Quantum myth 4: The only reality is the measured reality


by pellman
Tags: measured, myth, quantum, reality
Demystifier
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Jun5-08, 04:03 AM
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Quote Quote by Phrak View Post
Demystifier. Ok, I'll be listening, because I really want to know what you think. As I struggle to repair the state of mechanics as it lays today, how might I apply Ocaam's Razor?
Can you rephrase your question? I have no idea what exactly do you ask me.
Phycho
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Jun5-08, 05:02 AM
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Hurkyl, you've turned over to MWI proponent?

I'd say if theu niverse made copies of it self each split it would need infinite energy, yes, defendable position ? hell no
Hurkyl
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Jun5-08, 05:32 AM
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Quote Quote by Phycho View Post
I'd say if theu niverse made copies of it self each split it would need infinite energy
When you say 'copies itself', do you mean it sort of like passing the universe through a copy machine to produce a Star Trek-like parallel universe? If so, then there's no problem, because that has nothing to do with MWI.
peter0302
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Jun5-08, 08:53 AM
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Every time you add a new degree of freedom, you need more energy. It's basic thermodynamics.
Phrak
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Jun5-08, 11:39 AM
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Hurkyl- If I may paraphrase, what you are saying is that in the MWI, there is no physical splitting. Instead, for any system of particles, the wave equation of the system evolves unitarily. Is this correct? Though I suppose there may be more than one MWI interpretation.

-Demystifier. Sorry, it was a poor question on my part.
Phycho
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Jun5-08, 11:48 AM
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Quote Quote by Hurkyl View Post
When you say 'copies itself', do you mean it sort of like passing the universe through a copy machine to produce a Star Trek-like parallel universe? If so, then there's no problem, because that has nothing to do with MWI.
Hehe, I mean more, if a particle splits, it copies itself if this is true on a macroscopic scale.
Every second there are copies of you splitting off to other universes.
Is this the MWInterpretation you support?
peter0302
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Jun5-08, 02:11 PM
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What other MWInterpretation is there?

Perhaps the argument is over semantics (it usually is with people here). Each possible state of a particle has a particular probability amplitude - you might think of this as its "thickness." If there are two equal possibilities, both states are 50% as thick as the state from which the possibilities originated. And so forth. They split ad inifnitum.

So it's not as though "copies" are being made, so much as you're taking a hologram and dividing it in two (as you may or may not know, when you cut a hologram in half you get two copies of the same image, though you can view less of it in each one).

I think Hurkyl's argument is that since you're splitting - not copying - there's no energy problem. But that doesn't solve the basic thermodynamics issue that every time you add a new degree of freedom you need more energy, and there's no question that every quantum possibility is a new degree of freedom - and they quickly accumulate at gigantic rates - and so, it would seem, would the energy requirements.
Hans de Vries
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Jun5-08, 05:28 PM
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Quote Quote by peter0302 View Post
and they quickly accumulate at gigantic rates -

If the universe would split each 3.10-25 second (say, the lifetime of the Z-boson) in
two, then we would have something like 10^(1024) parallel universes after 1 second.

Written out in decimal (with 500 digits/meter) this is a number with a length of
circa 60,000 light years. Each further second the length of this written number,
giving the total amount of parallel universes, becomes longer by 60,000 light years.

That is, the length of the written number describing the count of different parallel
universes would grow with a speed of 2000 billion times the speed of light......


Regards, Hans
Hurkyl
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Jun5-08, 07:21 PM
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Quote Quote by Phrak View Post
Hurkyl- If I may paraphrase, what you are saying is that in the MWI, there is no physical splitting. Instead, for any system of particles, the wave equation of the system evolves unitarily. Is this correct?
Yes. When MWI uses the term "splitting", it is describing a behavior that a unitarily evolving system can demonstrate. The same is true of terms like "parallel universes".

I think a good example would be based on the famous experiment with a photon and half-silvered mirrors. After striking the first half-silvered mirror, there is one "world" with a photon in a superposition of being reflected and transmitted. This photon can self-interfere, and we find that the photon is guaranteed to reach detector 2.

Now, if the photon somehow interacted thermodynamically with the environment between the first and last mirror (thus destroying its coherence), it will have "split", and we now have two "parallel worlds", one where the photon was reflected, and one where the photon was transmitted. The photon can no longer self-interfere, so when it strikes the second mirror, it will go to either detector with equal probability.

(We could force a thermodynamic interaction by, for example, putting a device along one path that measures whether or not the photon took that path)


Quote Quote by Phycho View Post
Hehe, I mean more, if a particle splits, it copies itself if this is true on a macroscopic scale.
Every second there are copies of you splitting off to other universes.
Is this the MWInterpretation you support?
If you mean "copy" like a copy machine in which you started with one particle and now have two particles, then I'm not aware of that being any flavor of the many-worlds interpretation.


Quote Quote by peter0302 View Post
I think Hurkyl's argument is that since you're splitting - not copying - there's no energy problem. But that doesn't solve the basic thermodynamics issue that every time you add a new degree of freedom you need more energy, and there's no question that every quantum possibility is a new degree of freedom - and they quickly accumulate at gigantic rates - and so, it would seem, would the energy requirements.
I know that splitting is closely related to quantum thermodynamics (one buzzword: decoherence); splitting is supposed to be an irreversible process, which is only possible in the thermodynamic sense. (because unitary evolution is always theoretically reversible, even if not practical) Unfortunately, that statement nearly exhausts my hard knowledge about quantum thermodynamics.
Phrak
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Jun5-08, 10:46 PM
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Quote Quote by Hurkyl View Post
Yes. When MWI uses the term "splitting", it is describing a behavior that a unitarily evolving system can demonstrate. The same is true of terms like "parallel universes".

I think a good example would be based on the famous experiment with a photon and half-silvered mirrors. After striking the first half-silvered mirror, there is one "world" with a photon in a superposition of being reflected and transmitted. This photon can self-interfere, and we find that the photon is guaranteed to reach detector 2.

Now, if the photon somehow interacted thermodynamically with the environment between the first and last mirror (thus destroying its coherence), it will have "split", and we now have two "parallel worlds", one where the photon was reflected, and one where the photon was transmitted. The photon can no longer self-interfere, so when it strikes the second mirror, it will go to either detector with equal probability.
Thanks Hurkyl. But the truth is, now I'm really confused. MWI seems to recognize two distinct processes. The first, unitary evolution, or what might be called causal evolution, if I'm not abusing terminology. Secondly, splitting, a result of decoherence. What I'm getting at, here, is that decoherence is not recognized as causal evolution of the larger system consisting of particle plus environment, right?
Hurkyl
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Jun6-08, 06:25 AM
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Quote Quote by Phrak View Post
What I'm getting at, here, is that decoherence is not recognized as causal evolution of the larger system consisting of particle plus environment, right?
Actually, that's the neat part: decoherence is the result of ordinary unitary evolution of the particle + environment system!
reilly
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Jun6-08, 12:34 PM
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Quote Quote by Hurkyl View Post
Yes. When MWI uses the term "splitting", it is describing a behavior that a unitarily evolving system can demonstrate. The same is true of terms like "parallel universes".

I think a good example would be based on the famous experiment with a photon and half-silvered mirrors. After striking the first half-silvered mirror, there is one "world" with a photon in a superposition of being reflected and transmitted. This photon can self-interfere, and we find that the photon is guaranteed to reach detector 2.

Now, if the photon somehow interacted thermodynamically with the environment between the first and last mirror (thus destroying its coherence), it will have "split", and we now have two "parallel worlds", one where the photon was reflected, and one where the photon was transmitted. The photon can no longer self-interfere, so when it strikes the second mirror, it will go to either detector with equal probability.
You are describing a standard probability chain -- they have been used for many years without any ascription of reality to individual branches -- except in science fiction stories --. Why bother, when Hans has noted, conservatively, the description of the MWI universe defies physics, not to mention common sense. Where are these universes? In what sense are they real?

If, somehow, they are real, then what about inter-universe dynamics? Why not a subset of universes that conspire to create a superconducting super-universe? It all sounds to me like:if you can imagine it, it is real. But then, I could imagine that what I imagined is real isn't real. (Note that all this imagining is the direct result of physical processes, so clearly our individual rates of creating alternate universes go on unabated into mathematical territories , largely-yet- to- be -explored by humans. Think topological nightmares, non-separable subspaces, regions where the Axiom of Choice holds; regions where it does not. If I can think it, it's real, or is it?

And, by the way, is the one photon world you mention above, just one, or is it many worlds, all differing by slightly different molecular configurations of the silvered screen, differing by traffic patterns in New York City, differing by whether at cash register 12 in Store 18 in Rochester NY, Ralph asks for paper or plastic.

In fact, for the silvered screen and photon, there are huge numbers of possibilities. That is, we are effectively dealing with a scattering problem with, well more than 10^^23 target silver atoms. If we look just at the infrared portion of the emission spectrum of the silver atoms, we'll find that each atom has a probability to emit none to, say, 10^^(10^^10) or more low energy photons -- Poisson process and all that -- in any time interval you want. So, there are an arbitrarily large number of "universes" for the "one " universe; typical of Poisson processes of Poisson processes of ....... Is it not the height of irony, that MWI can only be realistically described by statistical methods -- those pesky Poisson processes certainly mess things up.
Regards,
Reilly
Hurkyl
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Quote Quote by reilly View Post
You are describing a standard probability chain -- they have been used for many years
I'm not familiar with the term "probability chain" in this context, but your comment is entirely unsurprising. The MWI invokes no new physics -- it merely uses a subset of existing physics -- it is only natural to expect its features to be familiar from other contexts.

without any ascription of reality to individual branches
I'm quite aware that there are many interpretations of quantum mechanics.


-- except in science fiction stories --. Why bother, when Hans has noted, conservatively, the description of the MWI universe defies physics, not to mention common sense. Where are these universes? In what sense are they real?
I thought we were talking about MWI. Why are you talking about science fiction?


If, somehow, they are real, then what about inter-universe dynamics?
They interact exactly as specified by unitary evolution. Observable effects are incredibly rare for conceptually the exact same reason that you never observe a vacuum spontaneously appear in your kitchen because all of the air evacuated into the living room: it's just too unlikely.

Why not a subset of universes that conspire to create a superconducting super-universe?
I can make neither heads nor tails of this question.

It all sounds to me like:if you can imagine it, it is real.
Let me know when you're done talking about science fiction.


Is it not the height of irony, that MWI can only be realistically described by statistical methods
I'm confused; quantum thermodynamics is the very foundation of the MWI! The whole idea is that quantum decoherence (a statistical phenomenon) closely approximates the effects of wavefunction collapse, thus obviating the need for using collapse in quantum mechanics. I don't understand how it could possibly be ironic that 'MWI can only be realistically described by statistical methods'.
peter0302
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Jun6-08, 06:47 PM
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Reilly, it's odd that you would have so much hostility toward MWI when you yourself believe that consciousness causes wavefunction collapse, which is no less outlandish than MWI.

In general it's funny to watch all the different people argue over their interpretations. The only sensible interpretation is that we don't know until we can find an experiment to disprove one or the other. That's what we should be arguing about. Not whether something sounds like science fiction or not.
GiZeHy
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Jun6-08, 07:26 PM
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Hi folks,

i am happy to see people in this thread, who are engaged with quantum physics and ask themselves kind of philosophical questions, because i believe that this is the main drive for many of us to understand how the universe, and all within it, behaves.

To approach the main question of the thread we must combine the knowledge of all sciences. It really is quite naive to argue that there is no reality beside the measured one. In fact, if one is intensely thinking about it, there is no direct answer to this question. I can only deduce it from experiences in this so called reality.

The main conflict thinking about it is that physics is a science to explain incidents that are measurable. It is the same with quantum physics. But how do you know that something does not exist when you cannot measure it? If one is getting results concerning a certain experiment, it does not mean that there are no other influences. Imagine that gravity cannot be explained in detail. We only create formulas of what we experience. With a grand united theory these will be expanded and used in another way.
(Beside: What about different realities because of different outcomes of experiments? Think about the particle/wave conflict. I think it is blowing enough minds that beholding an experiment or not affects the result of it)

Actually one could equate the measurements with experiences of a conscious mind, because the measurements are only a tool to enhance the perception of the senses. Think of a child and its reality. Is is aware of quarks, atoms, molecules, their forces and interactions and so on? No...probably not ;) Does it exist? What if everything exists but we cannot measure it, what if it only exists because we built something that is able to measure it? We see that there are many aspects to consider concerning this kind of question.
Hans de Vries
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Jun6-08, 07:47 PM
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Quote Quote by Hurkyl View Post
I'm not familiar with the term "probability chain" in this context, but your comment is entirely unsurprising. The MWI invokes no new physics -- it merely uses a subset of existing physics -- it is only natural to expect its features to be familiar from other contexts.

I'm quite aware that there are many interpretations of quantum mechanics.

Isn't the idea of an interpretation of quantum mechanics to find the underlaying
physics which produces the effects we see? So it *should* be new physics...

Quote Quote by Hurkyl View Post
I thought we were talking about MWI. Why are you talking about science fiction?

Ok, but when people are freely talking about other, parallel, universes in which supposedly
they can have other jobs, partners or children, you can expect such associations with
science fiction.



And all these stories are simply the logical consequence of the definition of MWI
you just gave two posts back, that is, all possible quantum outcomes continue to
exist
in one of a countless number of parallel universes.


If you are a specific mix of genes of both your parents, then all kind of other gene mixes
similar to you would live in other universes. All theoretically possible mutations during the
evolution of species on earth would live somewhere, separated into countless universes.
There are human like creatures with wings somewhere, mermaids, centaurs, they would
all exist in their own universe, parallel to us in the same space time.

This all is just the direct consequence of the elementary definition of MWI which states
that all possible quantum outcomes continue to exist in one of a countless number
of parallel universes.

And all these universes live in the same space/time in superposition and are non-interacting.
They can interact until they decohere, but we are not in danger of being hit by an SUV
driven by an intelligent dinosaur in a universe where they didn't mass-extinct.

How does such a superposition work at all? There's nothing like that known or observed
in current physics. All fields in a specific universe must be "labeled" with a unique label
which tells fields belonging to another universe that they should not interfere.

What if something goes wrong here and two different universes end up with the same
"label", Fields of different universes will interfere and in such a case you can run into
an SUV driven by a dinosaur.


Does this all sound strange? yes, of course it sounds strange, but it's just the logical
consequence of taking MWI serious....


Regards, Hans.
Phrak
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Jun6-08, 07:53 PM
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Quote Quote by peter0302 View Post
Reilly, it's odd that you would have so much hostility toward MWI when you yourself believe that consciousness causes wavefunction collapse, which is no less outlandish than MWI.

In general it's funny to watch all the different people argue over their interpretations. The only sensible interpretation is that we don't know until we can find an experiment to disprove one or the other. That's what we should be arguing about. Not whether something sounds like science fiction or not.
Additionally, it should not come as a suprise that, if the practice of scientific inquiry in physics is a sound means of discovering true things, it should lead to propositions that cannot be answered as either true or false.

In fact, I think it could be successfully argued, that if advances in physics do not lead to questions that cannot be formally answered, it should be in search of repair.

[ / waxing philosophical off]
Hurkyl
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Jun6-08, 08:25 PM
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Quote Quote by Hans de Vries View Post
Isn't the idea of an interpretation of quantum mechanics to find the underlaying
physics which produces the effects we see? So it *should* be new physics...
The idea of an interpretation of quantum mechancs is no more and no less than a method to connect the mathematical theory with something else (usually the 'real world'). And the main point of MWI is that unitary evolution appears to be sufficient to produce all quantum effects we see. (in particular, there is no need to further postulate a wavefunction collapse)

And one point that people seem to be fond of overlooking -- even if one adopts a different metaphysical philosophy about quantum mechanics, MWI is still a useful description of unitary evolution during the events where it does happen uninterrupted.

Ok, but when people are freely talking about other, parallel, universes in which supposedly
they can have other jobs, partners or children, you can expect such associations with
science fiction.
Given any science, you can expect associations with science fiction. If you want to levy criticism on MWI, it's your job to make sure you know what you're talking about. (in particular, it's not other peoples' job to educate the rest of the world so they stop confusing you about what MWI really means)

And all these stories are simply the logical consequence of the definition of MWI
you just gave two posts back, that is, all possible quantum outcomes continue to
exist
in one of a countless number of parallel universes.
Only in the sense that collapse (as postulated by CI) does not occur. MWI doesn't talk about anything that wasn't already present in the quantum state space.

There are human like
creatures with wings somewhere, mermaids, centaurs, they all exist in their own universe.
Assuming such things are actually physically possible, of course. (And assuming you don't mean 'their own universe' in a Star Trek sense)

How does such a superposition work at all? There's nothing like that known or observed
in current physics.
Yes there is -- it's right there in the Hilbert space.

All fields in a specific universe must be "labeled" with a unique label
which tells fields belonging to another universe that they should not interfere.
The "labels" on the components of a specific subsystem are how (and if) it is entangled with the environment.

What if something goes wrong here and two different universes end up with the same
"label", Fields of different universes will interfere and in such a case you can run into
an SUV driven by a dinosaur.

Does this all sound strange? yes, of course it sounds strange, but it's just the logical
consequence of taking MWI serious....
Please elaborate upon how that is a 'logical consequence of taking MWI serious[ly]'. I'm having great difficulty imagining how interference (as governed by the ordinary unitary evolution of quantum mechanics) could lead to such a 'merging' of 'universes' as you describe, and I'm having even greater difficulty imagining how it could lead to a 'universe' in which dinosaurs simultaneously went extinct and did not go extinct. Neither of these appear to be a possible outcome of a global-scale quantum erasure event.


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