A few weeks ago I wrote about the Human Genome Initiative, “biologists’ equivalent of the Apollo program.” But there’s an even bigger and more expensive initiative happening down in Texas that you might call physicists’ equivalent of Apollo.
This gigantic (in every sense of the word) project is called the Superconducting Super Collider, or SSC for short. (The fact that those are also the initials of the Saskatchewan Science Centre is purely coincidental, and I wouldn’t even mention it if it didn’t give me another opportunity to get the Science Centre’s name in print.) Its purpose, if you want to put it in the grandest possible terms (and I do) is nothing less than to recreate the conditions that existed at the very beginning of the universe.
The Superconducting Super Collider will accelerate two millimetre-wide beams of protons to within one kilometre an hour of the speed of light, then smash them together just to see what happens. What happens, naturally enough, is that a lot of the particles are destroyed, creating debris and releasing energy that can be detected and studied to learn more about the elementary particles that make up everything and how they interact with each other. It’s like figuring out what a couple of race cars are made of by running them into each other head-on then examining the pieces and skid marks. This is why such devices are also called “atom smashers.”
The SSC is the latest (and largest) in a long line of atom smashers. The first time a particle accelerator was used to study atomic structure was in 1932, when J. D. Cockcroft and E. T. S. Walton used an ordinary high-voltage transformer to accelerate protons to an energy of 700,000 electron volts. (An electron volt is the energy gained by an electron passing between electrodes having a potential difference of one volt.) Their accelerator created the first artificially produced nuclear disintegrations and earned the two English scientists a Nobel Prize.
During the ’30s R. J. Van de Graaff of Princeton University developed another kind of accelerator, using a generator he developed that could reach three million volts. Not only was it put to very productive use in nuclear research, it’s also done wonders for the Science Centre: it’s a Van de Graaff generator that makes visitors’ hair stand up in our popular static electricity show.
Other forms of accelerators followed. The betatron uses magnetic fields to accelerate a beam of electrons in a circular orbit. The linear accelerator, or linac, uses alternating electrical fields to accelerate charged particles down a long tube. The first one used for nuclear research accelerated protons to 32 million electron volts. Today, the Stanford Linear Accelerator boosts electrons to more than 50 billion electron volts by squirting them down a tube 3.2 kilometres long.
The cyclotron uses electrical and magnetic fields to accelerate particles in a spiral. Cyclotrons have reached energies of more than 700 million electron volts, but technical difficulties limit their size.
The next step was the synchrotron, in which every increase in the electrical field accelerating the particles is matched by an increase in the magnetic field holding them in a roughly circular orbit. It appears that the only limit to the energies a synchrotron can reach is the size of the machine.
In 1952 the first proton synchrotron boosted particle energy above one billion electron volts. The CERN Laboratory in Geneva has one that can reach 500 billion electron volts, as does the Fermi National Accelerator Laboratory in Chicago. With the addition of superconducting magnets (remember last week’s column?) the Fermi accelerator has raised that to one trillion electron volts. A further enhancement, a storage ring in which particles circulate in opposite directions until they’re finally smashed together head-on, has raised the level to 1.8 trillion electron volts.
Which brings us at last to the SSC. It, too, is a synchrotron using a storage ring and superconducting magnets (which, by the way, will have to be cooled with liquid helium unless the new materials I wrote about last week come to the rescue). It’s designed to reach energy levels of 40 trillion electron volts by smashing together two 20-trillion-electron-volt beams.
Remember what I said about synchrotron being limited only by size? To reach the 40 trillion electron volts mark, the Superconducting Super Collider is going to have to be big. Really, really, really big. It will be built underground, in a tunnel 3.5 metres in diameter, shaped into a rough oval 87 kilometres in circumference. It will require 10,000 superconducting magnets, each one 20 metres long and weighing more than eight tonnes, and will cost at least $7 billion U.S. It’s being built in Ellis County, Tex., chosen for its stable geological formations, its regional resources, its environment and its setting.
The Superconducting Super Collider will test the Standard Theory of the nature of matter. Specifically, it should be able to find Higgs particles, which physicists have theorized to explain how other particles come to have mass, but which can’t be seen at the current energies available. But even more important will be the discoveries which no one even suspects now. “We don’t know what will be there (at 20 trillion electron volts),” says Sidney Drell, chairman of the U.S.’s High-Energy Physics Advisory Panel. “That is the great surprise.”
There are those who argue against the project on the grounds of cost (particularly the fear that the U.S. government will shortchange other scientific funding to continue to pay for the SSC), environmental concerns (the project involves 19,000 acres of farmland), and because they feel its location was motivated by political concerns, not scientific ones.
But even the critics admit one thing: the Superconducting Super Collider, the ultimate particle accelerator, will give us new insights into how the universe is put together.
Will it answer all the questions? No. In fact, it will undoubtedly raise new ones.
But asking new questions, after all, is what science is all about.
