sol invictus
Philosopher
- Joined
- Oct 21, 2007
- Messages
- 8,613
Apparently so, and apparently it explains that individual charged particles follow predictable and mathematically quantifiable paths when exposed to EM fields. They individually and collectively share that trait.
That's true - but it's not useful when applied to 10^23 particles, because it's completely impossible to keep track of them all.
Yes one does have to learn to walk (with a single particle) before one can learn to run (with a bunch of them). It doesn't now however change the fact that these formulas relate to *PHYSICAL* things called "electrons", "ions" and "photons".
You still don't get it. Sure, the formulas of MHD "relate" to electrons, ions etc., because MHD is often used as an approximate description of fluids containing them. But it does not describe the particles or molecules the fluid is composed of in any way, shape, or form other than in huge quantities and under certain conditions. From the MHD description, you couldn't determine what the particles are.
Look - MHD can be used to describe an extremely hot plasma. It can also be used to describe salty water at room temperature. Precisely the same theory, the same equations with a few parameters different - and yet the particles involved are totally different. Why does it work? Because the collective behavior in both cases is governed by the fact that both are fluids and both are electrically conductive. It makes almost no difference what the particles are, and the MHD approximation doesn't describe those differences.
Yes I would, and of course the "properties" (like the freezing point) of water are of interest. For instance, water does not behave in space at all the way "Newtons theories" might expect.
Freezing point is a good example, actually. When water freezes, the hydrodynamic description totally breaks down. So that's one parameter you need if you want to know when hydrodynamics is valid (although of course knowing that still doesn't mean you know what the molecular constituents are). Similar things go for MHD - it will break down in various regimes (tus can tell you more about that than I can), and it's clearly desirable to know where. But MHD itself doesn't contain much information about where it will break down, any more than the Navier-Stokes equations for water tell you about the water-ice phase transition - that's something external you have to know about.
Don't you mean dihydrogen monoxide?
Oops - thanks.

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