[FRIAM] The theory of everything

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Sooooo... I'm familiar with both Reynolds and Mach from my days at Lockheed. But Mach, as I (probably don't) understand it, is tied to sound only because that's an indirect measure of the medium's compressibility, sound being compression waves. In thinking about these "low Reynolds number" organisms, I can't help but wonder what the analog for the "speed of sound" is for them. It strikes me that E. coli live way above "Mach 1", they live near Mach ∞, right? But if the medium is effectively incompressible, can there be pressure gradients across the organism's membrane? There must be, right? Since these things have internal architecture, including vacuoles, movement like the amoeba's "processes" seems more interesting than the poloidal rotation he mentions. Does the amoeba "push" against its medium? Or simply "grow through it"?

One of the coolest things about tissues to me is that they engineer their world, extruding their tools and infrastructure like so many dorks with 3D printers. I've only briefly skimmed the Purcell paper, but I didn't see anything about if/how microorganisms might do the same. If the amoeba-like ones "grow" through the medium, rather than pushing/pulling, then maybe the analog for the Mach number is related to diffusion and gradients, which makes Purcell's discussion of it on point, but doesn't go far enough.

On 7/6/20 8:02 AM, Jon Zingale wrote:
> The version of "Life at low Reynolds number" that I am familiar with is this
> one:
> http://www.damtp.cam.ac.uk/user/gold/pdfs/purcell.pdf


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