
David Deutsch’s New Theory of Reality - ghosh
https://medium.com/the-physics-arxiv-blog/deeper-than-quantum-mechanics-david-deutschs-new-theory-of-reality-9b8281bc793a
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tjradcliffe
Pretty much gibberish. No operational definitions, lots of floating
abstractions, with some falsehoods thrown in (starting with the description of
Shannon as _obscure_!)

Deutsch is a very clever guy, but to say "no one but a fool would bet against
the notion that something _could_ become important" is vacuous as well as
pompous. I _could_ become Pope--you cant prove I won't--but that is hardly a
bet worth taking.

Laws that govern laws are interesting, and symmetries that require information
conservation would also be interesting, and in fact the paper in question
([http://arxiv.org/ftp/arxiv/papers/1405/1405.5563.pdf](http://arxiv.org/ftp/arxiv/papers/1405/1405.5563.pdf))
looks interesting. The write-up unfortunately is not.

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andybak
He describes Shannon as 'unsung' not 'obscure' and I think there's some
validity to that. I grew up reading about the incredible scientific
developments - especially on the theoretical side - that happened throughout
the 20th century and Shannon's name was often mentioned but it was always in
passing (and sometimes with a subtle hint that he didn't really grasp how
broadly applicable his ideas were). It wasn't until I read about his life and
work directly that I learnt that this picture was rather inaccurate.

~~~
maroonblazer
Is there a particular book/biography on Shannon you'd recommend? I've not
found anything that looked particularly definitive.

~~~
andybak
I can't for the life of me remember what it was I read now. I thought it
_might_ have been David Deutsch's 'Fabric of Reality' or some similar bit of
broad, sweeping, pop-science but I can't find my copy right now to check.
(However that's a great book if you want a bluffer's guide to Popper ;-)

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trhway
>The conservation of energy is not a mathematical truth

[http://en.wikipedia.org/wiki/Noether%27s_theorem](http://en.wikipedia.org/wiki/Noether%27s_theorem)

"...every continuous symmetry of a physical theory has an associated conserved
quantity; if the theory's symmetry is time invariance then the conserved
quantity is called "energy" ...".

~~~
Strilanc
Looks like a poor rewording of something from the paper, where it basically
says that conservation of energy is a consequence of the laws of motion
instead of an assumption:

> In the theory we present here, the status of information in physics is
> analogous to that of (say) energy: given the laws of motion of physical
> objects, neither the concept of energy nor the conservation law for the
> energy-momentum tensor are necessary for making any prediction from initial
> data, yet our understanding of the physical world would be radically
> incomplete without them. The conservation law _explains_ some aspects of
> motion as consequences of a deeper regularity in nature – which is why we
> expect as-yet-undiscovered laws of motion to conserve the energy-momentum
> tensor too; but we don’t expect to _derive_ new laws of motion from it. It
> is a _principle_ – a law of physics that constrains other laws rather than
> the behaviour of physical objects directly.

~~~
jaekwon
Haven't read the paper or anything, just judging that quote out of context:

I think it's folly to try to differentiate a "law" from a "principle". That
said I'm taking his words out of context. He's saying that "information" is
something akin to "energy". Ok, but after the hand-waving there is nothing
left.

Does he say something more interesting? For example, we've explored many
truths about "computation" (e.g. Turing's Halting Problem && Godel's
Incompleteness Theorem) that so far have only been discussed in the abstract.
But to weave computation/information onto physics raises questions of how
these truths we've held in the abstract may also correspond to laws in the
physical. That is, it doesn't help us derive new laws of physics (in other
words, our laws of physics is always incomplete), but constrains what can be
explained by laws (which by definition must be consistent).

TLDR; I agree that information doesn't exist in the abstract but is tied to
our physical reality. I think that our inability to find a complete set of
laws of the physical universe is intimately related to HP and GIT. I wonder if
he gets into it.

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Myrmornis
IANAP but it's kind of fun to try to read the start of the PDF, it doesn't
seem to require much advanced math.

 _But information is not abstract in the same sense as, say, the set of all
prime numbers, for it only exists when it is physically instantiated._

This seems to be an important point to Deutsch, but it doesn't seem completely
obvious to me. E.g. I can reason about the effects of purely hypothetical
information which in fact does not exist.

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pnathan
I am not a quantum physicist by training, trade, or hobby, but I did do some
level of dabbling in information theory some time back.

This appears to be than a restating of aspects of information theory, with
extensions to quantum information. Is that something heretofore lacking?

~~~
jerf
Whatever the answer to that question is, you will not be able to determine it
from that article, which is little more than a pointer to the existence of a
theory, and one keyword from that theory, left all-but-entirely undefined.

~~~
pnathan
I read/skimmed the article (not the linked article, the actual PDF), trying to
deduce the novel contributions that were not already reformulations.

