
What things compute? - theaeolist
http://researchblogs.cs.bham.ac.uk/thelablunch/2015/07/what-things-compute/
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jerf
I tried leaving this as a comment on the blog, but "Couldn't open socket".

The author, and any reader who finds this interesting, should definitely also
read "Why Philosophers Should Care About Computational Complexity" by Scott
Aaronson:
[http://www.scottaaronson.com/papers/philos.pdf](http://www.scottaaronson.com/papers/philos.pdf)

This being the Internet, the natural assumption is that this is intended as
contradiction or argument, but I really do just mean, you'll really want to
read that too, as it informs the discussion in interesting ways.

~~~
SilasX
Specifically, section 6 (Compuation and Waterfalls), which gives the answer
that System X computes Y whenever it saves you the work of computing Y -- i.e.
if being able to use X as an oracle decreases the asymptotic difficulty of Y.

So waterfalls (probably) don't play chess in the sense that any mapping form
the waterfall to a chess program would itself be as complex as the problem
(and its execution). But a chess computer does, since its output has a very
simple mapping to actual moves (and in practice, most chess computers add a
view layer to provide that mapping transparently).

~~~
dgreensp
Your comment is so much clearer for having a Y. Asking "Does X compute Y"
instead of "Does X compute [anything]" makes all the difference.

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rndn
A computation substrate has state and can change its state within (feedback)
loops. An elementary particle suffices this definition: It has state because
its properties persist at least for some time, and it has feedback loops
(interactions with other particles) that change its state. The more elementary
particles locally affect each other, the more complex the state and feedback
loops can be. What kinds of computation you can perform on such a substrate
depends on the rules that govern the particles, in particular, how many
feedback loops they allow to simultaneously affect a local arrangement of
particles. It looks like there is an upper bound to this: No substrate can
compute more kinds of functions than a Turing machine, which is a hypothesis
that is closely tied to the conservation of energy and unitary (that the sum
of the probabilities of all possible outcomes of a system equals 1). However,
since matter decays, it is doubtful that anything around us can actually be as
infinitely precise as the theoretical idea of the Turing machine.

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exratione
I'm not sure I see the problem with "everything computes". If every physical
process can be shown to be isomorphic with one or more computational
algorithms, which seems like a very reasonable supposition at this point given
what we know about emulation, then that is just the nature of things. It seems
more like a useful insight than an unsatisfying answer.

~~~
danghica
If "everything computes" then you can not use "because it computes" as an
explanation.

~~~
hyperion2010
I do not see how this is a bad thing. It seems incorrect at some level, but
claiming that things that compute are somehow categorically different is an
appeal to magical thinking.

I would agree that claiming that a rock computes by not simply vanishing from
one plank time to the next is not satisfying. This leads me to think that
computation has much more to do with whether a particular being has reach a
thermodynamic local minimum than anything else (lava does not compute since,
despite being far more active than a rock, its behaviour can be explained by
the fact that it is a couple thousand degrees hotter than a normal rock).
Energy dissipation also does not fit the bill since stars dissipate energy but
do not compute.

Unfortunately the thinking surrounding things like proteins look incredibly
similar, their behavior changes as a function of ph and temperature, and most
arguments that a protein computes are based on defining a function for that
protein. This gets us nowhere, but it does suggest that it may not be possible
to define computation in a way that excludes systems dissipating energy to
reach thermodynamic local minima.

~~~
wrongc0ntinent
Re: "claiming that things that compute are somehow categorically different is
an appeal to magical thinking" \- This is not the case. The distinction that's
being made is one of perspective and purpose, i.e. implementing method to get
result. Or am I getting this wrong?

~~~
hyperion2010
You are getting it correct, but the idea that computation is defined based on
some purpose or from a limited subset of all perspectives is exactly what I
take issue with. If your notion of computation is dependent on purpose and
thus some teleological notion of function then saying something computes
doesn't tell us anything about that being, only about how human beings
perceive that being and its function. Again, this undermines the usefulness of
having a perspective/function independent notion of computation. The magical
thinking arises because we project our notations of function onto the being
itself and conflate our uses for that being with the intrinsic properties of
that being. Purposes/uses/functions are not intrinsic properties. Computation
may not be an intrinsic property, it may only be a relational property, which
would be an interesting result itself, but probably quite irritating to people
who want to make arguments that there is something intrinsically different
about certain kinds of systems.

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yellowapple
> In conclusion I want to shatter our presumed consensus: computers do not
> compute. Not even computers. We compute. Computers just help us along.

Define "us". Define "compute". Seeing as the former is very fuzzy, and the
latter is suggested by the article to be undefined, trying to use this to
"prove" that brains are not computers is, well, nonsense.

Consciousness is a side-effect of electrochemical interactions. Nothing more,
nothing less. Trying to believe otherwise - that consciousness is some
"special snowflake" that can somehow exist independently of the machine which
creates it - is about as folly as trying to believe a magical sky-wizard
sculpted mankind from clay. Whether this counts as "computation" depends on
how "compute" is defined.

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VLM
Its interesting seeing the gulf between the philosophers and the computer
scientists. I think your average philosopher would enjoy a trip down the
rabbit hole of automata theory and the hierarchy of things that can emulate
lower levels things vs things that look different but are at the same
computational level. Watching a non-CS philosopher rub a NFA up against a CFG,
for example, would be interesting. What would Marx say about the assumptions
of a DPDA wrt the labor theory of value (or anything else interesting?)

~~~
mdlincoln
Though it's probably not the largest sub-discipline, there are (and have been
for some time:
[http://www.wiley.com/WileyCDA/WileyTitle/productCd-063122919...](http://www.wiley.com/WileyCDA/WileyTitle/productCd-0631229191.html))
a fair number of philosophers who are very interested in computing and (as you
guessed) simulation as a way to approach their research questions.

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aidenn0
I can't think of a definition of "compute" that would both include analog
computers, but exclude e.g. a rock thrown.

I'm not sure how you could argue against the fact that in a near vacuum and a
fixed gravitational field, a rock thrown will compute a fairly accurate
approximation of a parabola.

~~~
resu_nimda
It feels like everyone in this conversation is just choosing their own
arbitrary definition of computation. The question is, why have you chosen that
definition, what makes it useful? As the author points out, if rocks compute,
then there is not much meaning to computation as a concept.

Computation in the colloquial sense refers to a sequence of events that
happens inside machines that were made by humans in order to calculate some
explicit mathematical results that the human operators have some interest in.
I think this is a fine definition, and one that includes computers but not
humans or rocks. I feel like the author erred in trying to redefine
computation into some other abstract concept, muddying the water such that
everyone is just talking about what "computation" means to them.

I think the real question we're getting at is, "what is the relationship
between what a human brain does to solve a problem, for example moving a body
into the correct position to catch a baseball, and what a computer does, which
we know is executing explicit math equations to calculate trajectories,
inverse kinematics, etc?" Right? We're talking about the illusion of intent,
of goals, of the desire to solve problems - and as far as we can tell, rocks
obviously do not possess those traits.

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aidenn0
"..there is not much meaning to computation as a concept."

I kind of do agree with this.

So, if I want to calculate a parabola, and construct a machine to launch rocks
at specific velocities and angles, then this machine is a computer, but if I
just throw a rock without wantint to calculate a parabola, no computation has
happened?

What if a kid is playing around with my rock launching machine? Is no
computation happening because the kid isn't trying to calculate parabolas?

~~~
resu_nimda
If the machine is just launching rocks at a specified angle and velocity, then
no it is not computing a parabola. The rock's trajectory traces a parabola,
but it has not been "computed" (in my view). A computation to me involves an
explicit mathematical result related to some specific intent or question, not
just physical objects playing out the laws of nature. The computer would have
to make a statement, a result - "based on my calculations, at time X the rock
will be at position Y."

~~~
aidenn0
Then you would clearly reject all analog computers, since e.g. an analog adder
just involves electrons playing out the laws of nature. A rock launching
machine is an analog computer for calculating a parabola. A specific result
might be "where is the intersection with some Y value, and you have a platform
at the height for that value. The distance the rock lands at would be the X
value.

~~~
resu_nimda
What is the point of reducing everything to nothing, or to the same thing? I
mean I get it, technically it's valid, but it's very boring, there's nothing
then to talk about. We are humans and we do have subjective experiences and
classify things into different groups, and trying to understand the
relationships and differences between groups gives us interesting things to
think and talk about.

But hey, if a rock and a computer are the same thing, and computation is
meaningless, words are meaningless, etc - why have you bothered to say
anything at all?

