A Mathematical Answer To the Parallel Universe Question

diewlasing writes to mention that Oxford scientists have proffered a mathematical answer to the parallel universe question that is gaining some support in the scientific community. "According to quantum mechanics, unobserved particles are described by 'wave functions' representing a set of multiple 'probable' states. When an observer makes a measurement, the particle then settles down into one of these multiple options. The Oxford team, led by Dr. David Deutsch, showed mathematically that the bush-like branching structure created by the universe splitting into parallel versions of itself can explain the probabilistic nature of quantum outcomes."

Comments

Yes...

[fyngyrz]

...but this is only a valid answer in some parallel universe.

Yeah, yeah, I know it only affects physical outcomes. Laugh anyway. It's Monday.

Re:Yes...

[Hoi Polloi]

In some parallel universe you simply posted a link to goatse.

Re:Yes...

[Selfbain]

And got a +5 insightful.

Re:Yes...

[fyngyrz]

...but in that universe, goatse is a picture of a cat going "LOL I'm all up in Schrodinger's box. I can have tuna?"

Re:Yes...

[MyLongNickName]

And yet, no matter how many parallel universes there are, he still never gets laid. Where's the justice?

Re:Yes...

[pegr]

...but this is only a valid answer in some parallel universe.
 
I have no idea. I didn't want to change the outcome of the article by reading it...

Re:Yes...

[Poltras]

I'm gonna start my OWN universe. With hookers and blackjack!

Re:Yes...

[madsenj37]

On second thought, forget the blackjack. /I love Bender.

Re:Yes...

[Dachannien]

Or maybe this. (Assuming the deep link works.)

Re:Yes...

[ObsessiveMathsFreak]

Right here in this universe of course.

Re:Yes...

[scribblej]

Ever check the HTTP headers on a request to the Slashdot webserver?

There's always a different, random Futurama quote in an X-Fry: or X-Bender: header.

Example:

$ curl -I slashdot.org
HTTP/1.1 200 OK
Date: Tue, 25 Sep 2007 05:41:42 GMT
Server: Apache/1.3.37 (Unix) mod_perl/1.29
SLASH_LOG_DATA: shtml
X-Powered-By: Slash 2.005000175
X-Bender: They're tormenting me with uptempo singing and dancing!
Cache-Control: private
Pragma: private
Vary: User-Agent,Accept-Encoding
Connection: close
Content-Type: text/html; charset=iso-8859-1

Re:Yes...

[zobier]

Ever check the HTTP headers on a request to the Slashdot webserver?

There's always a different, random Futurama quote in an X-Fry: or X-Bender: header. (Bender|Fry|Leela)

Why is this news?

[Valdrax]

It's just the Many Worlds interpretation of quantum mechanics, and I don't see anything in the article that's a shocking new revelation about it. The article's just a rehash of an idea that's been around since the 50s.

Re:Why is this news?

[ShatteredArm]

Yeah, the article seemed to be a little lacking in the "mathematical proof" area.

Re:Why is this news?

[Kristoph]

Well, I am not a physicist, perhaps you are ...

  Commenting in New Scientist magazine, Dr Andy Albrecht, a physicist at the University of California at Davis, said: "This work will go down as one of the most important developments in the history of science."

I would image something that is 'one of the most important developments in the history of science' might qualify as news. Don't you think? Even if proven not to be 'one of the most important' it certainly qualifies for recognition based on that possibility, IMHO.

]{

Re:Why is this news?

[MontyApollo]

The problem is that the brief news story was more focused on explaining what the Many Worlds hypothesis is to a lay audience and not really pointing out what the new breakthrough is really all about to a geek audience. Someone needs to link to science site and not a general news site.

Re:Why is this news?

[UbuntuDupe]

The moon landing was "one of the most important developments in human history", but that doesn't mean you should report it as news on slashdot forty years later!

Re:Why is this news?

[ZombieWomble]

As described in this article, the factor they claim to have "proved" does indeed make no sense - I was under the impression that the many worlds theory was defined so that this branching tree structure could describe the probabilistic nature, such that this result is a direct consequence of the theory. But I must admit, I'm more of a practical physicist, the minutiae of the underlying explanations for quantum mechanical processes don't really affect me much - is there any kindly passing mathematician who can explain what might be interesting about this result?

Re:Why is this news?

[Attila Dimedici]

Besides being "a physicist at the University of California at Davis", who is Dr Andy Albrecht? and why should I think that he is any more likely than Jack Thompson to recognize one of the most important developments in the history of science? If we are talking Nobel Prize in Physics (or some other prestigious award in the field of physics) winner, maybe there is reason to believe that he is right, otherwise he is just "some dude from California who knows enough to understand the math".

Re:Why is this news?

[CheshireCatCO]

Always hesitate to take people's word for the significance of a piece of work. This is especially true of their own work, naturally, but even friends and colleagues often mis-judge or lack perspective on the importance of a discovery. Furthermore, reporters often misquote or pull quotes from context to the point where they'd be considered falsification if this were a scientific paper. I've even been quoted by a reporter who made the entire quote up from whole cloth. (Seriously, I'd never said anything remotely like what was quoted. Fortunately, it wasn't really a bad quote and I wasn't too bothered, except by the principle.) Thus, when someone says something as hyperbolic-sounding as the quote there, I immediately suspect it.

I *am* a physicist, although I don't have Dr. Albrecht's credentials in this area, so he certainly has a more informed opinion than my own. However, based on my knowledge of the subject, the importance of this finding is in fact fairly over-rated. I don't think that it confirms anything unexpected *and* the theory is, as far as I know, not falsifiable. (I've never heard of a test which would differentiate between the Many Worlds view and the competing interpretations.) So you see, showing that you can't rule Many Worlds out is important, but it does strike me as really revolutionary.

Re:Why is this news?

[Anonymous Coward]

The Many Worlds Interpretation is not just an interpretation, it is a (slightly) different theory:

In conventional interpretations, the wave function "collapses" upon observation, to a single eigenfunction.

In the Many Worlds Theory, it NEVER collapses. The magnifying effect of an observation of microscopic fluctuations into macroscopic changes in the world (i.e., a geiger counter clicking or a track in a cloud-chamber) causes the universe to split into distinct branches corresponding to eigenfunctions. These distinct branches continue to interact with each other (although extremely weakly, because they are "far apart" in Hilbert space).

This should be falsifiable, although the technology to do so might not exist now. One must repeatedly perform an extremely accurate measurement whose macroscopic effects are minimal (so the different branches do not drift too far apart). "Extremely accurate"=accurate enough to observe the interaction of the other branches of the universe. I believe Dr. Deutsch has proposed such an experiment that may be conducted within the next 50 years.

Obligatory ...

[JeepFanatic]

But can this explain why all the men have goatees?

Re:Obligatory ...

[Hoi Polloi]

Better they have goatees than goatse.

the answer?

[CaptainPatent]

It happens to be that the answer to life, the universe and everything in that universe is 43

Ummm . . .

[Orange Crush]

. . . so it "can" explain (mathematically) the outcome of quantum level observations using the many worlds theory. But is it falsifiable?

Re:Ummm . . .

[kebes]

This is a fairly subtle point, so I'm not sure that I'm going to explain myself properly... but here's my best shot:

The Many-Worlds concept of quantum mechanics was originally presented as an interpretation of the theory. It was viewed by many as being ridiculous, or "non-economical with universes" as the joke goes. Work in fields like quantum decoherence has, over the last few decades, helped to explain how "normal" (classical) states emerge from quantum superpositions. Decoherence, briefly, explains how a superposition of quantum states evolves deterministically (no randomness!) into a discrete set of pseudo-classical states (due to entanglement with the many degrees of freedom available in the "environment"--i.e. the universe at large). This extension to quantum mechanics has been tested experimentally and verified.

The remaining issue in a theory of quantum + decoherence is that the classical states have the right probabilities, but there is still nothing to explain why we observe a particular classical state (photon measured spin-up instead of spin-down). However the (ad-hoc) postulate of wavefunction collapse, no longer being necessary to explain how the probabilities arise, can in fact be entirely removed if we allow that the global superposition never collapses.

Thus, a local observer (e.g. an instrument or a human) perceives a single outcome only because they are a participant in this "global superposition" (the superposition of the entire universe). The wavefunction of the universe as a whole evolves deterministically.


Okay, that was a long-winded preamble, and I still have not answered your question. The answer is that the existence of multiple universes cannot be falsified per se. But, then again, in this formalism Many-Worlds is not an axiom: it is a prediction. Given that it is a prediction of a thoroughly successful theory, we should be compelled to accept the prediction as correct even if we cannot directly test it. We can, at least, test other predictions of the theory. In principle, we can test for superpositions as big as we like (superpositions of entire galaxies, etc.), but we cannot ever test that final prediction: that the universe as a whole is also in a superposition. But, if we've tested the theory in every other way, can we really "throw away" the final prediction about the global superposition?

Now, I know many of you will counter-argue that non-falsifiable predictions are not science, and should be ignored as metaphysics, or even "meaningless." Perhaps. But allow me to draw an analogy: One of the fundamental assumptions of science is that there is such a thing as "physical law." That is, we can extrapolate from one measurement to others. Put otherwise, we accept that the laws of physics are the same here as they are in a distant galaxy. Note that, because of the expansion of the universe and the speed-of-light-limit, there are some regions of the universe that we cannot ever explore (even in principle, assuming our current physics is correct). Thus, the prediction that "the laws of physics are invariant across the universe" is itself unfalsifiable, yet we generally accept it to be true.

Similarly, we need but extend this logic into quantum mechanics, where if assume that the laws of physics are the same everywhere in the universe (and everywhere within the wavefunction of the universe), then we should accept that the global superposition is probably correct: i.e.: Many Worlds "exist" (but are inaccessible to us). I agree that this conclusion is uncomfortable, but it appears inescapable given our current understanding of physics. (Note: As a scientist I'm of course allowing for the possibility of future measurements disproving some part of this logic--this is entirely based on our current understanding.)

As I said, the point I'm trying to make is not obvious. Hopefully I've not muddled it beyond understanding.

Re:Ummm . . .

[kebes]

That the laws of physics are invariant (first explicitly stated in geology as uniformitarianism [wikipedia.org]) is not a prediction, but rather an axiom of science.

Agreed. It is an axiom of science as we do it.

With this understanding the status of many worlds and the absurdly large number of parallel universes it entails is quite different from uniformity of natural laws. One (spatiotemporally uniform natural laws) is an assumption necessary for the scientific enterprise to function at all. The other (laughably large numbers of entire freakin' universes) is a clear and moreover, literal violation of occams razor

Here I think you've misunderstood me. The point is that Many-Worlds is not an assumption: it is a prediction of certain theories (namely, modern unitary quantum mechanics).

So, given two axioms:
1. Laws of physics are invariant
2. Unitary quantum mechanics describes the universe

We obtain a wide variety of predictions, from transistors to molecules, and so on. One of the predictions is "the universe exists in a global superposition." The proliferation of branches is consequence of the theory, not an axiom.

We may find the prediction uncomfortable, but without a logical (or empirical) reason to discard it (but retain all the other predictions, which we like better), how can we ignore it? (Honest question... I'm not an expert in philosophy so perhaps I'm committing a fallacy.)

Positing even a single additional universe constitutes multiplying a nearly uncountable number of entities.

To emphasize, nothing is being posited (beyond the axioms mentioned; I'm assuming no one is disputing that science and quantum mechanics can say something meaningful about the universe).

Besides, the point is that unitary quantum mechanics is actually reductionist. It does away with a (superfluous?) ad-hoc assumption (about 'collapse of the wavefunction'). The resulting theory predicts a single object: a global wavefunction. That you or I call its various branches 'universes' doesn't mean anything is actually proliferating.

We now return you to parallel universes' proper place in our culture as the home of a bearded, agonizer wielding Commander Spock.

It's important to emphasize that the "Many Worlds" predicted by modern unitary quantum mechanics are not really the "wacky possibilities" seen on shows like Sliders. They represent the branches of superpositions of a global wavefunction. If you branch from a current position, the possibilities are deterministic and mostly uninteresting (e.g. an atom decays a moment later in one branch than another).

Yes, the global wavefunction would include many variations (maybe even variants where historical events played out differently because millions of quantum branches biased events a certain way instead of another way), but all of these variations are ruled by the same deterministic physics. And, importantly, it's not a matter of "whatever universe you can imagine is out there somewhere!"--the possibilities are strictly limited by deterministic evolution of the wavefunction and the initial conditions of the universe.

Re:Ummm . . .

[lawpoop]

I have another question, which might sound kind of naive. If we can accept that there are many universes, with new ones sprouting all the time, is there some constraint on how those universes are? That there might be an infinite set within a certain limit? Otherwise, if, in one of these other universes, the laws of physics are different, then those inhabitants or observers might be able to travel between universes -- just like in another universe where the speed of light follows different laws, they might be able to observe the whole universe.

Another poster asked "Why am I experiencing this universe?" To which a poster replied, "Because you are in this one. If you were in a different one you would wonder the same thing. That's the anthropic principle."

So then, if the anthropic principle holds multi-versally, then each observer is trapped in a universe of singular experience. But logically, if anything can change in a forked universe, including the laws of physics, we might imagine a universe where the inhabitants could traverse one or more universes. They might ask, "Why do I experience these universes?" Furthermore, there might be a universe where the laws of physics are such that inhabitants can traverse *any* universe -- a universal universe, so to speak. They wouldn't wonder why they were having a singular experience -- their universe would contain *all* universes. They would be experiencing everything! "Why do I experience everything?"

So what really is different between all the forking universes? They must have some commonality, at least in the laws of physics. If not, then there is the possibility of a universe where you can traverse universes. Am I off base here? Can the laws of physics be different in another universe, even if it is descendant of a universe with laws like ours?

Re:Ummm . . .

[kebes]

If we can accept that there are many universes, with new ones sprouting all the time, is there some constraint on how those universes are? That there might be an infinite set within a certain limit?

Short answer: there are constraints and limits.

Long answer:
First off, some of the discussion here is getting confused because people are equating the "many universes" of the Many-Worlds Interpretation with the "parallel realities" espoused by other theories (but, most prominently displayed in sci-fi), where "anything goes" or any possible arrangement of atoms (or even laws of physics) is possible, or even exists.

I'm talking about Many-Worlds, which is an untested prediction of modern quantum theory. I'm not talking about parallel realities (for which there is currently no proof and which no mainstream theory predict). In Many-Worlds, the branches evolve deterministically from the current state (according to the equations of quantum mechanics). This means that along each branch (each "universe" if you prefer), the laws of physics are invariant, and are exactly what we are used to (quantum mechanics + relativity). Moreover, because the universe is evolving from a specific initial state, there are constraints on what the branches will look like. You won't get "every wild thing you can imagine": only those branches which can evolve from a current state will be represented in the global superposition.

So the various branches of Many-Worlds look pretty much exactly like the universe you are comfortable with (planets, stars, galaxies). Along one branch an atom might decay and along the other branch it might not decay (yet)... In principle some branches may have quantum choices such that normally improbably things occur, but that's balanced out by the vast majority of branches which are, basically, boring.

Well if you can't believe in God....

[isa-kuruption]

Hey, if you don't believe in God because "you can't see him/her/it" then you can't believe in a parallel universe because, hey, you can't see it. Nor can you believe in dark matter/energy. /troll.

Re:Well if you can't believe in God....

[meringuoid]

And the whole dark matter/dark energy thing strikes me as a load of humbug... saying there must be some undetectable, magical force acting on all the matter in the universe because the calculations we've come up with so far are inaccurate strikes me as lazy and uncreative.

It worked once before. Calculations of the orbit of the planet Uranus were noticeably inaccurate; the planet wasn't quite where it ought to have been. One explanation was that this was the result of the gravitational effect of a large amount of dark matter. This dark matter was later found and named Neptune.

Re:Well if you can't believe in God....

[db32]

Yeah and the time difference between "I think it works like this" and "See we can prove it now" grows increasingly large the more complex the subject matter. You realize that our understanding of things is still limited by our vantage point in the universe and that we DON'T actually understand all the workings many claim to. Quantum anything is a pretty good example of one of those monkey wrenches of "AHA bitches, and you thought you understood how this works!, Gotcha" The part that is Science is the "Damnit...lets try again a different way".

Re:Well if you can't believe in God....

[Agenor]

There is a subtile difference between the perturbations in Uranus' orbit and current dark matter. With Uranus, we had very fine measurements - thousand's of arcseconds precision. They actually were able to say 'there must be a planet about there' -- and it was. With dark matter the data is much sloppier. Part of this is no fault of the astronomer: dust clouds and individual variation in stars make it hard to get good data that is accurate to 10%. The other part is the astronomer's fault - their data analysis can be sloppy. As I saw in thesis class: published research on B-V vs stellar magnitude fits can be very poorly done, throwing out far too many outliers or using too many coefficients. This data then feeds distance measurements, which feed galactic rotation measurements, and so on. There is an unsound foundation for most work past a few thousand light years.

The worst part is no one wants to correct this foundational work. There is not much glory in changing coefficients and contradicting published work only invites enemies.

My main point is that a certain amount of non-luminous matter is to be expected. I would not be supprised though, when that unglamorous job of correcting all these fits is done, that the quantity and location of 'dark matter' is revised downwards. That, or we find something more fundamentally wrong (like with the precession of Mercury's orbit).

Remember people used to believe in caloric.

Re:Well if you can't believe in God....

[The One and Only]

It also failed to work once before. Calculations of the orbit of the planet Mercury were noticeably inaccurate; the planet wasn't quite where it ought to have been. One explanation was that this was the result of the gravitational effect of the planet Vulcan, which orbited so close to the Sun that it was practically impossible to observe. Then relativity came out, and the new calculations were accurate.

One question...

[StandardCell]

How does this reconcile with reality as we see it?

From my perspective, even if this mathematical "proof" is true, it is only true in the ontological sense, i.e. that these branches can happen and maybe do happen, but not in reality. Then again, I believe the entire basis for the universe is ultimately ontological but that's a different matter.

My point is that these alternate "universes" may only exist in infinitesimally-small times (possibly below the Planck time threshold) and then simply cease to exist again as compared with our reality in the next moment, moment after moment.

Re:One question...

[nine-times]

I don't understand how you're using the word "ontology". Can you explain that some other way?

Raises the question

[dsanfte]

If there are an infinite number of parallel universes for each possible quantum outcome, why do we only experience -this- one?

Re:Raises the question

[Teresita]

Because in all of the others, you are not posing this question.

You got it 180 degrees out. The answer is the equivalent, but the reverse, of the Anthropic Principle. Every parallel universe also has copies of him asking that same question.

Re:Raises the question

[EvilSpudBoy]

If there are an infinite number of parallel universes for each possible quantum outcome, why do we only experience -this- one?

Because you are in this one. If you were in a different one you would wonder the same thing.

That's the anthropic principle.

Re:Raises the question

[Hoi Polloi]

How would you compare universes to be able to differentiate between them? How can you say which one you are experiencing? There is no "control universe" you can step back into.

Re:Raises the question

[pclminion]

My theory is that we actually ARE experiencing parallel universes. But the pressures of biological evolution have driven us toward brain structures which hide this fact. Maybe we actually ARE spread out across many different possibilities, but our conscious view of reality is as a single whole. Why? Because it made survival easier, perhaps. Or maybe, individuals with parallel awareness inevitably go insane and die out. Who knows.

Sometimes this parallelism "leaks through," in the form of quantum strangeness. But it's not the universe which is strange, it's actually us. Our brains contradict reality by trying to condense everything and the result is "weird" physics. Is the electron here, or there? Maybe it's both, but our brains decide to interpret it as a concrete one-way-or-the-other, because doing otherwise would require us to be consciously aware of all of reality, something which is probably impossible.

Re:Raises the question

[kebes]

I'm not sure if you were already aware, but there is indeed a concept called "Quantum Darwinism" which helps explain (using the results from quantum decoherence) why we observe things "classically" (single outcomes of experiments, non-entangled macroscopic states, etc.) despite the universe being fundamentally quantum.

Briefly, the theory shows (rigorously) how pseudo-classical states are the only ones that are robust against decoherence. Hence, those are the states that tend to persists for measurable periods of time. And those pseudo-classical states are the ones that give rise to other pseudo-classical states.

Moreover the main developer of these ideas (Wojciech Zurek) describes in his papers how what we typically term "memories" are inherently classical states (it's either "a" or "b"--not a superposition of both). He explains how macroscopic states will tend to be pseudo-classical, so of course any biological (macroscopic) creature will evolve to assume that reality is classical (it's an adaptive advantage and a good approximation of reality).

The point is that these larger-scale superpositions do indeed exist, but that local observers (e.g. instruments, or ants, or humans) can inherently only record/remember classical states, not quantum ones. So, our perception of reality (and memory of reality) is inherently a classical one.

Re:Parallel Universes conflict with Mind-Body Prob

[trolltalk.com]

Think about the "mind-body problem" Okay ...

I did ... and here's my solution. Basically, there are other branches where life sucks less, and others where life suck more, etc. I'm going to find the one where life sucks less and kill my alter ego so I can take their place!!!!!!!! (Of course, that means that there's ANOTHER me in an even suckier universe gunning for me, so better be quick!)

You'd better watch out - there may be a doppelganger of you looking to do the same thing...

Re:Publication?

[ZombieWomble]

You honestly think they waited for this to be peer-reviewed and published before they belted out the press releases? That would mean they may be expected to provide some detail, which would be madness!

Seriously though, there's no sign of a citation from any of the people running the story (most of which are nearly identical, so they're probably just copying from the same press release), and there's no sign of it on arXiv or from a quick trawl of journal feeds, so it's a very good chance that it's either unpublished work, or a conference paper somewhere. Not surprising, given how many "most significant discoveries in the history of science" turn out to be much less dramatic under the cold hard light of review than when they're first reported.

circular dependency

[u19925]

There is a circular dependency here. The author assumes that the parallel universe interpretation is correct and then argues that if this interpretation is correct, then we can derive probabilistic nature of quantum of mechanics. All this means is that the parallel universe is a self-consistent theory. Nobody has argued against this for the last 50+ years.

The problem with quantum mechanics interpretation is that as of now, no interpretation exists which is not bizarre in our traditional world view. Parallel universe is just one of them.

Re:Parallel Universes conflict with Mind-Body Prob

[Xtravar]

Life is like a dream. You never die in your dreams. You never die in your observed life. You just die in alternate universes. This carries on until you reach the next plane of intelligence (wake up) whereupon you realize that there was no mind-body problem to begin with.

Fixed!

1 = 2?

[Quiet_Desperation]

Where does the energy come from to give existence to this second universe? This whole splitting of the universe thing seems common in physics, so I'm sure I'm not interpreting this correctly. It seems like there's entire universes being created because of the uncertainty of a single particle.

Where is the paper?

[kmac06]

I would very much like to find the publication of this, or least more details given by the authors if anyone can fine a link.

By the way, Deutsch is a well known physicist, not some crackpot. One of the first problems discovered to be theoretically sped up by a quantum computer is named after him (link).

Occam's razor

[Biff Stu]

So they say they have a mathematical description of the parallel universe theory. One can construct a mathematical model that describes the geocentric solar system perfectly well, but the the heliocentric version is much simpler.

So, which is simpler?

(1) Shit happens.

(2) Shit happens. Parallel universes are created.

Re:Occam's razor

[Surt]

Occam's razor proves nothing (and is often wrong!). Phrase the question differently, which is simpler:

We're in the only universe, which just happens to be perfectly suited and tuned to our existence.
There's an infinite number of universes, and we're in one where we're possible.

Re:Occam's razor

[MyLongNickName]

Occam's razor is useless in situations like this. Basically Occam's razor comes down to a judgment call. 'Which "sounds more plausible"? 'is the question that is asked. To be honest when you get into this branch of physics, even things that have been damn well proven and the knowledge used to build workable devices... the concepts STILL sound impossible.

Re:Occam's razor

[hanssprudel]

So, which is simpler?

(1) Shit happens.

(2) Shit happens. Parallel universes are created. That isn't the choice. It is more like:

(1) (Copenhagen) The act of "observing" a particle at some point between the particle, the measuring apparatus, and your mind, somehow magically causes the particle to collapse from a wave state to a fixed one, without any other action on your part. Nobody has ever explained exactly what an observation is (we are, after all, made of particles too) nor when this happens.

(2) (Multiple worlds) Reality consists of particles in quantum waves of superimposed states. Period. When we observe a particles state, it's state becomes entangled with the state of the particles in our mind, and hence we observe the particle as collapsing to a single state "in each world".

I don't know about everybody else, but the fact that all states can exist, yet I can only perceive them separately, is no stranger to me than that all moments of time exist, yet I can only perceive each one separately.

Re:Occam's razor

[kylben]

Or how about: There's only one universe, and we are what happened to be possible in it. The odds of winning the lottery are tens of millions to one. The chance that someone will win the lottery is 100%.

Re:Occam's razor

[Xtifr]

The probability of the existence of other universes is unrelated to the probability of the existence of parallell universes. There could easily be $BIGNUM universes without any of them being parallel in the Many-Worlds-Interpretation of QM sense.

Of course, it is worth pointing out that speculation about a creator merely pushes the question of origins back a level: where did this hypothetical creator and his/her/their universe come from?

Re:Occam's razor

[maxwell demon]

Well, actually the MWI says the shit (i.e. wave function collapse) does not happen. The "split" is not a creation of new universes, but a change in our view of the universe. At the objective level, no split happens, and no wave function collapses. Instead, we ourselves get entangled with the observed objects (which is a normal result of any interaction in quantum mechanics). That interaction causes a "split" in the observed world, due to the fact that we ourselves, as observers, are part of it. We observe "shit happening", where no shit actually happens. Since in reality there's no collapse happening, all possibilities are still there, and therefore in a "parallel world" (which is just another projection of the same reality) a "parallel I" must have observed the other result.

Now, which theory is simpler:

Theory 1: As long as we don't look, everything follows law A, but as soon as we look, shit happens, and we have to apply law B.
Theory 2: Everything follows law A, all of the time. The true reason why law B seems to apply is that law A also applies to us.

Theory 1 is the standard Copenhagen interpretation. Theory 2 is the MWI.

Re:Occam's razor

[David Gould]

Occam's razor is useless in situations like this. Basically Occam's razor comes down to a judgment call. Right. Besides which, it's not a "Law Of Nature" anyway -- it's more a rule of thumb. Occam's Razor never "proves" anything. It just lets you make an educated guess as to which avenue of inquiry is, all else being equal (that part's important), more likely to be fruitful. (And thus, which one you'd be wiser to spend the effort to explore.)

Re:Occam's razor

[suv4x4]

Reality consists of particles in quantum waves of superimposed states. Period. When we observe a particles state, it's state becomes entangled with the state of the particles in our mind, and hence we observe the particle as collapsing to a single state "in each world".

Many people mix those up. Our "mind" doesn't have anything to do with it.

The wave function collapses when a particle interacts with a macrosystem. When two macrosystems are separate from each other, we have to assume the other macrosystem is not coherent with us until contact.

And remember contact *includes* photons reflected off the other macrosystem, so if we see it, otherwise put "observe" it, we're already in contact.

This is why "observation" causes collapse. Not because we're smart.

an old chestnut...

[Speare]

• An engineer says that the equation approximates reality;
• A physicist says that reality approximates the equation;
• A mathematician simply doesn't care.

idiotic circular logic

[frovingslosh]

....showed mathematically that the bush-like branching structure created by the universe splitting into parallel versions of itself can explain the probabilistic nature of quantum outcomes

Or in other words, this science fiction nonsense about parallel worlds, unscientific because it can never be tested or proven, and which was inspired by observations of quantum mechanics, is now supposedly able to explain, guess what, ... quantum mechanics, the very concept that the nonsense was built on in the first place.

The absurd number of parallel universes that would have to be created is mind boggling, since, at the very least, an entire universe would have to be created every single time any atom decayed (one for the universe where that atom happened to decay at that instant, another for the case where that atom didn't happen to decay). Strange that none of the wackos who advocate this, and I use the term very loosely, "theory", bother to expain where all of the mass and energy is coming from for all of these extra universes. Note that we are talking about far more universes than atoms in our own universe. Absolute hogwash.

Re:idiotic circular logic

[TrailerTrash]

My question would be, are the number of parallel universes countably infinite (same cardinality as the integers) or uncountably infinite (same cardinality as the real numbers)? If countable, this suggests that the number of quantum potential states in the universe are countable, and would seem to lend credence to the idea of an orderly deterministic universe. If uncountable, then the multiverse is infinitely deep - more satisfying, perhaps, in a religious worldview.

Unless, of course, God(s)(ess)(esses) constructed the universe deterministically, to compute something. I suspect it is to create the question to which 42 is the answer.

Re:idiotic circular logic

[lawpoop]

The absurd number of parallel universes that would have to be created is mind boggling, since, at the very least, an entire universe would have to be created every single time any atom decayed (one for the universe where that atom happened to decay at that instant, another for the case where that atom didn't happen to decay). What exactly is the absurdity scale you are using to measure the absurdity of this idea? Four parallel universes are okay, six are goofy, seven are silly, 10 are ridiculous, and 1000 or more are absurd?

Strange that none of the wackos who advocate this, and I use the term very loosely, "theory", bother to expain where all of the mass and energy is coming from for all of these extra universes. That's like asking where the mass and energy in our universe came from. It's the same answer in all parallel universes -- it was there all along. When they talk about a new universe branching, it's not a big bang event, where a new universe is born, it's an altered copy its twin, identical up until the point where the quantum decision was made. It has a completely identical history after a certain point and therefore, the same mass and energy. Parallel universes do not 'share' energy, nor information, nor anything else. They don't 'seed' or 'give birth to' each other. They are totally out of contact with each other. We wouldn't even know about other ones, if not for the math.

Note that we are talking about far more universes than atoms in our own universe. Absolute hogwash. I can't see why anyone modded you insightful here. You seem to be arguing from personal incredulity. Not that I'm claiming that these guys are right or their theory is true, but your skepticism seems more emotional than rational to me.

More links

[SiliconEntity]

Here is the New Scientist article being cited:
http://space.newscientist.com/article/mg19526223.700-parallel-universes-make-quantum-sense.html
However it is behind a paywall. See Google Groups for the whole thing.

There is a great quote by physicist Max Tegmark: "The critique of many worlds is shifting from 'it makes no sense and I hate it' to simply 'I hate it'."

As far as the meat of it, traditionally the Many-Worlds Interpretation has had two technical objections raised. The first is called the basis problem, and the second is deriving correct probabilities. The basis problem is that when the universe "splits" it's not clear how it should split. The math allows for infinite different ways to split, but we only see one way. This has been solved in recent years by the study of decoherence, which in MWI terms is like looking at the splitting process up close. Turns out it can only happen one way in practice. So that one's done.

The article is more about the other one, deriving probabilities. Actually it's easy to derive probabilities in the MWI, but they're wrong. The right probabilities are what is called the Born rule, and it's been hard to get those. David Deutsch came up with a new idea in 1999 where he proposed tying it in to decision theory. He said that we really care about probabilities because they influence how we make decisions about what to do. If we can derive a reasonable decision theory within the MWI, then we've essentially explained probabilities. His work had some shortcomings but subsequent efforts have largely resolved those.

So now for the first time, the two traditional technical problems with the MWI have reasonably good solutions. Hence we are back to, as Tegmark says, "I hate it" as the main objection to the theory. Since that's not really a good argument, it can be said that the MWI should be considered the most compelling candidate for an interpretation of QM.

One final link, here is one of the papers that extends Deutsch's idea about decision theory and pretty much closes the holes: http://arxiv.org/abs/quant-ph/0312157. It's pretty technical but still a lot more readable than most physics papers.

Re:Standard of evidence is getting low these days

[aminorex]

> if anyone would like to propose a repeatable and verifiable experiment for finding the universe where George W. Bush lost in 2000

Just look out of your window.

read one of Deutch's papers

[kwikrick]

or tried to, anyway. It seems to be related to the
paper the article talks about.

http://xxx.lanl.gov/abs/quant-ph/0104033

It's more of an information theory paper, it seems to me, and
not so easy to relate to any verifable theory of the
universe/multiverse.

Truly, what IS new about this???

[Jane Q. Public]

I do not see anything new here at all. The "many worlds" hypothesis has always depended on a hypothetical "probability tree" to describe the odds of quantum occurrences. This idea was new to me, oh, about maybe 30 years ago, and was not actually new then.

Are they trying to claim that their mathematical probability tree corresponds to a "real" probability tree? If so, on what basis do they make that claim?

To them, I say: "Show me evidence, and I will believe. Until then, stop bothering me with old ideas."

Better article on this subject

[mlimber]

I haven't found the "New Scientist" reference this article cites, but I did find another, better article on the subject: http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/09/21/sciuni121.xml

Oh really?

[mosel-saar-ruwer]

Math can prove that a mathematical system is consistent, and within that system can prove properties that result in that system.

Oh really ?

Re:How does quantum states end up in car accidents

[brunascle]

well, here's one way. use this site. if you get a 1, go drive head-on into someone.

It's not mass, it's information...

[argent]

Strange that none of the wackos who advocate this, and I use the term very loosely, "theory", bother to expain where all of the mass and energy is coming from for all of these extra universes.

The mass and energy isn't coming from anywhere, because there's no new particles being created. The particles are the same ones, in all universes, their state is just getting more complex, and each "parallel universe" is just a description of one consistent state of all the particles of the universe over all histories. We only observe the particles as as having measurable (subject to Heisenberg) positions and velocities because we're using other particles to measure what those positions are.

A better question might be "where is the information needed to describe the state of the particle stored". Or to put it another way "how many bits does God's Computer have, and can we hack it?"

Re:Universe means "one everything".

[Anonymous Coward]

The same way we can have sub-atomic particles. We fucked up and named something we didn't understand.