Wei writes:
> Suppose you want to crack a bank's encryption key, which is worth $4
> million to you, and there are two ways to do it. You can spend $2 million
> to build a quantum computer to crack the key, or you can spend $3 million
> to build a classical computer to do this. Now if you believe the Speed
> Prior is the correct measure, then you'll think that the quantum computer
> will very likely fail, and therefore you should go with the classical
> computer instead. But if you believe the Universal Prior is the correct
> measure, then you'll think that both computers will work and you'll go
> with the quantum computer because it's cheaper.
> However, there's another way to think about this situation that doesn't
> involve an objective measure. The fast-to-compute and the slow-to-compute
> universes both exist. (The fast-to-compute universes are the ones where
> quantum computers fail.) So when you adopt the Speed Prior you're really
> saying "I know the slow-to-compute universes exist (and my actions affect
> what happens in them), but I just don't care very much about those
> universe." 

I'm having a lot of trouble understanding this view.

Why should you care more or less about slow to compute universes?
What kinds of considerations would influence your decision to care about
such universes?

Isn't it an empirical question which prior obtains (speed vs universal)?
You want to maximize your gains, so you try to figure out from reason
and observation which prior is true.  For example you could build a small
quantum computer and see if worked.  If not that would suggest that the
speed prior is true, if it does work that suggests the universal prior
is true.

Suppose you observe that quantum computers don't work.  What does that
mean in your formulation?  Does it mean that you have decided to care
about a certain kind of universe?  Why should this fact change what you
care about?


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