Re: How does this probability thing work in MWI?

From: Fritz Griffith <>
Date: Tue, 23 Nov 1999 00:28:11 MST

>Subject: Re: How does this probability thing work in MWI?
>Date: Mon, 22 Nov 1999 17:24:34 -0800
>Fritz Griffith, <>, writes:
> >
> > ok, I understand that QM defines the probability of which universe we
> > end up in.
> > [...]
> > Unfortunately, for
> > every world that was expected to happen, there will be AT LEAST AS MANY
> > WORLDS THAT WERE UNEXPECTED BUT DID HAPPEN, observed as a whole by the
> > of all universes. So, no matter what kind of reasoning you apply to QM
> > probabilities, the unexpected will happen to all but a very small
> > of SAS's. How can we be so lucky as to be among that small minority?
>This is only a puzzle if you think that we need to be lucky to be among
>a small minority. But the only way that we'd have to be lucky to be
>among that minority would be if it were improbable.
>However earlier you wrote that you understood that QM defined
>probabilities about which universe we would end up in. And these are
>not equal probabilities. We are much more likely to find ourselves as
>certain SAS's than as others.
>Therefore we don't have to be "lucky" to find ourselves among a certain
>small minority of SAS's. In fact this is by far the most likely outcome.

All worlds are real, whether or not they will be ours. Therefore, you
cannot assign probabilities to how likely it is a world will exist; every
world has a 100% probability. You can say the same for anything within any
number of worlds. There is no maybe, it WILL exist. SAS's are simply
objects within worlds. You can say that all of them are real. When we
define probabilities for worlds, we are simply saying which SAS's we are
most likely to end up as. So you can imagine a split, which creates world A
and world B. World A is the expected world, where we observe the universe
to act as it should. World B is the unexpected world, where we observe the
universe to act strangely. Both worlds are real, both exist. So whenever
our world splits into a world we expect, there is another world, just as
real, which for all of time acted as expected, for which we had no reason to
expect anything different from. But all of a sudden, that world went
haywire, leaving us baffled.

The three important things to remember here are:
1. Both worlds are real.
2. The SAS's within each world are real.
3. Both worlds acted exactly the same for all of time until that one
moment. Therefore, the SAS's within the unexpected world had observed the
same physical laws, with the same degree of stability, as the expected
world, right up until that moment. They too expected to be in the likely
world; they had no reason to expect anything different. But, to their
incredible surprise, they didn't end up in that world.

Given these three conditions, I see no reason why our world is any more
likely to be one than the other.

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Received on Mon Nov 22 1999 - 23:36:35 PST

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