Friday, November 14, 2008

The Multiverse agony aunt

As a compliment to Jim's informative series on the anthropic coincidences I would like to draw attention to Max Tegmark’s excellent page on multiverse theories here. The various multiverses fall into four distinct categories:

Level I: (Open multiverse) A generic prediction of cosmic inflation is an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions.

Level II: (Andrei Linde's bubble theory) In chaotic inflation, other thermalized regions may have different effective physical constants, dimensionality and particle content.

Level III: Each quantum possibility correspondes to a universe. Suppose your throw a die that contains 6 sides. When the die fall, one could ask why the outcome is the way it is. The answer is: All 6 possible ways the die can fall is actually actualized in 6 different universes.

Level IV: (The Ultimate ensemble theory of Tegmark) Other mathematical structures give different fundamental equations of physics. This level considers "real" any hypothetical universe based on one of these structures. Since this subsumes all other possible ensembles, it brings closure to the hierarchy of multiverses: there cannot be a Level V.

I am delighted to inform you that all of these theories have the effect of turning reality into a sick joke, as evidenced by Tegmark’s agony aunt section in which his baffled readership struggle to come to terms with the implications.

Question : The personally troubling aspect of the multiverse theory, which, fortunately and unfortunately, seems quite plausible, is that---if every conceivable universe exists---that means that your similar being, and mine, somewhere out there is ( be gentle as I can be) an axe-murder and (not so gentle) worse! That is hard to accept for me in this universe, even if true. I guess the good news is that it isn't really me...but pretty darnn close to me since if every iteration is plausible then somewhere our "clone" has seen typed this email and then went out and robbed the local gas station, 7-11, next closest gas station, etc. etc.!

Tegmark : Things inconsistent with the laws of physics will never happen - everything else will. However, to cheer you up: even if some of your twins hold up gas stations, most of your twins certainly don't, given what I already know about your personality; it's important to keep track of the statistics, since even if everything conceivable happens somewhere, really freak events happen only exponentially rarely.

Quodlibeta Comment : Of course, the flip side of all that is, if you happen to be an axe murderer in this universe and this arises from a key flaw in your personality, the chances are that the vast majority of your other clones in the set of all possible universes will be axe murderers too, although statistically some will be peace loving hippies.

Question : Within the context of the multiverse, doesn't every conceivable physical possibility occur? If I'm driving my car and stop abruptly to keep from hitting a squirrel, don't I purposely run over that same squirrel in an alternate universe. And if so, isn't the number of universes that follow each outcome approximately the same?

Tegmark : No - and that's the crux. The laws of physics and your behavior evolved through natural selection create much regularity across the multiverse, so you'll try to spare that squirrel in the vast majority of all parallel universes where "you" are pretty similar to the copy reading this email (just as regards the above-mentioned gas station robbery). The fractions only split close to 50-50 for decisions that you perceive as a very close call.

Quodlibeta Comment : Why must these other versions of the questioner in the set of possible universes be driving cars?. Might they not be riding giant squirrels and swerving to avoid marsupials?.

Question : Doesn't the multiverse theory completely trivialize existence? It puts the burden for individual responsibility on the shoulders of the universe. Why do anything? If you decide to be a lazy slug, that just means that your particle clone elsewhere will be the one who wins the Nobel prize.

Tegmark : I'm not convinced that the existence of parallel universes implies that I should dramatically alter my behavior. Yes, some near-clones of me indeed win the Nobel prize, but only a very small fraction of them! As in the gas station question above, it's important to keep track of the statistics, since even if everything conceivable happens somewhere, really freak events happen rarely, in an exponentially small fraction of all parallel universes. It's these statistics that make existence complex and interesting rather than trivial.

Quodlibeta Comment : Great, now I don't just have to cope with the fact that most of my contempories are more successful than me, a large proportion of my clones in the multiverse are as well!. At least I have the satisfaction of knowing that statistically, a large percentage of them will be bums.

Having wiped the tears of laughter from my face, the question remains, should those of a monotheistic disposition believe in the multiverse?. I was delighted to discover that this topic came up during the Middle Ages when a number of clerics asked whether god could create more than one universe or whether he/she/it would be happy sticking with one?. In the event the Bishop of Paris was forced to intervene and said that yes, God could create as many universes as he wanted and there the matter was settled. Later John of Vassals said that God could create an infinite universe provided that it was not too infinite as this would be tantamount to creating another god. Thomas Bradwardine on the other hand (who later became archbishop of Canterbury) insisted that the universe was has to be infinite because god is infinite and exists in the universe. Moreover, present day commentators such as Peter Bussey of Glasgow University warn of the risk of ‘dumbing down God’. A multiverse is, after all, far harder for a deity to create than a single universe. On the basis of that it would be prudent to plump for a multiverse category, although you might want to 'fine tune' it to make it less silly.

Discuss this post at the Quodlibeta Forum

Click here to read the first chapter of God's Philosophers: How the Medieval World Laid the Foundations of Modern Science absolutely free.


Anonymous said...

Here is the real irony (and my personal favorite example of how the multiverse theory trivializes reality): in some possible universes, Richard Dawkins goes on speaking tours with William Dembski and Michael Behe to promote Intelligent Design.

In some subset of those universes, they are hyping an ID book that Tegmark has written.

Anonymous said...

There is no meaning in a multiverse until we put meaning into it. At least, that would be according to the subjective view of meaning. So there is no meaning that someone would necessarily need to put into a multiverse. For instance, if I have a clone who does things completely different than what I do in this universe, I'm still me in this universe, and I don't need to follow what any other me (in an alternate universe) is doing. I don't need to attach any significance to the other choices that my fellow me's made, because they aren't really me.

Personally, scientifically speaking I have to reject the multiverse not in terms of what it implies (meaning-wise), since we can make up whatever implications we want. I reject it moreso for the reason that, at least so far, a multiverse theory, to be consistent with quantum mechanics (as we know it), requires that the other universes be undetectable. And if quantum mechanics already explains microscopic phenomena without regard to other universes, why throw in extra "philosophical baggage" to carry around? The problem is, of course, still in the air, but that is how I see the subject so far.

As to "A multiverse is, after all, far harder for a deity to create than a single universe," I'm not sure I would necessarily agree. If anyone is in a position to judge the difficulty of an action, it would be God; but with God aren't all things "easy"?

Humphrey said...

@ Tom

That is true, although in another subset Dembski and Behe will be atheists writing damning reviews of Dawkins's book tour to promote intelligent design.

Humphrey said...


Its entirely subjective of course. I happen to think that a multiverse is more difficult, in addition to having to design all the foundational properties of the universe (quantum physics, general relativity etc..) so that they work together in the correct manner, you would also have to create some kind of universe generating mechanism. All this would have to have very specific meta-laws guiding its functioning within a restricted mathematical subset.

I suppose conceptually, the clones issue is no different from having an identical twin but I still feel a bit uneasy about it.

Anonymous said...

Does level 3 mean that the number of exisiting universes would double at every quantum event? That's rather a lot of universes. Do we retain our consciousness in just one of these with new ones springing into existence in the new universes or can our consciousness hop over to the other universe created at each quantum event? I can't get get my head around any of this in my current universe, though even as I write in millions of other universes I have grasped it completely.

Humphrey said...

@ Annonymous

I believe it is something to do with the many worlds interpretation. This resolves some of the paradoxes in Quantum theory by claiming that every possible outcome to every event defines or exists in its own "history" or "world. There is some disagreement as to whether we would notice the universe splitting into two or not. I believe Roger Penrose says that we would, and that the whole thing is a bit silly.

Anonymous said...


Thanks for your reply. Before I'd even heard of quantum theory I had the idea that the world could clone itself maybe every infinitessimally small fraction of a second with events taking a different course each time. I thought it rather silly as well. However, I do have the impression that ideas can be as silly as you like, as long as you can exclude the need for some kind of creator. I say that as an agnostic with atheist tendencies and theist sympathies.

Btw. should comments be here or on the Quodlibeta forum? Or is this a paradigm case of the world splitting in two?

PS. Ossum dinosaurs. They're smoking.

Humphrey said...

@ Anon

I suppose if history tells us anything it is that the silliest explanation is usually the best. For instance the Greek Philosopher Anaximander proposed that:

'from warmed up water and earth emerged either fish or entirely fishlike animals. Inside these animals, men took form and embryos were held prisoners until puberty; only then, after these animals burst open, could men and women come out, now able to feed themselves.'

Which was a wild stab in the dark and sounds crazy but isn't a million miles away from evolution. Although his idea that that humans had to spend part of this transition inside the mouths of big fish to protect themselves from the Earth's climate was a bit off base.

I think the comments should go on the posts themselves just to keep things organised. If it all spills over into a big argument then it can be moved to the forum, or if anyone happens to want to raise a discussion that can go into the forum as well. Since its Quodlibeta nothing is off limits, but it would help if it was on science, history or religion.

Humphrey said...

@ Anon

RE the smoking dinosaurs

Like I say, they were on the way out.