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Comment by huytersd | Hacker News Reader

Is it an absolutely perfect simulation? Like would we know the exact future of those hundreds of atoms in perpetuity?

No, for multiple reasons. To your first question, there's still simplifying assumptions. These things usually treat the nucleus as fixed and static, for example, and often other approximating assumptions are used. Outside of the interior of a star, radioactive elements, or when relativistic energies are involved, these are good approximations though.

More fundamentally, quantum systems are inherently random. You literally can't know the exact future of hundreds of atoms in perpetuity--that's not how quantum physics works.

But you can get an idea of minimum energy states, the energy barriers holding those states in place, and therefore what the stable outcomes might be.

The other reason the answer to this is "no" is that we don't even really understand how an atom even works its entirety yet. We don't know fundamentally know what makes the potential energy of an atomic nuclear be structured in the way it is.

EDIT: I thought I'd double check that since it's been a while since I studied physics formally; apparently it is possible to model light nuclei[1] (up to four nucleons) from the ground up now!

[1] https://en.m.wikipedia.org/wiki/Ab_initio_methods_(nuclear_p...

[1]

You are confusing exact solutions with the ability to solve. We know how atoms work and can solve for any property we might want to measure. Ab initio systems aren't very practical for large systems because of computational costs, but they would work if given infinite compute (or a quantum computer). We just solve them numerically instead of closed-form.

It's like polynomials: there's a quadratic formula, and a cubic and even quartic formula for exact solutions (although the quartic is ridiculous and no one would ever use it). Higher order polynomials have NO exact, closed-form solutions using standard arithmetic operations. But we can still solve any polynomial no matter the degree using numerical methods. To say that we don't even know how how degree 5 polynomials work would be flat out wrong.

I’d recommend reading up on Heisenberg’s Uncertainty Principle to understand why what you suggest is, to our knowledge, physically impossible.

Yeah, I’m aware. I was assuming some sort of aligned starting state with atoms whose configurations were perfectly known but I guess that’s not really possible.

If you're thinking "yeah but what if we really knew the starting configuration" then you're not really understanding the uncertainty principle. There is no hidden state that we just don't have access to.

Yes, that’s the realization I came to as well.

You’re one of today’s lucky 10,000. Even Einstein had trouble believing that quantum must be random, but it is. The EPR paradox proves that.

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