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Such a good comment. But I have a question for you. You said this is 'one of the major interpretations' of QM. But if the hypothetically greater future data is
by blueprint 4y ago
Such a good comment. But I have a question for you. You said this is 'one of the major interpretations' of QM. But if the hypothetically greater future data is not observable by anything outside of the universal wavefunction, then is it not the case that the entire system is evolving without external observation, i.e., the system itself does not have to be able to verify that it "knows" what outcome will occur for it to be able to generate new data by a causal mechanism. So it sounds like randomness is not proven by what you said is definition, alone. Is this what you meant by it being "one of the" interpretations of QM?
- mjburgess 4y agoWell I define random to mean whenever P(X|Y) is neither always 1 nor 0, or to put that in causal modal terms: given an exhaustive description of all possible causes of Y, say X, then if X causes Y, *NECESSARILY* Y given X causation is a form of necessity, necessarily Y occurs or it doesnt In this case P(Future|Past) and P(Past|Future) are somewhere between 0 and 1. This isnt consistent with causation. ie., All possible information about all possible causes of Y (the future), say X (the past) are insufficient to gaurentee any given Y (any particular future). The "interpretation" element of QM is to say that we are really in this case, ie., that we have X = all possible information. There are several ways of denying that P(Y|X) in the case of QM should be read this way. You can say X is incomplete, either by saying there is non-local information we don't have, or global information we don't have. Of the "global" kind, which of many worlds we are in is a kind of global ignorance. So that if we had, P(Y|X, which-world) then we'd observe P(Y|X, whichworld) = either 1 or 0 --- as with classical mechanics P(CatDead|PoisonBox, worldA) = 1 P(CatDead|PoisonBox, worldB) = 0 etc. and, eg., P(F|G,M,m,r) = 1 if F=GMm/r^2
- blueprint 4y agowhat do you mean by the term information? My question is, rather, whether a system needs to be able to know it knows that information for it not to still be causal. Because it doesnt observe its whole wavefunction
- mjburgess 4y agoI dont understand your use of "knows", knowing isnt part of the problem. Imagine, for simplicty sake, a world is a series of four switches which we can describe by 0 (off),1 (on). Eg., world A at time 0 is 0000, at time 1, 0001, ... Now a change from 0000 to 0001 is causal if in every physically possible world 0001 follows 0000, ie., P(0001|0000) = 1 Now suppose that we enumerate every possible world, ie., all the worlds containing only this kind of switch, and only four of them. Now if 40% of the worlds had 0000->0001 and 60% had 0000->1000, then P(0001|0000) = 0.4 The question is how can it be that the fourth switch behaves randomly? Ie., without any necessary flip from 0 to 1. Nothing at all can cause that switch to flip, by definition, the world contains nothing else in it. What property does the switch have such that it turns on 40% of the time? NONE. Consider two resolutions to this problem: bite the bullet and say the switch is "miraculous in some sense" in that it "just turns on" sometimes; OR, say that this thought experiment is physically impossible and we're missing information. Eg., that there's a hidden switch: 10000->10001 always, and 00000->11000 always, we just can't see the first switch, so it looks random.
- blueprint 4y ago"Imagine, for simplicty sake, a world is a series of four switches which we can describe by 0 (off),1 (on)." If that's what the world is then there's no "we"
- kgwgk 4y ago> if the hypothetically greater future data is not observable by anything outside of the universal wavefunction If there is a universal wavefunction evolving deterministically what would it mean to talk about the future holding more data than the past? There would be a direct one-to-one correspondence between the future states and the past states.
- blueprint 4y agoNo, I don't think that's correct. I'm not a professional but.. despite unitarity and maybe CPT symmetry, I think that a given "past" (by which I think we mean the universal wavefunction at some t?) has no way of recording what its own state is. If measurements were to be done of subsets or the whole of the wavefunction, then it would, I imagine, contribute to the state of the wavefunction so as to evolve it. But keep in mind as well when we say "data" we're talking about state which can be measured, aren't we? Maybe some state can't be observed; and, the "universe" also definitely limits its own certainty anyway.
- kgwgk 4y ago> when we say "data" we're talking about state which can be measured, aren't we? I don't know! If the "data" is about the state of the universe (i.e. the wavefunction) the "data" doesn't really change because of unitarity. You may be talking about something else - but it's not clear what.