In today's "Ask a Physicist" we look at why electrons don't fall into their atomic nuclei, destroying all matter in the universe in the process.
I'm going to skip the preamble, the dissection of the questions asked, requests for superhero questions, and needlessly wordy plugs, and do some old school quantum mechanics today. Our question comes from Lisa Hewus who asks:
Why is it that the negatively charged electrons do not "stick" to the positively charged protons of an atom when they are at their lowest energy state?
Or, to put it another way, "Why doesn't all matter in the universe immediately collapse?" I realize that this is a bit more fundamental than some of the other things we've talked about, so if you know the answer, please don't ruin it for the rest of the class.
For those who don't already have their hands wildly flailing in the air, you'd be forgiven if you had a mistaken picture of atoms like the ones drawn in the logos of the Nuclear Regulatory Commission or the Springfield Nuclear Power Plant. In the cartoon version, there's a nucleus at the middle with a bunch of electrons flying around in orbits, very much like the planets orbit the sun.
But this model has a serious problem. You need to constantly accelerate a particle to move it in an orbit, but if you accelerate a charged particle, it gives off radiation. That's how a radio transmitter works. The upshot is that if you really had a planet-like electron flying around a nucleus, it would constantly give off light.
The energy for that radiation would have to come from somewhere, and the electron is the only possible source. Just like in a gravitational field, the electron would lose energy by falling ever closer to the nucleus. This would happen ridiculously quickly. For a hydrogen atom, it would take about 1 hundred billionth of a second for the electron to slam into the nucleus, destroying the atom entirely. The fact that atoms last much longer than that is a pretty good sign that something is wrong with the model.
So if you're thinking about an electron flying around in a particular place at a particular time then you're thinking about it the wrong way. When I talked about the double-slit experiment a few weeks ago, I said that an electron doesn't go through one slit or another; it really goes through both simultaneously. In the exact same way, there isn't a "somewhere" that the electron "really" is when it's orbiting a nucleus. It literally is in many places at once – each with some probability. The distributions of probabilities are those orbital clouds that you may remember dimly from chemistry class. And it's not just our measurement uncertainty that stops us from figuring out where the electron is. The universe really doesn't know. It also doesn't know what the speed or momentum is, which is why it really doesn't make sense to think about an electron "orbiting" the nucleus.