How Likely is a Random Universe to Produce Your Twin?

Dan Shive (best known as the creator of El Goonish Shive) recently wrote a brief argument why alternate universes would probably not contain alternate "you"s. His argument looks correct, as far as it goes, but it is qualitative - lacking numerical estimates - and I don't see why it has to be. The data exists. Surely ballpark back-of-the-envelope numbers could be produced.

...but not trivially. Dan Shive's challenge can - and I think should - be broken down as follows.

( Read more... )

Now, I lack the knowledge of biology to, first, nail down these questions to their most correct forms, and second, assign probability estimates to relevant steps in the chain. But the most superficial examination of the situation seems to suggest at least one thing: any alternate universe measurably diverging a significant period before the birth of an individual is vanishingly likely to contain a copy of that individual. Which, of course, is what Dan Shive has pointed out.

And, as an obvious consequence of this, even if such a universe contained a duplicate of yourself, it would still be vanishingly unlikely for it to contain duplicates of anyone not your direct descendant. (Which would make for a heck of a paternity test, I have to tell you!)