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Author | Topic: Quantum physics: Copenhagen vs decoherence interpretations | |||||||||||||||||||||||||||||||||
Straggler Member Posts: 10333 From: London England Joined: |
Hi
I am not sure that non-locality is really what Randman is interested in. I may be wrong but it seems to me he is actually more interested in the possible role of the observer, consciousness etc in QM and the various interpretations that here are with respect to this. I just wanted to add something about one of the more misunderstood interpretations of Quantum Mechanics. The Many Worlds scenerio comes from assuming that quantum mechanics as it is currently formulated (or any quantum theory) applies at all levels. In case people think it sounds like some off the wall idea, it is actually the direct prediction of QM if you allow it to be applicable even at our macroscopic scale. With this in mind what is the current predominant interpretation of the Schrodinger's cat scenario? What do most physicists (well the ones that consider such things) subscribe to as the meaning of the collapse of the wave function in such a scenario? Is there a role for conscousness or not?Is the many worlds inerpretation widely accepted? On what basis is one interpretaion preferred over another and are there firm scientific reasons for these or are they just personal preferences at root? For thse unfamiliar with Schrodinger's cat Schrdinger's cat - Wikipedia
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Straggler Member Posts: 10333 From: London England Joined: |
Firstly thankyou for this clear and informed explanation.
Now I'll explain my notation. If a cat is definitely dead I will denote it: |Dead>. If it is definitely alive then: |Alive>. In Schrodinger’s cat experiment we have that the state is |Dead> + |Alive>. Now my symbols above can contain more information. For instance the state of the Cat being dead and me off in Budapest is: |Cat is dead and I’m off in Budapest> Any of these |Insert phrase> things are what may be called a wavefunction. Each of the |state> terms is the probability of that particular state being the eventual observed state. Is that right? Thus the sum of all the |state> terms = 1 (e.g. |Dead cat> + |Alive cat> = 1). Is that correct? Would each |state> be a term in the Schrodinger equation? Or are the staes as you have described them independent of time and thus not part of the Schrodinger equation?
Many Worlds:
In the case of many worlds dowe consider splitting worlds at the amcroscopic level (i.e. dead cats and alive cats) or the subatomic level or both? Presumably both?Quantum Mechanics applies at all levels. This means even large scale objects like you and I can be in superposition. So what happens in this model is that the state of the universe goes from: |State of World> =|I haven’t looked at the cat yet and the cat is alive> + | I haven’t looked at the cat yet and the cat is dead> To |State of World> =|The cat is alive and I see him alive> + |The cat is dead and I see him dead> There is no collapse here because the first state can evolve smoothly into the second in the standard formalism of quantum mechanics. One should also note that Many-Worlds is totally deterministic.So from any instant in time there are literally as many worlds branching off as ther are posible states for subatomic particles in the universe? Is that correct? If so the number of 'worlds' created at every instant must be vast beyond comprehension even in cosmological terms. Bayesian interpretation: The wavefunction only represents our knowledge of the system. Hence collapse is simply when we learn more. That is upon seeing the cat alive, we know the cat is alive and hence there is no probability for anything else. Collapse is therefore not a real event. Historical Copenhagen/ Bohr Interpretation:We are classical thinking things. Hence the quantum world makes no sense to us. The formalism of QM is the closest we will get to understanding it. It is a formalism for explaining our big classical world’s interaction with the small quantum world. Collapse is a part of that formalism. Like all of QM though we must not try to understand what it really is/means. That is all. Are these two not essentially the same? Both suggest that more knowledge/perception is the answer even if they disagree as to how possible that may be in practise.
Modern Copenhagen: This is actually the only model with collapse in it. Basically we have: |State of World> =|I haven’t looked at the cat yet and the cat is alive> + | I haven’t looked at the cat yet and the cat is dead> Goes to:|The cat is alive and I see him alive> Or |The cat is dead and I see him dead> With a 50:50 chance of each. This is collapse, because there is no way to go from the first state to either of the second two, in the standard formalism, without an instant jump. Dynamical collapse:Basically Modern Copenhagen with attempts at modelling what process causes collapse. Are there any theories as to what the mechanism of collapse might be? Do you personally subscribe to any of the interpretations that you have outlined above?
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Straggler Member Posts: 10333 From: London England Joined: |
1. Was my explanation of the difference between Bayesian and Historical Copenhagen in message 29 sufficient? Hmmm. I supect that the only person who can answer that is you. Based on my/our understanding of what you have said. I will try and describe my understanding such that you can assess whether or not I have "got it". Beyesian - There is an as yet undiscovered deeper theory that more definitely describes quantum phenomenon. Our current theories are statistical approximations that give practical results which will eventually be better explained by a true understanding of subatomic scales and the 'real' laws that govern these scales. A post-quantum theory is the ultimate answer. Historical Copenhagen - Our current theories cannot fundamentally be improved upon. They are as close to reality as we can get regarding the subatomic world given our macroscopic observational limitations and the need for this to interact with that which we are studying. QM is a macroscopic theory of microscopic phenomenon and as macroscopic beings it is the only sort of theory we can hope to obtain.
2. What do you make of the interpretations? I'd be interested in hearing what people think of the various interpretations. Preferences or dislikes, e.t.c. I don't claim to have sufficient knowledge on which to make fully informed declarations but my instinctive and vaguely rational answer are a follows - 1) Bayesian (as I understand it) - If a deeper theory of QM provided an effective quantum theory of gravity that would seem to be the measure of any such theory. There is certainly a gap to fill in this respect. But the inherent probabalistic nature of QM and the evidence for this suggest otherwise. 2) Many worlds - Seems to solve most practical objections to QM but intuitively seems like madness in any conceptual sense. That however may well be the best subjective reason to have any belief in it's veracity!! Many worlds is probably the underlying interpretation of QM as I was taught it as an undergraduate in the early 90s. Happy to be corrected so feel free to comment on my (mis)interpretations!!
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Straggler Member Posts: 10333 From: London England Joined: |
Your descriptions are perfect. I'm glad, the difference between the two can sometimes be hard to get across. Well any demonstration of understanding on my part says more about the clarity of your explanation than anything else. Percy was even talking about a new 'Hall of Fame' forum in relation to your post......
Many people have this opinion. That is the theory which underlies QM is also the theory which explains quantum gravity. In fact there has been a big debate on whether there is any point in attempting quantum gravity if we don't have the right interpretation of quantum mechanics or have replaced it with the correct theory.
What are the leading candidates for such a theory? String theory?
2) Many worlds - Seems to solve most practical objections to QM but intuitively seems like madness in any conceptual sense. Yes, that's what I think. Since it's the only theory where QM is totally right and the collapse mechanism is explained, it solves everything. However it sounds totally mad. I don't know what to make of it at the end of the day. Technically it makes the least assumptions of any interpretation. The funny thing is that I've met others who think:1. QM is the fundamental theory 2. Applies at all scales but disagree with Many-Worlds, not knowing it's the only thing consistent with (1) and (2). People find it difficult to learn that (1) and (2) lead to Many-Worlds. I think there is something about it that "feels" false to a human being. A fair amount of modern physics is pretty counter-intuitive. Many of the practical conclusions of relativity "feel" crazy. The difference might be that in many cases we can actually experimentally verify that the apparently "crazy" implications of the maths does indeed describe reality. Is it even remotely theoretically possible to verify or refute a many worlds interpretation of QM in any way at all? However I still think 'many worlds' takes counter-intuitiveness to new levels surpassing even relativity. It seems appropriate to quote Niels Bohr at this point."We are all agreed that your theory is crazy. The question that divides us is whether it is crazy enough to have a chance of being correct." Exactly when Many-Worlds became the popular interpretation. I know it was taught to undergraduates in Imperial College around that time.
Ah yes. Professor Chris Isham was the QM lecturer and quite a big name in the quantum gravity field at the time I think. I loved the semi-philosophical tangents he used to go off at during his lecture but struggled a bit with the maths content of the course. BTW - I have just got round to ordering the book you recommended by Crease and Mann. Should receive sometime soon and will let you know how I get on with it.
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Straggler Member Posts: 10333 From: London England Joined: |
What is the many worlds interpretation take on the notion of freewill? Does it exist? Or are my "choices" just statistical branches along an ever branching timeline?
Do I really choose which path in life to take or are there multiple "me's" taking all possible paths with the one I find myself existing in little more than a statistical inevitability? Does QM have anything to say at all regarding freewill as far as you are concerned? What is the common view of freewill as far the main advocates of MW advocates are concerned?
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Straggler Member Posts: 10333 From: London England Joined: |
What is the common view of freewill as far the main advocates of MW advocates are concerned? From speaking to them the common view is, to use your words, "choices are just statistical branches along an ever branching timeline". Do I really choose which path in life to take or are there multiple "me's" taking all possible paths with the one I find myself existing in little more than a statistical inevitability? The latter. How depressing and nihilistic!! Not that this in itself necessarily points towards it being wrong. Do the views of Roger Penrose regarding QM and it's relationship with consciousness, freewill etc. etc. have much support within the community of scientists working in QM and other areas of modern theoretical physics? BTW - The Second Creation: Finally got round to reading it. Not yet finished but a great read so far. The copy I have is quite old (1988 I think) but the principles it explains and the historical narrative approach are just what I was looking for. Edited by Straggler, : No reason given.
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Straggler Member Posts: 10333 From: London England Joined: |
Syamsu
Freewill, consciousness, determinism, many worlds interpretation of QM etc. etc. etc are fascinating topics. Maybe the people you mention have something intelligent to say on these matters. Or maybe they do not. I don't know. A serious thread on their conclusions may well be a valid and worthwhile opportunity for learning and debate. However after our last discussion one thing I am certain of is that you have absolutely no idea what you are talking about with regard to any of these matters. You have no idea what science actually involves. You have even less clue as to the implications of various interpretations of QM, or even of what QM actually relates to. Your incessant bleatings about GR, redshifts and other such things in the context of freewill and consciousness just confirm your woeful ignorance of all things scientific. You have a preconceived faith based position and in your ignorance you leap upon whatever random theory you think supports this position. You seem to do this indiscriminately and with no regard to your ignorance or how irrelevant the theory in question may be to your point of view. Nor do you seem to have any self awareness as to how ridiculous you make yourself and your position look in the process of doing this. Decision making toothbrushes, benevolent coffee cups, evil planetary orbits, irrational chocolate bars and dead brainless mice "choosing" the manner in which they decompose are just a few choice examples of your insanity in action. I suspect that even your fellow creationists, as low as their standards of reason so often are, cringe with embarrassment when you start making these ridiculous assertions in contexts that you so obviously know nothing about. You are desperate to dress up your beliefs in scientific clothing to give them some sort of superficial validity but instead you just succeed in displaying your unbounded depths of ignorance and stupidity. As if all of this were not frustrating enough you will also stubbornly insist that you are right even when quite evidently contradicting yourself, you don't listen to anything else anyone says, you point blank refuse to answer any questions or respond to any points and you have absolute unshakeable conviction that all your arguments are well founded, self evident and reasonable despite everyone around you demonstrating otherwise. You are not the persecuted messenger of the great paradigm shift in science towards the creationist dream. You are a harbinger of nonsense, scourge of reasoned debate, destroyer of intelligent conversation and current bane of EvC forum. This thread is discussing quantum interpretations. Son Goku is ably answering questions and explaining difficult concepts on this topic to those who genuinely want to know more. In my opinion we would be better off without your inane ill conceived ramblings cluttering things up. Edited by Straggler, : Spelling and rant factor amendment
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Straggler Member Posts: 10333 From: London England Joined:
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Strange that you would object to weirdness of toothbrushes deciding in a thread about quantummechanics. Evidently you know very little about the weird findings of qm in regards to interrference, and whichway information. You idiot. Listen to yourself.I studied QM for three years. Even taking this into account the biggest difference between you and I in terms of our respective knowledge of the subject is that I know how little I know. You on the other hand know so little and think you know so much that you can take what you think you know and twist it to support whatever ridiculous assertion fits your latest dogmatic fantasy. And you are right that I loathe science, and scientists generally also. Your declared pride in your ignorance is even more depressingly astonishing than the alarming level of conceited ignorance that you actually display.
You dismissed the free will paradigm, so nice going for getting nowhere at all in discussing quantum mechanics. If you had the remotest clue about anything whatsover you would realise that this is exactly what I was discussing. With someone who does actually know what they are talking about. Until you popped up with your uniquely absurd and relentlessly irksome brand of imbecilic drivel. You carry on if you so wish. I shall not be responding to any more of your pointless rubbish.
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Straggler Member Posts: 10333 From: London England Joined: |
Penrose's idea required the brain to be quantum mechanical. In the past few years we've become much better at telling when a given system is influenced by quantum mechanics or not. That sounds intriguing. What recent developments have occurred that make this more possible/reliable? Are you talking technological, mathematical, conceptual....??
Even more importantly neurologists say it doesn't hold up to what we know about the brain. Yes I had heard that regarding his theories.
Although I would be at odds with some physicists I think Schwinger and Feynman were the greatest physicists of the second half of the twentieth century.. I think Feynman is a bit of a hero for the vast majority of physics students of "my generation". Certainly inspired me to study the subject. Schwinger I guess was just less of a character and self publicist.
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Straggler Member Posts: 10333 From: London England Joined: |
Good link. When I have moe time I might post some more qustions regarding this.
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