Bruno Marchal writes:
I believe that the quantum theory does not allow cul-de-sac branches.
I also believe that the Godel-Lob theory of self-reference not only allow
cul-de-sac branches, but it imposes them everywhere: from all alive states
you can reach a dead end.
The Universal Dovetailer Argument shows that the physics (which has no dead
ends) should be given by the self-reference logics (with reachable dead end
I have been stuck in that contradiction a very long time ...
... until I realized the absolute necessity of distinguishing the first and
third person point of views. That necessity is implied itself by the
incompleteness phenomena, but that is technical (ask me on the
everything-list if interested).
The intuitive point here is that you cannot have a first person point of
view on your own death: 1-death is not an event, and should be kept out of
the domain of verification of probabilistic statements. Another intuition:
the finite histories are of measure null among the collection of all
histories (the continuum).
Can we clarify what is meant by "dead end branch" here? I assume that we are
only talking about branching from the first person perspective. It is
obvious that dead end branches exist from the third person perspective,
because we have all known people who have died while the rest of the
universe apparently continues. But the person who has thus "died" does not
include that death and subsequent branchings in *his* tree, any more than he
includes those branches in which an asteroid hit the Earth millions of years
ago and modern humans never evolved. His tree by definition includes only
those branches in which he survives, and in the multiverse, those branches
go on forever, even if sometimes it takes an apparent miracle to achieve
this. In Bruno's words, "you cannot have a first person point of view on
your own death".
Alas, when I put the above argument to someone hearing about QTI/QS for the
first time, they usually will have none of it. I explain that the brave
physicist who will be killed, or not, on the basis of some random quantum
event will experience only those multiverse branches where he is not killed,
and therefore from his perspective will always survive. The usual response
is: Yeah, but what if he ends up in the branch where he gets killed? I then
get bogged down in a long discussion about the philosophy of personal
identity, which isn't nearly as interesting as physicists volunteering to
get killed. Does anyone have a more elegant way of driving home the point?
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