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Is life a form of computation?

(thereader.mitpress.mit.edu)
222 points redeemed | 2 comments | 23 Sep 25 20:46 UTC | HN request time: 0s | source
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AIPedant ◴[23 Sep 25 22:19 UTC] No.45353525[source]▶
Articles like this indicate we should lock down the definition of "computation" that meaningfully distinguishes computing machines from other physical phenomena - a computation is a process that maps symbols (or strings of symbols) to other symbols, obeying certain simple rules[1]. A computer is a machine that does computations.

In that sense life is obviously not a computation: it makes some sense to view DNA as symbolic but it is misleading to do the same for the proteins they encode. These proteins are solving physical problems, not expressing symbolic solutions to symbolic problems - a wrench is not a symbolic solution to the problem of a symbolic lug nut. From this POV the analogy of DNA to computer program is just wrong: they are both analogous to blueprints, but not particularly analogous to each other. We should insist that DNA is no more "computational" than the rules that dictate how elements are formed from subatomic particles.

[1] Turing computability, lambda definability, primitive recursion, whatever.

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ants_everywhere ◴[23 Sep 25 23:32 UTC] No.45354218[source]▶
I think you may be forgetting about analog computers https://en.wikipedia.org/wiki/Analog_computer
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lmm ◴[24 Sep 25 00:07 UTC] No.45354506[source]▶
I don't think they are. The things analog computers work on are still symbolic - we don't care about the length of the rod or what have you, we care about the thing the length of the rod represents.
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ants_everywhere ◴[24 Sep 25 00:34 UTC] No.45354698[source]▶
analog computers don't generally compute by operating on symbols. For example see the classic video on fire control computers https://youtu.be/s1i-dnAH9Y4?t=496

OP's specific phrasing is that they "map symbols to symbols". Analog computers don't do that. Some can, but that's not their definition.

Turing machines et al. are a model of computation in mathematics. Humans do math by operating on symbols, so that's why that model operates on symbols. It's not an inherent part of the definition.

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AIPedant ◴[24 Sep 25 01:23 UTC] No.45355111[source]▶
No, analog computers truly are symbolic. The simplest analog computer - the abacus - is obviously symbolic, and thus is also true for WW2 gun fire control computers, ball-and-shaft integrators, etc. They do not use inscriptions which is maybe where you're getting confused. But the turning of a differential gear to perform an addition is a symbolic operation: we are no more interested in the mechanics of the gear than we are the calligraphy of a written computation or the construction of an abacus bead, we are interested in the physical quantity that gear is symbolically representing.

Your comment is only true if you take an excessively reductive view of "symbol."

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1. ants_everywhere ◴[24 Sep 25 01:50 UTC] No.45355339[source]▶
I'm not confused, and an abacus is a digital computer.

You keep referring to what we are interested in, but that's not a relevant quantity here.

A symbol is a discrete sign that has some sort of symbol table (explicit or not) describing the mapping of the sign to the intended interpretation. An analog computer often directly solves the physical problem (e.g. an ODE) by building a device whose behavior is governed by that ODE. That is, it solves the ODE by just applying the laws of physics directly to the world.

If your claim is that analog computers are symbolic but the same physical process is not merely because we are "interested in" the result then I don't agree. And you'd also be committed to saying proteins are symbolic if we build an analog computer that runs on DNA and proteins. In which case it seems like they become always symbolic if we're always interested in life as computation.

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2. AIPedant ◴[24 Sep 25 06:37 UTC] No.45357038[source]▶
This is where you are confused - in fact just plain wrong:

  A symbol is a discrete sign that has some sort of symbol table (explicit or not) describing the mapping of the sign to the intended interpretation
Symbols do not have to be discrete signs. You are thinking of inscriptions, not symbols. Symbols are impossible for humans to define. For an analog computer, the physical system of gears / etc symbolically represent the physical problem you are trying to solve. X turns of the gear symbolizes Y physical kilometers.