
Digital physics - xd
http://en.wikipedia.org/wiki/Digital_physics
======
JonnieCache
Greg Chaitin has lots of lectures about this up on youtube
[http://www.youtube.com/results?search_query=greg+chaitin](http://www.youtube.com/results?search_query=greg+chaitin)

He is a very watchable speaker. There's an amusing moment in one of them where
he talks about getting high on hyperoperators. I wish I could remember which
one it was.

Among other things he tries to convince you that real numbers are a figment of
our imagination, an obvious consequence of digital physics, but still quite
startling. He has decent arguments.

~~~
chii
is there any one particular lecture you recommend? i don't have time to sift
thru the large number of results from that search to find the gems.

~~~
JonnieCache
The one at lisbon and the one at Mälardalen university are good. They're all
good as far as I can tell.

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dchichkov
That quote from John Archibald Wheeler [a doctoral advisor of Feynman] ...
just beautiful:

"""

[...] it is not unreasonable to imagine that information sits at the core of
physics, just as it sits at the core of a computer. (John Archibald Wheeler
1998: 340)

It from bit. Otherwise put, every 'it'—every particle, every field of force,
even the space-time continuum itself—derives its function, its meaning, its
very existence entirely—even if in some contexts indirectly—from the
apparatus-elicited answers to yes-or-no questions, binary choices, bits. 'It
from bit' symbolizes the idea that every item of the physical world has at
bottom—a very deep bottom, in most instances—an immaterial source and
explanation; that which we call reality arises in the last analysis from the
posing of yes–no questions and the registering of equipment-evoked responses;
in short, that all things physical are information-theoretic in origin and
that this is a participatory universe. (John Archibald Wheeler 1990: 5)

------
virtualritz
I just noticed the Process Physics article on WP has been deleted (because it
is deemed fringe science by some) and isn't mentioned in there, even though
this is very related, imho.
[http://www.flinders.edu.au/science_engineering/caps/staff-
po...](http://www.flinders.edu.au/science_engineering/caps/staff-
postgrads/info/cahill-r/process-physics/)

------
ashleyw
I'm _certainly_ not qualified in this field, but I think it's inevitable that
we as a species will eventually simulate a universe. And if that's the case,
we've really got to ask whether we're a simulation ourselves. At the macro
level this seemingly arbitrary universe makes a lot of sense, which makes me
wonder if our universe is one in a long 'family' of simulated universes, each
making modifications along the way, deliberate or otherwise, evolving towards
the universe we have before us today (and beyond.) After all, once you have
the computational power to simulate one universe, it'll not be long before you
can simulate 10,000 simultaneously (..and only keep the fittest!)

~~~
JonnieCache
Presumably you've read [http://www.simulation-
argument.com](http://www.simulation-argument.com) ?

If not, then enjoy yourself.

~~~
ashleyw
No I haven't seen that, it's fantastic -- Thanks!

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helloTree
As a computer scientist I like the idea as I also believe that information
(and time or a unifying concept of them) is one of the most fundamental
building blocks of the universe, however we have to keep in mind that we leave
the territory of science here. The statement: "The universe is just a
simulation." is just not a scientific theory as this is probably unfalsifiable
[0] or am i wrong?

[0]
[http://en.wikipedia.org/wiki/Falsifiability](http://en.wikipedia.org/wiki/Falsifiability)

~~~
chriswarbo
Most digital physics proposals seem to be unfalsifiable, but there are
exceptions.

For example, statistical Physics tells us that a system can be full of
complex, random fluctuations, but it can still be 'stable' if those
fluctuations cancel each other out. Boltzmann hypothesised that we could just
be a random fluctuation in some otherwise stable system (perhaps a vast cloud
of gas). This hypothesis is falsifiable, since large fluctuations are far less
likely than small fluctuations. It's very unlikely that the room I'm in,
including me, is a fluctuation in a gas cloud, but the anthropic principle
says that I wouldn't notice all those small fluctuations which don't produce
me. If I am a fluctuation then I can predict that it's _incredibly_ likely
that the fluctuation is limited to this room, as anything larger would be far
less likely. However, when I step outside I find a whole city, which falsifies
the hypothesis. Likewise we can observe a whole planet, solar system, galaxy,
local group, cosmic web, etc. which goes exactly against the predictions of
the fluctuation hypothesis.

However, from a digital physics perspective we can get the opposite result.
Let's hypothesise that we're running on a giant Turing Machine and our program
is a random fluctuation on its tape; ie. a random series of bit flips on an
otherwise empty tape. Since small fluctuations are vastly more likely than
large fluctuations, we would expect to be part of a small program rather than
a large one. Again, the anthropic principle says that I'll never observe tiny
programs that don't produce me, but what can I say about tiny programs which
do produce me? Well, randomness and asymmetry is hard to produce using a
computer program: it must be encoded as part of the program, since it can't be
produced spontaneously. Hence I would predict small programs to have less
randomness and asymmetry than large programs, so I would predict a symmetric
and uniform Universe, which is largely what we see.

One falsifiable prediction of such a digital physics theory is that quantum
phenomena are actually pseudorandom, ie. deterministic and predictable, since
the only way to encode unpredictable values in a program is to write them out
bit-for-bit in the source. A pseudorandom number generator would require far
fewer bits, and hence is more likely; also, a smaller pseudorandom number
generator is more likely than a large one. If we find that quantum phenomena
cannot be predicted by any short program, we can falsify this hypothesis.

------
DanielBMarkham
I've believed in a "computational substrate" ever since I read Wolfram's NKS.
Great to see it getting more attention.

What with the holographic principle, it may be that the "real" universe in a
huge sphere, and the effects we observe simply due to overlap. Sort of like
Conway's Life played on a cosmic scale.

Cool stuff.

------
ignostic
This philosophy doesn't sit well with me. Physics at a particle or even mass
scale can be described mathematically, I'll give you that. That said, if you
are to understand the relationship between one particle and another, you need
some way to explain that relationship.

For example, the pull of one celestial body of matter on another (really the
sum of particles, but let's simplify) can be explained with math. But you
cannot communicate the RELATIONSHIP between the two without understanding the
concept of gravity and space-time. It would be claiming the universe is all 1s
and 0s, ignoring the fact that there must be a en/decoding method - a meaning
to the numbers - for them to make any sense.

The weaker claim that the universe CAN BE computed is to me fairly obvious,
but that adds little to any discussion among those who believe in causality.

~~~
aa0
I think you are misunderstanding what digital physics proposes. Yes the
information is 0s and 1s but the actual program does not have to be. Physics
is modeled by information and inherently seems to be connected to physical
values. Seems logical to me.

~~~
ignostic
That may well be, as I'm not a physicist or mathematician. I take issue with
the claim that the universe and the interactions therein can be described
mathematically. That seems to imply that you can explain it to a human
mathematically. Without context, concept, and relationship, how could this be?

~~~
aa0
Mathematics is just another flavor of language. English, French, Math...what's
to doubt? Math just requires some extra context in the form of natural speech
because it is a more narrow subset. It isn't limited, just less coherent when
variables are used without prior definition.

It's amusing that you find it hard for the universe to be described
mathematically when physics does just that.

I should note that digital physics does not imply that physics are purely
mathematical..they can be procedural -- ie. akin to a C program. When you get
down to it though..whatever is doing the higher level computation, the
processor, could be accomplishing the instruction set using purely boolean
logic.

------
aa0
Chatlin's constant
([http://en.wikipedia.org/wiki/Chaitin's_constant](http://en.wikipedia.org/wiki/Chaitin's_constant)),
linked by Digital physics, is also very interesting. It is the probability
that a random program will halt. When we get into 'random program' all kinds
of interesting questions come up.

For me, I immediately think of:

What instruction set are we considering? Is the instruction set bounded by
human language?

Human language does not have the same extent as thought -- or does it? Is the
indescribable as cardinal as the unthinkable?

What is the Chatlin's constant for average human thought process.. ie. a
subset of our brain programming?

Man, what an interesting subject.

~~~
chriswarbo
The instruction set doesn't matter. To calculate (the first few bits of)
Chaitin's Constant we can enumerate and run every program in some instruction
set, say x86 assembly, and measure the proportion of programs which eventually
halt. One efficient way to do this is to interleave their executions using
FAST
[http://www.idsia.ch/~juergen/toesv2/node28.html](http://www.idsia.ch/~juergen/toesv2/node28.html)

Any (Turing-complete) instruction set can be translated/compiled/interpreted-
by any other (Turing-complete) instruction set, given a suitable
translator/compiler/interpreter. Since we're running all programs, we will
eventually run all translators/compilers/interpreters, so no matter what
instruction set we choose, we will start running programs from every other.
The longer we leave it running, the more of a mixture we end up with. Since
Chaitin's Constant is the (uncomputable) result of letting such a scheme run
forever, it contains a perfect mixture of all instruction sets, and is thus
independent of whichever one we choose.

------
dsizzle
Conceiving the universe as the "output of a computer program" seems like an
empty idea, as computation depends on a physical substrate (its laws of
physics). It leads to an infinite regress: What laws of physics govern that
physical substrate? David Deutsch (mentioned in the WP article) has a
discussion of this (and many other related deep topics!) in his excellent "The
Beginning of Infinity" [http://www.amazon.com/The-Beginning-Infinity-
Explanations-Tr...](http://www.amazon.com/The-Beginning-Infinity-Explanations-
Transform/dp/0143121359)

------
mkrecny
Digital Digital Philosophy:

"Digital philosophy grew out of an earlier digital physics (both terms are due
to Fredkin), which proposes to ground much of physical theory in cellular
automata."

[http://en.wikipedia.org/wiki/Digital_philosophy](http://en.wikipedia.org/wiki/Digital_philosophy)

------
aa0
Just a thought. If physical information is stored as bits in a computer. And
the universe is essentially that memory plus a compute unit,

Is consciousness the derivative of information with respect to the difference
of information (ie. a clock cycle -- time?)

~~~
augustl
One interesting aspect of modelling the universe is that the universe is not a
single atomic entity. Speaking of what happens 8 lightyears away from us
"right now" makes no sense - there's no way information 8 light years away can
reach us faster than 8 (of our) years, so the shared "now" between us is just
theoretical. We can imagine that it's there, but we cannot know what's there,
or measure it in any way.

The only atomic thing is the way I percieve the universe right now. Someone
else will percieve it differently. I'm _not_ talking about the fact that your
blue might not be my blue, I'm talking about the fact that time might move at
a different pace (if you've accelerated or decelerated) and that you're a long
enough distance away from me that our lack of a shared "now" is not negligible
in calculations.

So a digital model of the universe would have to take into account that the
whole universe, again, isn't an atomic entity, and rather model that we have
different entities perceiving things as the universe has propagated to their
point of view, in their speed of time.

~~~
GrantS
This is a very person-centered view of the universe, no? We're made of the
same fundamental particles as everything else, no need to make special cases
for when perception and cognition arise in the universe -- they/we follow the
same physical rules as everything else. So as long as you're simulating the
right universe (i.e. the laws of physics are the actual laws of physics that
we experience), everything you're talking about just happens by definition,
right?

~~~
eru
I think augustl just used person-centric language for ease of expression.

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mathattack
It's intriguing, if perhaps an incorrect model. I am no physicist, but what
makes us sure there's a bottom?

~~~
chriswarbo
IMHO "bottom" is the point where any lower levels can only be pure
philosophical speculation. For example, if we exist as a pure computation
inside some computer, it makes no difference which of the myriad Turing-
equivalent models it's based on, since they're all equivalent.

Note that such a computer wouldn't have to be constrained by any of the
Physics that apply inside our computation; ie. there don't need to be space or
time limits.

~~~
mathattack
At the risk of sounding obtuse... When you say philosophical, do you mean non-
measurable? (Such as parts of string theory?)

To use an analogy, why can't particle physics be like a Mandelbrot which
doesn't have a bottom?

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iliis
Nice to know there's a name for this concept!

You can take the idea further and abandon any notion of time or even
discreteness altogether: If the universe is essentially information, this
information can be _completely_ described by some (mathemtical) language.
Note, this description doesn't have to be finite.

For the finite and discrete case this description may simply be a very long
bitstring/vector which contains every detail of our universe. If time is
discrete as well we can write a whole timeline as a matrix, a set of
bitstrings each representing one slice of 'now'. Notice how we now have one
static thing being a perfect representation of the universe. No need for a
computer or interpreter. Just a big table of ones and zeroes representing
everything from the big bang to your mother.

However, our universe might be continuous. You might still be able to describe
it with finite amount of information tough. A function like x -> x*x is
continuous and defined for infinitiely many values but can still be written
down just fine. Even infinite complex things like fractals can have a very
short descriptions. Or take pi. An infinite sequence of numbers describable in
a few sentences.

Point is, a universe need not to be discrete in order to be written down on a
sheet of paper. It just needs to be finite in an information theoretical
sense. And you may need a lot of paper.

I strongly suspect the universe is bounded. But what if it isn't? Can we still
se it as a mathematical entitiy? I think so, but I'd like some comments on
that. We have the well-defined set of real numbers and it contains _every_
real number, even those who are completely random up until the last of their
infinite digit. There are numbers in R which have an infinite Kolmogorov
complexity [1]. And yet, we can put them all in one set. We can even draw a
picture of all these numbers (it's just a line, but that's more than our
analysis professor would draw to illustrate something).

In conclusion: I think (and didn't proof) that even if the universe contains
infinite information and cannot be the result of some turing machine it can
still be tought of as a mathematical object. A thing like sqrt(2) or a
triangle.

\----

A second and orthogonal tought is about the 'reality' of all this. This is a
bit metaphysical and philosophical. If you are still reading please tell me I
went crazy. The idea is, if you have a perfect description of our universe (be
it a turing machine, a big matrix or some other complicated mathematical
thingumabob) is there a difference between the description and the real thing?
Obviously not, one is just words on a paper or bits in a computer and the
other a world full of loving and caring people and other stuff. How can I even
ask such a question? (Hint: I'm on the Internet and can write what I want.)
Well, imagine doing this whole computer simulation of our universe. Would you
feel any different when being run on some sort of computer? If you and
everything around you would be perfectly simulated would you notice it? Would
you even be able to? For the ones running the simulation the difference would
be obvious. But being part of the simulation you may have no way of knowing
that you are a piece of software. It would all seem and feel real. It would BE
real. And yet you are just bits. You could stop the computer, dump it's memory
and write it all down. Doesn't seem like such a difference between words on
paper and reality after all.

What I'm trying to explain is that a perfect description of something is
actually, in some sense, the _same_ thing as the object being described. It's
a bit like uploading the whole universe instead of just a brain. In the end
all you have is information. Doesn't matter if this information flows trough
transistors, is written in ink or just an element of the set of real numbers.

And if you say the number '4' 'exists' and so does 'pi' then why not 'the
universe' as well? If you say this then you just answered the question 'why do
we exist?' Because _everything_ exists. In the same sense as every possible
triangle 'exists' so does every universe. We just happen to observe one
specific instance.

The sad thing is: This doesn't really explain anything. If you say absolutely
everything exists you haven't made any predictable or verifiable claim. So it
may give you a philosophical answer to why are we here but it isn't much more
than '42'...

\----

[1] Some formal proof would be nice here. I didn't think it trough down to the
simplest axiom. Maybe it's enough to argue that there are only countable many
turing machines but uncountable many real numbers and therefore some real
numbers cannot have a finite description.

~~~
seanmcdirmid
Take some finite program and an infinite amount of memory. Now run that
program, and you can build increasingly complex spaces in that memory. This is
basically how automata work. If the finite program is the code of the
universe, "now" depends on executing the program up until now, so it's of
little use in giving us a shortcut to understand now (but we'd still like to
know what this program is!). Also, just knowing a snapshot of now doesn't give
us the future without knowing the program (and in any case, the time it takes
to compute the future is at least the amount of time it takes to reach that
future).

~~~
DennisP
Who says the computation has to run inside of time?

Consider our spacetime as a four-dimensional space, the pixels of which are
set by a computation running in a different dimension of "time." The number of
steps required to generate the final output is arbitrary and unrelated to
anything we observe, and there's no contradiction in supposing that, say,
information in our future could be an input to an iterated algorithm that
determines our present.

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AsymetricCom
hasnt this line of philosophy been logically killed by quantum physics? Also
digits are purely human concept.

~~~
pivnicek
I'm not sure if a digital universe would necessarily equate to a knowable
universe.

My main point of disagreement with the philosophy would lie in the ultimate
weakness inherent to a digital explanation: the infinite points in between.

~~~
kaoD
Which infinite points?

[http://en.wikipedia.org/wiki/Planck_length](http://en.wikipedia.org/wiki/Planck_length)

