# Re: aiming to complete Everett's derivation of the Born Rule

```On Wednesday, April 13, 2022 at 8:55:48 PM UTC+3 meeke...@gmail.com (Brent)
wrote:```
```
Decoherence has gone part way in solving the when/where/what basis
> questions, but only part way.
>

concern about decoherence but I see the glass as half-full; that is, with a
little more subtlety I hope that the matter can be formulated in clear
terms.

Surely collapse is easier to handle as a general concept (except, on the
other hand, that it requires new dynamics). I forgot to mention that *my
argument for deriving the Born Rule works with collapse, too* -- so it is
an alternative to Gleason's theorem.

Here I define colapse as an irreversible process, violating unitarity of
course, and I keep it separate from randomisation. The latter means that
each outcome is somehow randomised -- an assumption we can do without.

*Collapse can also be described in a many-world formulation!* It differs
from the no-collapse MWI only in being irreversible. My argument in outline
is
1. assessment that MWI-with-collapse is workable;
2. therefore, outcomes of small enough measure can be neglected in practice;
3. now Everett's argument can proceed, concluding that the Born Rule is a
practically safe assumption (to put it briefly).

So I have replaced two assumptions of Gleason's theorem, randomisation and
non-contextuality, by the assessment of workability only.

If you don't feel comfortable yet with formulating collapse in a many-world
setting, let us also assume randomisation (God plays dice), for the sake of
the argument, in a single-world formulation. That is, we ASSUME the
existence of probability; then the previous argument just guarantees that
this probability follows the Born Rule.

Of course I favour the first version of the argument, using the many-world
formulation of collapse, to avoid the "God plays dice" nightmare.

Thanks for the comments so far, because they stirred my thinking and
motivated fresh ideas, some of which I hope will prove helpful and worth
discussing, if and when they mature.

George K.

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