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I’m using a brief lull this weekend (including today) to catch up on some reading I should have done weeks ago. Here’s an interesting passage (Griffiths, pg. 103):

A deuteron can be pulled apart, but only by pumping enough energy into the system to make up the difference. (If it puzzles you that a bound state of p and n should weigh less than the sum of its parts, the point is that the binding energy of the deuteron—which, like all internal energy, is reflected in its rest mass—is negative. Indeed, for any stable bound state the binding energy must be negative; if the composite particle weighs more than the sum of its constituents, it will spontaneously disintegrate.)

This is interesting in light of the last Physics 129 problem set, where we were trying to describe the neutron’s charge distribution by breaking up into a proton and a virtual meson (labeling it “virtual” on the basis that neutron didn’t have enough rest mass to account for proton and a meson, of any mass). But maybe it wasn’t a “virtual” meson after all. Perhaps the neutron can be considered a bound state of two real particles: a real proton and a real π^-.

I’ll have to go through some estimates to see if this makes any sense at all.

Griffiths says in the introduction to Elementary particle physics,

If you were dealing with two macroscopic objects, and you wanted to know how they interact, you would probably begin by holding them at various separation distances and measuring the force between them. That’s how Coulomb determined the law of electrical repulsion between two charged pith balls, and how Cavendish measured the gravitational attraction of two lead weights. But you can’t pick up a proton with tweezers or tie and electron onto the end of a piece of string; they’re just too small.

Oh, really?

Well, I guess to be fair, we call it “optical tweezer” but it looks nothing like actual tweezers. But if you want superficial similarity tweezers, there’s always atomic force microscopy, which uses cantilevers that, fundamentally and materially, isn’t that different from tweezers or any other long, slender objects.