Coming in out of the cold: nuclear fusion, for real
For the last few years, mentioning cold fusion around scientists (myself included) has been a little like mentioning Bigfoot or UFO sightings.Skip to next paragraph
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After the 1989 announcement of fusion in a bottle, so to speak, and the subsequent retraction, the whole idea of cold fusion seemed a bit beyond the pale. But that's all about to change.
A very reputable, very careful group of scientists at the University of California at Los Angeles (Brian Naranjo, Jim Gimzewski, Seth Putterman) has initiated a fusion reaction using a laboratory device that's not much bigger than a breadbox, and works at roughly room temperature. This time, it looks like the real thing. [Editor's note: The original version misnamed the scientists' institution.]
Before going into their specific experiment, it's probably a good idea to define exactly what nuclear fusion is, and why we're so interested in understanding the process. This also gives me an excuse to talk about how things work deep inside the nuclei of atoms, a topic near and dear to most astronomers (more on that later).
Simply put, nuclear fusion means ramming protons and neutrons together so hard that they stick, and form a single, larger nucleus. When this happens with small nuclei (like hydrogen, which has only one proton or helium, which has two), you get a lot of energy out of the reaction. This specific reaction, fusing two hydrogen nuclei together to get helium, famously powers our sun (good), as well as hydrogen bombs (bad).
Fusion is a tremendous source of energy; the reason we're not using it to meet our everyday energy needs is that it's very hard to get a fusion reaction going. The reason is simple: protons don't want to get close to other protons.
Do you remember learning about electricity in high school? I sure do - I dreaded it whenever that topic came around. I had a series of well-meaning science teachers that thought it would be fun for everyone to hold hands and feel a mild electric shock pass their arms. Every time my fists clenched and jerked and I had nothing consciously do with it, my stomach turned.
In addition, I have long, fine hair, and was often made a victim of the Van de Graf generator - the little metal ball with a rubber belt inside it that creates enough static electricity to make your hair stand on end. Yeesh.
Anyway, hopefully you remember the lesson that two objects having different electrical charges (positive and negative) attract one another, while those with the same charge repel. It's a basic law of electricity, and it definitely holds true when two protons try to get close together. Protons have positive charges, and they repel each other. Somehow, in order for fusion to work, you've got to overcome this repulsive electrical force and get the things to stick together.
Here's where an amazing and mysterious force comes in that, although we don't think about it in our day-to-day lives, literally holds our matter together. There are four universal forces of nature, two of which you're probably familiar with: gravity and electromagnetism.
But there are two other forces that really only come in to play inside atomic nuclei: the strong and weak nuclear forces (and yes, the strong force is the stronger of the two, the weak is weaker. Scientists really have a way with names, dont they?) I'm going to focus on the strong force, as that's the one responsible for nuclear fusion.
The strong force is an attractive force between protons and neutrons - it wants to stick them together. If the strong force had its way, the entire universe would be one big super-dense ball of protons and neutrons, one big atomic nucleus, in fact.
Fortunately, the strong force only becomes strong at very small scales: about one millionth billionth of a meter. Yes, that's 0.000000000000001 meters. Any farther away, and the strong force loses its grip. But if you can get protons and neutrons that close together, the strong force becomes stronger than any other force in nature, including electricity.
That's important- all protons have the same charge, so they'd like to fly away from each other. But if you can get them close together, inside the volume of an atomic nucleus, the strong force will bind them together.