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What, in the real world, approaches the speed of light?

The electrons in every iodine atom in every molecule of thyroxine in your body?

For some hazy reason I thought it was only the innermost electrons which "approached" the speed of light.

Would you happen to give some indication of the average magnitude of the velocity vector for say, a 1s vs. a 4s electron in iodine?

And how much does the orbital angular momentum quantum number affect an electron's velocity within a value of the principal quantum number?

Full Disclosure: Don't blame me. I only worked on Born-Oppenheimer surfaces so I tended to ignore minutae of electronic motion :-)

You replied to my post, which didn't really make this claim. [See the original by "Right Wing Professor."] As a former low temperature theorist gone bad (there isn't nearly as much money in new theories of the universe as there is in software development), I haven't had much occasion to consider the "velocity" of orbital electrons. I guess you could calculate it easily enough as the expectation value of <p/m> Not entirely sure what velocity means for a bound electron, though...

... Sherman, set the Way-Back-Machine for the early Roaring Twenties of De Broglie and Bohr, when they still thought electron velocity was an observable ...

The Bohr result was Z * e **2/(N * 4 * pi * epsilon-zero * hbar). (N=1,2,...) which is about (2.2 * 10**6)(Z/N) m/s. I guess that's decent enough for a back of the envelope calculation. For Iodine, you'd have to replace Z by Z(effective.) Even in the most wildly libertarian estimate (I refuse to do a liberal estimate on Free Republic) which is full Z, the 1s electron for iodine is 53 * 2 * 10**6 m/s, roughly 1/3 of the speed of light. Not taking the calculation very seriously--which is wise--it's a strong plausibility argument for claiming the "inner electrons" (again, whatever that means) DO see relativistic effects. The 4s electrons would be pretty well shielded, but even without shielding you're already down to 1/12 of the speed of light--which I, naively, not being a high energy physicist--would say is not really relativistic territory: the gamma differs from 1 by 3.5 * 10**-3. Throwing in that Z(eff) is probably somewhere between 1 and 2, and not 53, I'd say I'm on your side: the 4s electrons are firmly in Newton country.

But again, I think RWP's original point (which he actually flubbed a bit--see my post) is valid, in that relativity is an everyday phenomenon, and that you, while correct, are picking nits.