5 ms·

Given the infinite number of ways the universe could have been, it seems kind of a mathematical truth that whatever it ended up being was incredibly improbable

Given the infinite number of ways the universe could have been, it seems kind of a mathematical truth that whatever it ended up being was incredibly improbable to begin with. I would tend to say that unless it is logically necessary for the universe to be what it is, the question of why it is what it is necessarily lacks an answer. We should expect the universe to be improbable.

guerrilla 5y ago
> I would tend to say that unless it is logically necessary for the universe to be what it is Well that's what he's asking and what I was asking with the 3D question: is it logically necessary? Maybe it is. It seems like it could be in the case of 3D.
- breuleux 5y ago
  That seems extremely unlikely to me. There are 1D and 2D cellular automata that are Turing complete and could arguably support life if they were scaled wide enough. Any virtual reality you can simulate on a computer could have been a physical reality. There isn't any requirement for it to have a spatial topology, there isn't any requirement for it to support life or any kind of complexity. Reality could have been a sprawling Mandelbrot fractal. Why not?
platz 5y ago
This assumes a differnt universe could have been possible. What pool are you sampling from? What notion of probability are you relying on? scott is not asking what other universes were possible. he's asking to explain why QM must be true in the universe that we do observe.
- Koshkin 5y ago
  A trivial answer is that the question is moot, as this universe is the way it is precisely due to the laws of QM themselves. (Conceivably, in other universes, ones that we do not observe, the laws could be different.)
  - platz 5y ago
    You're begging the question by asserting the universe = QM. QM is just a description. He's asking the if there is an alternative to QM that also fits the data, that could make the universe the way it is; if there isn't an obvious answer that could update our understanding of QM.
- breuleux 5y ago
  I mean, if QM wasn't true we would observe something else, wouldn't we? I don't understand how this is a meaningful question.
  - platz 5y ago
    No, he's asking how to fit the data we do observe, and why QM is the obvious conclusion compared to other theories that fit the data that we do observe.
    - breuleux 5y ago
      What other theories fit the data that we do observe?
      - platz 5y ago
        That's the counterfactual Scott is asking us to consider. See this comment for elaboration on exactly what kind of relevance rhis counterfactual has for QM https://news.ycombinator.com/item?id=30117928 https://news.ycombinator.com/item?id=30117928
        breuleux 5y ago
        I'm not a fan of the teleological angle I'm seeing here. The universe doesn't serve a purpose, it's not doing a "job", any level of complexity is needless. Putting that misgiving aside, I think I get what you're saying (correct me if I'm wrong): the question is whether the "simpler" or at least more naive classical rules of physics could be the foundation for a world that looks and feels exactly like ours, e.g. one that forms a substance that has the precise properties of water, one that can support a stable form of DNA with which to assemble living beings, and so on. The answer to that depends on how far exactly you are willing to depart from perfect fidelity. To put it another way: what is exactly the set of invariants that you aim to preserve from QM to classical? Do you need them to be exactly the same? Probably not feasible. Do you want water to behave exactly the same? I would tend to say it couldn't. Do you want it to have stars? To be able to evolve humanoids? To be able to evolve life? These are all interesting questions on their own, but they may all have separate answers.

guerrilla 5y ago

> I would tend to say that unless it is logically necessary for the universe to be what it is Well that's what he's asking and what I was asking with the 3D question: is it logically necessary? Maybe it is. It seems like it could be in the case of 3D.

breuleux 5y ago
That seems extremely unlikely to me. There are 1D and 2D cellular automata that are Turing complete and could arguably support life if they were scaled wide enough. Any virtual reality you can simulate on a computer could have been a physical reality. There isn't any requirement for it to have a spatial topology, there isn't any requirement for it to support life or any kind of complexity. Reality could have been a sprawling Mandelbrot fractal. Why not?

platz 5y ago

This assumes a differnt universe could have been possible. What pool are you sampling from? What notion of probability are you relying on? scott is not asking what other universes were possible. he's asking to explain why QM must be true in the universe that we do observe.

Koshkin 5y ago
A trivial answer is that the question is moot, as this universe is the way it is precisely due to the laws of QM themselves. (Conceivably, in other universes, ones that we do not observe, the laws could be different.)
- platz 5y ago
  You're begging the question by asserting the universe = QM. QM is just a description. He's asking the if there is an alternative to QM that also fits the data, that could make the universe the way it is; if there isn't an obvious answer that could update our understanding of QM.
breuleux 5y ago
I mean, if QM wasn't true we would observe something else, wouldn't we? I don't understand how this is a meaningful question.
- platz 5y ago
  No, he's asking how to fit the data we do observe, and why QM is the obvious conclusion compared to other theories that fit the data that we do observe.
  - breuleux 5y ago
    What other theories fit the data that we do observe?
    - platz 5y ago
      That's the counterfactual Scott is asking us to consider. See this comment for elaboration on exactly what kind of relevance rhis counterfactual has for QM https://news.ycombinator.com/item?id=30117928 https://news.ycombinator.com/item?id=30117928
      - breuleux 5y ago
        I'm not a fan of the teleological angle I'm seeing here. The universe doesn't serve a purpose, it's not doing a "job", any level of complexity is needless. Putting that misgiving aside, I think I get what you're saying (correct me if I'm wrong): the question is whether the "simpler" or at least more naive classical rules of physics could be the foundation for a world that looks and feels exactly like ours, e.g. one that forms a substance that has the precise properties of water, one that can support a stable form of DNA with which to assemble living beings, and so on. The answer to that depends on how far exactly you are willing to depart from perfect fidelity. To put it another way: what is exactly the set of invariants that you aim to preserve from QM to classical? Do you need them to be exactly the same? Probably not feasible. Do you want water to behave exactly the same? I would tend to say it couldn't. Do you want it to have stars? To be able to evolve humanoids? To be able to evolve life? These are all interesting questions on their own, but they may all have separate answers.