When does a physical system compute?

July 11, 2014 by David Garner

Can physical systems from bacteria to black holes act as a computer? A University of York computer scientist and colleagues from the universities of Oxford and Leeds address this question in newly published research which seeks to define unconventional computational devices.

Professor Susan Stepney, of the Department of Computer Science at York and her fellow researchers propose a framework which which defines and distinguishes scientific experiments, physical computation, and engineering technology.

The evolving focus on the physical basis of computing has been prompted by a growing interest in non-standard computing systems including quantum and biological computers. But there is no consensus on how identify if a physical system is operating as a or not.

The new research, published in Proceedings of the Royal Society A,introduces a formal framework that can be used to determine whether or not a physical system is performing a computation.

The researchers demonstrate how the abstract computational level interacts with the physical device level, drawing the comparison with the use of mathematical models to represent physical objects in experimental science.

This formulation allows a precise description of the similarities between experiments, computation, simulation, and technology, leading the researchers to conclude: physical computing is the use of a physical system to predict the outcome of an abstract evolution.

They give conditions that must be satisfied in order for computation to occur, and illustrate them with a range of non-standard computing scenarios. The framework also covers broader computing contexts, where there is no human computer user. They define the notion of a 'computational entity', and show the role it plays in defining when computing is taking place in physical systems.

Professor Stepney says: "Not every physical event is a computation, and for the first time we can distinguish which systems compute. In the future, this framework will enable the computational activity in biological systems and DNA to be precisely defined. We lay the foundations for computer science as a new natural science."

Explore further: The road to quantum computing

More information: Clare Horsman, Susan Stepney, Rob C. Wagner, and Viv Kendon. "When does a physical system compute?" Proc. R. Soc. A September 8, 2014 470 2169 20140182; DOI: 10.1098/rspa.2014.0182 1471-2946

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not rated yet Jul 11, 2014
My, aren't we edging ever so closer to Aristotelian metaphysics....
not rated yet Jul 11, 2014
I find it a rather neat definition; while i would argue that all inanimate matter processes information about itself in its interactions, 'computation' implies additional versatility - the ability to process information otherwise irrelevant to itself.
Jul 12, 2014
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not rated yet Jul 13, 2014
Does this mean that what was called a physical law or natural law is now seen as a computation?
Jul 13, 2014
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not rated yet Jul 13, 2014
Too abstract to be of use outside of computer science. But I like how they find computation to be the reversal of testing. (E.g. testing learns the theory, computing use what is learned.)

@DoieaS: "Only physical systems designed with people for dedicated purpose compute" is pretty much that the paper concludes. Information processing is thus separated from computing. E.g. basic vision processing such as line perception has no flexible computing "theory" model.

I'll agree that much ado has been made of nothing, or rather originally a mysticism/magic idea. (Platonic dualism.) But more by mathematicians than theoretical physicists as such.
not rated yet Jul 13, 2014
Bah, humbug. (I'm going to go Scrooge on this one.)

They're saying this: it's computation if it can be used by people for computation.

If it can't, then it isn't.

That's not a breakthrough concept. It's not an original insight. It's not even correct.

Consider: if you have a candidate computational system - say, a living cell - and you can't figure out a way to get abstract computations out of it, then there's no computation gong on, according to the definition they're offering.

If, later on, you *do* manage to assign abstractions to the cell's processes and extract meaningful computations out of it, *then* it's a computer. But the cell didn't change. What changed was our interpretation of the cell.

Nature probably has tons of computational systems that are excluded if the definition hangs on utility to computer scientists. I think that's conceptually both stupid and near-sighted.
Jul 14, 2014
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