Deterministic Quantum Mechanics?

  • Thread starter Phrak
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  • #1
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Thanks to Noobie!, in this thread

https://www.physicsforums.com/showthread.php?t=280861",

I wonder, is there any interpretation of quantum mechanics is not devoted to constructing a deterministic quantum mechanics? It comes as something of a shock to me to realize that this is what "making sense" of quantum mechanics has been all about. Am I wrong?

If that isn't enough, why should some of us be so compelled to have physics deterministic; what is it about indeterminism that is so unacceptable?
 
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  • #3
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Regarding your first question, there is also work attempting to show that quantum randomness is irreducible:

http://arxiv.org/pdf/0811.4542v1

Completely not what I was asking for--which is wonderful. Thanks colorSpace!
 
  • #4
atyy
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My understanding is that determinism is not the problem. The problem is that textbooks such as Landau and Lifgarbagez say a measurement is something carried out by a "classical" apparatus. Isn't everything quantum mechanical? If not, what is the "objective" way to distinguish between a "quantum mechanical" and "classical" apparatus?
 
  • #6
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Completely not what I was asking for--which is wonderful. Thanks colorSpace!

Welcome! :) Non-determinism may seem to be the end of scientific research, but my impression is that researchers like Anton Zeilinger are (at least) as much on the forefront of research in quantum physics as those who, for example, prefer the deterministic many worlds interpretation (especially, of course, regarding the research of entanglement with its non-local-correlation properties). The same, I think, can be said about the history of quantum physics.
 
  • #7
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my impression is that researchers like Anton Zeilinger are (at least) as much on the forefront of research in quantum physics as those who, for example, prefer the deterministic many worlds interpretation (especially, of course, regarding the research of entanglement with its non-local-correlation properties).

I also think so:
"Bird's view": Deterministic, Multi-world (Time is not an arrow but rather a tree), No paradoxes.
"Frog's view (observer view)": Random, Single arrow of time, Full of strange paradoxes.
 
  • #8
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If that isn't enough, why should some of us be so compelled to have physics deterministic; what is it about indeterminism that is so unacceptable?

The Theory of Everything should look like:

TOE(x) = 0

Where TOE is some formula, and x is some variable.
Then you just build the whole multiverse from scratch: you analyze the equation and find out that the solution exists only if x is complex and it is in 11-dimensional space, for example. You get the BULK, branes etc. So the physics is just a pure mathematics, and the TOE does not require any words to be explained (like after we write F=ma we need to say that F stands for a force (what is it?) m is mass, a is acceleration (and you have to explain what is time etc, otherwise what is a difference between F=ma and A=BC?)

(All ideas above belong to Max Tegmark)

So when we get finally an equation for TOE the 6th Hilbert's problem (http://en.wikipedia.org/wiki/Hilbert's_problems) will be solved automatically, without any special efforts.

So physics is pure mathematics, but how can you introduce a probability into the pure mathematics? Beginning from the fact that there are 2 different definitions of the probability: http://en.wikipedia.org/wiki/Probability - frequenism and Bayesians school.
 
  • #9
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I also think so:
"Bird's view": Deterministic, Multi-world (Time is not an arrow but rather a tree), No paradoxes.
"Frog's view (observer view)": Random, Single arrow of time, Full of strange paradoxes.

Fine, I think this way:

"Full of strange paradoxes" means "full of interesting possibilities".

Even in MWI, interference and entanglement and other quantum effects are still strange things, and at that point, I'm willing to consider more strangeness. To assume that there are a trillion fully-conscious observers created when a double-slit experiment is performed (or anyway) seems more like a mathematical trick than like a physical explanation. The uncertainty principle still allows particles to do things they wouldn't otherwise, so what I want to hear is: Let's find out what else is possible.
 
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  • #10
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Phrak is quite right in isolating the key factor behind quantum mechanics which has caused most distress to scientists and philosophers. Bohmians gave up their previous insistence about locality once Bell, actually a Bohmian himself, proved that Bohmian theory was not compatible with both locality and Determinism. In fact they had a choice to maintain either locality or Dterminsim, and they chucked locality for their more philiosphically important mantra - Determinism. The argument over whether the universe is utlimately Determinstic or not is actually philosophical.

The same scientific mass delusion has been committed by much of the Determinstic science community when dealing with chaos theory. It is often claimed: "if we knew all initial conditions..... " we could predict x, y or z. This is complete rubbish statement and means nothing at all. It's the same as me saying "if i had wings i could fly" - therefore i am a bird? No this is not a logical statement or truth and frankly it is highly embarssing that much of the Determinstic scientitifc community condone such a misrepresentation of logic and the facts. Its shameful because they know what they are doing.

So even leaving aside the loud and clear non-determinstic signal from nature found in the HUP at microcopic scales, the N body problem, and the known fact that we can not know all initial conditions which influence even reasonably simple open ended non linear systems; some folk will just continue to ignore what nature is telling us.

But Determinsitic dogma is a very human response to uncertainty and the unknown. So it is healthy for us to want to make better and better approximations and it's practically useful for an advancing society.

However any serious claims that our universe is deterrmnistic are basically a load of crap. Nature has been telling us the opposite for the last 100 years - some people just are not ready to give up their human need for "certainty".
 
  • #11
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1 "Full of strange paradoxes" means "full of interesting possibilities".
2 Even in MWI, interference and entanglement and other quantum effects are still strange things, and at that point, I'm willing to consider more strangeness.
3 To assume that there are a trillion fully-conscious observers created when a double-slit experiment is performed (or anyway) seems more like a mathematical trick than like a physical explanation.

1 AGREED

2 Well, I would say there are 2 different things: old MWI (Everett, 195x) and current theory based on the Quantum Decoherence. Lets call that interpretation QD(ecoherence). MWI is a logical consequence of QD, not an axiom. That differs QD from the classical MWI.

For QD interference is not a problem at all; because Universe splits only thru QD, so if there are no irreversible systems (2 slit for exaple) then decoherence does not occur and we see an interference pattern.

3 I agree with you, in fact, this is the only thing I dont like in MWI.
However I have a solution for that problem (it leads to even stranger consequences)
If youare interested let me know (I have to go in few mins. so cant type it right now)
 
  • #12
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Dear Phrak,
It is possible to have deterministic QM which relies only on the evolution equation, without discontinuous wavefunction collapse, without hidden variables, and without including all projections as in MWI. Basically, the evolution is deterministic, and the only source of randomness is the incomplete determination of the initial conditions. Each new measurement adds information about the initial conditions, in a nonlocal way (that is, not by obtaining the information, but by choosing it). Please see http://philsci-archive.pitt.edu/archive/00004344/ for details.

“The apparent wave function collapse can take place smoothly, without discontinuities. The projections on the observable's eigenspaces can be obtained by a delayed initial condition, imposed to the smooth time evolution of the observed system entangled with the measurement device used for the preparation. Since the quantum state of this device is not available entirely to the observer, its unknown degrees of freedom inject, by the means of entanglement, an apparent randomness in the observed system, leading to a probabilistic behavior. Thus, we can construct a Smooth Quantum Mechanics (SQM), without the need of discontinuities in time evolution. The probabilities occur therefore because not all the systems involved have determined quantum states. The evolution is deterministic, but for an observer, who has access only to an incomplete set of initial conditions, it appears to be indeterministic.”
 
  • #13
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My understanding is that determinism is not the problem. The problem is that textbooks such as Landau and Lifgarbagez say a measurement is something carried out by a "classical" apparatus. Isn't everything quantum mechanical? If not, what is the "objective" way to distinguish between a "quantum mechanical" and "classical" apparatus?

Perhaps determinism isn't the problem. Quantum mechanics is incomplete where the observer is not treated as quantum mechanical as you say. As far as I can tell, decoherence theory offers both to compete it and obtain determinism.

The arxiv paper linked by colorSpace offers, not determinism, but introduces a notion as to, how it should not be deterministic.

But, though I'm happy to read about indeterminism, is there really any valid reason to expect determinism?

Edit: I should rather say "Is there any compelling reason?"
 
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  • #14
Pythagorean
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If that isn't enough, why should some of us be so compelled to have physics deterministic; what is it about indeterminism that is so unacceptable?

Science is deterministic. We only call scientific, what can help us to determine things that we haven't yet observed. (I.e. we make predictions and then test them).

But more importantly, it's consistent. You can do the same experiment over and over and get the same results.

Indeterminism is unacceptable because it doesn't help you make predictions. If I kick a can and the can just happens to fly independently on it's own every time I kick it (even in double-blind, syncopated, random trials) that's fine; that's deterministic enough for me.

We know our view of how I kicked the can isn't as easily determined. It might have been difficult to explain a hundred years ago that this was electron repulsion between my foot and the can. And we still may be somehow wrong with that interpretation today.

So interpretations don't always have to be deterministic. They just help us grasp the idea in whole, and attach the abstract to our intuitive understanding.

What IS deterministic, is the actual meat of physics (which isn't the interpretations. They're more philosophical). The small "truths" and experiments verifying those small truths.

For example, when I kick a can, the can will take motion up from the energy I provide it. This is a small truth. I realize there's exceptions, but I ignore those cases for interest in the case on Earth in a parking lot.

I'm not making any statement about the determinism of the entire universe, that would be a "big truth". Science is merely the label we use when we operate from a deterministic view. Each scientist is free to have his own interpretations about what's going on behind the scenes until we can consistently prove it one way or another.

Each scientist is also free to draw his own interpretations on how the universe "is" (is it deterministic or not?) but I tend to feel that the invalid assumption that's already been made here is that it can only exist as one or the other.
 
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  • #15
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However I have a solution for that problem (it leads to even stranger consequences)
If youare interested let me know (I have to go in few mins. so cant type it right now)

Sure, sounds interesting. :)

EDIT:
For QD interference is not a problem at all; because Universe splits only thru QD, so if there are no irreversible systems (2 slit for exaple) then decoherence does not occur and we see an interference pattern.

Don't you have decoherence when the photons hits the screen, since now its location is fixed, and when there was interference, the location is random for a specific observer ?
 
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  • #16
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Don't you have decoherence when the photons hits the screen, since now its location is fixed, and when there was interference, the location is random for a specific observer ?

Yes, correct, this is a decoherence which occurs after the interference.
So I dont see any problems with an *interference*

So what I promised...

The quantum reality (bird’s view) is transformed into the world we observe (frog’s view) via quantum decoherence. This is just mathematical result of mapping a quantum reality into a state of a microscopic object with a huge number of degrees of freedom.

However, microscopic systems (processors, brains) are “protected” from the quantum fluctuations (unless specifically designed to detect them). Noise from heat fluctuations do not affect the processor of my laptop and it gives the predictable results no matter how every specific molecule moves.

So (what I was thinking before) the quantum reality is mapped twice: Bird’s view is mapped into frog’s view (classical physics) via the decoherence, to an ansamble of the moving molecules, and the second stage, where states of individual molecules are mapped into ‘processor bits’ belongs to the technology. The quantum behavior ends at the first stage. In fact, it gives huge 'branching ratio' for every event.

But the macroscopic systems can not observe movements of all parts they consist of in principle because the number of states of processor on the IT level (memory, registers) is much much less then the number of states if we look at the processor as a collection of molecules. So for processor (or for our consciousness) different paths (path N1234: molecule H2O N 9223 in row 3445 :) split into H+ and OH-, path N1235 – the same, but another molecule split, etc) – they all lead to the *same* state of a processor or the same state of our consciousness.

In that case, if there any physical meaning in distinguishing these different branches of reality? Or, like on Feynman diagrams with virtual particles, different branches of reality also interfere?

Where the quantum coherence ends, as we have a hierarchy of ‘microscopic states’? Does it end just because a frog contains too many moving molecules, or because a frog can observe? As a choice of final states for the quantum decoherence process is arbitrary, can we say that decoherence occurs (for us) only when it ‘hits’ our consciousness? In that case, weird quantum things can happen on the microscopic level, in our every day live, but we just do not feel them.

Look at the blue sky. It is blue because some fluctuations of air. Are you splitting every seconds into 10**<i dont know how many> copies just looking at the blue sky? Or these all branches end at the same state - "I see blue sky" and I dont split.
 
  • #17
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Look at the blue sky. It is blue because some fluctuations of air. Are you splitting every seconds into 10**<i dont know how many> copies just looking at the blue sky? Or these all branches end at the same state - "I see blue sky" and I dont split.

So how many copies of yourself would you expect to exist right now? It doesn't seem easy to tell whether things would converge or diverge, or find a balance at some level. Of course, you could easily make them diverge a lot, if you wanted to.
 
  • #18
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So how many copies of yourself would you expect to exist right now? It doesn't seem easy to tell whether things would converge or diverge, or find a balance at some level. Of course, you could easily make them diverge a lot, if you wanted to.

Too many to tell you, because I was splitting 40 years from my birth :)

Of course all it is just a pure speculation, because we dont know what is a 'consciousness'. However I feel more comfortable thinking that the branching ratio is not so huge.

For example, lets say I have a TRUE RANDOM generator: I press a button and it displays 9 random decimal digits. If I do it I can not avoid saying that I had been just split into 1 billion copies.

However, if I press the button but dont look at the screen I am not split at all because my state of counsciousness is the same no matter what number had been displayed (I dont know that number)
 
  • #19
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For example, lets say I have a TRUE RANDOM generator: I press a button and it displays 9 random decimal digits. If I do it I can not avoid saying that I had been just split into 1 billion copies.

Or if one uses quantum random number generators for all the lotteries in the world. :)
Everyone who buys a ticket would win in one world. :)

However, if I press the button but dont look at the screen I am not split at all because my state of counsciousness is the same no matter what number had been displayed (I dont know that number)

Well, that's still a question. The photons still reach you and everything else, and the effects may propagate rather than cancel out. I mean, there is a lot of Heisenberg uncertainty in this world. :)
 
  • #20
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Well, that's still a question. The photons still reach you and everything else, and the effects may propagate rather than cancel out.

Actually, that was the very first question I asked in this forum:
https://www.physicsforums.com/showthread.php?t=277618

However, I did not know that there are too many people who do not accept MWI. There are even adepts of the Copenhagen Interpretation!
 
  • #21
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Science is deterministic. We only call scientific, what can help us to determine things that we haven't yet observed. (I.e. we make predictions and then test them).

But more importantly, it's consistent. You can do the same experiment over and over and get the same results.

It shouldn't come as a suprise, that sooner or later, science, as a tool to discover true things by repeatability should fail were it not modified. Where the results of measurement in quantum mechanics are not fully determined, but described by weighted random variables, it seems to indicate that the tool of repeatability is challenged. But there's always wiggle room. Perhaps quantum mechanics is deterministic, but not knowably deterministic, for instance. (MWT seems to fit this bill.)

I think it is a measure of the scienctific method's strength that, using it, the early quantum theorists obtained a theory that tests the viability of the method.

Somehow, however, I think I have missed your point.

Each scientist is also free to draw his own interpretations on how the universe "is" (is it deterministic or not?) but I tend to feel that the invalid assumption that's already been made here is that it can only exist as one or the other.

I don't see how things could be both.
 
  • #22
Pythagorean
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Somehow, however, I think I have missed your point.

somewhat. But I can still address what you said. Even in QM, as long as we know the failure rate and range, we can still make use of repeated events. Since we know the error in trajectory (or the uncertainty in this case) we know it will always hit a target of a certain size (or at least with 99.9999999999% or better chance).

We also can predict that you're so very not likely to tunnel through a wall in your lifetime (or the lifetime of the universe, even!) that we may as well say it will never happen.


I don't see how things could be both.

let me provide you with an example then. Let's say Copenhagen interpretation is true. We have a bathtub full of water and hooked up to a drain that works like any standard bathtub nowadays.

When we pull the plug, it may be a determined case that it will go down the drain. However, in light of the Copenhagen Interpretation, there's no necessary path for each individual particle (down the quarks and leptons) to take to get down the drain.

In the same way, it's determined that humans will die, but how they arrive at their death or live their life may not be "determined" by anything more than a mixture of concrete truths and their willful, random choices.

The entropy of the whole universe is always increasing, but the local entropy (wrt to both time and space) is subject to a series of random events.
 
  • #23
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Actually, that was the very first question I asked in this forum:
https://www.physicsforums.com/showthread.php?t=277618

However, I did not know that there are too many people who do not accept MWI. There are even adepts of the Copenhagen Interpretation!

Perhaps, if you apply this idea of converging branches to the measurement process, and find that a measurement of a property in superposition will converge all branches, then you are perhaps back to something like the Copenhagen interpretation. :) Of course, if there are no hidden variables, this would have to be a process where the result would be probabilistic depending on the amplitudes, yet given that, this would be a process converging all branches into one. :) Or almost one, since Heisenberg uncertainty will remain.
 
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