That's why I like this group so much, very interesting stuff to read, even if
it isn't about Haskell. The problem is that I understand only 1% of it, even if
it is about Haskell ;-)
Regarding this "the universe is a turing machine": until a couple of years ago,
I also was someone that believed that (A) the universe (and life) could be
simulated by a computer, and that - given enough time and survival of the human
race (which is unlikely) - we might (B) create a universe and life ourselves
one day. I was raised as an atheist, but recently I'm trapped in my own
reasoning (a bit like Godel's theorem) causing me to deduct that IF you believe
in (B), THEN you can't exclude the possibility that (some) GOD might have
created the universe... But this has nothing to do with Haskell anymore, so
I'll shut up :)
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
Sent: Sunday, December 30, 2007 12:28 PM
To: haskell-cafe@haskell.org
Subject: [Haskell-cafe] Quanta. Was: Wikipedia on first-class object
Ketil Malde writes:
> I guess I should disclaim the rest of my post right away: I don't know
> much about quantum anything, beyond what I read in the newspapers.
I answer here, but there were other contributions, of Ryan Ingram, Miguel
Mitrofanov, and Andrew Bromage, which I acknowledge. People, we are
reopening (recursively) a Pandora box, and this discussion will lead
nowhere, as always, when people speculate whether the Universe is a Turing
machine...
I would like to point out that it started on a subject NOT related to
computing, but to simulation. This was, btw. one of the points Feynman
stressed upon in his talks on the relation between quanta and information
processing.
But Feynman was a physicist, and we have different sensibilities from a
typical computer scientist, for whom the Universe is a specific "model".
For us, things change, you speak about the "state transformers". A particle
moves, and some Turingard will say that this is just some data processing.
Some say that "thinking is computing", which for me is stupid as hell,
since nobody really knows what thinking is. Frankly, reducing the world to
computerese is as sensible, as works of La Mettrie (1701-1751) about the
human soul as *mechanism*.
Ketil, you say about my objection that we can simulate quanta:
> You could raise the same argument for (digital) computers compared to
> brains - although my brain might be able to, it's not practical for it
> to do the computations performed even by simple computer programs.
>
> But the difference is quantitative and practical, not qualitative and
> theoretical. (Arguably, I know. I invoke Occam.)
No, it is qualitative and theoretical. You can simulate *some models of
quantum systems*, not the quantum reality, since we have simply no idea
what is the quantum information, and how to cope with the non-separability
(EPR). This implies a non-modularity of the simulating programs. If you
manage to *really* split an entangled system, and send one half of it to
another galaxy, you will *really* face the EPR paradox, an experiment on
Earth conditions the issue of the measurement faraway. But physically, the
experiments there are independent. So, in a simulation, the measurement here
should do something horrible with the random number generator used to
generate the measurement instance faraway. You have a kind of particularly
nasty side-effect. (BTW. Amr Sabry really reasons in terms of these side-
effects, although he tries to be purely functional...) On the other hand,
a physicist will tell you, that in Nature there cannot be any "side-effects"
in quanta, the unitarity forbids them. In two words, a simulator of a
quantum system becomes fast as complex as the simulated system itself...
> If I understand correctly, a quantum computer might solve problems in
> NP [conditions discussed by others...]
> As far as I can tell, it doesn't imply the
> ability to compute anthing that wasn't computable before.
Bother...
Look, ALL, ABSOLUTELY ALL what all those "computationalists" (I call them
Turingards, which is a very impolite term, look into the French dict.
what is the meaning of "ringard"), *reduce* the behaviour to information
processing, but Nature does not process information, whatever you may say
about it. This is *our* interpretation of physical phenomena. The
"information" is a distilled concept. Of course, there is entropy, whose
relation to information is extremely profound. But Nature does not solve
equations, nor implements algorithms. Nature does not compare things for
equality; on the other hand it "has" some equalities built-in, such as the
*true* indistinguishability of quantum particles, which invalidates all
classical combinatorics of the state counting, and changes the entropy.
I still don't know whether anybody knows what is the relation between the
entropy of quantum systems and their "informational contents"...
Again, thin
