Fish don’t swim, they’re swum

Matt Webb1 on how human perception limits our understanding of how the world around us really works:2

Fish swim by using the surface physics of their skin to create and exploit low pressure micro vortices in the water.

fish somehow exploit the vortices to reduce the amount of energy they need to combat the momentum of the flowing water.

And, in particular:

It appears that if there are no useful vortices already formed in the water (e.g. by rocks etc) – the trout can actually make some itself - and then extract energy from them.


The skin is vital:

The scales create a ‘one way surface’.

Vortices in the water are generated by the skin, and the side-to-side movement of a trout is the fish slipping between the vortices, pinballing between them, propelled on them like a boat on wind. (Shown, says the article, by the fact a dead trout on a line in moving water will still exhibit the characteristic swimming action.)

All of which leads to this REMARKABLE line: [Emphasis added. JR]

Fish don’t swim, they’re swum.

ARGH. Too good. Am dead now.

All of which leads Matt to this conclusion:

[Emphasis added again, because this is the really important bit. JR]

LOOK: wheels are great because they make movement easier – but it turns out there are other mechanisms (surface physics, rapidly evolving vortices, one-way skin) which similarly lower the energy for motion.

But they are hard for us humans to imagine. And hard to discover! And hard to do! These new kinds of wheels operate at scales which are outside the human everyday. We don’t derive them as simple solutions to equations. We stumble around in the dark and find them in the corners.

The whole post reminds me of the truth of a quote I remembered from when I read something Arthur C Clarke wrote3 many years ago: "The Universe is not only stranger than we imagine; it is stranger than we can imagine."

  1. Apologies to Matt for the lengthy quote from his post - though it's only a small portion of one of the examples he quotes in his original post. I urge you (obviously) to follow my link to his original post, because it's definitely worth it. I just wanted to capture the way he gets to that last phrase he quotes from his source. Mind blown! 
  2. NB: All the phrases that Matt quotes in his post and show as second-level quotes here are from this site. Here at Sore Eyes, as I've never adopted the neat quotebacks system Matt uses at Interconnected I have to faff around with multiple levels of quoting text and liberal use of bold text to get something that's at best 25% as elegant as the method he uses on his site. That's entirely on me. 
  3. I misremembered that as a phrase from Arthur C Clarke, but in fact he was slightly adjusting an observation made by J B S Haldane. Whoever said it first, it definitely applies here.