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MilkyJoe
2010-Apr-18, 10:32 PM
I can't help but think it's a load of nonsense.

01101001
2010-Apr-18, 10:40 PM
I can't help but think it's a load of nonsense.

Many-worlds interpretation (Wikipedia (http://en.wikipedia.org/wiki/Many-worlds_interpretation))? I wouldn't call it a theory, except in the popular nontechnical meaning of 'hypothesis'.


The decoherence approach to interpreting quantum theory has been further explored and developed[10][11][12] becoming quite popular, taken as a class overall. MWI is one of many Multiverse hypotheses in physics and philosophy. It is currently considered a mainstream interpretation along with the other decoherence interpretations and the Copenhagen interpretation.

So, that sort of stakes it out as popular.

I'm not sure we can do anything about what loads you think are sense and what loads are not.

DrRocket
2010-Apr-19, 12:17 AM
I can't help but think it's a load of nonsense.

It is an interpretation. It is not a theory, simply because it changes none of the predictions of quantum mechanics. It gives precisely the same predictions and therefore is experimentally indistinguishable from the Copenhagen interpretation.

It does not matter if it is popular or not. It is a valid, if somewhat odd, interpretation of fundamental quantum mechanics.

I don't particularly care for it, but no one can disprove it without disproving quantum mechanics and the usual Copenhagen interpretation. There are bigger fish to fry.

astromark
2010-Apr-19, 12:30 AM
I can't help but think it's a load of nonsense.

I can understand you drawing that conclusion... as we have not the slightest clue of other universe or multi realities... Many Worlds...
But it must be added that if it happened once. Then could it have happened millions of times. Yes.

Geo Kaplan
2010-Apr-19, 12:41 AM
I can't help but think it's a load of nonsense.

You're certainly free to think so. However, we can't reject it solely on the basis of such aesthetic considerations.

Ken G
2010-Apr-19, 01:31 AM
DrRocket is correct, many worlds is neither a theory nor a hypothesis, it is what is known as an interpretation of a theory. That means it is not unique (quantum mechanics is notorious for all its possible interpretations)-- you can use it to help you get quantum mechanical predictions right, or you can use other interpretations, or even no interpretation at all (you can just think of it all as a mathematical recipe). Its goal, like all interpretations, is to convey a sense of understanding, a sense of connection between quantum theory and the real world. Its validity rests in how it can help some people write correct equations, yet some feel it has greater value as a description of reality itself. Personally I feel that view is naive, but it is held by far greater physicists than myself, so I do not say so too loudly.

For those who are iffy on "many worlds" (and for those who confuse it with the totally different multiverse concept), the basic idea stems from the fact that quantum mechanics describes reality in terms of deterministic evolution of "pure states" or "wavefunctions" that include all the information that exists in the reality itself (insofar as we can frame such a concept using physics). But humans do not actually do physics that way (we don't track all the information present in the reality), so there is a fundamental disconnect between quantum physics and, well, physics. I would call this a disconnect in language-- the sublanguages we use in physics don't match perfectly, or even all that well, and the result is some inscrutable outcomes when meaning is passed from one language to the other. The inscrutable outcome is called the "collapse of the wavefunction", wherein a pure state of a quantum system acts like it is no longer a pure state, but rather a combination or "mixture" of states with random correlations, approximating a "probability distribution" (that's what people mean when they use language like "electron clouds" to talk about the location of an electron in an atom). The mixture appears when a measurement occurs, which means, when we stop tracking a vast amount of information relevant to that system because the required information is too vast to track. The final, and perhaps most inscrutable of all, step is when an intelligent mind queries the mixed state and decides which of the statistical probabilities is "actualized".

So far this is all true in any interpretation of quantum mechanics-- the interpretation appears when we try to decide what is "actually happening" when this language disconnect occurs. The two main ideas are the Copenhagen interpretation and the many-worlds interpretation. In the former (generally taught to students and is based on an empiricist perspective), we basically throw in the towel and just admit that we have no language that can cross from the macro to micro domains, so we accept the presence of a "Heisenberg gap" and don't worry too much about what is going on in there-- the language disconnect is unbridgeable by anything we could call physics. In the latter (often favored by mathematical physicists and based on a rationalist perspective), the language of quantum mechanics (and the associated mathematics) transcends the "Heisenberg gap", and carries on with or without our efforts to frame it in the language of human macroscopic experience (concepts like distance and momentum, for example). The state of the system continues to be a pure state, and is never a mixed state, it's just that the system has become vastly complex and involves coupling among all the quantum subsystems comprising the macroscopic entities. These couplings tend to usher the pure state of the entire system into separate branches with little or no correlation between them, so little correlation indeed that each branch may effectively be viewed as a different "world" out of "many". In the final step, the action of an intelligent mind processes the information from just one of these branches, having no access across the disconnect that stems from the lack of coherence among the different branches. That intelligence becomes a kind of minion of that one branch, such that even though the probability associated with that branch relative to all the rest is absolutely remote, that intelligence can treat it as the sole thing that "actually happened"-- and make no errors in future predictions because of the absence of coherence or correlation across the different branches.

The many-worlds view has obvious appeal to the rationalist temperament-- it allows the equations of quantum mechanics to reign supreme, and the "unitary evolution" of pure states into pure states of ever increasing complexity to carry on despite the "illusion" of wavefunction "collapse". However, it suffers from the core paradox of allowing that the same intelligence that notices the patterns that give rise to a theory of unitary evolution to become emprisoned into a tiny subspace of that unitary evolution. Can a prisoner in a cell do experiments entirely in that cell which can tell him/her about what is beyond the walls? Or is that just a kind of delusion?

Fortunately, physics can proceed without answering those questions, as it is likely that no demonstrable answer will ever be forthcoming. As with any fundamentally pedagogical divide, you are welcome to choose your own preference.

MilkyJoe
2010-Apr-19, 01:38 AM
OK, the theory/interpratation I mean is the one where a universe is created for every possible outcome of an event.
I believe there could be other universes, which could never interact with each other because they don't really exist to each other.

DrRocket
2010-Apr-19, 02:23 AM
OK, the theory/interpratation I mean is the one where a universe is created for every possible outcome of an event.
I believe there could be other universes, which could never interact with each other because they don't really exist to each other.

You re free to believe that. No one can prove you wrong. Nor can anyone prove you right.

But your stance is not consistent with your initial statement that "I can't help but think it's a load of nonsense."

01101001
2010-Apr-19, 03:11 AM
I believe there could be other universes, which could never interact with each other because they don't really exist to each other.

A lot of this topic seems to be about what you believe or can't believe. The place for that is probably the ATM section, where you can try to persuade people to agree with you for the advancement of science.

Here in Q&A, we don't care much what you believe. It's a place to get your questions answered, not your beliefs announced.

MilkyJoe
2010-Apr-19, 09:50 AM
It's a place to get your questions answered, not your beliefs announced.

I did ask if it was popular. That's a question.
I think I got confused anyway, so a new question is: what is the theory that says new universes (or time lines or something) are created for every possible outcome of an event?
I knew Hugh Everett came up with it (or at least is the one better associated with it) so I Googled him and the Many-Worlds Interpretation came up, and it sounded like the one I was thinking of.

astromark
2010-Apr-19, 10:37 AM
I am not so full of my self importance as to think any other reality might exist for any alternate some thing or other that I had any thing to do with...:o:...
... Yes, you did ask that ( sort of ) and I think It needs to be said that if there is more Universe than this one... Then they might be many. When we go down this thought process then maybe a infinite number of Universe and that could be argued then that every possible commutation of it reality exists.
But that does not rule it so... I do not like that idea. This Universe could equally be the only one... Now thats a problem because when you see it written it looks completely wrong. So for no reason other than applied logic. I go for multi... but not a single other me. Thanks.

Ken G
2010-Apr-19, 12:39 PM
I did ask if it was popular. That's a question.Yes, and I mentioned in post #6 that it is indeed popular among mathematical physicists and people who take a very rationalist viewpoint (that the fundamental way to access truth is via mathematical thinking). It is not at all a "fringe" interpretation, yet it is also rarely taught because it asserts elements of reality that are not experimentally testable, whereas the Copenhagen approach, which is taught, has a more empirical foundation.

I think I got confused anyway, so a new question is: what is the theory that says new universes (or time lines or something) are created for every possible outcome of an event?Yes, that's what I was talking about in post #6. The "every possible outcome" is just the "pure state" that the deterministic equations of quantum mechanics describe. Observations, on the other hand, only result in "one outcome" (as per the way we experience macroscopic reality, and the language we frame as a result). Which one, the former or the latter, is what physics is trying to describe is the crux of the difference between the many-worlds and Copenhagen interpretations.

Kwalish Kid
2010-Apr-19, 02:21 PM
Yes, and I mentioned in post #6 that it is indeed popular among mathematical physicists and people who take a very rationalist viewpoint (that the fundamental way to access truth is via mathematical thinking).
It would be incorrect to simply call the multiple worlds interpretation a "rationalist" theory in this sense.

DrRocket
2010-Apr-19, 04:14 PM
Yes, and I mentioned in post #6 that it is indeed popular among mathematical physicists and people who take a very rationalist viewpoint (that the fundamental way to access truth is via mathematical thinking).

Then why do I personally think it is a crock ?

(While still recognizing that it cannot be disproved.)

Ken G
2010-Apr-19, 04:34 PM
Then why do I personally think it is a crock ?

(While still recognizing that it cannot be disproved.)Because there is no theorem that says all people who take a rationalist viewpoint must favor many-worlds, the statement was that it is "popular among" that subclass. Which is true. (Besides, I think you are a closet empiricist. :))

Ken G
2010-Apr-19, 04:35 PM
It would be incorrect to simply call the multiple worlds interpretation a "rationalist" theory in this sense.Because....?

Cougar
2010-Apr-20, 03:29 AM
I knew Hugh Everett came up with it....

Hugh Everett, John Wheeler's grad student at Princeton, pioneered the modern approach to quantum physics. Murray Gell-Mann, (http://en.wikipedia.org/wiki/Murray_Gell-Mann) and his grad student James Hartle, have carried on that work. Gell-Mann writes:



We consider Everett's work to be useful and important, but we believe that there is much more to be done. In some cases too, his choice of vocabulary and that of subsequent commentators on his work have created confusion. For example, his interpretation is often described in terms of "many worlds," whereas we believe that "many alternative histories of the universe" is what is really meant. Furthermore, the many worlds are described as being "all equally real," whereas we believe it is less confusing to speak of "many histories, all treated alike by the theory except for their different probabilities." ... it is not necessary to become queasy trying to conceive of many "parallel universes," all equally real.

I figure Gell-Mann's "reinterpretation" is essentially equivalent to the quantum mechanical concept Everett was trying to explain, and it doesn't require constantly adding another whole universe into the picture.

This all makes even more sense after reading Gell-Mann's The Quark and the Jaguar.

Ken G
2010-Apr-20, 04:21 AM
HI figure Gell-Mann's "reinterpretation" is essentially equivalent to the quantum mechanical concept Everett was trying to explain, and it doesn't require constantly adding another whole universe into the picture.

This all makes even more sense after reading Gell-Mann's The Quark and the Jaguar.I guess I would have to read that book, because that quote makes it sound like a completely different interpretation than Everett's, rather than a minor tweak in the language. For one thing, Gell-Mann (a luminary in the field, no question) seems to frame the issue in terms of how we are trying to describe our past, but Everett's approach is an interpretation of the future. That seems like a pretty fundamental difference! I once had in my sig that "physics doesn't predict the future, it predicts the past that hasn't happened yet", by which I meant that we never test a prediction of the future, we test a prediction of the past made even farther in the past. I wonder if Gell-Mann's point is similar here-- all physics ever gives us is a theory of the past, but one that contains predictive elements within that past. We can still use it to predict tomorrow's weather, but we won't know if we were right until it is weather that has already happened-- as such, the interpretations we give to physics might inherently be about ways to look at the past, not the future. But Everett's approach was to imagine a web of potential futures all branching out from the present, so it was very forward-looking.

Cougar
2010-Apr-20, 01:36 PM
For one thing, Gell-Mann (a luminary in the field, no question) seems to frame the issue in terms of how we are trying to describe our past, but Everett's approach is an interpretation of the future.

That word "history" bothered me a bit, too. I can't imagine Gell-Mann being casual with his vocabulary. So I re-read a bit further into this chapter....


By "history" we do not mean to emphasize the past at the expense of the future ... A history is merely a narrative of a time sequence of events -- past, present, or future.

Many alternative narratives of the universe? Many narratives, all treated alike by the theory except for their different probabilities?

Ken G
2010-Apr-20, 01:49 PM
Many alternative narratives of the universe? Many narratives, all treated alike by the theory except for their different probabilities?OK, that clarifies his usage, he is saying that "many narratives" is better than "many worlds," which seems easy enough to agree with. But it brings us to the second somewhat odd element of this language-- the statement that the only difference is the probabilities, without recognition of the key difference: one of the narratives actually occurs!

If we are in a poker game, say, and are aware of certain possibilities for our opponents cards, it is easy to imagine we are in a "many narratives" situation, all treated equally, where the only difference is the different probabilities. That doesn't quite reach the situation involved in the many-worlds vs. Copenhagen dichotomy. That dichotomy is distinguished, of course, not by the treatment of the probabilities (which is the same), but rather the treatment of the outcomes. In other words, the difference lies in what you do with the narratives that are no longer relevant to your situation-- as soon as you know the opponent does not have the King of spades, for example, do you simply discard that narrative and say "that narrative is not part of the reality", or do you say "that narrative has entered a different branch of reality that is no longer relevant to mine." The only reason you'd ever take the latter rather bizarre view is if the deterministic theory you are using to predict how your opponents will behave at the poker table has no mechanism to discard narratives, it seems to indicate they all happen on an equal basis and the relevance of each is something you have to assert in a way that is external to the deterministic theory (which is the situation in quantum mechanics). In actual poker, we would instead take the view that our theory was simply not privy to the complete reality, it was a kind of simulacrum. So we have the core issue for quantum mechanics: are physics theories descriptions of reality, or simulacrums?

So to me, the main difference between the narratives is not their probabilities, it is what do you do with the experimental fact that only one of the narratives becomes relevant to you going forward. If you use a theory that says you are like a stick on a river that takes a certain fork in the stream, at which point all other forks become irrelevant, does that mean you really are in a situation like that? Or do you recast the theory in a form that says those forks do not actually exist, they were just potential things the river could have done but didn't actually do? With a real river, you might imagine a different observational perspective that could tell if the fork was there or not, but with the reality we experience, there is no such "other observation" that could be done. Does that mean it isn't physics any more? I see that as a fundamentally empiricist vs. rationalist dichotomy. When does a "narrative" graduate into a full-blown "world"?

grant hutchison
2010-Apr-20, 09:53 PM
The approach Gell-Mann has championed is called "consistent histories" or "decoherent histories", both of which are useful search terms. Vlad Gheorghiu's personal page (http://quantum.phys.cmu.edu/CHS/histories.html) at Carnegie-Mellon provides an introduction and some references, including a link to a free textbook (http://quantum.phys.cmu.edu/CQT/index.html) written by Griffiths himself.

It's a way of computing classical probabilities, and there's a little Q&A here (http://quantum.phys.cmu.edu/CHS/quest.html) (another page from Gheorghiu's webspace) which perhaps raises more Qs than it As.

As far as I recall, Gell-Mann deals with Many Worlds by shrugging and in effect saying: "They're just probabilities, the outcome of some calculations; why fret about their reality?" Copenhagen's "shut up and figure" approach, in other words.

Grant Hutchison

Ken G
2010-Apr-21, 12:09 AM
Yes, it all comes down to the "meaning of the wave function." Gell-Mann's approach sounds like a way to make many-worlds sound like Copenhagen, but it seems to me in so doing he is obscuring a pesky question that does not so easily go away, about that "wave function." If the wave function is a calculational tool that physicists invented to determine probabilities based on various constraints (like what we are choosing to track and what we are choosing to ignore and "average over" in any given situation), then you get Copenhagen. If the wave function is an expression of the information that is actually present in the reality, and physicists have merely discovered it, then you are more or less forced into a many-worlds kind of picture. The key question is, is there such a thing as the 'wave function of the universe'?

Boratssister
2010-Apr-21, 01:21 AM
So am I getting this? , the universe is unique and this universe is the only way a universe can be, OR the universe is just one of an infinity of universe's and we just happen to be in one that harbours intelligence. The former dictating the shape of the future and the latter leaves it to chance. The former having just one narrative, the latter an infinity of narratives... lol just not knowing really gets my goat. Isn't reality a bugger to get your head round? Whats it all about?
I'll go for a single universe and this is the only way a universe can be........

Ken G
2010-Apr-21, 01:35 AM
So am I getting this? , the universe is unique and this universe is the only way a universe can be, OR the universe is just one of an infinity of universe's and we just happen to be in one that harbours intelligence.Your reference to harboring intelligence sounds like you are mixing in what is called the "multiverse", which has to do with the laws of physics and how they could be different in other worlds (it dovetails with the "anthropic principle" but is not related to many worlds). Many worlds is strictly about quantum mechanics, and how the equations of quantum mechanics give us no way to pick one outcome over another, as though they all had to happen but we only process, notice, or are involved in, one particular outcome. Many worlds places our intelligence and perception into a single compartment of a vast reality, rather than allowing that our intelligence and perception is the reality they way Copenhagen does. It all comes down to how seriously you take the equations as expressions of reality itself, rather than just a procedure for making statistical predictions.


The former dictating the shape of the future and the latter leaves it to chance.Actually, you have this one backward-- the Copenhagen school, which says there's just one reality and it is what we perceive and interact with, is the one that leaves it to chance-- it says that we have no way to tell in advance what reality will do. The many-worlds approach says the laws are completely deterministic, but the chance comes in when our intelligence processes only some tiny piece of what actually happened-- we are living in a "chance" branch of a determined future, but that is the fault of our intelligence, not the laws of physics. In a sense, intelligence is what happens down each of those branches, when there are brains involved.
The former having just one narrative, the latter an infinity of narratives...Yes, now you have it, that's the key element.


lol just not knowing really gets my goat.I tell my kids, if someone is trying to get your goat, just tell them you don't have a goat!

Cougar
2010-Apr-21, 01:44 AM
Vlad Gheorghiu's personal page (http://quantum.phys.cmu.edu/CHS/histories.html) at Carnegie-Mellon provides an introduction and some references, including a link to a free textbook (http://quantum.phys.cmu.edu/CQT/index.html) written by Griffiths himself.

It's a way of computing classical probabilities, and there's a little Q&A here (http://quantum.phys.cmu.edu/CHS/quest.html) (another page from Gheorghiu's webspace) which perhaps raises more Qs than it As.

Oh, I don't know. That Q&A seemed quite good:



Consistent histories is, in brief, "Copenhagen done right." ... textbook quantum theory... gives the misleading impression that one cannot apply statistical ideas to quantum processes in the absence of measuring devices.... By contrast, in the consistent histories approach probabilities are introduced as part of the axiomatic foundations of quantum theory, with no necessary connection with measurements.

ravens_cry
2010-Apr-21, 04:03 AM
I rather like the many universe, because it allows time travel without completely breaking my head. No grandfather paradox, your grandfather is happily tottering along in a parallel universe, even if you kill this one. It does mean, however, that a time travel experiment will appear to be a failure to the universe that initiates it.

astromark
2010-Apr-21, 08:53 AM
Yes, 'Ravens_cry' I see it like that. :think: After reading Kens post #24. and claiming to actually comprehending it but, still hanging on to " This is the only way it can be' Yes I can live with that... The problem being that no amount of discussion will answer the question, will it ?
The many worlds and, multi universes ( Univarie ):o: Would not be the same. I see a new problem... :wall:

Boratssister
2010-Apr-21, 10:10 AM
Thanks ken g- it seems schrodingers cat could help us...
So in this many narratives scenario its quite likely that in these other universe's I have just died! I knew I was a survivor.

Ken G
2010-Apr-21, 01:14 PM
Thanks ken g- it seems schrodingers cat could help us...
So in this many narratives scenario its quite likely that in these other universe's I have just died! I knew I was a survivor.Indeed, if one takes the many worlds view completely seriously, in some "world" you will be an astonishing survivor-- you will reach an age of thousands of years old in a tiny number of those worlds, simply by miraculously avoiding death! (This is the idea behind Max Tegmark's "quantum suicide" idea, although for some reason that I don't understand he imagines that one consciousness will inhabit whichever world that person still survives in, but it seems to me that each such person, and consciousness, are different, so it's no different from someone else's life continuing after mine ends, they are just more similar to me than other people are.)