Hi Saibal,
Your thesis is very interesting, as far as I understand it.
I am sure you are right about the fact that renormalisation
theory can put light ... on the question "what is a physical
system and what is a physical simulation of a physical
system?".

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I see more and more my own Z1* as a sort of renormalisation
on the computationalist indeterminacy (*Too* many worlds with
comp). The quantum would be the result of renormalising
classical comp indeterminacy!
Do you know the Hopf algebra of renormalisation? (cf
the Connes and Kreimer "Lessons from Quantum Field Theory"?
(hep-th/9904044).
My interest for Hopf algebra grew from the reading of the
the Kitaev "fault-tolerant quantum computation by
anyons" (quant-ph/9707021) (what crazy paper!), but your
remark + your thesis + Connes and Kreimer adds still deeper
motivations.
BTW you said (to the FOR list):
>In quantum field theory Feynman diagrams are used to perform perturbative
>computations. Now, here it is clear from the start that virtual particles
>and ghosts, as they appear in these diagrams, don't exist. Only the
>external lines represent real physical particles.
What makes you so sure? I guess it's my incompetence in Quantum
Field Theory, but this is not clear for me. I would appreciate
a short comment on the MWI view of QFT, perturbation and renormalisation.
>All this is very clear
>because the Feynman rules are derived from a well defined theory that is
>well understood.
Ah ?
Bruno