RE: Interested in thoughts on this excerpt from Martin Rees

From: W. C. <>
Date: Fri, 04 Aug 2006 21:18:28 +0800

>From: Bruno Marchal
>Are you sure that this is possible, even just in principle? Actually, just
>to show me that it could be possible in principle you have to give me your
>fundamental assumptions. Actually it looks like you are assuming the
>a) there is a physical universe (well, with comp this is already

I remember other people mentioned before. *Normal* people can't accept that
there is no physical universe.
Even Buddhists won't say that.

>b) accepting "a)" you assume that that universe has an origin (this would
>be impossible even in principle in case there is no origin)

Just like everything, it's more reasonable that there was an origin than no
origin, even for the universe.

>c) Accepting "a)" and "b)" you assume "physical laws" making time travel
>possible (which is of course controversial; this could be in principle
>possible with very special assumption, which could also be false in
>principle with other assumption).

Time travel is as possible as teleportation of human beings.

>If you do theoretical reasonings you have to make clear the assumptions
>which are making things "possible in principle". Up to here, I can follow
>you (I can imagine such fundamental assumptions).

Of course, there are many details and assumptions to say PUA is possible.
My point is that PUA is possible just like teleportation of human beings.
I think they have similar possibility.

>Your "2" and "3" are unfortunately definitely impossible with comp without
>deciding your PU (your Perfect Universe) being trivial. This is not obvious
>(but follows from diagonalization similar to those I have already
>illustrated). Let me just say that it can be shown that if you want your PU
>enough rich for Universal machine to appear, then you cannot, even in
>principle, filter those "bad" machines will easily makes your PU unperfect.

Just like I can make a PC program running perfectly. I don't see why *this*
universe can't be perfect.

>So the PUA *is* incompatible with comp. The most basic contradiction is
>given by the consequence of the UDA: there is no physical universe: only
>computations/dreams some of which "coheres" so as to provides local first
>person plural notion supervening on them. But even in the case those
>coherence would define "for all practical purposes" a "physical universe",
>and even if it has some sort of physical origin and you can teleport
>yourself to its origin, the laws of computer science will eventually
>prevent you of reprogramming "the universe" to satisfy your goal of making
>it perfect.

Which laws of computer science? My computer science says I can make a
perfect program.

>From: Stathis Papaioannou
>Yes, but it's still possible to imagine what would happen *if* something
>were done that at the moment seems impossible. If sodium chloride were
>produced by a machine which causes the transmutation of hydrogen into other
>elements, would it still taste salty? I would say that the answer is "of
>course", whether or not such a machine could ever be built. I don't even
>see how it is *logically* possible that pure NaCl could taste different
>depending on where it came from.

I still can't compare teleportation of human beings with NaCl. Too far away!



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Received on Fri Aug 04 2006 - 09:20:33 PDT

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