Exponential vs. damped alternate histories

[eclectic_boy]

I was just reading through an old discussion on Jed's journal that touches on the question of whether any small change in the past would have automatically led to a radically altered present -- and the equally-strong-from-the-other-side question of whether a radical change in the past might still have led to some things being unchanged in the present, e.g. George Bush still being President of the United States even if Hitler had conquered Europe, or (going back some centuries) da Vinci still having been a great 15th-century artist even if Christianity had never arisen.



Seems to me there's a distinction that needs to be made between events keeping on (or returning to) the same trajectory they took in the real timeline, and individuals being the same as they really are. I can almost believe in the former, but the latter not at all: You can argue that events are governed by statistical mechanics, where huge numbers of individual interactions average together to create a rise in the welfare state, or the expansionist desire of one nation. You can even claim that some things are 'in the zeitgeist', and would happen mostly the same way regardless of exactly who was around or what situation they were in -- things like Darwin's and Wallace's simultaneous theories of evolution.
But to the extent that an individual is based on nature rather than nurture.... well, to have our George Bush be born in an alternate universe not only does the exact same sperm have to reach the exact same egg (meaning many timings need to exactly replicate themselves), but the same needs to be true for the eggs and sperm that created his parents, grandparents, and so on back to the event that changed the timeline. I can't see how that number of precise timings could duplicate itself with any changes to the universe beyond minor ones.

So while events might end up in approximately similar places, I can't imagine any of the same specific people being born. Wave your hand in the air and in a few minutes there'll still be the same air pressure everywhere in the room, because that's a statistical property arising from septillions of air molecules... but the position of molecule number 137 will be utterly different. We're individuals and care about the microscale, while many historical events may only depend on the macroscopic average.


EDIT: Okay, some further reading has shown me that my musing is old news, pointed out by several people a few months after the original discussion. But I feel at least mollified by the fact that the pointing out was done by two people I think very highly of, Ben Rosenbaum and Ted Chiang... I just have to latch on to these discussions in a more timely fashion in the future (or an alternate present).

Comments

[ultranurd.livejournal.com]

Isn't there some very small, albeit non-zero, probability that a person's exact genetic code could be produced by a different combination of ancestors?

[eclectic-boy.livejournal.com]

I'm willing to say this is an epsilon so small it's not worth considering. Of course, there's an interesting dissonance in the way I'm treating it as if it can't happen when if we assume alternate universes in which every possible combination of differences occurs then it obviously does happen on some of them.... but choosing to look into an alternate history in which the Black Death never reaches Europe and yet the chromosomes still come together the same way to make Johnny Depp seems a ridiculous extreme of cherry-picking.

[wayman.livejournal.com]

Er, bad editing in the previous version!

What happens if you add a theological wrinkle, and say that people are a combination of body and soul, where only body is genetically-based, and where souls are reborn in a Buddist-like system? Does this create a greater chance that a soul, by its Nth corporeal rebirth (say, around the late 20th century) into a region/culture which (by Jim's events-may-be-similar theory) is similar to our current environment, is likely to wind up being Johnny Depp-like in a way that would be relatively-to-extremely recognizable to us?

[elysdir.livejournal.com]

And even if you leave out the souls part, I can imagine a theory of history in which someone Johnny Depp-like needed to arise out of the environment in which he did arise; and if you're already translating from fictional-world terms to real-world terms for narrative purposes, you might take a shorthand and call the character Johnny Depp even if you don't intend that he has the same chromosomes as the version in our world.

Also, I can't remember whether anyone made this point in the assorted discussions, but one other factor to consider is that somewhat different chromosomes from the same parents, raised in the same environment, might well have produced someone very similar to Johnny Depp. Siblings are sometimes pretty similar to each other (though obviously they're often quite different).

[eclectic-boy.livejournal.com]

Oh, totally -- that's why I included "to the extent that an individual is based on nature rather than nurture". I tend to think that for most Great Individuals of history, there's something unusual and extreme about their nature -- they're unusually smart, or charismatic, or fast, or whatever, and a sibling getting the same nurture just wouldn't have the same skills.
But there are clearly anecdotal cases arguing in your favor -- George W. and Jeb Bush, anyone?