RE: Quantum accident survivor/ personal identity

From: Stathis Papaioannou <>
Date: Tue, 11 Nov 2003 22:28:13 +1100

On 10 November 2003 David Barrett-Lennard wrote:

"...It seems to me that the concept of identity is not fundamental to
physics. It's useful for classification purposes as long as one doesn't
stretch it too far and expose its lack of precision..."

David, I used to puzzle over the definition of this word also, but
enlightenment did not come until I realised that granting it the status of a
basic and precise concept was the cause of all the philosophical mischief.
The "problem of personal identity" mostly goes away if we admit that there
is no objective, yes-or-no answer to the question of whether two SAS's are
the same person, and instead speak only of greater or lesser degrees of
similarity. Of course, there are cases of common usage which most people
would not question - that I am the same person today as I was yesterday, for
example - but even here, I would argue that the identical/non-identical
cutoff is (a) quantitative rather than qualitative, and (b) in the final
analysis arbitrary. Certainly, the atoms comprising me-today are not all the
same as those comprising me-yesterday, and if we consider me-last-year, none
of the atoms may be the same. In fact, if we consider physical continuity
the important factor in survival, the person that lived in my house last
year is as thoroughly dead and gone as if he had been killed and cremated,
and the ashes scattered to the four winds! Add to this all the other
actually or logically possible adventures an individual could be subjected
to - brain or body transplant, memory loss and dementia, uploading to a
computer, melding or splitting of mind, destructive and non-destructive
teleportation, resurrection in the far future or in Heaven, multiple or
infinite versions in MWI - and it becomes clear that, if it has any meaning
at all, "personal identity" must be a very slippery and plastic concept
indeed. I feel much better for having got rid of mine!

Stathis Papaioannou
Melbourne, Australia
11 November 2003

-----Original Message-----
From: David Barrett-Lennard []
Sent: Monday, 10 November 2003 6:40 PM
Subject: RE: Quantum accident survivor

I'm trying to define "identity"...

Let's write x~y if SAS's x and y (possibly in different universes) have the
same identity. I propose that this relation must be reflexive, symmetric
and transitive. This neatly partitions all SAS's into equivalence classes,
and we have no ambiguity working out whether any two SAS's across the
multi-verse have the same identity.

Consider an SAS x that splits into x1, x2 (in child universes under MWI).
We assume x~x1 and x~x2. By symmetry and transitivity we deduce x1~x2. So
this definition of identity is maintained across independent child

This is at odds with the following concept of identity...

>I am, for all practical purposes, one
>and only one specific configuration of atoms in a specific
>universe. I could never say that ' I ' is ALL the copies, since I NEVER
>experience what the other copies experience

It seems necessary to distinguish between a definition of identity and the
set of memories within an SAS at a given moment.

Is it possible that over long periods of time, the environment can affect an
SAS to such an extent that SAS's in different universe that are suppose to
have the same identity actually have very little in common?

What happens if we "splice" two SAS's (including their memories)?

It seems to me that the concept of identity is not fundamental to physics.
It's useful for classification purposes as long as one doesn't stretch it
too far and expose its lack of precision.

This reminds me of the problem of defining the word "species". Although a
useful concept for zoologists it is not well defined. For example there are
cases where (animals in region) A can mate with B, B can mate with C, but A
can't mate with C.

- David

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Received on Tue Nov 11 2003 - 06:29:45 PST

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