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by justinpombrio 3239 days 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_uncertaint...
1 comments
jamesrcole 3239 days 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.

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justinpombrio 3239 days 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?

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jamesrcole 3239 days ago
The many worlds case I was responding to is different to the coin case you are taking about. In the MW case we know enough to see that the situation is not at all random. In your example you're postulating a coin that may well actually be random.
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matt_kantor 3238 days ago
I don't understand what you mean here. I think "the many worlds case I was responding to" in your comment is justinpombrio's "which way you will see a photon go in a half-silvered mirror", but that's functionally identical to the "indexical coin flip" referred to by the LessWrong article, where the coin flip causes a bifurcation, landing heads in universe A and tails in universe B. From within the multiverse it is impossible to know ahead of time which universe you will observe, same as the photon example. It's "random" in the sense of being absolutely unpredictable (otherwise MWI would not be experimentally equivalent to alternative interpretations of quantum physics).

So, does indexical randomness fit your definition of "fundamental" randomness? And what did you mean when you said "a coin that may well actually be random" if it wasn't the indexical kind of coin?

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jamesrcole 3238 days ago
> does indexical randomness fit your definition of "fundamental" randomness?

No, it does not. MW is determinsitic. The fact that you don't know which universe you will observe is a limit on your knowledge. It does not make the things actually random.

There are other interpretations of QM where there is literal randomness, independent of an observers knowledge.

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justinpombrio 3238 days ago
By "a prefect coin", I was referring to a half silvered mirror.
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