The greatest mystery to me is the quantum function in relation to the probability wave function.

If reality propagates in quanta (discreet packets) what medium lies in between? From the (very) little I understand, this is where the probability wave function must occur.

And if the probability wave is merely a function, would that not be comparable with the mathematical function, a concept which IMO is metaphysical in nature? The mathematical function allows the expression of 2+2=4.

I cannot divest myself from Bohm’s “implicate and explicate order”, the implicate being a function, the explicate being the instantiation of that which was implicate. As I understand it Bohm refers here to the function of potential, i.e. a potential wave function, which allows for quanta to become instantiated (explicate) in chronological order, creating time (when) in the process. The location (where) these quanta become instantiated (explicate) is the function of the probability function (implicate) contained within the potential wave function.

If reality propagates in quanta (discreet packets) what medium lies in between? From the (very) little I understand, this is where the probability wave function must occur.

No, reality does not propagate in quanta, it interacts in quanta. In the two split experiment it is no use to talk about the path of the photons, there is no way to know through which slit a photon went without disturbing the interference pattern. However, the photon is measured at a single place. A measurement always is also an interaction, and this occurs at a well defined place.

Write4U - 27 November 2011 09:55 PM

And if the probability wave is merely a function, would that not be comparable with the mathematical function, a concept which IMO is metaphysical in nature? The mathematical function allows the expression of 2+2=4.

Your use of the word ‘metaphysical’ does not correspond to its usual meaning, so I can say nothing about that.

Write4U - 27 November 2011 09:55 PM

I cannot divest myself from Bohm’s “implicate and explicate order”, the implicate being a function, the explicate being the instantiation of that which was implicate. As I understand it Bohm refers here to the function of potential, i.e. a potential wave function, which allows for quanta to become instantiated (explicate) in chronological order, creating time (when) in the process. The location (where) these quanta become instantiated (explicate) is the function of the probability function (implicate) contained within the potential wave function.

I don’t know Bohm’s framework of QM. The few things I know is that it is empirically equivalent with the Copenhagen interpretation of QM. But it introduces a quantum potential (oh, sure you love this!) that does not become less with the distance. In other words, the state of a particle depends on all other particles in the universe. (I think it is sometimes called hyperdeterminism, as events are not just caused by local events but by all events in the complete universe.)

No, reality does not propagate in quanta, it interacts in quanta. In the two split experiment it is no use to talk about the path of the photons, there is no way to know through which slit a photon went without disturbing the interference pattern.

I thought the idea is that it cannot have gone through one slit or other (like bullets of a gun) because if it had there would be no interference pattern as there would be nothing to interfere with.

I expect I’ve got that wrong but it might help to see where I’ve gone wrong.

I thought the idea is that it cannot have gone through one slit or other (like bullets of a gun) because if it had there would be no interference pattern as there would be nothing to interfere with.

If we think of particles on their way, we must suppose that a particle goes through one slit only. But then it is inexplicable what the influence of the other slit is, when the particle does not fly through it. So the only way to say a Q-particle on the run is to see it as a wave, these are smeared out over space and can go through two holes at once.
However to understand the detection, which is very localised at one single point, the wave picture in its turn is inexplicable: the wave should arrive at all detectors, not at just one. And at the moment I have detected a particle, I know it cannot arrive somewhere else.

So maybe you understand my short ‘Quantum adagium’: A path, a wave;
an interaction, a particle.

Just repeat this 10 times every day before you go to sleep, and one day you will understand all of QM…

After doing some reading yesterday about the Einstein/Bohr debate, I found following interesting side track. Bohr’s father was a friend of the Danish philosopher Harald Høffding, who originally was very influenced by Søren Kierkegaard. According to the text I read it was Kierkegaard’s stress on the point that a subject cannot take himself out of the system (Kierkegaard’s critique on Hegel) was a stimulating idea for Bohr about the position of the observer in QM. Reading in Wikipedia however it is said that this is mere speculative. Well, whatever, the idea is interesting, even if disputed.

It is obvious that Einstein believed in a completely observer independent universe, which could be described as such.

After doing some reading yesterday about the Einstein/Bohr debate, I found following interesting side track. Bohr’s father was a friend of the Danish philosopher Harald Høffding, who originally was very influenced by Søren Kierkegaard. According to the text I read it was Kierkegaard’s stress on the point that a subject cannot take himself out of the system (Kierkegaard’s critique on Hegel) was a stimulating idea for Bohr about the position of the observer in QM. Reading in Wikipedia however it is said that this is mere speculative. Well, whatever, the idea is interesting, even if disputed.

It is obvious that Einstein believed in a completely observer independent universe, which could be described as such.

Right. Well, a lot of Copenhagen-interpretation-philosophy I’ve read seems to me basically a version of substance dualism, whereby the magical human mind brings the world into existence by observation. This is absurd, I know that renowned physicists like Feynman, Weinberg and Stenger reject it, and yet it percolates in the background of any discussion of QM.

I imagine (though I haven’t looked into it) that the problem might stem from some physicists who developed the Copenhagen interpretation having been influenced by some not very good, dualistic philosophy. When I hear Kierkegaard and Hegel, that goes some way towards confirming my suspicion.

Right. Well, a lot of Copenhagen-interpretation-philosophy I’ve read seems to me basically a version of substance dualism, whereby the magical human mind brings the world into existence by observation. This is absurd, I know that renowned physicists like Feynman, Weinberg and Stenger reject it, and yet it percolates in the background of any discussion of QM.

Well in this Copenhagen interpretation-interpretation you are right. But I see the Copenhagen interpretation as saying that we can only talk about observables. As we cannot look ‘under’ what we observe in QM, it is no use to speculate about the real nature of quantum objects. It is exactly to see the wave function as something real that leads to your mentioned absurdities. If the wave function is real, then we must identify the cause of its collapse in a measurement. And that would then be an observer. Now you are amidst in dualism. But if there is nothing to collapse, there is no cause needed for it.

The modern view seems to be quantum decoherence: the explaining of the seemingly collapse of the wave function as the interaction of a quantum system with a classical system, i.e. a system in which quantum events dissipate in their environment. The brain, as a classical system does that too, as any classical measuring instrument. In this way there is no need for a conscious observer anymore, and we avoid dualism.

dougsmith - 29 November 2011 05:08 AM

I imagine (though I haven’t looked into it) that the problem might stem from some physicists who developed the Copenhagen interpretation having been influenced by some not very good, dualistic philosophy. When I hear Kierkegaard and Hegel, that goes some way towards confirming my suspicion.

I do not quite share your aversion against continental philosophers. If you strip off the metaphysical ballast there remain nearly always some valuable ideas.

Well in this Copenhagen interpretation-interpretation you are right. But I see the Copenhagen interpretation as saying that we can only talk about observables. As we cannot look ‘under’ what we observe in QM, it is no use to speculate about the real nature of quantum objects. It is exactly to see the wave function as something real that leads to your mentioned absurdities. If the wave function is real, then we must identify the cause of its collapse in a measurement. And that would then be an observer. Now you are amidst in dualism. But if there is nothing to collapse, there is no cause needed for it.

OK, that makes ... some ... sense. But there still must be stuff going on unobserved. The question is how to model that. The only way to model it responsibly is by using the equations that work to save the phenomena. Right?

GdB - 29 November 2011 06:10 AM

The modern view seems to be quantum decoherence: the explaining of the seemingly collapse of the wave function as the interaction of a quantum system with a classical system, i.e. a system in which quantum events dissipate in their environment. The brain, as a classical system does that too, as any classical measuring instrument. In this way there is no need for a conscious observer anymore, and we avoid dualism.

But all these systems are quantum systems. So it’s always just a quantum system interacting with a quantum system. So what exactly is this “collapse” then, and what triggers it?

OK, that makes ... some ... sense. But there still must be stuff going on unobserved. The question is how to model that. The only way to model it responsibly is by using the equations that work to save the phenomena. Right?

Just forget to picture it, i.e. do not try to understand what it is in any everyday notion. But now do not ask me what the difference is between picturing something, or make a model of it. We just are not able to check our model empirically below what we can observe.

dougsmith - 29 November 2011 07:52 AM

But all these systems are quantum systems. So it’s always just a quantum system interacting with a quantum system. So what exactly is this “collapse” then, and what triggers it?

As far as I understand it: when the entanglement with the original system gets lost because the system we are measuring is interacting with many, many other quantum systems, i.e. the measuring device. Said otherwise (from here):

Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way.

Just forget to picture it, i.e. do not try to understand what it is in any everyday notion. But now do not ask me what the difference is between picturing something, or make a model of it. We just are not able to check our model empirically below what we can observe.

Well, I don’t think that’s an adequate answer. I don’t think ‘picturing’ is the appropriate goal, since of course what is going on at the level of the very small may be in many ways fundamentally non-visualizable. But it should be able to be modeled. And indeed what we find below are models of just that kind.

GdB - 29 November 2011 08:39 AM

As far as I understand it: when the entanglement with the original system gets lost because the system we are measuring is interacting with many, many other quantum systems, i.e. the measuring device. Said otherwise (from here):

Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way.

OK. That link from Wiki is very valuable. It also leads me to the measurement problem, which is basically the problem of how measurement appears to do something to the pre-existing quantum state. This is also the question of how we get from modeling unobserved processes to empirical observation.

There we also find that ‘quantum decoherence’ is only one model among several, including Everett’s Many Worlds model and so-called consistent histories model. (I’m not sure if the latter is different from quantum decoherence or only a refinement of it. Perhaps the latter).

My sense from reading through this stuff is that we’re too close to it to have a completely worked out theory, and likely we’ll have to wait for a more complete physics to figure out precisely what’s going on. Either that or the various models will need resolution, at least for someone like me to really be able to know which to accept. (Perhaps that’s also a corollary of not having a grasp of the mathematics involved).

Well, I don’t think that’s an adequate answer. I don’t think ‘picturing’ is the appropriate goal, since of course what is going on at the level of the very small may be in many ways fundamentally non-visualizable. But it should be able to be modeled. And indeed what we find below are models of just that kind.

Here there are positions possible: we could say, ‘yes, it is modelled, see the mathematical formalism’. Or we can say ‘No, we cannot model it, we cannot dive under what is observable’. I think to make an adequate model of quantum reality, one must give up some precious thought about reality, to name a few:
- reality is deterministic
- events are caused by other local events
- reality exists independent of any observer
- that reality is knowable in principle to the last bit (completeness)

Refusing to accept one of them leads to some of the extreme interpretations of QM:
- Bohm’s intrinsic order and the many worlds theory stick to determinism: Bohm gives up locality, for that, Everett that we live in one single universe
- the old fashioned Copenhagen interpretation gives up observer independent reality
- the ensemble interpretation gives up that reality is knowable and deterministic

For an overview see here.
I personally opt for the last: no model possible.

The problem is that no progress in physics will change that: any follow-on theory must at least make the same predictions as present QM, at least in the limiting case. But that means already we have to give up some of our presuppositions listed above. In the end, all above theories make exactly the same empirical predictions, they are empirically equivalent.

Does the tree make noise when it falls and nobody hears it? Yes.
Can we know the exact location of an electron before we measure it? No.

I think to make an adequate model of quantum reality, one must give up some precious thought about reality, to name a few:
- reality is deterministic
- events are caused by other local events
- reality exists independent of any observer
- that reality is knowable in principle to the last bit (completeness)

To be clear, one doesn’t have to give up all of these. One only has to give up one or another. “Reality exists independent of any observer” is a sine qua non for any reasonable theory, IMO, since otherwise we are left with a kind of incipient dualism, observer/world, where this dualism makes no real sense.

I know that Bohm’s and Everett’s theories are standard ones along the lines I’m after, though it would appear there are others.

GdB - 30 November 2011 10:09 AM

Refusing to accept one of them leads to some of the extreme interpretations of QM:
- Bohm’s intrinsic order and the many worlds theory stick to determinism: Bohm gives up locality, for that, Everett that we live in one single universe

Right. I have no issue giving up locality. Quantum entanglement seems to require that.

GdB - 30 November 2011 10:09 AM

- the old fashioned Copenhagen interpretation gives up observer independent reality

I thought so, too, but the comparison chart on the wiki page you cited says there isn’t any observer role in Copenhagen. I suppose it’s in error?

GdB - 30 November 2011 10:09 AM

Can we know the exact location of an electron before we measure it? No.

Sure, that’s from Heisenberg. I don’t think that’s a problem. If the model tells us that there’s a grainedness to reality, a smallest length/interval/etc. below which it’s either impossible to speak (the Planck length) or a finest accuracy beyond which it’s impossible to know, that’s OK. So long as the equations are suitably precise about these limits, which they are, it’s something that, while surprising, is comprehensible in its own way.

Particles are physical, but is particle information physical? Entanglement requires us to give up locality, it also asks to give up SOL restriction. If a particle in transit has any physical properties, i.e. smeared out, how can it exceed SOL? But apparently it can transfer its information in a non physical probabilistic wave function, which then can only be measured by “collapsing” it, instantiating (re)creating) the physical properties of the particle.

Would it not follow that the term quantum “leap” is a misnomer? IMO a quantum “event” is an event where the original particle is converted to a non-physical state and it’s information is retained as part of the implicate order throughout the universe and a new particle is created (on demand or by probability function) elsewhere, maybe anywhere, from the original information acquired (implicated) into the intrinsic order.

In such a system all questions re location, speed, observer reality, would be explained. If we assume a non-physical (meta-physical) dimension, which needs not answer to any physical laws and restrictions other than some general universal constants and functions, as we are beginning to identify, seems to me that a physicists life would become less complicated…..