A Science Fiction Riddle

Before I give my answer, should we invite participation from others? Much like we did for the Hundred Year Tree? If we can get participation, seems like that could be fun?

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Hi Joshua,

This is pure fiction, a CS Lewis styled imagination. Not Scientology.

OK, let me guess. Perelandra?

Looking back at the captured planet scenario I proposed, I’d be the first to acknowledge that it is, after all, astronomically unlikely (sorry about that pun) - especially my suggestion about egg-swapping between the two planets. And as you point out, hyper-deterministic evolution wouldn’t explain the ability of the aliens to interbreed with us. Creationism would be a more rational inference.

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Let me have a second shot at this, from a different angle.

May I assume that we, at least, are attacking this as if there is a God, whatever his role may or may not be?

Both Vincent and Joshua deny the possibility of the evolutionary process to operate separately on two separate worlds to produce interbreeding species. And that’s obvious, because interbreeding is the usual definition of one species, and how could one species be produced in two entirely independent galaxies?

I’d suggest that even if, per impossibile, the two worlds were identical twin worlds in the initial conditions, the natural processes we know would surely have at least enough contingency to prevent convergence on an interbreeding species so long into the tree of life - the process is simply not that precise: our “accidental” chromosome fusion alone would render fertile (if any) offspring impossible.

A little thought shows that, were God to wish evolution to produce that situation in the two worlds using natural processes and initial conditions alone, “with no necessity for supernatural intervention” (Collins, Language of God) the process is still not that precise, and the means would be insufficient. Unless any of you guys know different?

But to produce two identical (interbreeding) species is actually no more difficult than producing a single one of them to match a teleological template - that it, it is no more possible for God to “plan” or “intend” mankind, as the species we are, using entirely “the laws of nature” than it would be for him to produce our identical aliens as well as us. And if God did not intend to produce us as the species we actually are, but only something vaguely like us, then it is misleading to say “God intended mankind.”

So Vincent is right - the SF scenario favours special creation - or at least highly directed evolution. But if so, then the same must be equally true for the contention that “God used evolution to produce mankind.” The natural process in both cases is insufficiently precise for the teleological purpose - there must have been divine action of some kind, whether miraculous, concurrent or occasionalist is irrelevant, during the process.

Vincent also agrees with me (in another discussion) on the impossibility of Molinism covering the problem: conceivably God might choose to create the one universe in which “chance and necessity” produce mankind - just as he might choose to create the one universe where it produces two identical species in different galaxies. But all that would tell you is that he used a rather cack-handed way of directing every mutation in the history of evolution to his desired end - which, as I said in my post on Molinism, is a designed universe by any other name.

For God to visualise a range of possibilities and to realize only the one that matches his will is exactly what I have done with this post - I have created it as it is, by design.

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So, anyone else interested should try and give this a shot. Invite a theologian if ytou know one to contribute an answer this week.

In a week or two I’ll give what I’m thinking.

I see no problem with God engaging in “highly directed evolution”. I think that’s pretty much the whole point.

Hi! Our host invited me to take a stab at this one, so here we go.

Before I had a chance to read all the replies, I had a few ideas.

  1. Homo sapiens is some sort of attractor in biochemical phase space. This is essentially the convergent evolution hypothesis that has been previously explored and rejected, with an extra wave of the hands towards a justification.
  2. A species which has transcended biology travels through space as silicon-mediated minds, then synthesizes biological bodies using native species as templates in order to interact in a way that is comfortable for the locals. I like the incarnational aspect of this one. It turns out to be basically a variation on ideas already proposed by jongarvey and Argon.
  3. The Bekenstein bound says that the maximal amount of information needed to describe a physical system is proportional to the radius of a sphere bounding that system. For finite systems, that puts a finite bound on the information needed to describe them. Some have postulated this implies that if you go far enough out into space, you’ll find an identical Earth because there are only finitely many possible contents for Earth-sized spheres. So maybe these folks have traveled far enough to be from our doppelgänger planet.

That last one does not appear to have been already proposed, at least in that form, so that’s my guess for now.

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Thanks for joining us @AndyWalsh. Looking forward to discussing your book with everyone July 1, on science, fiction, and theology.

I’m not sure about that. The Bekenstein bound is:

S \leq \frac{2 \pi k R E}{\hbar c}

Where S is the entropy (i.e. information) and E is the mass-energy, and the rest are constants. But mass energy increases proportional to the volume of the sphere, so the bound is:

S \leq \frac{8 \pi^2 k R^4}{3\hbar c}

So, as the radius increases, the maximum entropy dramatically increases, faster than the volume of the sphere. Given that false predicate, the consequent is certainly suspect:

For that to be the case, we’d have to be seriously going far beyond our galaxy, and perhaps beyond the boundaries of the visible universe. Even then, it would still be stunning for them to be reproductively compatible, not just visually the same.

So, I’m not buying this one.

Yes, this one could be plausible.

What if these aliens can show this is not the case? What if they have a history and planet of their own? Perhaps they are just as surprised as are we that they are reproductively compatible. What then?

Yeah, not buying it. Could explain why they look like us, but not why we are reproductively compatible.

Oy vey, so many ‘if-then’ conditionals!

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It’s all in fun =).

I’d say it’s just further evidence that the universe just isn’t wired for “casual sex.” All in fun, of course! : )

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Is this a riddle with a specific answer, or are we trying to persuade you with a solution?

The bound is still finite, even if it grows quickly. As I understand it, that’s the key element. (For the record, the idea that the Bekenstein bound implies identical states if you travel far enough away is not mine; I believe I first encountered it as part of Tegmark’s multiverse hierarchy.)

Oh, for sure we’re talking about extraordinary distances. You did say they were from very very far away. As for reproductive compatibility, I think that’s implied by the fact that the exact same information describes their world as ours. And yes, it would be stunning, although possibly explained if there was a deliberate effort to search out matching worlds.

Switching to the attractor scenario:

Well, if it is truly Homo sapiens that is the attractor, then that implies compatibility. And while such an attractor is exceedingly small relative to the overall phase space, mathematically that’s not impossible. One can have an attractor of arbitrarily small measure, at least for some dynamical systems.

Switching to the synthesized body scenario:

I probably was too terse, but I was imagining that the aliens have a history and planet of their own, a history that includes developing the ability to move their minds between biological bodies and silicon storage. But I gather you mean that these particular reproductively compatible bodies were from the other planet, hence the surprise.

The surprise rules out a lot of other scenarios wherein the aliens themselves either arranged the compatibility or faked some of the tests. But I suppose it doesn’t rule out deliberate intervention by other parties. I’m now imagining some sort of galaxy-scale zoo in which we are unwitting exhibits. Maybe the zookeepers used some sort of CRISPR-like technology or the ever-popular nanobots to surreptitiously change the aliens to have genomes compatible with ours.

Or maybe we should conclude that we ourselves and our new alien friends are all characters in a sci-fi universe with biologically disinterested writers.

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Nope, just a game. The rules are not explicit, but come out in my answers.

Yes yes yes. I’m not saying you are uninformed. I’m just saying that this is a vanishingly low probability explanation for the story. Science fiction, sure. But in our galaxy? The chances of a reproductively compatible race on another planet is implausible, less likely than discovering that Octopi can breed viable offspring with horses. Or the discovery of a shark-whale hybrid in fisherman’s net.

Not reproductive compatibility. Think about it. White rhinos and black rhinos are not reproductively compatible. Asian elephants and African elephants are not reproductively compatible. In our understanding of biology, there may be attracters for a form (look at fish and whales), but it is much hard to imagine attracters that could give rise to reproductive compatibility.

That is a cool idea.

Now, that is a seriously creative and potentially plausible theory. I’m sure people would wonder this in the moment, and perhaps find out its true. That was beyond my own creativity Andy. I love it.

Well of course that is the case in Star Trek. They care a great deal about physics jargon, but are totally disinterested in biology.

My big brother used to decide the rules of the game as we were playing it, too. Explains my resulting personality disorder.:scream:


This describes a great deal of popular sci-fi, unfortunately. Have you read my BioLogos piece about physics and biology in Star Wars and sci-fi generally? (link)

I did appreciate that in The Martian, botany is equally as important for problem-solving as rocket science and engineering are. Another recent story I appreciated was (is? I’m not sure if it is cancelled or on hiatus) the comic series Surgeon X which highlights the challenges posed by increasing antimicrobial resistance. So maybe the future for biology in storytelling is brighter than the past.


Maybe the “Ancient Aliens” that the History Channel keeps going on about, took a sample of people back with them, and bred them for the past whatever thousand years, and now they have returned to breed with us, and…I dont know take over the internet?? or cable news? (wait! that explains, Fox!).

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Side note…would Homo sapiens 300 kya, be able to interbreed with Homo sapiens today?

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Why not. The Neanderthals did. Apparently.

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