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Multiverse

March 10th, 2003 · No Comments

Just been to a very interesting talk by Prof. Hugh Mellor on the subject of the Multiverse. The idea* behind the Multiverse is that there are uncountable numbers of other universes out there that have slightly different properties to ours, owing to different initial conditions. We can never see any of the other universes in the Multiverse aside from our own.

*There are several ideas, but I have outlined the general one used. I think I have gotten Prof. Mellor’s argument correct; my apologies if I’ve made any mistakes in writing it.

Why did people come up with the idea? Because it’s an attempt to explain why our universe has the particular properties that it does, that allow complex phenomena like life and consciousness to exit. There’s a familiar argument that says that the fundamental constants of our universe, like the strong and weak nuclear force, are such that if they were different by only a miniscule amount, life couldn’t exist. These fundamental constants were caused by the initial starting conditions of our universe at the big bang. This argument is known as the anthropic principle.

So, this is a bit troubling for scientists. If the initial conditions of a universe that lead to life are so fragile, isn’t it a bit unlikely that we just happen to be living in such a universe, just by chance? Isn’t it more likely that these conditions were… designed? Well, maybe so, and it’s not as if all scientists don’t believe in God. But they would like to think that there is some other explanation for why we live in this particular universe, why our universe had such a convenient start. Hence the Multiverse – if there are uncountable numbers of universes out there with different starting conditions, then, say some scientists, surely there’s no problem with the fact that we live in such a convenient one?

Prof. Mellor disagrees, and this was the central point of his talk. Let’s try a thought experiment. Imagine that you are about to be executed, and there’s a firing squad of fifty people all aiming at you. They all fire at the same time, and they all miss. I think that we’d all be surprised if that happened. But the only reason why we’re surprised is because it is incredibly unlikely that they’d all miss, given the accuracy of the rifles, the willingness and training of the men, etc etc. This is not a valid analogy for the start of our universe and thus the anthropic principle, because we know that it is almost certain that we’re going to get hit.

Imagine instead that you pop into existence in a new universe surrounded by fifty bullets. All of these bullets have a particular trajectory. Let’s say that they all miss. Should you be surprised? No. Why not? Because you don’t know what the probability is that they appeared in that configuration. It’s not like being in front of a firing squad, where they’re all trying to hit you. You just don’t know why the bullets are going in their particular directions.

But say you are surprised that you didn’t get hit. Would it be any less surprising if you were told that there were uncountable numbers of other universes where people were hit? Prof. Mellor says no – the other universes don’t explain anything, because you still don’t know why you happen to be in this particular universe, and you have no reason to believe that things should have started differently.

I was quite taken by Prof. Mellor’s argument; it seems reasonable. It doesn’t claim to give a reason why our universe had its particular initial conditions (given a single universe model) – but neither does the Multiverse model either. Maybe there is a reason, and maybe we can eventually find it. But we don’t have it yet, so the Multiverse model is unnecessary.

Tags: lecture · philosophy · physics · science · spec

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