5 ms·

> if you make some reasonable assumptions Not everyone agrees on what is "reasonable". I have no problem giving up locality, but "true" randomness (i.e., info

> if you make some reasonable assumptions Not everyone agrees on what is "reasonable". I have no problem giving up locality, but "true" randomness (i.e., information generated without an algorithm) seems like a philosophical cop out. Note that something can also be globally deterministic but indeterministic from the perspective of a subsystem. In this sense, the universe would appear random as far as we're concerned, but not random to whoever is simulating the universe (this is often called superdeterminism, but I think that's a silly word—the universe is either deterministic or it isn't).

justinpombrio 9y ago
The probability of an event depends on your knowledge. Whether something is deterministic is a question of probability. Hence whether something is deterministic can depend on your knowledge. If the universe is deterministic to its simulator but random to us, I would call it random. Besides this difference in terminology, I think we agree.
- jamesrcole 9y ago
  Your knowledge of something can't change or determine whether it is deterministic or not.
  - justinpombrio 9y ago
    Do you agree that the probability of an event depends on your knowledge? For example, what is the probability that the bottom card of a shuffled deck is an ace? Peek at the top card, it's an ace of spades, now what is the probability? Would you agree that something is determined iff its probability is zero or one? I'm guessing the disagreement is here - what definition would you use?
    - cool_shit 9y ago
      You are right, according to quantum mechanics. If you have a pair of electrons in a product state and measure the spin of one of them, you instantly know what the "other particle's" spin is going to be (if you knew what the initial state was). When you "peek at a card", you "make a measurement" and alter the system. For anything that exists outside of a light-cone around the first electron, a measurement of the second electron will be truly random from the measurer's perspective.
    - jamesrcole 9y ago
      There's two kinds of probability in question. One concerns a lack of knowledge, like in your cards example. In that case, the probability is an expression of your state of understanding of the deck, and is not a property of the deck itself. The physical details of the deck and the situation it is part of could be entirely deterministic and we could still talk about this kind of probability. In this case your knowledge is independent of whether it is probabalistic or not. The other is whether the universe contains fundamental randomness, such that you could say it is literally "probabalistic". And in this case whether that is true or not is independent of our knowledge of the probabilities.
      - justinpombrio 9y ago
        There's a third kind -- indexical randomness, or not knowing who you will be -- that appears in many-worlds. Many worlds is in some sense completely deterministic. Yet with indexical uncertainty you still cannot possibly ever know which way you will see a photon go in a half-silvered mirror. Is that fundamental randomness or not? http://lesswrong.com/lw/jlb/logical_and_indexical_uncertainty/ http://lesswrong.com/lw/jlb/logical_and_indexical_uncertaint...
        jamesrcole 9y ago
        > Is that fundamental randomness or not? I would say, not. There's no actual randomness from an objective point of view, it's just a lacking in your understanding of things. I think that map/territory confusions are the source of so many problems and should be rigourously avoided. I think it would be a map/territory confusion to consider it a kind of actual randomness.
        justinpombrio 9y ago
        > I think it would be a map/territory confusion to consider it a kind of actual randomness. Even though it makes perfect sense to apply probability theory to it? We found a perfect coin, one that we know that you can't predict in advance even in principle, and you want to avoid considering it a kind of randomness? Why does the mechanism by which the universe implements randomness -- in this case via determinism -- matter?

justinpombrio 9y ago

The probability of an event depends on your knowledge. Whether something is deterministic is a question of probability. Hence whether something is deterministic can depend on your knowledge. If the universe is deterministic to its simulator but random to us, I would call it random. Besides this difference in terminology, I think we agree.

jamesrcole 9y ago
Your knowledge of something can't change or determine whether it is deterministic or not.
- justinpombrio 9y ago
  Do you agree that the probability of an event depends on your knowledge? For example, what is the probability that the bottom card of a shuffled deck is an ace? Peek at the top card, it's an ace of spades, now what is the probability? Would you agree that something is determined iff its probability is zero or one? I'm guessing the disagreement is here - what definition would you use?
  - cool_shit 9y ago
    You are right, according to quantum mechanics. If you have a pair of electrons in a product state and measure the spin of one of them, you instantly know what the "other particle's" spin is going to be (if you knew what the initial state was). When you "peek at a card", you "make a measurement" and alter the system. For anything that exists outside of a light-cone around the first electron, a measurement of the second electron will be truly random from the measurer's perspective.
  - jamesrcole 9y ago
    There's two kinds of probability in question. One concerns a lack of knowledge, like in your cards example. In that case, the probability is an expression of your state of understanding of the deck, and is not a property of the deck itself. The physical details of the deck and the situation it is part of could be entirely deterministic and we could still talk about this kind of probability. In this case your knowledge is independent of whether it is probabalistic or not. The other is whether the universe contains fundamental randomness, such that you could say it is literally "probabalistic". And in this case whether that is true or not is independent of our knowledge of the probabilities.
    - justinpombrio 9y ago
      There's a third kind -- indexical randomness, or not knowing who you will be -- that appears in many-worlds. Many worlds is in some sense completely deterministic. Yet with indexical uncertainty you still cannot possibly ever know which way you will see a photon go in a half-silvered mirror. Is that fundamental randomness or not? http://lesswrong.com/lw/jlb/logical_and_indexical_uncertainty/ http://lesswrong.com/lw/jlb/logical_and_indexical_uncertaint...
      - jamesrcole 9y ago
        > Is that fundamental randomness or not? I would say, not. There's no actual randomness from an objective point of view, it's just a lacking in your understanding of things. I think that map/territory confusions are the source of so many problems and should be rigourously avoided. I think it would be a map/territory confusion to consider it a kind of actual randomness.
        justinpombrio 9y ago
        > I think it would be a map/territory confusion to consider it a kind of actual randomness. Even though it makes perfect sense to apply probability theory to it? We found a perfect coin, one that we know that you can't predict in advance even in principle, and you want to avoid considering it a kind of randomness? Why does the mechanism by which the universe implements randomness -- in this case via determinism -- matter?