Why am I trans, and that person cis? I might as well ask why a bubble formed here, and not three millimetres to the left; why a storm grew in this part of the ocean and not that one; why that part of a leopard’s fur is dark and that one is light.

Fluid dynamicists spend a lot of time thinking about instabilities: when a heavy fluid accelerates into or sits on a light one, you get ‘fingers’ of material sinking in; when one fluid shears past another, the boundary twists into waves and vortices; where pressure suddenly drops below a certain point, cavitation bubbles form and then collapse.

We can’t say exactly where each vortex, or finger, or bubble will form - the system is chaotic, and a tiny variation in the initial conditions can produce a hugely different result. But we can work out that there will definitely be vortices in certain conditions: we can do some calculus and find out if a tiny change will be flattened back out or grow into a bigger and bigger change.

Though they may start small, and unpredictably, these fluid instabilities can make enormous differences to the world. The motion of continents is driven by unstable convection currents; Hawaii, and many other island chains, sit on a chain of volcanoes created by a plume of hot material.

We get it Bryn, you’re a nerd who likes physics. What’s this got to do with gender?

We can analyse the way our society produces people with genders and so on (I was reading this entry into the debate earlier today, though it has nothing specific to say about trans people); and we can observe, and attempt to theorise, how there seems to be some kind of self-exciting instability that makes the ‘socialisation’ process result in trans people instead of its ‘intended’ result, good little straight cis people ready to make babies and surplus value. Knowing this, we can think about how that plays out, conditions that make it likely, the violence it produces, and what role we end up playing in the system overall

What we won’t get is a predictive theory of ‘this person will be trans, this person will be cis’. I think it’s entirely possible that people might be the same in all the ‘relevant’ variables (like ‘did they experience childhood abuse’ or whatever), and yet one ends up determining that they need to transition and the other doesn’t.

(I’m not sure how useful this metaphor is for anyone but me, but it got lodged in my head on my way home tonight, and I figure I might as well exorcise it into a post - in case anyone else finds it helps them. )