My favorite philosopher Michael Huemer has an interesting article entitled “Existence if Evidence of Immortality” arguing for reincarnation which I discussed previously on this blog in a post entitled “The Bayesian Case for Reincarnation.” The argument, as summarized in a blog post from Huemer, is:

Premise: There is a nonzero initial probability that persons are repeatable (can have multiple lives).

Also, the probability that you would be alive now

giventhat persons are repeatable is nonzero.Evidence: You are alive now.

Claim: The probability that you would be alive now, given that persons are

unrepeatable, and that there is an infinite past, is zero. Rough explanation: there were infinite opportunities for you to exist in earlier centuries, which, if persons are unrepeatable, would have prevented you from existing now.

If L = [You live now] and H = [multiple existences], then P(H) is the probability of the reoccurrence hypothesis and P(¬H) is the probability of the single existence hypothesis. P(L|H) is probability that you live now given multiple existences and P(L|¬H) is the probability that you live now given a single existence. Using Bayes’ Theorem, we can find that the probability of multiple existences given current existence is one:

In a recent podcast appearance, Huemer was speaking with Parker Settecase on his show Parker’s Pensees about his reincarnation article as well as a rough draft of a chapter tentatively named “Disembodied Souls are People Too” in a forthcoming book about extreme philosophy. This discussion is very interesting, and I recommend giving it a listen. There was some interesting points made at the end that I wanted to highlight. If you would like to listen, you can here at 1:15:30 or you can read my approximate quotes:

What happens is as long as there is a non-zero probability of reincarnation and there is a non-zero probability of you being here now if there is reincarnation then you get probability one for reincarnation…you need the zero probability—the zero probability that you would be here now if people could only live once in all of time. If you don’t have that zero, then you need—you actually need the numbers for the other probabilities.

We should believe that P(L|¬H) = 0 because of the infinite nature of time, a point addressed in the original article. If time is not infinite, then this would not necessarily be true and you would need the other probabilities to make an accurate calculation.

Suppose you think people are just physical objects and physical objects can’t recoccur. How certain are you of that? And as long as you don’t say 100%, the argument is just going to go through! Right? So, the probability of you being here now, if that’s true, is still going to be zero.

Some objected to the idea of multiple existences having a non-zero probability. Well, you could object to this by merely asking what probability they assign to P(H). As long as it’s not 0, which is an unreasonable level of certainty, then the argument still works. You could believe P(H) = 0.00000001 and the argument would still work.

A very interesting implication of this argument is that it seems to present evidence for dualism or the existence of an immaterial soul if you think that a physicalist view is incompatible with this viewpoint. Huemer explains:

You might think ‘oh, reincarnation requires a soul’ and so—that’s not strictly true. You know, so like logically speaking you could be a physicalist that believes in reincarnation. This would be an odd view but this is possible, right? because like, you could think ‘oh yeah—you know—we are space time worms’, which is like a common view of personal identity especially if you are a physicalist and you might think and also it could be a gappy space time worm.

I find this to be a very interesting discussion, and I actually think that Huemer is correct on this. I think that there may be ethical implications and other fascinating areas of this theory to study. For example, perhaps someone would begin to worry that they would be often reborn as an entity which suffers tremendously. I don’t think that is likely, because I think any evolutionary process which produces sentient beings wouldn’t make life terrible because it would be maladaptive since they would just commit suicide too frequently or adopt anti-natalist attitudes.

Many would probably object to the reincarnation argument on account of the absurdity heuristic—this stuff sounds pretty outlandish, but I think that explanations for the existence of sentient life, space, time, and all of the wild stuff about the universe are always a bit absurd. We evolved in an environment which did not expose us to blackholes, wormholes, atomic particles and so forth. We would expect that at the extremes of science and philosophy, things do not conform to our intuitions so well.

1. There are many well-known problems with reasoning with infinities (Pascal's Mugging, etc.). I'm profoundy reluctant to conculde anything with certainty based on calculations involving infinities.

2. Conventionally the universe is 13.8 billion years old, which is a long way from infinitely old. And it may well have a finite end. Of course there may be "other universes", or even an infinity of them, in some sense. But maybe not.

I don't think you've got "evidence" here of anything, let alone probability 1.0. At the most we can say "we can't prove it's impossible".