barycenters

Good evening, cherished readers of this already-depraved sector of the net known as nomenclature. I’m here to get out ahead of myself, really, and start one of the series of posts I’ve always wanted to, every single time I wanted to start blogging — and I’m going to do it on beers. That’s right; how else am I going to get you to suffer through how preposterously neoliberal I sound when confined to sentence case, eh? eh? …Lord, okay. It’ll get better eventually, probably. In my defense, you’re reading a science-based blog written by a talking molecule — what were you expecting?

Anyways, barycenters are a weird thing. Well, let’s back up — models are a really weird thing. To make the entire history of intellectual inquiry a short story, a theory — or model — of reality is just something you make up to explain observations you make of reality. This can be something as simple as ripping a piece of notebook paper perfectly down the seam every single time, or something as complicated as, like, quantum physics or whatever. They’re just, essentially, special ideas that make magical sense of the world, really. What else could they be, even? You should be seeing now that you model all sorts of nonsense in your head every day, right down to things as mundane as why that asshole cut you off in traffic last Tuesday (his wife was eight centimeters dilated goddamnit! it was a fucking emergency!) or whatever — that only becomes a theory when you get paid to do it, really. Fortunately for those fearful of any further ranting from me on, like, life and Stuff, this series is just going to pertain to those theories — but I’ll be talking about them like the models that you and I make in our everyday lives to explain phenomena.

Two Bodies

If you’ve ever talked to a dweeb (like me) that has entirely too many hours in Kerbal Space Program, about Kerbal Space Program, you’ve probably heard of two-body physics simulations. These simplistic physics simulations allow the calculation of three-dimensional orbits about celestial bodies with calculative ease, making the task simple enough that even the worst laptop you could fathon could reliably keep up when asked to perform them regularly. The simplification they make is that gravitation occurs only between a secondary object subjected to the gravitational force of a primary object; immediately, this fails to completely model reality because in the real world, both bodies exert gravitational force on one another. This force is negligible between a spacecraft and a celestial body, but enough to produce the tides when the interaction is had between two celestial bodies at range; let alone closer.

Only when several bodies are allowed to attract one another in a simulation do results begin to truly predict reality over long periods of time, and the best results are found when all bodies in a system attract one another simultaneously. This is, of course, a nightmare to compute, but is the only way to go if you’re planning a real-life long-term space mission that cost $2 billion dollars and two billion man-hours in haggling to fund. Still, at the end of the day, $2 billion is thrown at a model, a model where the bodies of the solar system are allowed to gravitate one another of hours and hours, truly innumerable compute cycles; a model validated by billions of human-hours of labor, yes, but a model no less.

Has this produced a significant error yet? No. New Horizons, the farthest-trekking deep space mission launched by any space agency yet, was only 72 seconds late — and it took 9 years for it to reach Pluto from Earth. Still, simplistic n-body physics where every body as a point mass is allowed to gravitate fails to capture reality even still. Indeed — and this may break your brain — but celestial bodies are not point masses, or big video game objects you can clip into, or otherwise imaginary. They’re just big clumps of dirt. Earth, as a big clump of dirt, only allowed Newton to imagine the deranged nonsense of ‘gravitation’ and ‘force,’ even, because every single atom within every single microcrystalline segment of every single fragment of dirt simultaneously attracts every single atom everywhere else in the entire universe with a force informed by their distance from one another and their masses. Truthfully, when you’ve got all that dirt hanging out in space, it tends to just clump up due to this for the same reason — though this seems more likely in the brain when things like the inverse square law and remembered — and stars and all this other nonsense form, ultimately, from the same attractive forces between trillions upon trillions upon trillions upon… yeah. This fact rears its ugly head in the form of gravitational anomalies, which can be mundane geographical findings or significant celestial body features that you can use to dispose a spacecraft — they’re literally caused by extra dirt. Still, simpler n-body simulations can satisfactorily simulate so much real space travel, and this is because the largest dust clumps are a massive deal.

Barycenters are a great example of this. Whether you pretend your celestial bodies are “point masses” and allow them all to gravitate one another individually because that makes it “better” or you accept that it is all dust and simulate it in your brain like the champion of mentation you really are, dynamical points — in short, something totally made up that looks totally real — called barycenters are going to emerge. Mathematically, a barycenter represents the center of mass of a several-body system you’re simulating on a laptop or careening through as a particle; they take up such a central role in talking about astronomy because, well, everything seems to orbit one. The Earth and Moon, for one, collectively appear to orbit the Earth-Moon barycenter — simple enough, right? — but it only gets worse. Name a system, any system, and it posesses a barycenter that explains the orbital behavior of the contained bodies better than just “oh, shit, heliocentrism, I guess.” Take that Gallileo, you fraud! I’m serious! Well, sort of — thanks Gallileo, sorry about you dying or whatever — but the solar system (including the Sun) revolves around the center of mass of all mass in the solar system. In our solar system, that point is usually outside of the Sun, too, thanks to Jupiter and Saturn meandering out beyond the asteroid belt at the masses they posess; this means that even the Sun has an orbit within the frame of reference of the godforsaken solar system. Insane. Nothing else can really be said other than that aren’t you really fucking glad you don’t have to simulate every single goddamned particle in the Solar System to harness that observation for the future? If you aren’t an astronomer, imagine really hard how an astronomer would feel.

Feels really relieving, right?

— geosmin j.