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This is similar to the anthropic principle, where we can make certain claims by looking at the conclusion: our existence.

We can see that our universe is huge and therefore rare. A smaller universe would be a more likely occurrence than a large one such as ours. (We don't have to know the absolute rarity of universe creation to know the relative rarity of other universes in relation to our universe's size: smaller universes are created more often than larger universes.)

My question is about an implication of this anthropic argument: if our universe is so rare, and if smaller universes occur an absurdly larger number of times than universes such as ours do, then why didn't our sapience occur in a more common, smaller, universe? There would be way more chances for sapience to occur so, all else being equal, we'd expect to be in one of those more likely universes.

Yet here we are, in an absurdly unlikely (almost infinitely rare) universe. This either means this is the only universe, OR it means sapience is so rare that it requires such a rare universe to occur as a prerequisite.

Sapience cannot occur in a more common universe because even if the chance of sapience was above 0, the sapiences in common universes would vastly outnumber our sapience in a rare universe and thus our existence would most likely have to have occurred in one of those common universes. This would imply something else: that we're alone in this observable section of our infinitely-rare universe and will never meet sapient aliens!

Since sapience is so rare as to require an infinitely-rare universe, sapience cannot be said to occur more than once in any reasonable region of the universe because if it could have, then we would have most likely occurred in a more reasonable universe to begin with.

Since this still leaves room for this being the only universe, the chance of there being no sapient aliens within a reasonable distance from us is 50%, right?

  • What is universe ? Is it "all" ? If so, what does it mean to speak of a "smaller one" ? – Mauro ALLEGRANZA Jan 15 at 16:24
  • Maybe there is a Multiverse with an infinity of alternatives and thus an infinity of different ... what ? Humans-like, aliens, alternative forms of life ? – Mauro ALLEGRANZA Jan 15 at 16:27
  • What do you mean with "sapience" ? Wisdom ? Or do you simply means "hono sapiens" ? – Mauro ALLEGRANZA Jan 15 at 16:29
  • "the chance of there being no sapient aliens within a reasonable distance from us is 50%" Why ? Reasonable distance ? – Mauro ALLEGRANZA Jan 15 at 16:30
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    The problem with anthropic arguments is that they require bold assumptions about the probability distribution over the sample space of universes, which we have no way to justify. Why would "smaller" universe be more likely than a "large" one? On what basis are such assessments based at all? One needs a generation theory for the universes, without that anthropic reasoning is vacuous. Aside from that, the leap from sapience across universes to sapience across regions in one of them assumes some sort of uniformity of laws and matter distributions, which there is no reason at all to assume. – Conifold Jan 15 at 19:49
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Your argument rests on a number of unsupported assumptions, chiefly this one:

smaller universes are created more often than larger universes.

So perhaps it's better phrased as so:

If there are many universes, and the majority of them are smaller than this one, then does the anthropic principle indicate that the size of this universe is decisive in the development of intelligent life such as ourselves? And furthermore, is the decisive factor the fact that intelligence is so rare, that only a huge universe is big enough to offer enough opportunities for intelligence to evolve?

Frankly, that's such a large stack of assumptions, that it's hard to offer a meaningful response.

We can write a coherent story that proceeds through those assumptions to arrive at the observed data that we are intelligent, and that our universe "seems" large to us, but that doesn't mean that story is true. For example, perhaps there's an unknown reason that all universes must be at least this size or bigger. In that case, the size of the universe we find ourselves in would be entirely unrelated to the rarity of intelligence.

  • I said this could be the only universe. Keep in mind that a universe bigger than ours makes no sense since there's a fundamental size limit to an observable region of space regardless of the size of the universe. Cases of such observable size limit regions may be more likely than cases of smaller regions since any case larger equals the size limit while any case smaller doesn't. We'd calculate to the rarity limit since larger chances become less likely until they become virtually impossible and don't add any meaningful chance self-discovery. rurors. Max size regions are actually most likely. – Hierarchist Jan 16 at 17:21
  • @Hierarchist This is a sophisticated argument, and one that sounds plausible. But it doesn't really connect back to anything except conjecture. If we knew there to be multiple universes, and most to be smaller, (or that our own universe is in some other way "rare") that might give us something to work with, but we don't know either of those things. // On the other hand, the fact that we're apparently alone within our observable spacetime cone does imply that sentient life is too rare to appear twice within that region. But that's a much simpler and more direct inference. – Chris Sunami Jan 16 at 18:26
  • I'm not basing this monosapience argument off of the apparent (lack-of) evidence, but of looking at all possibilities and assuming we are in the most likely scenario. – Hierarchist Jan 17 at 0:48
  • How can we even know whether our Universe is huge? Maybe, as Universes go, ours is a tiny and insignificant one. – IMil Jan 17 at 1:32
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We can see that our universe is huge and therefore rare.

There is only one universe by definition, as already pointed by Aristotle over two millenia ago (though he called it the All), and most recently by Lisa Randall, the physicist at the puzzlingly fashionable term - the multiverse.

Hence by definition, we cannot quantify the rarity or the superfluity of the unverse. It stands outside that quantitative framework and so your implicative 'therefore' has no real standing. The proper philosophical attitude to the whole of the universe is not such a quantification, but thaumazein, or wonder.

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