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Against Realism

by DrChinese
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kvantti
#91
Sep13-06, 08:18 AM
P: 83
Quote Quote by Hurkyl
kvantti, setAI: people have already responded to your assertions many times. If you don't want to be crackpots, you would do well to stop mindlessly repeating them without any regard to the received criticism.
Umm, sorry, I think this was my first message in this thread... I apologie if I have missed something (I don't follow these forums too often).

Quote Quote by Hurkyl
In the quantum computer: where else?

In fact, when I learned quantum computation in one of my classes, we learned it from a solidly Copenhagenist viewpoint.
Yes, you can always say something like "all the different calculations are performed simultanously as a superposition of every possible calculation", but that isn't exactly a physical description of what is happening in a quantum computer... it is more or less a description of the mathematics.

OK, let's assume that the MWI is false (which it, ofcourse, might be). How would you explain the physical behaviour of a quantum computer?
kvantti
#92
Sep13-06, 08:52 AM
P: 83
Quote Quote by Chaos' lil bro Order
Tell me then, how does the quantum computer in our Universe communicate with all the other 'virtual quantum computers' in the other Universes?
Through quantum interference. Different universes can interfere with each other if the quantum state of the system involved is coherent (as in a quantum computer).

Quote Quote by Chaos' lil bro Order
Also, where is this quantum computer you speak of? This is such an abstract idea that the quantum computer calculates some of the sub-problems in other dimensions that I'm not sure it warrants a response. I'm ignorant on this subject, but what experiments have been done to confirm your quote?
IBM has the most advanced quantum computer nowadays with seven qubits. See this.

Oh and mathematically you can just say that "all the different calculations are in a superposition in the quantum computer during the calculation", if you don't want to think the MWI way.
Careful
#93
Sep13-06, 09:38 AM
P: 1,667
Quote Quote by Hurkyl
Huh? I mean to say that I think RQM > MWI > Copenhagen > Bohm.
But what is YOUR idea about quantum mechanics ?!! This entire discussion is about one's favorite color of spaghetti, while all the pasta tastes the same. It seems to be much more intelligent to place this question in the light of some problematic aspects of modern theoretical physics : (a) the problem of vacuum energy vis a vis the cosmological constant (b) the issue of realism (c) the problem of time (d) the validity of special relativity at all energy scales. Then, depending upon your answers on these (and other) issues you will find yourself confined to one of these religions, or you feel the logical need to dig deeper into QM itself. One question to start with for example is wheter one truely believes gravity to be necessary to even obtain a well defined theory of quantum electrodynamics.

Careful
NateTG
#94
Sep13-06, 09:41 AM
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Quote Quote by kvantti
OK, let's assume that the MWI is false (which it, ofcourse, might be). How would you explain the physical behaviour of a quantum computer?
That's not a useful stipulation. MWI, Bohmian Mechanics, and the Plug and Chug interpretation all make identical predictions so the only way that MWI can be scientifically falsified is if all of the other interpretations also have the same problems.

Moreover, and this is something people love to ignore, physics does not and will never explain anything rather, physics is a collection of theories that make predictions. Statements like 'things fall because of gravity' are misleading - it would be better to say 'we call the tendency of things to fall gravity'.

As such, interpretations of quantum mechanics are (from a scientific point of view) really primarily interesting because they can lead to experimentally verifiable predictions. Otherwise, we might as well be discussing how many angels can dance on the head of a pin.

The fact is that (assuming the physics is correct) the quantum computer will work regardless of whether you think of it as a bunch of intereacting 'worlds', a winding maze of particle paths, or a black box.
RandallB
#95
Sep13-06, 10:40 AM
P: 1,544
Quote Quote by Hurkyl
Quote Quote by RandallB
They said IF they actually make a true Quantum-Computer, it will, (IMO they won’t).
They already have. They just haven't made a "big" one.
What does that mean – something like a little bit pregnant but not really yet?

Plus even if they can come up with Q-C or other proof of MWI convincing to those that are not already convinced, that still only ‘proves’ one reality.

MWI is one thing but it doesn’t call for more than one reality!
The idea that one reality where say MWI is correct and BM is wrong;
and a second reality where say BM is right and there are no MW’s of MWI; ----- And Are both true ?????

IMO that is beyond an ‘ad hominem fallacy’ it just logically ridiculous.
What argument would not fall on its own merit trying to support such a thing with anything like rational logic?
AnssiH
#96
Sep13-06, 11:19 AM
P: 249
Quote Quote by kvantti
Well, here is a challenge for you (and for everyone who doesn't believe in the MWI) from Deutsch (as presented in his book The Fabric of Reality):

Explain where the calculations made by a quantum computer are performed when it solves the sub-problems associated with a single problem. Eg. when factoring a 250-number digit using the Shor's algorithm, the number of sub-problems is about 10^500 (the number of particles in the universe is about 10^80).
And yet, a quantum computer solves all the sub-problems at the same time. So how can it solve 10^500 problems during only one calculation, if we have only one computer in only one universe?

(It would take classical computer 10^500 times the time of a quantum computer to perform the same operation)

And for the question why the MWI has become "some sort of religion": it gives a coherent, local and deterministic description of reality and in my point of view, it would be illogical that there would be only one universe. Didn't you think that there are "other dimensions" when you were a kid?
Like I've said in about every post to this thread, we make certain assumptions about "what exists" in reality and about how they behave to come to explain how the reality works to our selves. The above questions, about where the "calculations" happen and so on, only make sense in so far that you want to talk about "calculations" (and the related entities and concepts that you imagine is performing these "calculations", in this case in multiple universes) and MWI makes sense only in so far that you make certain assumptions about such things as the reality of a photon and interference between universes.

In fact, if you take a look at the opening post here:
http://www.physicsforums.com/showthread.php?t=130623
you'll notice how one can say the "calculations" happen or rather simply "exist" in static manner in spacetime just by insisting that spacetime really exists the way Einstein believed it to exist (Of course it will be difficult to explain why there seems to exist any "moments" at all, but that's a different discussion). One way to put it would be to say that the photon moves back and forth in time so that all its possible trajectories interfere, but this is wrong vocabulary because there is no motion in spacetime.

I am confident that all interpretations have their own answers about how the phenomena happen so to come to predict the exact same observable phenomena. So after all is said and done, many-worlds interpretation is just that, an "interpretation". At this stage we cannot pick and choose any QM interpretation to be the real deal.

Also if you have followed my posts in this thread you might have noticed how I've asserted that - quite likely - the reason why QM seems so damn odd to us is that we are trying to explain a behaviour of such entities that do not exist in such manner as we imagine them to exist. It is like explaining the behaviour of a rainbow after asserting it is an object which originates from a pot of gold, and only once one realizes how rainbow is rather the interference pattern on the surface of the observer, its behaviour starts to make sense.

Likewise, if you insist on the information between atoms to travel in the form of tiny billiard balls and on top of that imagine the motion of those billiard balls to exist in newtonian sense (only look at it from one inertial frame) you may be forced to assert that the photon exists in many worlds so to exhibit the behaviour we observe. We may have to question the nature of many things to come up with more accurate answers, like the nature of space, matter, light, motion(/time), energy... Maybe even discard these concepts to understand this system we call "reality" from a completely new angle.

(On a related note, have people formed opinions about this idea of discrepte, stepwise spacetime expansion causing quantum behaviour?
http://www.estfound.org/
Haven't had time to really look into it, does it show some obvious weaknesses right off the bat?)


So, just what NateTG is saying, physics really is quite literally a collection of theories or rather assumptions about what exists and how they behave. And like I said before, because of how our understanding works physically, we can only deal with reality by assuming there exists such and such entities and asserting they have such and such relationships between each others. Because this is the only thing we are capable of, it seems to us that reality really is like this, but little bit of philosophy can show that this is not exactly true; reality does not actually work with concepts. The mental model we have about reality in our head really is just an expression of the real thing, and it is not accurate or even "the metaphysically correct way" to express reality. (And any math you produce is also merely describing the behaviour of some "entity" you imagine to exist metaphysically in that sense)

And btw, MWI gaining ground as the "favourite way" to describe reality in some circles doesn't mean it is true, it just means it is one of the easiest ways to "imagine/visualize" QM phenomena in your mind. Think about how you try to visualize any black-box system when you are trying to back-engineer how its behaviour comes about, and you will realize how the assumptions with which you find it easiest to imagine the functions of the black box don't mean that is actually what happens inside. There are always many ways to produce some desired behaviour. Any system builder/programmer knows this very well.

And my comments about MWI becoming a religion are referring to how I find that MWI-people are continuously asserting theirs is "the only possible interpretation". Please understand that no one is saying it "cannot be true", but that it is not something that has been proven to be true in any sense. I am certainly happy to see many sensible people at this thread who still understand this, and I hope MWI won't become so standard that considering other options will be viewed as heretical or crackpot. It is important to be honest about it being just an interpretation unless you want to see everyone believe in it like a religion. And you don't want this to happen if you believe in scientific method, yes?
Chaos' lil bro Order
#97
Sep14-06, 12:16 AM
P: 683
Quote Quote by kvantti
Through quantum interference. Different universes can interfere with each other if the quantum state of the system involved is coherent (as in a quantum computer).
.
Are you talking about p-branes?

What defines two events in MWI anyways? I mean what is the smallest increment of information, whether it be spacial, temporal, or any other physical property you can think of, that must occur before the 'father' universe splits into two and the 'daughter' universe is birthed?
Hurkyl
#98
Sep14-06, 12:45 AM
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Quote Quote by Careful
This entire discussion is about one's favorite color of spaghetti, while all the pasta tastes the same.
Right -- but I was talking to someone who thinks spaghetti has to be purple, and thinks that my motivation for saying all pasta tastes the same is because I'm an idiot that doesn't like purple.
AnssiH
#99
Sep14-06, 12:54 AM
P: 249
I believe the idea is rather, that all the possible universes exist "all the time" and interfere with each others. So the model is relying on certain ideas about how photons exist and how they interfere with other photons in other universes.

So, when someone is claiming this is the only way QM could work, I might just as well start asserting that when a rainbow seems to mimic the motion of the observer without delay, it can be explained in non-local terms only by assuming we are seeing a rainbow of a "different universe" every time we move.

Sure, this would make the phenomenon local, but in the case of rainbow we now know enough about how it exists to be able to see how its observed "motion" occurs in completely classical terms and within one universe, and yet there is a different rainbow visible for every observer, or rather that we should not assign identity to a rainbow; there is no rainbow at all without an observer. (This is a case of realism where something cannot exist without an observer, in completely classical sense)

Likewise with QM, the motion or the "apparent trajectory" of the photon really does depend on where it's going to be observed (one way or another), and to assume there really was a photon (with identity) in flight is already an assumption that is likely to be wrong to some extent, and will lead you to assert there must be multiple universes and we are merely observing photons from one.

So, what I'm saying is... dig deeper gentlemen.
Careful
#100
Sep14-06, 01:37 AM
P: 1,667
Quote Quote by Hurkyl
Right -- but I was talking to someone who thinks spaghetti has to be purple, and thinks that my motivation for saying all pasta tastes the same is because I'm an idiot that doesn't like purple.
Hehe, I noticed that, but you also said that you might choose for the relational colored one, once this color would gain more popularity. My point being that whatever interpretation you pick, you keep on being stuck with some embarrasing shortcomings of the formalism itself. For example, I have to think hard about Bell inequality violation and spin statistics in Barut self field (although I could put them in by hand), but there is absolutely no problem with realism, time, special relativity and vacuum energy (tell that to some QG people - all their deep problems vanish in thin air).

Cheers,

Careful
Hurkyl
#101
Sep14-06, 02:05 AM
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Quote Quote by Careful
Hehe, I noticed that, but you also said that you might choose for the relational colored one, once this color would gain more popularity.
I prefer RQM over MWI now -- but if I was asked to choose between the popular interpretations I'd have to pick MWI since AFAIK, RQM isn't one of them yet.


you keep on being stuck with some embarrasing shortcomings of the formalism itself
Embarassing shortcomings are in the eye of the beholder.
Careful
#102
Sep14-06, 02:25 AM
P: 1,667
Quote Quote by Hurkyl
I prefer RQM over MWI now -- but if I was asked to choose between the popular interpretations I'd have to pick MWI since AFAIK, RQM isn't one of them yet. Embarassing shortcomings are in the eye of the beholder.
This is exactly the miss-election attitude I was referring to in the beginning, I remember asking you what YOUR view towards QM is. Embarrasing shortcomings are not in the eyes of who percieves them, but in those minds which do not wish to adress them even when it is well known that the latter issues are definetely problematic. String theory does adress the vacuum problem by making a supersymmetric ansatz : at that moment, you can say whether you find such mechanism using exotic particles credible or not (I certainly don't). Anyway, if you do not believe some detailed matter content to be responsible for the cancellation of the vacuum energy, then the most direct step would be to question the phenomenon (in either the renormalization procedures) at its very roots.

Careful
kvantti
#103
Sep14-06, 09:45 AM
P: 83
I was writing a long post and my computer crashed so I'm pretty frustrated at the moment and therefore I will state my matter briefly:

NateTG:

That is an instrumentalist point of view. I'm glad that not all physicists are instrumentalists.

AnssiH:

You obviously believe in some sort of "hidden variable" theory. Fair enough. But keep in mind that even you are interpreting quantum mechanics from your own point of view, and in my eyes it doesn't differ from the Copenhagen interpretation; you and CoI state that the formulas of quantum mechanics do not describe reality as it is, but only probabilities of observations within reality. The difference between CoI and your interpretation is that the CoI doesn't explain how the "probablities" can interfere and entangle... it just says they do. You seem to have your own vision how they actually do interfere (as we all do).

The MWI says just the opposite: the formulas of quantum mechanics describe reality as it is. What would be simpler? The concept of multiverse emerges naturally from this kind of thinking. It also explains quantum interference and entanglement in a very simple manner.

Quote Quote by AnssiH
It is important to be honest about it being just an interpretation unless you want to see everyone believe in it like a religion. And you don't want this to happen if you believe in scientific method, yes?
Yes, it is "just an interpretion" of quantum mechanics. But it also a "theory" of multiverse. A theory that most quantum cosmologists and quantum computer researchers find compelling, because it offers explenations of the physical behaviour of the quantum system they study, rather than just "cold mathematics".

Quote Quote by AnssiH
-- you'll notice how one can say the "calculations" happen or rather simply "exist" in static manner in spacetime just by insisting that spacetime really exists the way Einstein believed it to exist.
This isn't true in the case of quantum computers; the calculations are based upon quantum effects, such as quantum interference and entanglement, so you can't just say "it just acts as if the different calculations would interfere, but actually they don't; the calculation and the result just already exist in a static spacetime." Quantum computers actually prove that quantum interference and entanglement are real phenomenom; not just illusions of "static spacetime." And that been said, you can't say that a photon moves as if it would interfere with itself; it actually does interfere with itself.
tehno
#104
Sep14-06, 10:24 AM
P: 363
Sorry for interrupting this discussion,I'm really no expert on this but I can't resist not to ask.
With their capability of processing information can a quantum computer one day answer the ethernal question of finite strategy games:say Chess or GO?Estimation is that there are about [tex]~10^{60}[/tex] legal chess positions.
kvantti
#105
Sep14-06, 11:18 AM
P: 83
Quote Quote by Chaos' lil bro Order
Are you talking about p-branes?

What defines two events in MWI anyways? I mean what is the smallest increment of information, whether it be spacial, temporal, or any other physical property you can think of, that must occur before the 'father' universe splits into two and the 'daughter' universe is birthed?
Here is a FAQ considering the MWI. You'll probably find answers for your future questions there. A single universe is irreversibly split into many universes when the quantum system involved in the splitting decoheres. But that doesn't mean the decoherence causes the splitting; the universes split all the time, be there interactions or not. Decoherence only distinguishes the universes from each other and therefore they can't interfere with each other anymore.

Quote Quote by tehno
Sorry for interrupting this discussion,I'm really no expert on this but I can't resist not to ask.
With their capability of processing information can a quantum computer one day answer the ethernal question of finite strategy games:say Chess or GO?Estimation is that there are about [tex]~10^{60}[/tex] legal chess positions.
Yes, a quantum computer can resolve this kind of calculation very fast.
NateTG
#106
Sep14-06, 01:04 PM
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Quote Quote by kvantti
Yes, a quantum computer can resolve this kind of calculation very fast.
Quantum computers are not proven to solve NP hard problems in polynomial time, and, in fact, are strongly expected no to.
AnssiH
#107
Sep14-06, 02:11 PM
P: 249
Quote Quote by kvantti
You obviously believe in some sort of "hidden variable" theory. Fair enough.
No, I don't particularly believe in hidden variables or copenhagen. I believe our ideas about what exist are currently wrong at a deeper level than where any of the mainstream interpretations reach. (Like what is "motion" and so on) I believe one day someone will figure out a really simple deterministic explanation and everybody will slap on their forehead and go "doh!"

Well okay maybe there's some arguments back and forth first :)

This isn't true in the case of quantum computers; the calculations are based upon quantum effects, such as quantum interference and entanglement, so you can't just say "it just acts as if the different calculations would interfere, but actually they don't; the calculation and the result just already exist in a static spacetime." Quantum computers actually prove that quantum interference and entanglement are real phenomenom; not just illusions of "static spacetime."
Obviously to interpret this in terms of static spacetime you also have to assume that what we see as a photon is in fact just a wave-like connection between two atoms over spacetime (i.e. something with "volume", which occupies all the possible "trajectories". and in such manner that the shape of the "beginning" of the travel is affected by the shape of the "end").
If you keep thinking about photons as little balls it won't help you at all to look at it from the point of view of its own inertial frame (where "delayed choice" experiments are not "delayed choice" at all), unless of course you imagine the situation as if this little ball bounces back and forth in time over every possible trajectory. But to think about it this way you are confusing a whole new concept of "time progression" within spacetime itself, so...

Of course no one can say which idea of photons is more correct metaphysically, but this is just what I'm saying about how our ideas about what exists and in what manner are just assumptions, and they are bound to remain as assumptions forever, although I believe we can still peel much deeper than where we currently are.

And that been said, you can't say that a photon moves as if it would interfere with itself; it actually does interfere with itself.
Of course it does, although again, if you talk about the phenomenon in different terms, it may become meaningless to say it metaphysically interferes with itself, because it is meaningless to assign any identity to the photon in the first place. If you consider the so-called "photon" to literally be the "beep" that the atom does (i.e. when we say "the atom received a photon"), and the beep to be caused by a wave-like energy finding its way over all the possible routes to that atom (note that this is different from a wave propagating to all directions), you could only say there is wave-like energy that interfered with itself and no photon with identity ever made any journey.

But the trick is of course that you'd have to consider this to happen not over space but over spacetime. And let it be said that my confidence in the existence of spacetime is not particularly high either, I think spacetime too is a concept that is very much incorrect from what really exists.

So, if I have to make a bet about an interpretation, just for fun, I bet they are all going to be considered ridiculous when some assumption about something very fundamental will fall in place and show us more accurate view of all the phenomena we observe. Something akin to the shift from relative motion to relative time in relativity. (here I go again, praising relativity... silly me :P )

You may be tempted to say "maybe MWI is just this idea", but to me MWI is like all the other interpretations, and they are basically arguing about whether everything is made out of "earth, air, water and fire" or from "solid, liquid and gas", or perhaps the fundamentals are "opaque" and "transparent" matterpieces, when they should be concentrating on much much deeper issues. Something like, how could inertia be fundamental? Think about that.
Chaos' lil bro Order
#108
Sep14-06, 08:34 PM
P: 683
Quote Quote by kvantti
Here is a FAQ considering the MWI. You'll probably find answers for your future questions there. A single universe is irreversibly split into many universes when the quantum system involved in the splitting decoheres. But that doesn't mean the decoherence causes the splitting; the universes split all the time, be there interactions or not. Decoherence only distinguishes the universes from each other and therefore they can't interfere with each other anymore.



Yes, a quantum computer can resolve this kind of calculation very fast.

'A single universe is irreversibly split into many universes when the quantum system involved in the splitting decoheres.'

Fair enough. Now tell me the variables of the 'quantum system' and what constitutes 'decoherence'. I'm tired of all these big words being thrown around without any real meaning behind them. This is not true understanding IMO, its akin to cut and pasting a wikipedia entry or repeating popular phrases found in books like 'The elegant Universe'. Can this thread get down the to nitty-gritty already, its becoming muddied with pop-science and its really pissing me off now.


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