Re: relevance of the real measure

From: Wei Dai <weidai.domain.name.hidden>
Date: Fri, 21 Dec 2001 17:13:42 -0800

Here's my proposed alternative to our current "standard model", which says
all possible universes exist and some objectively true measure exists on
the set of universes.

Instead, let's just say that all possible universes exist, period. There
is no objective measure. Instead, measure enters into the utility function
as a way of specifying how much one cares about each universe. The measure
is therefore an arbitrary and subjective choice.

The goal of the theory of everything then, is to tell us if how we should
behave given the utility function (and measure) that we do adopt. For
example one thing it might tell us is that if we adopted the Speed prior
for our utility function, then we should act as if we expect large
scale quantum computation to be impossible.

On Fri, Dec 21, 2001 at 03:21:49PM -0800, hal.domain.name.hidden wrote:
> There may be subjective reasons not to re-run favorable experiences,
> such as that it makes you vulnerable to unexpected threats.

But still, the only reason to do anything would be to increase the number
of times you can re-run favorable experiences.

> In any case,
> we can't rule out a priori that making yourself happy in this way is
> the best course of action.

I'm not saying that it can't be the best course of action for *anyone*,
I'm saying that it can't be the best course of action for *everyone*.

> I'm not sure why it is inadequate to say that you care because you live
> in the universe and its reality affects you. You can't just choose
> whatever reality you like.

Suppose I live in the FAST multiverse. Why should its reality affect me in
this particular way, so that I care about each universe in proportion to
its Speed prior?

> That is true; in the multiverse, people in high-measure worlds will come
> to expect and predict high-measure (high-likelihood) events, while those
> in low-measure worlds may come to predict low-measure events. So there is
> some symmetry here. However again I would break the symmetry by saying
> that each of us is more likely to encounter the high-measure worlds and
> people, because that is what measure means. We are effectively unable
> to observe the low-measure worlds. So the universe that we are able to
> perceive and predict will have the same properties as if there were only
> a single world.

Just because you won't observe something, doesn't mean you shouldn't care
about it. For example some people put significant effort into writing
wills and setting up foundations which they will never see the effects of.

> Imagine that we create computer simulations of two worlds with conscious
> inhabitants. We can't just add a measure parameter and set it arbitarily
> to say that the first world has measure .9 and the second .1. When we
> tweak our measure parameter it will not affect the subjective lives
> of the people in the simulation. Measure does not work that way.
> Somehow it does relate to subjective probabilities.
>
> You can get this in one way by relating it to duplicate instantiations,
> such that worlds of measure .9 have 9 times as many duplicates as worlds
> of measure .1. I don't personally find this to be helpful because
> it requires assumptions which to my mind are equally as arbitrary as
> directly requiring measure to have the required properties of subjective
> probability. But in the simple case where we are running simulations
> on a computer that would probably work. Run one 9 times as often and
> you could plausibly suppose that the inhabitants will be more likely to
> experience that world.

When you run it 9 times as often, it still doesn't change the subjective
lives of the people in the simulations. They won't notice any difference.
And it's still not obvious why the people in the simulations should care
about one world 9 times more just because it has been run 9 times as
often.

> However you get to it, you have to think of measure as more than a label
> attached to a universe, devoid of other meaning. That is the only way
> to get predictions from the multiverse model.

The thing is, we need a decision theory, otherwise it's not clear what
predictions mean. To be cute about it, I could say that without a decision
theory, a prediction is no more than a number (probability) attached to a
statement, devoid of other meaning. Once you think in terms of decision
theory, it seems that measure only has meaning if you give it meaning by
making it part of your utility function.
Received on Fri Dec 21 2001 - 17:16:37 PST