pilot-wave theory revised

Originally posted by DeepThought
Do you think all entangled particles are primordial? To prepare an entangled state one has to interact with it in the first place. A decay generating two entangled photons involves an interaction. The atom couples with the electromagnetic field.

I am afraid I don't know enough about entanglement to know what you are on about.

It is not an error to dispute that a piece of equipment does not count as an observer.
Yes, it is.

What Wikipedia says is the opinion of the last person who edited it.
That doesn't make it automatically wrong.

The polaroid is the piece of film that polarizes the light, it is not the film recording the event.
Sorry, I misunderstood your post. I am used to the phrase 'polarized lens' rather than polaroid - which is a brand name for a camera.

The photographic film does not have a perspective, it is a piece of film.
Perspective is not required, that's my whole point.

Saying it's macroscopic is no good, why do you think macroscopic objects are not subject to quantum theory?
I did not claim otherwise.

For clarity I do not agree with the Copenhagen interpretation, but if one is using that then von Neumann's Conscious observers are necessary as it is the only place where the wavefunction can collapse.
Well if that's the case then its absolute nonsense. But as I rather doubt that you are right about the Copenhagen interpretation.

But you dismiss the notion that consciousness is involved at your peril. You are arguing with Johnny von Neumann he was a smart guy and you might want to think twice about what you are saying.
Well he's not here to argue it is he? Can you link me to any scientific paper by him making such a ridiculous claim?

Originally posted by DeepThought
But you dismiss the notion that consciousness is involved at your peril. You are arguing with Johnny von Neumann he was a smart guy and you might want to think twice about what you are saying.

Seriously, lets think for a moment about what the claim entails.
Suppose for a moment that all the conscious observers in the universe live on Earth. Does this mean that until light from a distant Galaxy reaches us, there is no physics going on, or it all one massive quantum wave with anything goes until some observant astronomer looks through his telescope and bam!, the wave function collapse and the galaxy becomes real? And is the astronomer in question also part of a quantum wave that has not yet collapsed until I decide to observe him?

Originally posted by twhitehead
Seriously, lets think for a moment about what the claim entails.
Suppose for a moment that all the conscious observers in the universe live on Earth. Does this mean that until light from a distant Galaxy reaches us, there is no physics going on, or it all one massive quantum wave with anything goes until some observant astronomer looks through his telesc ...[text shortened]... n question also part of a quantum wave that has not yet collapsed until I decide to observe him?

Yes. Penrose made a similar point. You have all possible states for the universe in a linear superposition. This can include ones quite different to ours. When the first viable observer evolves in one of the states the wavefunction of the entire universe collapses to leave the one with the viable observer in. One problem with Schrodinger's cat is that there is no reason the cat shouldn't be a viable observer, Penrose got round this by making the cat a porcelain cat and instead of poison there is a hammer connected to the radioactive atoms detector.

Von Neumann's position is reasonably well summed up in a Wikipedia article [1], if you want to read something really weird read the page on "Delayed Choice Quantum Eraser".

This stuff gets even stranger when you consider relativity. Let's do the EPR experiment with a few extra observers. Two of them are stationary with respect to the source of entangled photons, but very far away from it, call them A and B. The two others are moving relative to the lab frame at a significant fraction of the speed of light but in opposite directions, call these two C and D. A and B report their results to the other observers as quickly as physically possible. The photons are emitted, suppose in their frame of reference A and B make their observations at the same time. Which observer collapsed the wavefunction of the entangled state? A or B. Let's ask C and D. C will say that observer A reported first and D will say observer B reported first. So it is not even clear which observation caused the wavefunction collapse.

Incidentally when I say an observer isn't just a piece of equipment it is because of the problem von Neumann spotted which is identifying when the wave function collapse happened. I'm perfectly happy to have idealised quantum observers who can be shrunk to fit inside a proton.

I dislike it for the same reason Einstein did, what with being heavy on universes, but if you want a realist interpretation of quantum theory Everett's Many Universes has the benefit of actually making sense.

[1] http://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_interpretation
[2] http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

Originally posted by twhitehead
Stranger and stranger. I never realized so many physicists take such nonsense seriously.
My own understanding of the Copenhagen interpretation is that the universe can be thought of as a series of black boxes. The moment information flows out of a box, it 'collapses' the wave function for what is in that box, to a smaller set that is still possible based ...[text shortened]... stood, so the introduction of consciousness into the whole thing is a complete misunderstanding.

In practice the basic philosophy is "Shut up and calculate.", Undergraduate courses in quantum mechanics are dominated by the problem of solving the Schrodinger equation for a hydrogen atom, infinite and finite square wells, the simple harmonic oscillator (really the most important one) and perturbation theory. It is essentially a technical subject. Assuming two 20 lecture courses, there'll be one or maybe two lectures on the actual interpretation of the theory.

I've never heard of your black boxes model. The difficulty I have is what causes the information to flow out of the box? Given that entangled states between particle pairs can exist over large distances I've got to ask what you mean by a box? Come to that what do you mean by "flow of information"?

Most physicists would rather not have a theory based on Cartesian dualism (what I mean by idealist philosophy in my first post). The problem is that until there is an interpretation which makes sense and explains wavefunction collapse in a physicalist way then it can't really be ruled out.

Here I'm using physicalist to mean that there is only one type of substance in the universe, matter. Mind is not a separate substance, but some sort of emergent behaviour subsisting on matter. Cartesian dualism has matter and mind as separate substances interacting via the brain.

Originally posted by humy
http://phys.org/news/2014-09-fluid-mechanics-alternative-quantum-orthodoxy.html

personally, although I am uncertain of the validity of the pilot-wave interpretation of quantum mechanics, I still favour it over the Copenhagen interpretation which I think is erroneous in its logic (don't have a problem with something being causeless. Just think we should be ve ...[text shortened]... gen interpretation and the pilot-wave interpretation is just one of the realist interpretations.

I bethink myself now of the David Hilbert quote, "Physics is too hard for physicists."

It annoys me that the Copenhagen Interpretation is touted as something akin to canon in the popular science books and television programs, because it's BS. But it's precisely because it's so outlandishly daft and blinkered that it sells so well. "See kids? Fact is stranger than fiction!" It's like throwing a pinch of astrology into a course about orbital mechanics just to "jazz things up" and hold the interest of the ADD sufferers in the audience.

Originally posted by DeepThought
I've never heard of your black boxes model. The difficulty I have is what causes the information to flow out of the box?

Any interaction.

Given that entangled states between particle pairs can exist over large distances I've got to ask what you mean by a box?
Any set of particles/states grouped together. For it to be useful, it makes sense to use collections that are co-dependent in some way, so poison + cat for example.

Come to that what do you mean by "flow of information"?
Any interaction that carries information about the state of the contents of the box. So, for example, Schrodinger cats fate is sealed the moment information about its state leaves the box. Not when some conscious scientist finds out about it.
Suppose the cat were to die, and in so doing, falls down. The impact of its falling triggers a switch that sends information to a computer outside the box, which records that the cat has died. At this point, from the point of view of the computer, and anything within it sphere of influence, the cats wave function of life, has collapsed.
One could argue that for a scientist nearby that has not yet been influenced by this activity in any way, the wave function has not collapsed, and for him, the cat, the box and the computer are all in an entangled state. But I must emphasize that consciousness doe not come into it. If the scientist is influenced in any way by the cats death, whether he is consciously aware of it or not, then the wave function has collapsed as far as he is concerned.

Originally posted by twhitehead
Any interaction.

[b]Given that entangled states between particle pairs can exist over large distances I've got to ask what you mean by a box?
Any set of particles/states grouped together. For it to be useful, it makes sense to use collections that are co-dependent in some way, so poison + cat for example.

Come to that what do you mean by "fl ...[text shortened]... consciously aware of it or not, then the wave function has collapsed as far as he is concerned.

Any interaction is too wide. I can justify that statement, but this post is huge so I'll leave it unless you are going to challenge it again.

You have the wavefunction collapsed by the computer, but not as far as the scientist is concerned. Either you have the wavefunction as something non-physical, you're interpreting it as some sort of Bayesian knowledge thing (this is a known interpretation), or this is a variant of the many universes interpretation.

The slight problem with your set up is you have continuous observation of the cat. Suppose the computer checks on the cat after one half-life of the atom which determines moggies fate.

Let AC(x, t) be the wave function of the Alive Cat at time t, DC(x, t) is the wave function of a dead one. D(x, t) is the wave function of the computer (D for detector) up until it makes a measurement, with AD(x, t) and DD(x, t) being wave functions of the computer when it has registered an alive or dead cat. E(x, t) is the wave function of the (conscious) experimenter, with AE(x, t) and DE(x, t) having the same meaning as for the cat.

We set up the experiment, at this point the wavefunction is:

W(x, t0) = E(x, t0)D(x, t0)AC(x, t0)

The cat is definitely alive at this point so we can use the wavefunction for a living cat. We wait for one half-life and the cat's wavefunction evolves into 1/sqrt(2) (AC(x, t1) + DC(x, t1)). I'll drop the factor of root 2 from now on as it doesn't add much. Just before our cat mortality detector does it's thing the overall wave function (up to normalization) is:

W(x,t1) = E(x, t1)D(x, t1)(AC(x, t1) + DC(x, t1))

if the wavefunction collapses at this stage (lets say to alive) it will be:

Wcat(x, t1) = E(x, t1)D(x, t1)AC(x, t1)

Wcat(x, t1) just means the wavefunction if wavefunction collapse happens now.

The detector does it's thing, the uncollapsed wavefunction is now:

W(x, t2) = E(x, t2)(AD(x, t2)AC(x, t2) + DD(x, t2)DC(x, t2))

If the detector collapses the wavefunction it would be:

Wdet(x, t2) = E(x, t2)AD(x, t2)AC(x, t2)

had the wavefunction collapse happened earlier the system would have evolved continuously into:

Wcat(x, t2) = E(x, t2)AD(x, t2)AC(x, t2)

Note that Wcat(x, t2) = Wexp(x, t2).

The experimenter comes along and we get:

W(x, t3) = AE(x, t3)AD(x, t3)AC(x, t3) + DE(x, t3)DD(x, t3)DC(x, t3)

Where the first term corresponds to a universe where the cats been lucky and the second term corresponds to a universe where the cat's been unlucky. The experimenter is in a linear superposition, but isn't conscious of it, in fact the experimenter has been copied with the only difference being whether his brain is in a state of mourning or relief. This is the basis of Everetts many universes interpretation.

If the experimenter collapses the wavefunction we would have:

Wexp(x, t3) = AE(x, t3)AD(x, t3)AC(x, t3)

and had the collapses happened earlier we have:

Wcat(x, t3) = Wdet(x, t3) = Wexp(x, t3)

So by now the outcome of "early" and "late" collapse is indistinguishable even at the level of wavefunctions.

You seem to have Wdet(x, t3) but there is no reason to prefer it to Wcat or Wexp. The Everett interpretation does have a different wavefunction, but it is:

W(x, t3) = AWexp(x, t3) + DWexp(x, t3)

There may be a way to distinguish this from the collapse type interpretations, but I don't know what it is.

The key point I'm trying to make is that there is no way on God's green Earth that you can distinguish the collapse happening early and the collapse happening late, and you can't experimentally demonstrate that it is definitely not because of the consciousness of the the experimenter. In a dualist outlook the experimenters body (including his brain) can be in a linear superposition of states right up until the point that his mind collapses the wavefunction. There is no experimental way of ruling this out.

Originally posted by DeepThought
.... and you can't experimentally demonstrate that it is definitely not because of the consciousness of the the experimenter.

Maybe not, but I see no reason whatsoever (other than an ego problem) for singling out said consciousness as the 'cause' of the collapse.
But I am less interested in so called collapse of the wave function, and more interested in what happens when it doesn't collapse and cannot be collapsed. When the black box remains closed.
In the two slit experiment, there is a 'black box' period in which we can never know which route a given photon took. So it remains forever the case that as far as we are concerned, the photon appears to have taken both routes. The whole 'wave nature' of light is dependent on this fact. And no, consciousness has nothing whatsoever to do with it.
Light behaves like a wave whether you observe it or not.