Friday, October 15, 2010

TGD: Chapter Four - The Multiverse, Big Crunches, Black Holes and other Strangeness

Today I want to talk a little bit more about the anthropic principle and the question of why our universe is fit for life. It's an interesting question and it's not one that can be answered easily without appealing to God.

The simplest and most straightforward way to address this problem is to claim that our universe couldn't possibly have been any different from the way it is now. This argument is often made by theoretical physicists trying to put together a unified theory that can explain the entire universe. Once we finally have this theory, they argue, we will see that the universe has to be the way it is.

Surprisingly, Dawkins considers this argument unsatisfying. Even if there truly is only one way that the universe could have been, we can still wonder why that one way is so well set up for the eventual evolution of life.

Dawkins gets around this objection by arguing that there may be multiple universes with different physical laws, some of which allow intelligent life to develop. He argues that, as unlikely as this may seem, it is still more likely than the existence of God. This based on the dubious argument he made earlier that it is extremely unlikely that God exists.

I don't think Dawkins' argument here holds water.

People who oppose intelligent design theory rightfully point out that the God hypothesis doesn't actually address the problem. Simply saying, "God did it," might be a valid explanation, but it doesn't help us understand our universe any better. In the same way, "There are billions of alternate universes," might be a valid explanation, but it doesn't actually tell us anything about our universe.

Since neither hypothesis makes for a good scientific theory, the only thing we can argue about is which idea is simpler or more likely. The end result is that we end up arguing about what words like "Simple" really mean. From one perspective, a single universe-designing entity seems relatively simple. From another perspective such an entity is prohibitively complex; even more complex than a billion or more alternate universes. At the end of the day, the argument is almost purely subjective.

In this section Dawkins presents a couple of different variations on the multiverse hypothesis. I want to take a bit of time to comment on each of these.

Another form the hypothesis takes is the serial universe model. The idea here is that our universe is destined to collapse in a "big crunch" and when it does a new big bang will occur and a new universe will form. If we assume that this process has been going on for a long enough period of time, then there have might have been a billion universes already and we're living in one that happened to be fit for life.

The big problem with this theory is that not every universe is guaranteed to collapse. In fact, the most recent evidence indicates that our universe is destined to continue expanding indefinitely, so this theory has fallen out of favor.

Another theory that Dawkins brings up is that every time a black hole is formed a new universe is created inside the black hole. The theory is that the universe inside the black hole might "inherit" similar properties to the parent universe. This system creates a lot of universes where black holes can form and, as a side affect, quite a few universes where stars can form and life can evolve.

I don't know much about this theory, so I don't know how all the details are supposed to work out. What happens to he "baby universe" when the black hole evaporates? Or what happens if the parent universe collapses? Dawkins likes this theory because of its superficial resemblance to the theory of evolution, but it seems to me that this theory creates more problems than it solves.

Finally, in both of the above theories, you can't actually observe or interact with these hypothetical alternate universes. In one case the alternate universe exist either before the "big bang" or after a future "big crunch". In another case, the alternate universes hide behind the event horizon of a black hole.

This is important, because if we could interact with these other universes, they wouldn't really be alternate universes at all. They would just be another part of our universe.

This is the final clue that a multiverse hypothesis doesn't really solve the problem. If we suppose that there is more than one universe out there, then we need to consider the laws that govern their creation and existence, just as we do for objects in the universe. Ultimately we will need a new set of laws to explain objects in the multiverse. How likely is it that those laws will be any simpler, any less contrived, than the laws that govern our universe?

In the end, we'll just be asking the exact same questions about the laws of the multiverse that we now ask about the laws of the universe. Where do we go from there? Hopefully, scientists will have more sense than to propose a multi-multiverse.

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