Quantum Mechanics and randomness

Post questions or suggestions here.
Locked
User avatar
Diebert van Rhijn
Posts: 6469
Joined: Fri Jun 03, 2005 4:43 pm

Re: Quantum Mechanics and randomness

Post by Diebert van Rhijn »

Perhaps the following might be interesting for anyone exploring the philosophical meaning and accurate definition of randomness and indeterminism. It's an article in PDF by Antony Eagle - a philosophy lector and fellow at the University of Oxford and Exeter College: Randomness is Unpredictability.

I'll quote a bit from section 3.2, page 14 to give you an idea how the topic is approached.
3.2 Randomness is Indeterminism?

The comparative neglect of the concept of randomness by philosophers is in large part due, I think, to the pervasive belief in the pernicious hypothesis that a physical process is random just when that process is indeterministic. Hellman, while concurring with our conclusion that no mathematical definition of random sequence can adequately capture physical randomness, claims that ‘physical randomness’ is “roughly interchangeable with ‘indeterministic”’ (Hellman, 1978, 83). Indeterminism here means that the complete and correct scientific theory of the process is indeterministic. A scientific theory we take to be a class of models (van Fraassen, 1989, ch. 9). An individual model will be a particular history of the states that a system traverses (...)

Is it plausible that the catalogue of random phenomena we began with can be simply unified by the assumption that randomness is indeterminism? It seems not. Many of the phenomena we enumerated do not seem to depend for their randomness on the fact that the world in which they are instantiated is one where quantum indeterminism is the correct theory of the microphysical realm. One can certainly imagine that Newton was right. In Newtonian possible worlds, the kinds of random phenomena that chaotic dynamics gives rise to are perfectly physically possible; so too with random mating, which depends on a high-level probabilistic hypothesis about the structure of mating interactions, not low-level indeterminism. Our definition of indeterminism made no mention of the concept of probability; an adequate understanding of randomness, on the other hand, must show how randomness and probability are related—hence indeterminism cannot be randomness. Moreover, we must at least allow for the possibility that quantum mechanics will turn out to be deterministic, as on the Bohm theory (Bell, 1987b).

Finally, it seems wrong to say that coin tossing is indeterministic, or that creatures engage in indeterministic mating: it would turn out to be something of a philosophical embarrassment if the only analysis our profession could provide made these claims correct.

One response of behalf of the pernicious hypothesis is that, while classical physics is deterministic, it is nevertheless, on occasion, a useful idealisation to pretend that a given process is indeterministic, and hence random. I think that this response confuses the content of concepts deployed within a theory, like the concept of randomness, with the external factors that contribute to the adoption of a theory, such as that theory being adequate for the task at hand, and therefore being a useful idealisation. Classical statistical mechanics does not say that it is a useful idealisation that gas motion is random; the theory is an idealisation that says gas motion is random, simpliciter. Here, I attempt to give a characterisation of randomness that is uniform across all theories, regardless of whether those theories are deployed as idealisations or as perfectly accurate descriptions. We must also be careful to explain why the hypothesis that randomness is indeterminism seems plausible to the extent that it does. I think that the historical connection of determinism with prediction in the Laplacean vision can explain the intuitive pull of the idea that randomness is objective indeterminism. I believe that a historical mistake still governs our thinking in this area, for when increasing conceptual sophistication enabled us to tease apart the concepts of determinism and predictability, randomness remained connected to determinism, rather than with its rightful partner, predictability.
User avatar
Philosophaster
Posts: 563
Joined: Sat Aug 20, 2005 10:19 am

Re: Quantum Mechanics and randomness

Post by Philosophaster »

Neil Melnyk wrote:You say that if we dig deep enough into the physical factors that a dice roll is determined. However, if there are truly random inputs into the physical system on a low level shouldn't this result in our not being able to determine the outcome of a dice roll accurately?
The bits of quantum randomness smear each other out, resulting in a deterministic system on the macro level.
Unicorns up in your butt!
Kevin Solway
Posts: 2766
Joined: Mon Sep 17, 2001 8:43 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by Kevin Solway »

Philosophaster wrote:The bits of quantum randomness smear each other out
There's no guarantee of that.
User avatar
Pincho Paxton
Posts: 1305
Joined: Fri Sep 28, 2007 10:05 am

Re: Quantum Mechanics and randomness

Post by Pincho Paxton »

You say that if we dig deep enough into the physical factors that a dice roll is determined. However, if there are truly random inputs into the physical system on a low level shouldn't this result in our not being able to determine the outcome of a dice roll accurately?
It's a nice thought. Our hands are moving from a sentient force that has no beginning to it. It may be random actually. Never took it into consideration. It's the scale of the die that is hard to judge. A coin toss eliminates most of the randomness. I'm going to have to vote inderterministic I think...with a degree of doubt.
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

David Quinn wrote:So the probability distribution is causally created by all sorts of local variables, while a specific outcome within the distribution arises without any cause at all?
That seems to be the case. The event is caused, but the specific outcome doesn't seem to be.
Those aspects can also be classified as "things".
You are free to redefine anything in any way you want. you always do anyway.
So I can't see how any aspect of the event can be without cause.
That's your problem, not mine.
Forethought Venus Wednesday
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

Neil Melnyk wrote:You say that if we dig deep enough into the physical factors that a dice roll is determined. However, if there are truly random inputs into the physical system on a low level shouldn't this result in our not being able to determine the outcome of a dice roll accurately?
of coruse. however, for macro objects, the likeihood of non-classical behavior is so minuscule that for all practical intents and purposes, we can ignore it.
I get the sense that "random" is just a practical term meaning "we can't predict it" and that "true randomness" is something like "absolute truth".
Not quite. The confusion is that events like die rolls are apparently random but are actually prdictable, so I used 'truly random' to distinguish these not-quite-random events (mostly chaotic ones) from actual non-deterministic ones.
Forethought Venus Wednesday
User avatar
David Quinn
Posts: 5708
Joined: Sun Sep 09, 2001 6:56 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by David Quinn »

vicdan wrote:
David Quinn wrote:So the probability distribution is causally created by all sorts of local variables, while a specific outcome within the distribution arises without any cause at all?
That seems to be the case. The event is caused, but the specific outcome doesn't seem to be.
At the very least, the outcome would depend on the things that are actually there. For example, a particle decaying requires a particle capable of decaying to be there in the first place. It is in the nature of the particle that it will decay, just as it is in the nature of a rock to continue being a rock (unless destroyed by external or internal factors).

-
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

Like I said, the event is caused. Nonetheless, it seems to have an uncaused aspect, the random outcome within the probabilistic distribution.
Forethought Venus Wednesday
User avatar
David Quinn
Posts: 5708
Joined: Sun Sep 09, 2001 6:56 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by David Quinn »

It just happens?

-
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

Delusions are painful to lose, aren't they?

Yes, the quantum die coming up 6 rather than another number 'just happens', it seems. The quantum decoherence is caused, the probabilistic distribution result is caused, but there is nothing causing one rather than another result -- it happens randomly, as far as we can tell. And there is nothing you can do to prove the logical impossibility of this.
Forethought Venus Wednesday
User avatar
Nick
Posts: 1677
Joined: Mon Nov 28, 2005 8:39 pm
Location: Detroit, Michigan

Re: Quantum Mechanics and randomness

Post by Nick »

vicdan wrote:Yes, the quantum die coming up 6 rather than another number 'just happens', it seems. The quantum decoherence is caused, the probabilistic distribution result is caused, but there is nothing causing one rather than another result -- it happens randomly, as far as we can tell. And there is nothing you can do to prove the logical impossibility of this.
We can never empirically predict whether anything at all is going to happen with absolute certainty. So essentially the quantum realm is no different than anything else. It just so happens that these events are more difficult to model. In other words, we don't have the means to observe the immediate causal chain of events. So yes Victor, the quantum realm is random in the same way me typing this sentence is random, if that's how you want to define it.
Kevin Solway
Posts: 2766
Joined: Mon Sep 17, 2001 8:43 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by Kevin Solway »

vicdan wrote:events like die rolls are apparently random but are actually predictable
"Predictable" in the sense of "1 chance in 6". Yeah, great.

Even if you had all the resources of the world, with all manner of laser sensors, and all the world's computing power at your disposal, you might still only be able to able to predict the result, say, 1 chance in 3, which is still rubbish.

You could never, ever be able to accurately predict a single result of a die roll with absolute, 100% certainty. This is a purely logical truth that cannot be circumvented. That is, it's not even theoretically possible for you to make certain (100% certain) predictions about the future regarding such matters.

It is clear to me that you haven't thought this through.
Kevin Solway
Posts: 2766
Joined: Mon Sep 17, 2001 8:43 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by Kevin Solway »

vicdan wrote:Like I said, the event is caused.
Which event? The group event of "randomness" or the very many individual events which make for "randomness"?

For example, take the white noise on a television set, and let's say that it is an example of true randomness, whether or not it is. Let's assume that the random "pattern" you see is caused. Are you saying that the individual pixel-dots that make up this "pattern" are not caused, or caused?

If the individual events that make up randomness are caused, then there's nothing left over to be uncaused. There is no other "aspect".
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

It's like talking to a wall...
Forethought Venus Wednesday
User avatar
DHodges
Posts: 1531
Joined: Tue Jan 22, 2002 8:20 pm
Location: Philadelphia, PA
Contact:

Re: Quantum Mechanics and randomness

Post by DHodges »

I must admit that I got a bit lost as to exactly what sort of events we were talking about that would be considered truly random, and had to back up and do some reading.

Victor, does this cover what you have in mind?

The Quantum Casino
Similarly, in the quantum world when we are measuring a property of a particle we are fundamentally prohibited from digging deeper to analyse the quantum mechanism to try to predict the result (due to the Heisenberg Uncertainty Principle). That's a fundamental limit on physics. We just have to accept that the result of the measurement we get will be random. We can do not better. We can never do any better. This is why we have to consider the quantum behaviour of nature as being fundamentally random: because no deeper layer can ever be accessible to our analysis.
Kevin Solway
Posts: 2766
Joined: Mon Sep 17, 2001 8:43 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by Kevin Solway »

DHodges wrote:The Quantum Casino
Similarly, in the quantum world when we are measuring a property of a particle we are fundamentally prohibited from digging deeper to analyse the quantum mechanism to try to predict the result (due to the Heisenberg Uncertainty Principle). That's a fundamental limit on physics. We just have to accept that the result of the measurement we get will be random. We can do not better. We can never do any better. This is why we have to consider the quantum behaviour of nature as being fundamentally random: because no deeper layer can ever be accessible to our analysis.
I note that the quoted text very wisely says nothing about anything being "uncaused".
User avatar
Philosophaster
Posts: 563
Joined: Sat Aug 20, 2005 10:19 am

Re: Quantum Mechanics and randomness

Post by Philosophaster »

vicdan wrote:It's like talking to a wall...
Do you enjoy arguing with architecture? :-P
Unicorns up in your butt!
Kevin Solway
Posts: 2766
Joined: Mon Sep 17, 2001 8:43 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by Kevin Solway »

Firstly, I'd like to know exactly what it is about a dice throw that is "predictable" - and preferably also an example of how one can perfectly predict future events, instead of just guessing what they might be. Because if all you mean by "predictable" that we can guess what might happen in the future, then you aren't saying anything.

And secondly, I'd like to know exactly what it is that is "uncaused". Saying that something is "uncaused" just because it appears random, or may even be random, is not an argument.
Kevin Solway
Posts: 2766
Joined: Mon Sep 17, 2001 8:43 am
Location: Australia
Contact:

Re: Quantum Mechanics and randomness

Post by Kevin Solway »

Diebert van Rhijn wrote:Perhaps the following might be interesting for anyone exploring the philosophical meaning and accurate definition of randomness and indeterminism.
Personally, I thought the whole piece said absolutely nothing.

If there was anything in there, it was so well hidden that I doubt anybody could possibly find it.

I loved this bit: "It seems wrong to say that coin tossing is indeterministic."

He doesn't seem to know whether tossing a coin is indeterministic or not, but he is swayed against this designation on a whim. It sounds like he has no idea what indeterminism is, for if he knew precisely what it was then he would be able to say outright whether tossing a coin was indeterministic or not.

I think his whole article was one long henid, published just so he could keep up his publication count.
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

Philosophaster wrote:Do you enjoy arguing with architecture? :-P
On occasion. It builds character. :)

But usually, no.
Forethought Venus Wednesday
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

DHodges wrote:I must admit that I got a bit lost as to exactly what sort of events we were talking about that would be considered truly random, and had to back up and do some reading.

Victor, does this cover what you have in mind?
Close enough, yes.
Forethought Venus Wednesday
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

Kevin Solway wrote:Firstly, I'd like to know exactly what it is about a dice throw that is "predictable" - and preferably also an example of how one can perfectly predict future events, instead of just guessing what they might be. Because if all you mean by "predictable" that we can guess what might happen in the future, then you aren't saying anything.
In theory, because the die throw is a classical event, if we measure its original position and momenta (linear and angular), as well as gravity and the exact mechanical characteristics of the surface the die lands on, we can predict how it will come up with near-perfect accuracy. See DHodges' earlier point about coin-flipping machine in vacuum.
And secondly, I'd like to know exactly what it is that is "uncaused". Saying that something is "uncaused" just because it appears random, or may even be random, is not an argument.
Fuck you. First you hang this 'indeterminism' shit on me, now you go for 'uncaused'. You guys are the ones who jumped from non-determinism to causation. My point has been from the beginning that there exist non-deterministic events, events the specific outcomes of which (e.g. 6 rather than 5 on a quantum die) are not dependent on the initial conditions. Whether you want to take that to mean that the outcome is 'uncaused' is your business.

You boys keep trying to fit reality into the narrow framework of your silly wanna-be thinking. Guess what? The Universe does not conform to your prejudices.
Forethought Venus Wednesday
User avatar
Imadrongo
Posts: 724
Joined: Mon Mar 26, 2007 9:52 am

Re: Quantum Mechanics and randomness

Post by Imadrongo »

vicdan wrote:You boys keep trying to fit reality into the narrow framework of your silly wanna-be thinking. Guess what? The Universe does not conform to your prejudices.
What Universe are you talking about Mr?? If we define Universe as Nature, masculinity, ... pure wisdom..., etc, it can be logically deduced that it does! -The absolute truth hurts-.
User avatar
vicdan
Posts: 1013
Joined: Sun Mar 18, 2007 11:48 am
Location: Western MA, USA
Contact:

Re: Quantum Mechanics and randomness

Post by vicdan »

And if I define 2 to be 3, 2+2 will be 6.However, this says as little about math as your silly definition games say about the Universe.
Forethought Venus Wednesday
User avatar
DHodges
Posts: 1531
Joined: Tue Jan 22, 2002 8:20 pm
Location: Philadelphia, PA
Contact:

Re: Quantum Mechanics and randomness

Post by DHodges »

Kevin Solway wrote:Personally, I thought the whole piece said absolutely nothing.

If there was anything in there, it was so well hidden that I doubt anybody could possibly find it.
Really? I thought it was very good, and made some points that I was trying to address, as well as going further into some things I hadn't thought of. Some key points were:

Randomness is an intuitive notion, not something with and easy and precise mathematical definition;

Randomness has to do with information - a string may appear random or not depending on whether you have certain information about it; one measure of randomness is the amount of incompressible 'information' it contains.

In random sampling, the key part is whether your sampling method is random with respect to (relative to) the variable you are measuring;

You can't infer backwards from (e.g., a string of numbers) conforming to a stochastic distribution to saying there is "true randomness," in particular, a stochastic distribution is never inconsistent with determinism;

It's meaningless to talk about the "randomness" of a single observation;

Similar (and related) to the stopping problem with a Turing machine, it's generally much easier to prove that a string is not random than than to prove that it is.

I thought the paper made these points better than I was likely to; I hadn't commented on it because I haven't finished the paper. (I've read about the first twelve pages so far.) I wanted to clear up some of these mathematical points before attempting to see how they might apply in the quantum realm.
Locked