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Asked by rajathjackson to Chris, Dave, David, Fiona, Jack on 18 Jun 2013.
Question: It seems there are many theories on multiverse or parallel universes so, if you had the chance to vote for any of them which one would you prefer and why?
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Jack Miller answered on 18 Jun 2013:
I guess ultimately it’s not for us to vote on theories, but for nature to tell us which one is right!
It turns out that all of these multiple universe theories are often connected to our world, usually by changing the fifteenth decimal place (slightly) in something a particle physicist might be able to measure. Therefore, by building better particle physics experiments, we’ll eventually get a much better understanding of the universe we live in.
Hope this helps!
— Jack
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Chris Mansell answered on 18 Jun 2013:
I agree with Jack that we need to ask nature. We do this by doing experiments. At the moment, I am not aware of a great deal of experimental evidence for the different theories on multiverses and parallel universes but I hope the people working directly on this question make some progress because it is really interesting.
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David Freeborn answered on 18 Jun 2013:
Hi rajathjackson,
This is an interesting question. As Jack and Chris say, we don’t really get to vote on theories, which is a bit of a pity. You’re right, there are a bunch of theories that predict a multiverse or parallel universes, although it’s all very, very speculative right now, and a lot of physicists are sceptical.
I don’t think I’d opt for the Many-Worlds interpretation of Quantum Mechanics. It’s a really interesting interpretation and it’s becoming more popular, but not one many physicists believe in, yet. I don’t think it’s consequences would be as exciting as some of the others, because each of these parallel worlds would obey exactly the same laws of physics.
Chaotic-Inflation cosmology and String Theory both predict that there could be billions and billions of Universes, each with slightly different laws of physics. This is very cool indeed- because some of these Universe would involve things we can’t even imagine as possible happening. It’s great fun to mathematically model such universe, and it would be even cooler if they really exist!
My favourite might be Max Tegmark’s “Ultimate Ensemble” theory though, although that is extremely speculative indeed! If it’s true, then every single possible Universe exists, as long as it has consistent mathematical laws. That means anything we can conceive of, and a lot of things that are totally beyond our imagination are all true. I think that’s definitely a very cool multiverse theory indeed.
Comments
rajathjackson commented on :
I actually meant which one among those theories do you think is more reasonable than others according to your understanding of those theories?
Jack commented on :
So, I think the only one of us who actually works on these sorts of things is David (he’s a theoretical particle physicist). My understanding is that they’re all “reasonable”, in that they’re all usually specifically constructed so that there’s no evidence for or against them, but that if they _were_ true, they’d explain things in a neat way, and maybe predict something we can’t measure yet.
There’s a very big and scary mathematical theorem, called the AdS/CFT correspondence theory that basically states there’s a formal mathematical correspondence between crazy string theories (of the type that involve multiple dimensions curled up on themselves) and the types of theory that we know govern our universe to really high accuracy. It’s a very general statement, which basically says that “string theories of this type have some vague connection to our world”, in that it’s possible to reformulate the laws of our universe as we understand them in a string-like way (if that makes any sense at all). This is, to my knowledge, about as close as you’re going to get for the moment to reality with these sorts of problems!
If this seems odd and weird to you, don’t worry; it does to everyone else as well!
David commented on :
OK, as to which of the theories are most plausible:
I don’t think that the Many Worlds interpretation of Quantum Mechanics is likely. It just doesn’t seem plausible to me that an extra Universe is created every time a wavefunction collapses, and the Many Worlds advocates really haven’t given a mechanism whereby this happens.
I’m actually a fan of Hidden-Variables Quantum Mechanics, which says that there are variables in the Quantum World we can’t detect. If we could understsand them, then we’d see a deeper theory “beneath” quantum mechanics, that explains why it’s so weird. There are some very good physicists working on this idea right now, and I think the idea might be more plausible than Many Worlds theory.
Chaotic-Inflation theory could well be true- in fact, we’re starting to get some experimental evidence from satellites that it just *might* be true. That would be really exciting.
Some very good physicists are convinced- but I don’t think the data is going to be able to prove it for many years yet.
(Read about it here: http://io9.com/5714803/does-our-universe-show-bruises-where-it-collided-with-other-universes)
String Theory could well be true; it’s very hard to know so far, because there is just so little evidence. I personally find it plausible, but there are a lot of alternative theories that are equally good. I guess I’d want to hedge my bets on this one!
Chris commented on :
I know that quite a few of the philosophers in the Philosophy Department at Oxford University defend the many-worlds interpretation of quantum mechanics. This was actually originally known as Everett’s relative state interpretation. I am open-minded about this interpretation.
I am not very qualified to comment on other multiverse theories. I am tempted to think better theories that don’t involve parallel universes will be developed within our lifetimes but that is just a guess.