

Rebooting the cosmos? - jackfoxy
http://motls.blogspot.com/2011/06/rebooting-cosmos.html

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jerf
This debate always reminds me of an older debate, about how the universe must
have a maximum speed, and how the universe can not have a maximum speed, as
outlined in [1]. The resolution was ultimately that yes, both were actually
true, and the failure of understanding was somewhere else entirely: Galilean
transforms are the wrong way to add two velocities, you need Lorentz
transforms, and both of Zeno's arguments are thus satisfied.

Similarly, while you don't get it from this source as he has made his
decision, there are some reasons why everyone has gone to discrete models. But
I suspect the ultimate resolution will have both elements, which the essay
does mention at the end, and that contra what the author says, there won't be
an "ultimate" to either of them; I bet the universe can not be discrete _and_
it can not be continuous, and the truth is some weird combo of the two in
which ultimately the question is simply sidestepped, not resolved, much like
the resolution to Zeno's paradoxes.

[1]: <http://www.mathpages.com/rr/s3-07/3-07.htm>

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dto1138
Hey, I'm not a particle physicist, but I've read a bunch of books by people
who think the universe is a computer. (Three Scientists and Their Gods, A New
Kind Of Science, and The Recursive Universe (this last is out of print and
much better than Wolfram's newer but more turgid ANKOS.)

I don't think the universe is a computer either, but I don't think this guy
understands what that would mean anyway.

From the article: "I just find it obvious that pretty much by definition,
discrete objects are always less fundamental and less complete than the
continuous ones. A discrete description of some object or phenomenon is always
an approximation."

Now the whole thrust of the "computer-universe-ism" people's argument, if I
read them correctly, is that the universe is really a discrete structure, in
which case a discrete model of said structure would not be ANY kind of
approximation. I.e. to what are the integers (a discrete structure) a
(supposedly poor) approximation? What about the two-element set {0,1} or (say)
groups? (The group theory bit is a trick for the author.)

We'd better leave these questions to be answered by empirical data---or if we
need philosophers to chime in, better ones than this.

~~~
andrewflnr
I think his point regarding whether discrete or continuous descriptions are
more fundamental is that you can (always?) describe a discrete system
continuously, but you can't always reduce a continuous system to a discrete
description. Continuity is more general, and since we seem to see it a lot,
it's probably the way the universe actually works.

At least that's how I feel about it. But hey, I'm not a particle physicist
either.

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btilly
It should be noted the Motl is a prominent physicist who is very smart, very
sure of himself, very outspoken, and sometimes very wrong. See
<http://en.wikipedia.org/wiki/Lubo%C5%A1_Motl> for more.

That said he makes good points, and knows physics much, much better than most
of the people proposing digital theories.

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russell
The universe is continuous not discrete and those who believe otherwise are
insane. I'll take his word for it. It is certainly outside my comfort zone,
but interesting nonetheless.

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shin_lao
Or you could use Gödel's incompleteness theorems and say the universe cannot
be a computer (as we understand it) because computers (as we understand them)
are part of the universe and therefore cannot describe the universe.

Then the discussion could go on and you could reach a definition of "computer"
vague enough to be able to say "the universe is a computer".

~~~
Sniffnoy
...that is not what the incompleteness theorem says.

~~~
jackfoxy
Yes. I'm not a mathematician, but I believe Gödel's incompleteness theorems
only address arithmetic. I heard of a book that focuses on common misuses of
Gödel's theorems, but don't have a reference. Anyone know of such a book?

