# Re: How does this probability thing work in MWI?

```I think there is an additional complication if you factor in the possibility of
duplicate universes, i.e., more than one instance of exactly the same universe,
with its unique history, observers, etc. This can provide a potential path for
weighting the probabilities, but only if you link the 'normality' or
'simplicity' of a possibility to the number of instances that are realized.```
```
Why should it be the case that each bitstring representation gets one universe?
To me, the most natural scenario is that each universe has an infinite number of
instances (exact copies or duplicates of same bitstring representation), so the
probability distribution in this case is undefined and you cannot define any
probabilities.

Since we do not feel this to be the case (if we're discussing likelihood of,
e.g., white rabbit universes), we possibly have a very unnatural situation where
some contingent universal non-uniform mathematical distribution f is governing
the number of instances of each universe, across the entire universe ensemble.
One benefit of this case is the probability distribution f may even be used to
rule out the existence of certain very contrived, complex universes (f->0). The
question then becomes, what is this distribution f?

Fred

Fritz Griffith wrote:

> I have read the Everett FAQ
> (http://soong.club.cc.cmu.edu/~pooh/lore/manyworlds.html), and I think it's
> one of the most comprehensive descriptions of MWI I have found on the
> internet.  I have one question though - in question 24: "Does many-worlds
> allow free-will?", it says, "If both sides of a choice are selected in
> different worlds why bother to spend time weighing the evidence before
> selecting? The answer is that whilst all decisions are realised, some are
> realised more often than others - or to put to more precisely each branch of
> a decision has its own weighting or measure which enforces the usual laws of
> quantum statistics.".  My question is, where does this weighting come from?
> Do some branches occur more often than others?  Or is there just some sort
> of assumed probability as to which world will be yours?
>
> Fritz Griffith
>
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