People, galaxies, and complexity

Which is more complex, a person or a galaxy ? I have been to several seminars recently about various aspects of simulating galaxy formation and structure, on a variety of scales from large scale clustering to nuclear gas flow. Work of this kind is getting gradually more impressive, partly because better physics is going in, partly because algorithms are improving, and partly of course because folks are using bigger computers and gobbling up more CPU hours, thus achieving simulations with more resolution, more particles, or more timesteps. Obviously this must lead to more realism… but you get this strange queasy Borgesian feeling … if we simulate in enough detail to get it right, the galaxy in a box becomes indistinguishable from the real thing. What then have we learned ? Surely understanding involves some kind of encapsulation, some boiling down to a deep but simple statement ? Some kind of emergent law ?

At lunch after one such seminar, I was trying to provoke some of the locals with sceptical thoughts of this kind. Tom Abel had a good answer : the aim of massive simulations should not be to make it look right, but to see patterns and consistencies emerge. The simulations are not explanations, but experiments. Nonetheless Tom and his co-workers make very convincing looking – and stunningly beautiful – pictures. Although we love telling each other how little we know, in fact you could make a good case for the idea that we understand galaxies better than we understand people.

In popular talks I often go beyond this, claiming that people are quantifiably more complex than galaxies. (This is all about flattering the punters of course.) Now, you could go about defining  complexity in a number of ways. Its not about specifying the phase-space position of every molecule, otherwise a bucket of water is more complex than an iPod, and that ain’t right. One useful method is to ask how many instructions it takes to make something. To make a person, you take the information in the DNA molecule. The human genome has about three billion base pairs, and each of those needs 2 bits to specify one of four bases. So in total the information needed is about 750MB, or about one CD. Its instructive to compare that to printed text. A character from the alphabet needs 5 bits, but lets add other stuff and round up to one byte per character The book in front of me has 72 characters per line and 46 lines per page. So DNA is equivalent to 5.2 million lines, about 113 thousand pages, or maybe a couple of hundred moderately fat textbooks. To specify a person you don’t need an entire library, but you do need several shelves of books. By contrast, you can do a pretty good job simulating a galaxy with a few pages of C code. I believe that even the goriest codes are around the 50,000 lines mark. So there you go. A person is a thousand times more complex than a galaxy.

Well, I am sure many of you will be squirming and spotting all the cracks in that argument. It does remind me of the old story about Fred Hoyle, who claimed in a lecture that a star was a “pretty simple thing”. From the back of the room, someone called “You’d look pretty simple from ten parsecs, Fred.” (Special no-prize for anyone who can shed light on this urban myth.)

However, its pretty hard to come up with something objective. As I said, we don’t want to get into the list-every-molecule game. Perhaps this says something important about information. I can never resist the feeling that whenever somebody asks “how much information is there in X ?” the answer is “what do you want to know ?”. For this reason, I suspect that the infamous question of whether a black hole destroys information is an incoherent one. But I had better stop there or I will get stomped on by people cleverer than me. So. There you go. Galaxies simpler than people. From our point of view.

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20 Responses to People, galaxies, and complexity

  1. Do galaxies contain people?

  2. andyxl says:

    Good point Anthony. Maybe only this one ? And of course that thought heads us down the “list all the molecules” road….

  3. Hi Andy. It’s a complex issue, but I think I agree with you – the initial conditions for a human being (DNA) do seem much more complex than for a galaxy.

    But if we had a better understanding of how complex galaxies really are, maybe we would think differently? And maybe we’re setting the bar too low? The animations and pictures are dead impressive, but there’s still a long way to go…

    … but a long way to go to where? Will we just keep on doing better and better simulations to reproduce the ever-improving observations until we finally reach the conclusion that our understanding of the laws of physics was right all along?

  4. Michael Merrifield says:

    This issue has always struck me as the great paradox of the simulator, Anthony. Their ultimate ambition seems to be to put the basic physics in one end, grind a handle, and have something that looks just like the real Universe emerge at the other end, at which point they will declare that they have succeeded. But that seems an awful lot of cost and effort to learn what we already know from the real thing: that the Universe is a consequence of its laws of physics. So, the ultimate success is the ultimate failure of not telling us anything we didn’t already know.

    Of course, that isn’t strictly fair. They might fail in this grand venture, from which we might learn that we are missing some fundamental physics, which would be very interesting. And if they do succeed, they will then be in a position to really “play god” by messing with the laws of physics to see which ones really drive different aspects of the Universe, which we could never do with just the one real Universe, since it seems to have no user-serviceable parts (without voiding the warranty, anyway).

  5. Paddy Leahy says:

    …as Wigner said “I’m glad to see the computer understands the situation, but I would like to understand it too.”

    This issue of relative complexity is why I find AGN so fascinating, especially the ones with jets. There is a level of organization going on there that just doesn’t feature in most other astrophysical objects (including galaxies).

  6. andyxl says:

    Interesting you should mention Wigner, Paddy. One of the classic papers on understanding the molecular basis of entropy, Jaynes 1965 (Am.J.Phys. 33, 391) , quotes a private communication from Wigner, who said “entropy is an anthropomorphic concept”, by which he meant that that its value depends not just on the state of the system, but also on the experiment we wish to do, which determines which parameters are “of interest”. Obviously a good source of aphorisms that Wigner chap.

  7. Martin E. says:

    According to Riccardo Giacconi’s autobiography, Wigner was a bit of a pompous ass. He had special parties at his house where you had to come with pre-cooked witticisms worthy of the Master. He himself made awesomely dumb pronouncements such as “There is no such thing as architecture.” huh? Riccardo didn’t get invited back after contesting this pearl. Guess you can be ever so smart and ever so stupid all at the same time. [The rest of us make do with fairly smart and fairly stupid most of the time.]

  8. […] spend a lot of time making computer simulations of the Universe. Some discussion on The e-Astronomer’s blog has set me thinking about […]

  9. I don’t think that ‘instructions’ can give you the required amount of ‘complexity’. You can use the human genome to specify the sum total of – human genes. That’s the obvious bit. But it doesn’t tell you how those genes will be expressed in each human. Humans only differ from each other by about 0.1% of their genetic material, but does that mean we’re 99.9% identical?
    It’s partly the interaction of genes and their environment (on all scales from cellular to global) that introduces additional layers of complexity.

  10. andyxl says:

    Pippa – just because people differ through the accidents of history doesn’t make them much more complex than they would be if their histories were identical.. just – different. Otherwise an old car would be more complex than a new bicycle, once we looked at all the scratches and worn tyre patches..

    … but maybe there is such an argument for the brain, which actually does some re-wiring as it gains information ?

  11. John Womersley says:

    So, as Michael says, you can imagine plugging in the laws of physics, running a sufficiently accurate simulation and getting out a universe rather like ours, and that’s all great… but then you are still left with the problem of what do you plug in and simulate to get the right laws of physics to come out? Where do the apparently arbitrary parameters come from – the coupling constrants that define the relative strengths of the forces, the different masses of the u and d quarks that make sure the neutron is just a bit heavier than the proton and so on? Is this all just the anthropic principle and those 10**500 solutions of the string landscape at work?

  12. andyxl says:

    John, I always those those Lattice QCD simulations were an extreme version of the Pierre Menard problem. Thousands of hours on some of the world’s biggest computers and what have you done ? Calculated the mass of the proton !!! Wooo !!! Err,,,, didn’t we know that ? Can we calculate something we didn’t know ?

  13. Pippa Goldschmidt says:

    hi Andy,
    it’s not just brains that re-wire and change due to the incoming information. Genes can express themselves differently (the genes themselves don’t change, I’m not going all Lamarckian here) leading to differences in physical characteristics of their host organisms, and this is due to external factors.
    So I still think that if you’re trying to summarise the complexity of people (and I’m not sure I fully understand what that is, but as you’ve said, it’s a function of scale!) you need more than just genomes.
    I’ve been wrestling with this sort of question a lot lately as I’m working at the Genomics Forum here at Edinburgh Uni. Very interesting it is too..

  14. John Womersley says:

    Andy, my point was that a universe with things like galaxies (and humans?) in it may be a natural consequence of the laws of physics – but we don’t know if those laws of physics are a natural consequence of the universe. If it really requires fine tuning of those laws at the levels we currently think to get a sensible universe to come out, then in some sense the laws of physics are more complex than either a galaxy or a person – or at least they need to be specified to way more significant digits than the number of digits it would take to describe the DNA in a person. Which is weird.

  15. andyxl says:

    John – I can’t quite grok the laws of physics being a consequence of the universe, rather than vice versa. Guess I am not cut out to be a proper theorist. But huge numbers of digits needed to specify universe… hmm.. interesting. My head hurts.

  16. michael Merrifield says:

    I thought the driving force of occam’s razor was that anything deemed an advance in science should explain previous phenomena in simpler terms — thus, going from epicycles to Kepler’s laws to Newtonian gravity was deemed to be progress because each explanation was simpler than the last. If an explanation of the origins of the laws of physics turns out to be more complicated than the laws of physics themselves, doesn’t that mean that it is headed in the wrong direction?

    Probably shouldn’t try to think about these things with a head full of flu… Then again, maybe best considered when a little feverish!

  17. Martin E. says:

    About counting genes to measure human complexity: I’m reading a really good book on language (“The First Word” by Christine Kenneally). She has a little lecture in Ch.11 on how in the last 5 years the view of genes as a blueprint has been tossed out; genes interact with their environment, turning on and off depending on e.g. the organism’s exposure to sunlight; some genes only turn other genes on and off. So clones – genetically identical – can look very different. So we can’t calculate our complexity from the number of genes.
    This whole recent upset came from deciphering the human genome and finding we had about the same number of genes as a roundworm. I don’t think its too anthropomorphic to say we are more complex than worms. Counting genes is not good biological thinking, even if similar things work in physics.
    A lot of the reason we think we are complex is because of what we think in our brains. We are genetically and physically a type of chimpanzee; any difference in our complexity is literally in our heads: our culture, language and the rest.
    How you gonna quantify that?

  18. andyxl says:

    Martin – sounds like you are confirming what Pippa was saying. Genes can be turned on and off. But I don’t think this changes my crude “instruction book” calculation. That gives the maximum number of available switchable-on genes. And if we discount the brain, then to an order of magnitude, I am not sure a person IS much more complex than an earthworm. So yup, I guess its the brain what matters.

    I don’t know how to measure the complexity of the brain, but there have been attempts to estimate its information capacity. Estimates range from a few TByte to a PByte. You can follow the trail from a web forum discussion here.

  19. Pippa Goldschmidt says:

    hi
    I think genetics has showed that a reductionist approach (i.e. breaking organisms down into their constituent components to explain overall behaviours) doesn’t always work, and that a more systemic approach may be better suited, sometimes…
    Also – yeah, most genes seem to be generic across different species. We don’t just share a significant number of genes with earthworms, but also pumpkins, daffodils…
    And on your queasy Borgesian feelings that simulations may be approaching the complexity of the ‘real thing’
    have you read about the simulation argument by the philosopher Nick Bostrom, who argues that as it is likely that future civilisations will run complex simulations of their history in an attempt to understand their origins, it is quite possible we are simply in one of those simulations.
    All jolly fun.

  20. andyxl says:

    … in a giant computer called the Earth ?

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