Reply To: Some Web Buttons I Made

[Arvid]

Well, that’s most of what I meant by decrying the Bohr atom, was this picture of the proton in particular, as a hard, positively-charged billiard ball, that must be made of positively-charged parts that would fly apart if given a chance.

Here’s a picture that helps me visualize the whole thing—I can’t pretend it’s justifiable from a quantum-mechanical standpoint. Think of trying to stuff some cotton batting into your couch cushion. It’s really good stuff—so fluffy that it forms a cloud 40 or 50 miles across on this scale—but I’ve got big hands, so I just keep squeezing and squeezing and squeezing until I’ve got it compressed so small that it’ll fit inside the cushion, so I jam it in and zip it up. Problem is, just like compressing a spring, I’ve stored a tremendous amount of energy in it by squeezing it so tight, and it’ll just burst right back out.

So why doesn’t it just combine with the proton to form a neutron? I’ve undoubtedly given it enough energy for it to do so. I think you have to look one layer deeper and realize that the proton is composed of three quarks, staying fairly close together in the center of what we call the “radius” of the proton. Just like the atom, most of the proton is empty space too. The quarks are kept from wandering apart by the color force, but since it has three different kinds of charge, it’s even harder to explain than electric charge, so just take it as read.

It helps me to think of the hydrogen atom as formed of 4 quarks—3 colored quarks that form the proton, and one “colorless” quark that’s only held to them by the electric force, so it’s not bound nearly as tightly. If I force it into proximity with the other quarks, some “magic” has to happen to change the consistency of my cotton batting so it’ll stay inside my couch cushion. We call this magic the weak force. It can change the identity of the electron into a down quark and therefore the proton into a neutron. If you sit around waiting for magic to happen, though, it might take a while—most times when you force an electron into a proton it won’t.

Well, now we’ve mentioned the color force and the weak force, so it appears that we’ve made the problem worse. Maybe it’s elephants all the way down! It may help people to realize that there’s more than one kind of charge, though. Gravitational charge is called “mass” and there’s only one kind. Color charge has three kinds. It’s just a fact of life at the quantum level that if we add enough energy to do something like turn a proton and electron into a neutron, we may just create new particles out of the vacuum that can do unexpected things. The world is a much more interesting place than Lord Kelvin thought it was!