Via the Zeitgeister, a fun panel discussion at the Perimeter Institute between Seth Lloyd, Leonard Susskind, Christopher Fuchs and Sir Tony Leggett, moderated by Bob McDonald of CBC Radio’s Quirks & Quarks program. The topic is “The Physics of Information,” and as anyone familiar with the participants might guess, it’s a lively and provocative discussion.
A few of the panel members tried to pin down Seth Lloyd on one of his favorite catchphrases, “The universe is a computer.” I tackled this one myself at one point, at least half-seriously. If the universe is a computer, what is it computing? Its own evolution, apparently, according to the laws of physics. Tony Leggett got right to the heart of the matter, however, by asking “What kind of process would not count as a computer?” To which Lloyd merely answered, “Yeah, good question.” (But he did have a good line — “If the universe is a computer, why isn’t it running Windows?” Insert your own “blue screen of death” joke here.)
So I tried to look up the definition of a “computer.” You can open a standard text on quantum computation, but “computer” doesn’t appear in the index. The dictionary is either unhelpful — “a device that computes” — or too specific — “an electronic device designed to accept data, perform prescribed mathematical and logical operations at high speed, and display the results of these operations.” Wikipedia tells me that a computer is a machine that manipulates data according to a list of instructions. Again, too specific to include this universe, unless you interpret “machine” to mean “object.”
I think the most general definition of “computer” that would be useful is “a system that takes a set of input and deterministically produces a set of output.” The big assumption being that the same input always produces the same output, but I don’t think that’s overly restrictive for our present purposes. In that sense, the laws of physics act as a computer: given some data in the form of an initial configuration, the laws of physics will evolve the configuration into some output in the form of a final configuration. Setting aside the tricky business of wavefunction collapse, you have something like a computer. I suppose you could argue about whether the laws of physics are “the software” or the computer itself, but I think you are revealing the limitations of the metaphor rather than learning something interesting.
But if we take the metaphor at face value, it makes more sense to me to think of the universe as a calculation rather than as a computer. We have input data in the form of the conditions at early times, and the universe has calculated our current state. It could have been very different, with different input data.
And what precise good does it do to think in this way? Yeah, good question. (Which is not to imply that there isn’t an answer.)
Even if we assume infinite resources, there exists one problem no Turing-based computer can solve; the halting problem.
I’ve always considered “is the universe a computer?” to be a meaningless question, whose one saving grace is that it’s close in ideaspace to some extremely meaningful questions. Namely, supposing we choose to see the universe as a computer (which of course we can if we want), what is its clock rate? How much information can it store? What exactly can we get it to compute? Can it solve NP-complete problems in polynomial time?
But it’s not surprising that most popularizers are solely interested in whether the universe “is” a computer. The other questions have the huge disadvantage that we actually know something about them.
why isn’t any logic gate a computer? And why isn’t the difference between Nature and a computer that nature computes us and we compute computers?
Can it solve NP-complete problems in polynomial time?
Sure. At least some portions of it can.
And which portions would those be?
Sorry which Universe are we talking about here?
I have to admit: I’m coming to despise all efforts to try and capture reality in dippy, inapt metaphors. It just seems, in the end, lazy. It doesn’t provide any new insight into anything, and is almost always an excuse for putting in the time to understand the always hard to classify or generalize quirks of any given subject.
It may be a computer, but not in the Von Neumann sense which is far too deterministic. Perhaps a self-referential simulation or something akin to the analog computers of the 1960s.
Just a breather from the discussions: Those who watch Futurama – remember the God-bot from Godfellas?
That was the first thing I had in mind when I read the title (granted, though, the God-bot is actually a galaxy)
I’d recommend Seth Lloyd’s exhaustive treatment in his book: “Programming the Universe: a Quantum Computer Scientist Takes on the Cosmos.” (Knopf, 2006)
Of course, when he starts to ask, “How many bits are there in an apple?” then determines that “the meaning of meaning is not clear,” you know you’re in for a ride.
Interesting for a former physicist like me who is a now writer is his discussion on ambiguity. He first discusses this in terms of language, but does not recognize it for the superposition it represents. Resolving verbal ambiguities involves the calculation of probabilities derived from the real-time context.
Sure, ambiguity usually returns an error message in computer programming.
But if we are living in a cosmic quantum computer, it must be able to compute ambiguity/superpositions … or the world would end with every political ambiguity uttered by our ruling DemoRepublicrats.
“It makes people with Computer Science degrees feel more important.”
More precisely: it enables them to pretend that what they are doing is science.
By that definition, dropping a computer off of a bridge is computing.
Scott wrote: “what is it’s clock rate?” this is exactly what I am trying to get at and does that clock rate vary over time? If so how? and “how much information can it store?” also isn’t this limited by the surface area of the universe per the BB?
Thank you for articulating more precisely my inquiry.
e.
“It makes people with Computer Science degrees feel more important.”
More precisely: it enables them to pretend that what they are doing is science.
Dear Poke and Yahoo,
I’m sure you didn’t intend the emotional pain caused by stereotyping an entire field. But assumptions and prejudices can truly be hurtful. While you might not realize this, individuals with computer science degrees aren’t all alike, but are in fact a glorious rainbow of nerds who cherish their diversity, just as our physicist friends cherish theirs. Not all of us agree that “the universe is a computer,” or indeed that the question itself makes any sense. Some of us are even doing things that could plausibly be described as “science” — take a look; you might be surprised! Incidentally, Seth Lloyd is not a computer scientist; he’s in the mechanical engineering department. Thank you for your understanding.
This has been a message from the Computer Science Anti-Defamation League.
33 Lewis: precisely. MONIAC is a better analogy than Intel.
Those parts of it which can model a Universal Turing Machine capable of solving NP-complete problems. Most commonly produced by a complex interaction between Si and fabs, or a process involving cellular mitosis.
Almighty Bob, you seem to have missed the phrase “in polynomial time.”
True. Sorry.
As I have argued before, the universe cannot be a computer/program etc for the following reason: true randomness cannot be produced by mathematical processes, because mathematics is a logical system. All presumptive randomness from “random variables” etc. is either just declared output without producing the goods, or the “goods” (genuinely random sequences) must be put in by hand, as by digits of roots etc. The decay of specific muons (not to be confused with the percentages left over time, I mean the actual “hits” themselves) in a computer model would require highly contrived arrangements to be put in by hand, like carefully selected roots and reseeding and all that to avoid artifacts that would blow the output as being phony. That’s all she wrote, really.
Not possible from pure mathematics, no, but some people involve a little extra physics in their RNGs.
“The universe is a computer” is a nice metaphor Neil, but I’ll agree that that’s about it.
As I’ve said before, if you take the assumption that the universe is a computer realistically, then reasoning from experience, you have to conclude that it is almost certain that the program contains a bug.
I was just referring back to “past questions” in place of the one today.
Sean:A thousand years from now, the twentieth century will be remembered as the time when we discovered quantum mechanics. Forget wars, computers, bombs, cars and airplanes: quantum mechanics is a deep truth that will continue to be a part of our understanding of the universe into the foreseeable future.
Schrodinger’s Cat So it’s kind of embarassing that we still don’t understand it.
I thought it relevant to the progression of computer technology and it’s description of the universe?
Right, it’s deep, and I agree with those who think we still haven’t solved Schrodinger’s Cat and the “collapse of the wave function.” I have seen descriptions/explanations of “decoherence” here and elsewhere, and they always use a fundamentally circular argument (that cannot be brushed off by appeals to the deeper finery of a particular argument.) The Art Deco always references density matrices and other probabilistic concepts and even saying “if a measurement occurs then” and etc, in a way which slips in the collapse or others in effect before explaining itself etc. As I said, waves interacting and interfering with other waves, absent a particular incidental localization or quantization “added by hand” (of mathematician or “God”) just stay a bunch of waves rippling through each other. If you don’t agree, show me without cheating.
Q “Is the Universe a Computer?”
A Only if it is a “Laptop”, and is actually on somebody’s lap, who is actually operating from “outside” of the compuniverse !
Next question is:Does the Universe have an “input” programmer or a self aware calculator?
http://en.wikipedia.org/wiki/Calculus_ratiocinator
If the universe is actually metaphored with a physical computer, then one can legally ask this: for input and output processes, does input materialize as an internal or external function of the universe?
logging off….or technically inputing an output command!
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So we can figure out how to crash it. [insert evil geek laugh]
There’s a science fiction story for you.
Actually, there is a science fiction story about that… I think it ran in Analog, or maybe Asimov’s, a couple of years ago. It features a bunch of scientists who are trying, for unknown reasons, to bounce a giant laser pulse off some distant object—possibly the Andromeda galaxy. All the scientists are puzzled when the pulse doesn’t come back… except the head scientist, who (SPOILER ALERT) had really been planning all along to crash the universe! Bwahahahaahahaha!
The funniest thing about this is that I don’t even read science fiction magazines… I read that story in a friend’s room at camp. I don’t remember the year, the camp, or the friend’s name, but I remember the story to this day. 🙂