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Comment by tempsolution | Hacker News Reader

Good luck assuming that life needs a planet and an orbit. All you need is a way for particles to make explicit decisions and experience some sort of consciousness (but even that is debatable, since few life forms on earth seem to have that).

And I would even question that you need particles. Particles might just be what we can experience in 3 dimensions.

I always find it funny how humans are so eager to draw generalized conclusions based on their own meager 100 years of scientific existence. We should be more humble and realize that we know jack shit about anything.

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I had a similar reaction to you. People seem to have very limited imaginations when thinking about the types of things that could exist. Or maybe the title is incomplete. Maybe the paper is saying something more like, "Could life exist in a plane that otherwise has the same or very similar physics and chemistry as the universe?" In which case I could understand the skepticism about life's existence.

OP was referring to an orbit in the dynamical systems sense: https://en.wikipedia.org/wiki/Orbit_(dynamics) which is far more general. It simply refers to a dynamical system where the trajectory of a particle repeats. If you have a system of particles in 2D space, governed by central forces between the particles, you won't have any particles that behave periodically in general, regardless of what those forces actually are. (There's actually some caveats to that statement. I believe the theorem OP's quoting assumes that the system has rotational symmetry, but giving up that symmetry may or may not actually give you stable orbits). Having some underlying periodicity is pretty important for more complex structures to emerge, otherwise it's just random chaotic motion.

I mean, there are obviously a huge number of caveats associated with that, to the point that it's meaningless when we ate discussing "possible universes". There is no rule that a n^-2 force cannot exist in a 2d universe... which would obviously result in stable orbits.

I mean come on, we have forces in our universe which are not n^-2. All this proves is that gravity couldn't work in the same way in a 2d universe..... so?? Heck, what about discrete universes? What about nonlocal universes?

Stable orbits are not only about planets and stars. They are about the stability of a universe with any central forces. Take a wrong number of dimensions and your life form will collapse or explode (along with its environment).

That assumes your universe is essentially Euclidean, at least at a scale where these effects matter.

Not all spaces are Euclidean - or even approximately Euclidean via a mapping and/or at specific scales.

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