AM

arkajad

Oct1-10, 09:02 AM

Does dBB make any predictions that have not already been made by QM, which are or can be verified?

dBB does not make any predictions, but I know some predictions based on dBB and on other models. For instance for tunneling times. These predictions may be at present hard to test, but they are different for different models. When testing will be available one would have to go back to the theory in order to see how the predictions are sensitive to various modeling assumptions about the experimental details.

ThomasT

Oct1-10, 09:13 AM

@Thomas
I do not necessarily agree that physical evidence suggests anything by itself. It suggests what we want it to suggest.I don't know what you mean by this.

The same evidence can suggest different things to different people - depending on their knowledge and understanding.I don't know what you mean by this either. I mean, I don't know what you're getting at.

I agree that so far dBB is not yet realistic, but do we care about a given model being realistic or not? I think what we should really care about is the predictive and explanatory power.dBB has less predictive power than standard qm. And since it's explicit nonlocality is contrary to what current theoretical and experimental physics suggests about reality, it occupies a fringe niche position wrt theoretical physics, as it should.

arkajad

Oct1-10, 09:24 AM

dBB has less predictive power than standard qm.

Which should not be a surprise taking into account how much has been invested in the standard qm and how little in the alternatives. You will say that people invest in what is good and do not invest in what is not so good? Well, look what happens to many real investors - after a crash they say (if they do not commit suicides): Oh, I should have invested in something else...

ThomasT

Oct1-10, 09:32 AM

The problem is that I seem to hear that "quantum" randomness has nothing to do with our ignorance of the variables involved ... Then you're hearing it incorrectly. Quantum randomness has everything to do with physicists' ignorance of the variables involved. Why do you think that qm is a probability theory? It's because physicists don't know what's happening in the reality that underlies instrumental behavior. They're probing this underlying reality in a more or less random, haphazard way. And then they're making some inferences regarding these probings, and fornalizing some of them, and then doing more, more or less random haphazard, probings. It isn't an exact science. It's probabilities based on the behavior of detection devices. That's all there is.

arkajad

Oct1-10, 09:38 AM

@ThomasT
But it is also possible that even knowing all the variables involved a given process can still be considered as random - simply because of its complexity - you will never have the computing power to calculate the result within a given error margin. Still you may be able to use probability theory in such a case.

ThomasT

Oct1-10, 09:38 AM

Which should not be a surprise taking into account how much has been invested in the standard qm and how little in the alternatives. You will say that people invest in what is good and do not invest in what is not so good? Well, look what happens to many real investors - after a crash they say (if they do not commit suicides): Oh, I should have invested in something else...Well, the best minds in physics have decided to endorse standard qm, which means that they endorse the Born-Copenhagen interpretation. And from what I know of qm, this is the most sensible way to think about it.

ThomasT

Oct1-10, 09:41 AM

ThomasT

Oct1-10, 09:45 AM

By the way, arkajad, you write very good English. Better than me really. I'm impressed but not really surprised. I've looked over some of your publications and I can honestly say that I don't think I'm qualified to even begin to understand any of them. So, whatever you say about pretty much anything I think I have to defer to your judgement.

wuliheron

Oct1-10, 09:54 AM

You can't predict the outcome of a complex deterministic machine when it it goes through a certain number of iterations. There is absolutely nothing particular about quantum randomness that would distinguish it, by objective tests, form sufficiently complex deterministic schemes. What is amazing in quantum theory is its apparent nonlocality of computation, not its "randomness".

You can turn your own argument on its head and say that there is nothing to distinguish the supposidly deterministic from the random. Just because I roll the dice six times and get snake eyes every time does not mean the dice are loaded in some sort of metaphysical sense. All it means is that I observe what we could call order. Thus we use the convenient fiction that we "know" something is a deterministic system in some sort of metaphysical sense even though by definition metaphysics cannot be proven.

For me the nonlocal nature of quanta is no more or less puzzling than their wave-like and particle-like nature or their random and orderly nature. For all I know the very concepts themselves are relative like up and down and have no meaning whatsoever outside of specific contexts. Likewise, they may describe something entirely different just as up and down describe a dimension rather than up or down being an absolute. As usual what I suspect is that the depth of this particular puzzle is such that we are missing a very subtle relationship rather than some easy answer such as everything is orderly or random or wave-like or whatever.

arkajad

Oct1-10, 09:56 AM

As usual what I suspect is that the depth of this particular puzzle is such that we are missing a very subtle relationship rather than some easy answer such as everything is orderly or random or wave-like or whatever.

Perhaps. But perhaps the answer is hidden in plain sight.

wuliheron

Oct1-10, 10:09 AM

Perhaps. But perhaps the answer is hidden in plain sight.

That seems unlikely after a century of looking, trillions of dollars spent looking, and some 90% of all the scientists who have ever lived being alive today. It also would seem to buck the general trend that the more progress we make the more complex the answers become. Before he died John Wheeler stated that he now believed if we ever found a ToE it would be a simple equation with no metaphysical explanation for why it worked. It seems the more questions we answer, the deeper the remaining mysteries become.

ThomasT

Oct1-10, 10:30 AM

For me the nonlocal nature of quanta is no more or less puzzling than their wave-like and particle-like nature or their random and orderly nature.How do you know that the 'nature' of quanta is nonlocal?

As usual what I suspect is that the depth of this particular puzzle is such that we are missing a very subtle relationship rather than some easy answer such as everything is orderly or random or wave-like or whatever.And I suspect that the deep answer is that everything is orderly, and wavelike. I guess we're all entitled to our own opinions about questions that we'll never answer.

ThomasT

Oct1-10, 10:36 AM

Perhaps. But perhaps the answer is hidden in plain sight.I think there's much truth in this. If nature is fundamentally wavelike, and if there's a fundamental wave dynamic, then wouldn't it be evident on any and all scales of behavior? My explanation for the arrow of time is to simply drop a pebble into a calm pool of water and point out the expanding wavefront. Any disturbance in any medium at any scale behaves in this way.

I think that electricity, magnetism and gravity can be explained in terms of this fundamental wave dynamic. And I have no idea how to do that.

nismaratwork

Oct1-10, 10:40 AM

That seems unlikely after a century of looking, trillions of dollars spent looking, and some 90% of all the scientists who have ever lived being alive today. It also would seem to buck the general trend that the more progress we make the more complex the answers become. Before he died John Wheeler stated that he now believed if we ever found a ToE it would be a simple equation with no metaphysical explanation for why it worked. It seems the more questions we answer, the deeper the remaining mysteries become.

So the answer is '42', but we'll never know the question that tells us why eh?

arkajad

Oct1-10, 11:01 AM

"Before he died John Wheeler stated that he now believed if we ever found a ToE it would be a simple equation with no metaphysical explanation for why it worked."

The last paragraph in his "Geons, black holes & quantum foam" is a little poem:

"I'd like to know
what this whole show
is all about
before it's out."

I think he is watching us and waiting. So, we better hurry up.

wuliheron

Oct1-10, 11:18 AM

Wanting to know and expecting to get an answer are two different things. Also, if he is watching I doubt we need hurry. In fact, he may already know the answer, lucky dog. That is, assuming there is an answer and the question isn't meaningless to begin with.

latter

Oct1-10, 12:07 PM

In uncertain.p at the heart is the claim that there is no cause.because if there was a cause people wouldnt say its not just the tecHnology or equipment.what they actaully mean is there is no cause to it.Because if there was a cause then it wouldnt simply be technology eqiupment,or our acceptance that there is a cause but we as humans can never know it.
you have to get in to your head that there is a implicit claim.of no cause at the heart of the uncertain.p.and not just use the phrase uncertain.p to cover this fact up.

Now if the no cause claim was true then you would have a form of pure randomness.
the fACT that what happens is a pacticle doing something slightly to what we would expect makes me suspicious.
if it was pure randomness born from a "no cause" anything could happen at that moment the universe could blow up a horse could appear now in front of your nose white light could appear everywhere .not just particles doing something slighly different even though it seems radical its nothing compared to what could happen because anything can happen with no cause and this is what you have to grasp "anything can happen".not just something slightly different.
of course this form of randomness can never be proved because to prove it you would need a cause.and if you had that cause it wouldnt be this form of randomness.
so here you go a form of pure randomness.
the random where people choose things i cant remmeber my thoughts on this form of randomness..

arkajad

Oct1-10, 01:28 PM

That is, assuming there is an answer and the question isn't meaningless to begin with.
Well, that's up to us to find it out. Human beings are quite good at giving meaning to things that would be meaningless without them. I mean it is ok to exploit the existing qm as much as we can and even further, but those other dimensions are lurking out there and the old idea of merging, somehow, quantum theory with some kind of geometry has not been exploited enough - I think. Klein's idea didn't work the way we would like, but there is so much of beauty in "geometric quantization" that it would be a surprise if it was purely accidental. Now, what geometry has to do with randomness is an interesting question; but here we have all the research on chaos from hyperbolic dynamics. And meaningful chaos can be practically indistinguishable from meaningless randomness.

inflector

Oct1-10, 03:07 PM

A nonlocal model is possible, and extant (dBB). But it isn't a mechanistic model. It's as nonrealistic as standard qm is.

How are you defining realistic? dBB is a nonlocal realistic interpretation of QM. According to dBB particles really exist and the wave function is a real wave not just a mathematical device. The very distinguishing characteristic of dBB is the fact that it is a NONLOCAL and REALISTIC theory.

dBB does not make any predictions, but I know some predictions based on dBB and on other models.

dBB has less predictive power than standard qm.

Which should not be a surprise taking into account how much has been invested in the standard qm and how little in the alternatives.

dBB uses exactly the same equations as standard QM. Most consider it to be only an interpretation of QM and as such it is experimentally as verified as QM and is indistinguishable from the other interpretations in this respect.

wuliheron

Oct1-10, 03:09 PM

Your argument reminds me of Plato who used his influence in Rome to have all of Democritus' books burned as, "ugly and demeaning". He too was enthralled by beauty and order, but it engendered an irrational ugliness and hate within him. Perhaps any answer we do find will be so obscure as to allow each to interpret it however they desire or merely choose to accept it humbly as a gift and use it for the good of all.

inflector

Oct1-10, 03:17 PM

Your argument reminds me of Plato...

I assume you were replying to arkajad?

arkajad

Oct1-10, 03:31 PM

Most consider it to be only an interpretation of QM and as such it is experimentally as verified as QM and is indistinguishable from the other interpretations in this respect.

Why should one care about what "most consider it" to be. One should care what it is and not what it is "considered to be". And to know what it is one needs to study it and to use it. Tunneling times predictions are different from those of the standard qm for the simple reason that in standard nonrelativistic qm time is not an "observable" like position or momentum or energy. Therefore all questions about time of arrival must be dealt in qm by some kind of rather arbitrary tricks. This is not so in some of the alternative theories, including dBB.

inflector

Oct1-10, 03:41 PM

Why should one care about what "most consider it" to be.

It's called a theory or an interpretation by different groups. I haven't seen anything that tells me it is anything other than an interpretation. But I'm open to being educated.

And to know what it is one needs to study it and to use it. Tunneling times predictions are different from those of the standard qm for the simple reason that in standard nonrelativistic qm time is not an "observable" like position or momentum or energy. Therefore all questions about time of arrival must be dealt in qm by some kind of rather arbitrary tricks. This is not so in some of the alternative theories, including dBB.

What are the specific reasons that the arbitrary tricks of which you speak cannot be applied with dBB?

I haven't seen any data or papers that suggest that dBB provides different predictions. Since you must know something I don't here, can you point out any specific papers?

wuliheron

Oct1-10, 04:11 PM

I assume you were replying to arkajad?

Yes, sorry if that wasn't clear. I'll try to quote people more often.

nismaratwork

Oct1-10, 06:40 PM

Why should one care about what "most consider it" to be. One should care what it is and not what it is "considered to be". And to know what it is one needs to study it and to use it. Tunneling times predictions are different from those of the standard qm for the simple reason that in standard nonrelativistic qm time is not an "observable" like position or momentum or energy. Therefore all questions about time of arrival must be dealt in qm by some kind of rather arbitrary tricks. This is not so in some of the alternative theories, including dBB.

Because with few exceptional minds aside, when you're swimming upstream in a well established field you're going the wrong way. QM doesn't present the pat answers that dBB does, but what it DOES do is be infallibly predictive so far... dBB can only MATCH QM.

I also note that you said alternative theories, plural... what other theory exists which matches the predictions of QM other than... QM... and dBB?

arkajad

Oct1-10, 07:49 PM

I also note that you said alternative theories, plural... what other theory exists which matches the predictions of QM other than... QM... and dBB?

Theories with a a dynamical state reduction. There are several such.

"(QM) but what it DOES do is be infallibly predictive"

And when it fails it is said that it is beyond its domain of applicability or that we have a wrong model. Clever.

nismaratwork

Oct1-10, 08:12 PM

Theories with a a dynamical state reduction. There are several such.

I'm genuinely unfamiliar with them! I thought that QM and dBB were the only two in the building so to speak, do you have any links to these others that I can read about? I would appreciate it, and if they're the type to violate PF guidelines just PM me... I'm curious, not trying to sucker you.

Pythagorean

Oct2-10, 12:23 AM

I'm genuinely unfamiliar with them! I thought that QM and dBB were the only two in the building so to speak, do you have any links to these others that I can read about? I would appreciate it, and if they're the type to violate PF guidelines just PM me... I'm curious, not trying to sucker you.

It's an easy google; it pertains to the EPR paradox.

nismaratwork

Oct2-10, 08:26 AM

It's an easy google; it pertains to the EPR paradox.

Done... so something like this? http://arxiv.org/abs/0907.2327

arkajad

Oct2-10, 09:12 AM

@nismaratwork
And references there.

nismaratwork

Oct2-10, 10:29 AM

@nismaratwork
And references there.

OK, gotcha, thanks arkajad, Pythagorean, I obviously have a lot of reading to do.

kfmfe04

Oct2-10, 12:01 PM

Pulling balls from a bag (with replacement) produces a stationary random distribution; ie the higher moments of the distribution is bounded/fixed and is not a function of time.

Is this also true of qm randomness? Aren't there different degrees of mathematical randomness?
I suspect that qm randomness is "messier" but I don't understand it enough to assess.

arkajad

Oct2-10, 12:25 PM

Pulling balls from a bag (with replacement) produces a stationary random distribution

Not necessarily. For instance you may like a particular ball and pull it from the bag every time. It produces random distribution if it is random to begin with.

kfmfe04

Oct2-10, 07:09 PM

Not necessarily. For instance you may like a particular ball and pull it from the bag every time. It produces random distribution if it is random to begin with.

Is your point that if I like a particular electron, I cannot pull it every time because qm randomness is more random in that sense? Please clarify.

arkajad

Oct3-10, 03:06 AM

Is your point that if I like a particular electron, I cannot pull it every time because qm randomness is more random in that sense? Please clarify.

No one knows for sure. It's like looking at a message that looks like a random pattern of letters. It may well be an encrypted message. Once you know the decrypting code - it becomes meaningful. Is there some meaning in the apparent randomness of quantum events? There may be, but it may be beyond our decrypting capabilities. But such speculations belong rather to the philosophy section. The fact is: we can simulate quantum phenomena (double slit experiment, EPR, whatever) on our classical computers using pseudo-random algorithms and we can make our simulations to approximate real phenomena to a reasonable degree. It is just computationally very costly. Nature does it naturally in an apparent effortless way. And that's a mystery.

ThomasT

Oct4-10, 06:20 AM

Pulling balls from a bag (with replacement) produces a stationary random distribution ...
Not necessarily. For instance you may like a particular ball and pull it from the bag every time. It produces random distribution if it is random to begin with.I have to agree with kfmfe04 on this. It doesn't matter how much I might like a particular ball, if I don't know the order of the balls inside the bag to begin with, even though I know which balls are in the bag and that they're in a particular order to begin with, then my ball pulling will produce a random distribution.

I suppose that the "to begin with" wrt quantum physics is it at the level of physicists' "pulling balls from the bag" -- since, as you seem to indicate, "no one knows for sure" what's in the "bag" that physicists are probing to begin with?

So, might one say that, unlike the circumstantial ignorance which produces the random distribution of balls pulled from a bag, quantum randomness is based on a profound, principled (via qm), and quite possibly permanent ignorance of the deep reality of nature.

nismaratwork

Oct4-10, 08:01 AM

I have to agree with kfmfe04 on this. It doesn't matter how much I might like a particular ball, if I don't know the order of the balls inside the bag to begin with, even though I know which balls are in the bag and that they're in a particular order to begin with, then my ball pulling will produce a random distribution.

I suppose that the "to begin with" wrt quantum physics is it at the level of physicists' "pulling balls from the bag" -- since, as you seem to indicate, "no one knows for sure" what's in the "bag" that physicists are probing to begin with?

So, might one say that, unlike the circumstantial ignorance which produces the random distribution of balls pulled from a bag, quantum randomness is based on a profound, principled (via qm), and quite possibly permanent ignorance of the deep reality of nature.

In QM, it's also possible that the type and number of balls is constantly in a state of flux, independent of our examination... although I still don't see how that makes the example "more random".

yrreg

Oct5-10, 07:22 PM

I have not read to the end of the thread so far.

My idea is that the randomness in quantum mechanics is according to my intelligent thinking only random to our direct or indirect empirical evidence.

On the basis of indirect empirical evidence I like to bring in the nose in our face which on the one hand is supported by direct empirical evidence as regards its objective or empirical existence, on the other is an indirect empirical evidence for what I like to call dark order that prevails all the way from QM and even deeper, deeper and deeper and deeper that scientists want to go into, up to the nose in our face, which is stable in our face and is working or serving to enable us to breathe comfortably when we are in a healthy state of living existence.

Yrreg

Pythagorean

Oct6-10, 02:48 AM

I certainly hope QM isn't the "end" of science.

latter

Oct9-10, 05:19 PM

with regards to this idea "pulling balls from the bag"being in any way random is a assumption based on believeing the intial conditions are exactlly the same each time.
it also come from us having absolutlly no idea really why are arm,hand is where it is in space .
there is a assumption that this is some how random.
take a gun fixed in position firing at target, when the bullet goes in a different position you immediately think of the wind and then other reasons because you know the gun is fixed in same position(ie:at some point the experiment was in exactly the same position as before) ,people are assumming that the pulling balls from a bag has a similiar fixed intail conditon this then leads to the assumption that because balls are different each time that this must be random .this is not true.
it is that we can not connect the way are hand moves and clenches with with early events in the past,for instance i might of moved my hand left and down and clenched because it is a mixture of a agrument with the with the wife 3 weeks ago and other people have be wearing red a lot lately.and this is the cause of the position of my hand at this moment in time.of course that is a example it could be anything and that is the point we dont think about it atall. its not genneral knowlegde.this problem coupled with thinking the intial conditons start the same each time leads us to assume that a random event has occured.

also the way the balls are picked up and put into the bag is also not random there are connections to the past.
therefore dis regarding uncertainty p. for now
and only relieing on pulling balls from a bag we cannot say there is something random from this atall. it is compeletly determined and if all intial conditions could be know we could predict the order of picked balls with ease.
remmeber this is disregarding uncertainty p.
picking pulls from a bags is a determined process and there is no random in it.