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Physics for Poets

You know we come in two sorts. We are either attempting to comprehend the true nature of reality or we’re melting ice in a bucket. Some of us are poets. And some are merely prose stylists.

Now, I was taught Solar System Dynamics* by Carl Murray at QMC and Professor Murray is a “Physics for poets” type. You may have seen him. Queen Mary is a very media savvy college and the likes of the BBC drag out Carl to give brief comments on NASA probes to the outer planets.

I actually have an early draft of his book**, scrawled upon and tea-ringed by my twenty two year old self… Let’s have a look shall we…

ssd

OK, so that’s the poetry. Now let’s turn to the back and have a butcher’s at the Physics. Those of you of a nervous disposition when it comes to math might want to look away now because in Appendix 2, lurking Smaug-like is The Disturbing Function. It is only expanded to fourth order in both direct and indirect parts, possibly both canonical and secular if not also real and imaginary***

ssd1

ssd2

Now you wanna know the best bit? That’s pages one and two. I left out the next 34. Also that is written in a very condensed form and, as I said, only to fourth order. Disturbing function. It disturbed me alright. And I had just graduated with a top-notch degree from a top-notch University and I was young and funded and in London and it was the age of Britpop and life was cool and we used to hang in the same clubs as Jarvis Cocker and a friend of a friend shagged Sophie Ellis Bextor (before she was famous, or even sixteen) round the back of a kebab shop on Fleet Street but I digress… Though you get the general idea of invincibility. Because the scamps that we were we got up to some capers I can tell you…

But what, you are no doubt wondering does that have to do with the disturbing function? And what indeed is the disturbing function for? Well, it’s a partial solution to the vexed three body problem. You see you can’t get a closed form (neat) solution to the mutual gravitational interaction of three bodies. Even treating them as point masses. It just don’t integrate. So we have the disturbing function. And I’m sure you’ll agree it’s a bit of a ‘mare ain’t it?

Two bodies – fine. Keplerian Orbits and all that jazz and they’re easy but bring in a third body and it gets messy. So why am I boring you with all this astrophysical dullness? Simple. The disturbing function has to be worked out on computers. The principle of it goes way back but nobody got it right. It was not until computers were used that the expansion was possible with any degree of accuracy. You might think it looks evil but just imagine trying to work it out, sat at a ledger, by candlelight. Science has wrestled with few demons worse than that.

But surely the three-body problem is simple? It should be down? It should be on the canvas and it’s second thrown the towel into the ring by now? No. It’s alive and kicking. It may just be three point masses interacting by a 1/r2 field but it’s nightmarishly difficult. We have cludges like the disturbing function not because we aren’t smart enough but because the problem cannot be solved. Not because it’s too complicated but because it can’t be solved in principle.

And that’s particle mechanics. And as any fule knows particle mechanics is much easier than dealing with a continuum such as a fluid. Like the atmosphere for example. The atmosphere also interacts with the oceans. Both interact with the biosphere which is of course an adaptive system. All interact with our tame G2 yellow dwarf (aka Sol) which quite frankly we don’t really understand that well at all.

I have mentioned Solar System Dynamics but that wasn’t really my field. My field was fluids. And if any bugger tells you the “science is settled” on global warming then I advise you to laugh yourself hoarse and remember the disturbing function. Because anyone who claims that the “science is settled” is claiming that a scientific problem several orders of magnitude more complex**** than anything ever solved before is indeed down.

And not just that but solved by the fiat of a committee. With the help of a failed politician and profoundly successful cunt.

And then remember the disturbing function and our limits. Maybe even remember the ultimate “Physics for Poets” physicist, Richard Feynman. Whilst designing the “gadget” at Los Alamos in the forties his wife, Arline, was dying of TB, a bacterial infection. We have never known it all and complexity is the eternal stumbling block. You want an atom bomb designing? You want a laser? You want a moon-shot? Ask a physicist. You want complexity? Ask someone else. Because we are poets and we just don’t know.

*It used to be called “Celestial Mechanics” but I think we can all agree that that sounds needlessly messianic.
**I say book but it was a really a spiral-bound draft back then typeset in Latex and photocopied.
***There are imaginary numbers. They are multiples of the square root of -1.
**** Science, especially physics is exceptionally good at tackling the difficult. It is remarkably poor at tackling the complex. In principle all biology reduces to chemistry and all chemistry to physics. Except that ain’t how it is in practice. There is still a place for the bug-collectors and the smell-merchants and that is for a good reason. You can write out the Schroedinger equation for a dog but it won’t get you anywhere. If you wanna know dogs then you’ll get much further going to the park and throwing a stick.

8 Comments

  1. DavidNcl says:

    I found the whole non-linear dynamics / turbulent flow stuff profoundly depressing when I was 20. At 50 I rejoice in it. We’ve only begun; centuries – even millennia – of work lads, still to do. Get to it.

    Maybe in a very distant future our descendants will be able to understand humans or societies or climates from the quarks (or stringy bags or 3d holographic qbits or whatever) up. But it will be fuck of a long time.

  2. Pa Annoyed says:

    NickM,

    Speaking of celestial dynamics, here’s a nice (not safe for mathophobes) application for a simplified and approximated version of the 3-body problem. Or if you just want to look at pretty pictures, there’s slides 13 and 20 here, which show cross-sections through an orbit (a necessary simplification so you can see what’s going on). I think there are some better pictures around but I forget where they were. I thought you might find it interesting.

    In case it’s not immediately obvious, they’re magic orbits that allow you to fly between the planets without expending any energy or reaction mass, so long as you don’t mind your orbit being a bit chaotic. Apparently, they’ve used it in practice for planning a couple of missions.

    But of course, the solar system is simple and predictable compared to the weather – even the ancient Greeks noticed that. Do you know what resolution the climate computers model the atmosphere at?!

  3. Sam Duncan says:

    Eeeeeexactly. I guessed about halfway through where you were going with that, Nick.

    I didn’t understand a word of the explanation of the function, let alone all the letters and squiggly lines, but I can recognise that it’s bloody complicated, and that the more variables you bung into a problem the more bloody complicated it gets because they interact with all the others. (In other words, I sort of understand maths; I just can’t do it. Much like sport, now that I think of it: I know exactly how to bowl a googly, but my hands – and arms, and legs – just don’t work like that.) And there are a lot of variables in the climate.

    It used to be called “Celestial Mechanics” but I think we can all agree that that sounds needlessly messianic.

    Way cooler, though. (Bonus points for the Hitchhiker’s reference, I think…)

  4. El Draque says:

    I agree with you, Sam, I am also fascinated that people can do maths and understand those equations. My brain just hurts. I’ve read the popular ones like Hawking, but the serious ones, well, it’s another language.
    Respect all round.
    I too guessed what the point was, good bit of subtle drift.
    Reminds me of another great man, Friedrich Hayek. His argument for a free economy was that nobody – no government, no bureacrat, no scientist – can ever know what everyone wants and balance the different wishes of different people, not least because they change with time and with the cost of delivery.
    The result of trying – is serfdom.

  5. West2 says:

    It is far simpler than at first glance.

    Complexity and understanding are in-verse to each other.

    (day job beckons…)

    west
    —-

  6. Nick M says:

    Well, Sam thanks for noticing the Hitchhiker reference. Doug Adams was worth a whole ton of popular science writers.

    Exactly, ED. I have never read Hayek but to me that’s bleeding obvious. I dunno what you do for a living but lets imagine you sell jeans for a living. Now predict whether or not I wanna buy a pair of pants tomorrow.

    Well… I do want to buy some new strides. But not tomorrow. I have a job on in Buxton 20 miles away then. And there is absolutely no way you could know that.

    You need a physicist – an exact scientist – sometimes to know when to walk away.

  7. Rob Fisher says:

    Great post. I’m with Sam on understanding maths but not being able to do it.

    Seems even particle mechanics don’t always work out as expected: ISTR there are a few space probes that aren’t quite where they are expected to be.

    By the way, for some reason canonical and secular numbers makes me think of Anathem by Neal Stephenson, which I think you’d enjoy.

  8. RAB says:

    I wish I had been good at maths, but it is mainly gobbledegook to me.

    Funnily enough I was chatting to my friend, a professor of maths at Bristol Uni, while walking our dogs only yesterday. He is definately in the poetry camp.

    I keep telling you Nick, you should write a Science Primer.
    You would make a fuckin fortune, and God knows there is need of one, the state Science Education is in in Britain.

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