Monday, March 1, 2010

The multiverse and fine-tuning

I was telling a friend about the multiverse explanation for fine-tuning. He asked me a question that I had never thought about: Why assume that the conditions in different universes would be the same? Maybe it's all the same, and so the multiverse does not help with fine-tuning.

In fact, it seems the point can be strengthened. The constants in the laws of nature appear to be the same on earth, on the moon, in M 110 and around distant quasars. By induction we should assume they are the same everywhere. Granted, on some theories other island universes are not connected to ours (though on other theories, there is a containing de Sitter space, and on some theories the other island universes are just very far away). But while that may weaken the induction, it does not destroy it. Even before Europeans heard about Australia and Australians heard about Europe, each group had reason to suppose that apparently basic constants in the laws of nature would be the same in the other place, even though the two places are not landwise connected. Granted, however, the judgment whether some constant is basic is defeasible—thus, if one mistakenly takes the local gravitational acceleration to be a basic constant, one will mistakenly think it is the same on a high mountain as in a valley. But while a judgment of basicality is defeasible, it can still be reasonable.

Now, some multiverse theories grow out of a particular physical theory that implies a variation of constants, say because there is given some universe-generating process. So the point does not damage all multiverse-based explanations of fine-tuning. But it does raise the evidential bar: for, the defeasible presumption is that if there are other universes, they are very much like ours.

7 comments:

James said...

Here's a thought. Not necessarily a particularly good one, but a thought nonetheless. Suppose one accepts some kind of multiverse hypothesis. And suppose, not implausibly, that for each universe that exists, there is another one that had precisely the same initial conditions. Plausibly, on naturalism, these universes will be identical to each other. In which case there will be an identical individual to me having identical thoughts to me (though with different referents). This individual will presumably be thinking about me thinking about him at this very moment. Which seems odd.

Doug Benscoter said...
This comment has been removed by the author.
Doug Benscoter said...

(Post above deleted because of typos)

James, not only that, but it seems to me that there would be infinitely-many individuals having these thoughts. I think Craig does a nice job explaining how multiverse theories make it impossible to judge anything as implausible. If I won he lottery ten times in a row, people would legitimately be suspicious that the lottery was rigged. Now suppose I respond by stating, "You shouldn't really be surprised that I won the lottery ten times in a row. After all, in this infinite multiverse, there are infinitely-many lotteries going on, and in some of these I win ten times in a row!"

If someone responded in this way, I'm sure everyone would have a good laugh.

Oh, and Dr. Pruss, that post gave me something to think about. I don't know why this issue hasn't been discussed more in the context of the fine-tuning argument and the multiverse objection.

enigMan said...

Furthermore, Doug, you (or rather, identical copies of you) win ten times in a row in infinitely many of those lotteries. And so that is not even an uncommon event, since infinity divided by infinity is not necessarily a small number.

Incidentally, the idea of a universe-generating process does not seem to solve the atheist's problem. That process is either completely random, generating all logically possible universes, in which case it is not really a process, just a brute fact that all logically possible universes really exist (whereas logical possibility does not naturally imply actuality), or else it generates only some of those universes, in which case it remains to be explained why it is such that some of its products have these very nice constants of ours.

Bert Power said...

I don't think you need to make the concession you do. Without some kind of relation between the universes, the theory is unintelligible.

I.e. the idea of two things with no relation whatsoever to each other is unintelligible. This difficulty often escapes our notice because we are the inevitable victims of "picture thinking". We really imagine the two universes side by side in some kind of space even when we theoretically exclude such a connection. But of course if they were both in a common space, or a common time, they would be part of a single universe. For time and space are both create co-extensively with a universe.

Now on a theistic hypothesis, there might be two universes because they would flow out of a common source (they would share that relation). But what relation would an additional universe share with ours? None. If there can be such a thing as sheer "otherness", if things can co-exist and no more, it is at any rate a conception which my mind cannot form.

James said...

AP,

The "multi" in multiverse" has to mean many different laws. N number of universes with laws identical to this one would not be "multi" in the relevant sense. Otherwise, the hypothesis could not do the work it is supposed to do.

Granted, if one advanced a hypothesis of many universes that was indifferent to whether there was one set of laws or many, this argument would give a reason to believe there was one set of laws; but my understanding is that it is a multitude of laws as such that we hypothesize.

JMC

Doug Benscoter said...

enigMan, I agree. I think that's Robin Collins' view, as well.