briefly wading back into the fray

From: Jack Mallah <>
Date: Sat, 7 Feb 2009 10:05:14 -0800 (PST)

--- On Fri, 2/6/09, russell standish <> wrote:
> So sorry Jacques - you need to do better. I'm sure you can!

Russell, I expected there might be some discussion of my latest eprint on this list. That's why I'm here now - to see if there are any clarifications I should make in it. I intend to make it better - and perhaps I'll have you guys to thank!

Don't expect me to stick around. I see the list hasn't changed much - Bruno is still pushing his crackpot UDA. I could tell you what's wrong with his MGA, but I'm here to deal with the QS paper first.


> I mentioned the interesting comment on how we should expect to find ourselves a Boltzmann brain shortly after the big bang, but there was no follow up to this. I have no idea how he came up with that notion.

I wrote
"If one denies that the amount of “a person’s” consciousness can change as a function of time after it begins to exist and as long as there is at least some of it left, then in the quantum MWI, since there deterministically is some slight amplitude that any given particle configuration (such as that of a person’s brain) exists even shortly after the Big Bang, there would again be no reason to expect that a typical person would be the result of normal evolutionary processes – you would have been ‘born’ way back then."

Seems pretty straightforward to me:
1. Initially, before evolution occurred, a typical Boltzmann brain (BB) had about the same measure as a brain which was like what we consider a normal person's (an atypical BB).
2. The typical BB's all together vastly outnumbered the atypical ones, so they had much more total measure.
3. We are assuming here that a person's measure can't change as a function of time.
4. Therefore the initial measure advantage of the typical BB's would hold for all time.

Perhaps I should spell out the steps like that in the paper, but I thought it was self-explanatory already.

> His discussion of the Born rule is incorrect. The probability given by
> the Born rule is not the square of the state vector

Russell, Jesse Mazer has already pointed out that it is your discussion of my discussion of it that is incorrect. It's true that people use various terminology (maybe I should have said squared norm instead of squared amplitude) and I was trying to keep technicalities to a minimum. See

> After observation, the state vector describing the new will be
> proportional to the eigenvector corresponding the measured eigenvalue,
> but nothing in QM says anything about its amplitude. Indeed it is
> conventional to normalise the resulting state vector

That only makes sense in a collapse interpretation (or for practical convenience). My guess is you looked up the Born Rule in some textbook and naturally it did not have an MWI perspective.

> What I think he is trying to discuss, somewhat clumsily, in the
> section on measure, is the ASSA notion of a unique well-defined
> measure for all observer moments.

The charge of 'clumsiness' is too vague for me to do anything about, so perhaps you could be more specific. As for self-sampling, I didn't want to use that term because it can create the confusion that something random is really going on. Instead I covered the Bayesian issues in my sections on the Reflection Argument and Theory Confirmation.

> He goes on to mention rather briefly in passing his doomsday style
> argument against QI, but not in detail.

I think the argument is presented in full. What part is missing?

> Which is just as well, as that argument predicts that we should be neonatal infants!

I remembered that odd confusion of yours has been discussed on the list before, so I Googled it. I found a 2003 post by Saibal Mitra that covers it. I think I must have posted about it too, in the old days.

> "... once you take into account the possibility of dying then you will see a decrease. But ignoring that, the measure should be conserved. The measure for being in a particular state at age 30 should be much smaller than the measure for being in a particular state at age 4, but after summation over all possible states you can be in, you should find that the total measure is conserved."

Suppose you differentiate into N states, then on average each has 1/N of your original measure. I guess that's why you think the measure decreases. But the sum of the measures is N/N of the original.

This is trivially obvious so I saw no reason to mention it explicitly in the paper. If there are people other than Russell with the same confusion, then I may add it in.

> He also mentions Tegmark's amoeba croaks argument, which is not
> actually an argument against QI, but rather a discussion of
> what QI might actually mean.

I quoted Tegmark verbatim. He says "my brain cells will gradually give out (indeed, that's already started happening...) so that I keep feeling self-aware, but less and less so, the final "death" being quite anti-climactic, sort of like when an amoeba croaks."

'Final death' - those are his words, not mine. You may not agree with him, but I don't see how you can deny that he is arguing against QI.

The discussion on amnesia and personal identity is very relevant, as perhaps people will realize that personal idenity is not well defined and that the whole QS/QI thing doesn't make any sense.


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Received on Sat Feb 07 2009 - 13:05:26 PST

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