Do you believe in a multiverse?

Actually there are some ways in which the many universes interpretation can be verified, although you'd need to be pretty brave for one of them.The first involves playing Russian roulette with the firing of the bullet dependent on the probability of a quantum event happening. It doesn't really matter so much what that probability is, but if you had say, a 99% probability of the bullet firing and 1% chance of it not firing, this means that for every 99 universes in which you would die there is a universe in which you survive.Repeat the process 10, 100, 1000 times. If you find yourself still alive at the end of it, its pretty good evidence of many universes (obviously there'd also be one hell of a lot of dead yous).This idea has been extended so that if we live in a multiverse, there should be at least one universe in which we are immortal (see here).Quantum computing may also allow us to distinguish between the Copenhagen and Many-worlds interpretation of QM. This site gives a little more info (as does this and this.)Also, there are some suggestions that the Anthropic Principle may imply a multiplicity of Universes. Lee Smolin's fecund universes theory, which he expounds in his book The Life of the Cosmos, states that the physical constants of the Universe are fine-tuned to allow for conditions to maximise black hole production. Black holes then give rise to other Universes where the physical constants are slightly different. This is in direct analogy with biological evolution (differential reproductive success of black holes, you might say).If Smolin's ideas are true, we would expect to live in a Universe with physical constants to provide a near maximal number of black holes (anything else would be vastly unlikely). This means that if we were to perturb any one of the 40 or so physical constants in either direction, we would expect less black holes to form in our Universe.No-one knows the effect of changing all of the constants on black hole production as yet, so its no more than philosophically satisfying conjecture. It is testable though, and verifiable.PE

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Mrs Hardy: "And how is Mrs Laurel?"
Stanley: "Oh, fine thank you."
Mrs Hardy: "I'd love to meet her some time."
Stanley: "Neither do I, too."

But that doesn't mean it can't be tested - advances in quantum computing may mean that we find out whether or not its true in our generation. I disagree with your assessment here - if you were to win the lottery 100 times in succession, then would you really put that all down to luck?If we set up the bullet example with a 50-50 chance of the gun firing, had 10,000 trials, and you found yourself alive at the end of it, it is so statistically improbable that you've no other realistic option but to conclude many universes. And by increasing the number of trials, you can make the improbability of it happening by chance as small as you like. Sure you could assume it was all down to chance, but then you have to accept the fact that there's also a chance that all our experiments on everything (physics, biology, chemistry etc) have been freakish outliers and the predictions borne out have been total flukes.If you can compare it to the fact that someone has got to win the lottery, then by analogy, one of the yous pulling the trigger has to survive - and this only makes sense in the many worlds interpretation. True.When I was talking about quantum suicide I was talking about infinite universes. The fecund universes idea only requires 10^229 universes or so, from what I can remember.PE

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Mrs Hardy: "And how is Mrs Laurel?"
Stanley: "Oh, fine thank you."
Mrs Hardy: "I'd love to meet her some time."
Stanley: "Neither do I, too."

I think we might be talking past one another slightly. Here's what I think we agree on:

• The many-worlds interpretation (MWI) of QM is conjecture
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• There need not be an infinite universes, there could be very very many, or a few. Or just the one.
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• At this time, any hypotheses that involve more than one universe are simply that - hypotheses with little or no evidential backing (unless you count QM, which is debatable).

Here's what I think we disagree on (sorry for any strawmen here):

• The MWI is on a par with many other conflicting theories about the Universe and so is as good or as bad as any of the rest of them
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• The Quantum Suicide experiment is not sufficient to distinguish between Copenhagen and MWI, and would not constitute proof of at least a phenomenally large no of separate universes.

(The experiment was not devised by me btw. Credit where its due - its generally attributed to Hans Moravek, Bruno Marchal and Jan Tegmark - you can download Tegmark's paper here. He'd do the experiment himself, but his wife won't let him!) Thats a fair point. In the higher echelons of physics, theories are selected for their aesthetic qualities and elegance of explanation, as there is an overriding belief (faith, if you like) that Mother Nature herself is elegant. Whether or not this approach constitutes science, I leave to the philosophers (I've seen art defined as "what artists do", so go figure).Suffice to say, when you have two main interpretations of a physical process (QM) and one requires you to abandon notions of reality and what it means to exist, then I'm more likely to prefer the other one especially as it can, in principle at least, be tested. You can build an experiment to check the gun very easily. Every few 'clicks' you could fire the gun into the air to ensure it was working properly. You could do all sorts of things like fire at head or fire in air based on the decimal expansion of pi (i.e. 3 times at head, then 1 time in the air, 4 times at head, 1 time in the air,5..,9..etc) and assuming the gun fired as normal in the air you could perform a sufficient number of trials to rule out anything but the MWI. Its up to your imagination really. The conceptual point of the experiment is that the experimenter sets up a quantum experiment where it is very likely that he dies. If he survives, then it means that all quantum actualities do in fact "happen" and MWI is the correct interpretation.Like I said above, I think we're slightly talking past one another - you're accentuating the fact that this is unsupported conjecture (which it is) and I'm saying that we shouldn't instantly assume that outlandish and seemingly implausible concepts like MWI cannot be tested. I also think you're unfairly dissing MWI by associating it with crackpot theories - I saw somewhere that there's a rough 50-50 between Copenhagen and MWI amongst physicists, but with several big hitters (Hawking, Feynman, Deutsch) in the MWI camp.PE added by edit: "or just the one"[This message has been edited by Primordial Egg, 03-29-2004]

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Mrs Hardy: "And how is Mrs Laurel?"
Stanley: "Oh, fine thank you."
Mrs Hardy: "I'd love to meet her some time."
Stanley: "Neither do I, too."

No worries - take your time.In he meantime, this is quite germane:http://www.hep.upenn.edu/~max/everett_newsci1.gif
http://www.hep.upenn.edu/~max/everett_newsci2.jpg
{Changed the import of rather large graphics files to just links for the same. Slow to load on slow connections (like mine), and also probably a copywrite violation. Click on links to see. - Adminnemooseus}As is this (but I haven't read all of this, yet).PE[This message has been edited by Adminnemooseus, 03-30-2004]

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"Probably the toughest time in anyone's life is when you have to murder a loved one because they're the devil." - Emo Philips

I'd like to go into what you think those a priori assumptions actually are, if you don't mind. Other than the obvious argument from personal incredulity about the existence of multiple universes, the idea seems to answer more questions than it raises. The one problem seemed to be its apparent testability, but even this can be resolved.
I think it does a good job of explaining why there is something rather than nothing but is rather expensive on Universes. We shouldn't find ourselves too surprised, in the whole scheme of recognising how tiny we are in the Cosmos, to discover that the Big Bang was merely the beginning of the local region of Spacetime, and the whole Multiverse is bigger and weirder than our wildest imaginations.Its an interesting point you make later on: I don't think its simpler at all - a wavefunction collapsing in the presence of a conscious observer making a measurement sounds incredibly complicated to me. Its cheap on Universes certainly, but expensive on coherence (no pun intended!). I guess the choice is how much you value one over the other and that's all based on incredulity.Aside: if you have two competing ideas - how do you determine which is the simpler? Many people start off with God as the Creator of the Universe (or conversely, the Big Bang) as the "simplest" explanation, without realising just how complicated that "simple" explanation is. Why is the Copenhagen interpretation, with its conscious observers and its limitations on reality, any simpler than MWI?Now onto your comments on Quantum Roulette: Actually, via your "gaping fault" you've identified why the experiment is so good. I'll explain further....Imagine that its you performing the experiment. The first shot goes off and you die. What do you experience? Answer: nothing. You are dead.
In a parallel universe the shot didn't go off. What do you experience? Answer: a 'click' on the gun, probable urinary discharge and an overall sense of relief.Now just before the experiment there would have been an infinite number of universes exactly the same, where the same you would have gone through exactly the same life and made the same decisions. The Universes would be identical up until the point where the gun fires / doesn't fire.If you were some pan dimensional being looking down at the experiment, you would see scores of experimenters dying. As big a number as you can imagine.If you were the experimenter, you would experience a never ending sequences of empty 'clicks'. After all, in your head, how can you experience anything other than being alive?So you're right in the sense that in most Universes you die, but what you actually experience is a miraculous coincidence to contrive to make you live. Of course, you'd have a tough time explaining this to somebody after the experiment. If you're saying this isn't a very practical experiment then maybe so, you'd have to put your life on the line. An offshoot of the idea has been used to attempt to solve the upcoming pensions crisis in Europe. Normal experience also seems to contradict the idea of something being in two places at the same time. Why one and not the other? Oooh I don't know about this. Reminds me of that old maths puzzle:Q. I throw a coin in the air 20 times and it lands heads every time. What is the probability it will land heads on the 21st attempt?A. 100%. The coin is loaded.If you really got 10,000 heads in a row that wouldn't mean anything fishy to you? Honestly?Imagine all the experiments and all the independent lines of research which confirm, say, the Neo-Darwinian Theory of Evolution. What's the chance that all of these experiments are the result of some spectacular fluke with freakish confirmations across labs all over the world? Remember, simply by increasing the number of trials on Quantum Roulette, we can make the probability of any interpretation other than MWI even smaller than the chance that the ToE is complete luck (we wouldn't even have to increase n (the number of trials) to an unfeasibly large number as the probability falls exponentially. It should all be manageable).Wouldn't catch me doing it though PE[This message has been edited by Primordial Egg, 03-30-2004]

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"Probably the toughest time in anyone's life is when you have to murder a loved one because they're the devil." - Emo Philips

Hi Chimp - just reposting this since the other thread's been closed. I don't think this necessarily holds if we define God to be infinite. What I would agree on is that if the multiverse idea holds then the probability of a super-intelligence with the ability to create universes existing "somewhere out there" is 1. Whether or not we ourselves are in such a Universe goes back to the age-old question of whether or not this notion is testable.Also, if we define God to be the infinite, then what exactly does this mean. What does it mean to say that infinity is intelligent?There seems to be a logical contradiction here: You seem to be implying that God being infinite, is an absurdity, which I'm sure you didn't mean.Also, you are invoking a logical justification for acausality, but only asserting that acausality must derive from an intelligence. Can you go into your thought processes for how you arrive at this?Your argument, it seems to me, boils down to a modified Kalam argument i.e God as the uncaused cause, responsible for our Universe - I don't see the relevance of multiverses at all.PEPS I think this did deserve its own topic "Does the existence of multiverses imply the existence of God" or somesuch, but AdminMoose was right to ask you to structure your thoughts more clearly.