Armageddon Science (3 page)

There simply isn’t a means on Earth of producing antimatter anywhere fast enough to meet the needs of an antimatter weapon program. At current rates it would take millions of years to make a single gram of antimatter. This is a problem Dan Brown recognizes in his book. He likens it to building an oil rig to produce a single barrel of oil. This would, of course, make for very slow production of oil that was very expensive.

Unfortunately, Brown then suggest that, just like with the oil rig, all we need to do is produce lots more antimatter from the same technology, because once we’ve got over the construction cost, it’s relatively cheap to produce. This is true of oil, but not of antimatter. It still takes much too much money to make antimatter for it to be an energy source as Brown suggests it could be. But there’s a bigger problem—efficiency.

It’s easy to think of antimatter as a very efficient source of power, because it produces vastly more energy per gram than any other source, including conventional nuclear energy. In that sense, it is efficient. But there’s another meaning of efficiency where it fails woefully. For an energy source to be practical, it has to produce more energy than you put in to produce the source in the first place.

To make antimatter takes considerably more energy than is released when the antimatter annihilates. Imagine it took two barrels of oil’s worth of energy to produce one barrel of the black gold. You wouldn’t bother to make the oil—it wouldn’t be commercially viable. Similarly, you would never use antimatter as an energy source. Unless you’ve already got some antimatter, it isn’t an energy source, it’s an energy sink. You would be better off directly using the energy required to make it than you would using antimatter.

And then you would need to put the antimatter somewhere. This is anything but trivial—in fact, it’s a huge challenge. You need to contain a substance that destroys matter on contact. It’s not like storing a strong acid, where you just have to find the right kind of resistive material. It doesn’t matter what kind of container you use, it will be zapped by the antimatter. So how do scientists cope with the tiny quantities they currently work with? They use insubstantial containers—vessels that make use of electromagnetic repulsion to hold antimatter in place.

Visitors to Shanghai in China will have experienced something similar. They can ride on a maglev train from Pudong airport to the city. This train has no wheels. It is lifted off the rails by magnetic levitation. Just as two toy magnets will push away from each other, strong electromagnets in the train and the track repel one other, holding the train cars floating a tiny distance above the track.

Containers (also called traps) for antimatter work in a similar way. The air is removed from the container, leaving as good a vacuum as possible. Strong electromagnetic fields are set up, acting from different directions, to produce a pinch point in the center of the container where anything with the same charge would be forced to sit by repulsion. Charged antimatter particles—typically positrons (antielectrons) or antiprotons—are injected into the trap and sit suspended by the field, not touching any normal matter.

This is described quite well in
Angels and Demons
(though the traps employed are too pretty and cinematic in their appearance). But Brown then blows the whole idea when he has an antimatter bomb hidden in the Vatican. When the Swiss Guards want to search for the device, they are told by the book’s heroine that the antimatter has the chemical signature of pure hydrogen.

Now, it is entirely possible to make antihydrogen, with an antiproton as its nucleus and a positron in place of the normal electron. As we’ve already seen, such antiatoms have been made at CERN since 1995. But an antiatom will inevitably be destroyed within a tiny fraction of a second of its creation, because there is no way of storing it. Unlike charged particles, the neutral antiatom can’t be held in an electromagnetic field trap. There is no way to get a grip on it. So the antiatoms annihilate almost immediately. If, as Brown suggests, the antimatter in the bomb had the chemical signature of hydrogen, it couldn’t be held in safe suspension. It just wouldn’t work.

Even if the antimatter bombers had been more sensible and used positrons or antiprotons, they would have had a problem. Imagine what happens as we pour more and more positrons into an electromagnetic trap. Each of those positrons has a positive charge. They will all be fighting to get away from one another. The more we put in, the harder it is to keep them in place. Only tiny amounts of antimatter—perhaps a few million particles—can be stored in a trap before the repulsion becomes too great and they start to leak out.

There wouldn’t be such a problem with antiatoms, like the antihydrogen in
Angels and Demons,
because the atoms aren’t charged. Large amounts could be squeezed into an antimatter bottle, just as much as normal hydrogen could be stored in a bottle made of ordinary matter. But there is no physical or magnetic container on the Earth that could keep those antiatoms in place and stop them from annihilating immediately with the matter around them. We can’t make an antimatter bottle.

We do have an example of handling a significantly bigger amount of dangerous charged particles, though—in a fusion tokomak. This is a vast magnetic container, shaped like a ring doughnut, that is used to contain the sunlike plasma that it is hoped will one day be at the heart of fusion power plants. Although the plasma isn’t antimatter, it would be very destructive if it came into contact with the walls of the tokomak. And there is considerably more matter in a tokomak like the Joint European Torus at Culham, England, than in any antimatter trap. But a tokomak is a big structure, the size of a large office building. It isn’t exactly portable, and certainly couldn’t be used to transport an antimatter bomb around.

Before antimatter can be stored, however small the quantity, it needs to be produced. At any one time there is a small amount of antimatter on the Earth from natural sources—both from emissions from nuclear reactions and from the impact of cosmic rays on our atmosphere. Usually, such particles are destroyed so quickly that we can’t do anything with them; but catch them quickly enough and they are valuable in a medical device, the positron-emission tomography or PET scanner.

For the PET scanner to work, a chemical based on a large molecule that the human body will process—typically the sugar fluorodeoxyglucose—is injected into the bloodstream. This carries with it small quantities of a radioactive isotope with a short half-life like carbon 11 or fluorine 18, which emit positrons as the nucleus decays. The large molecule is carried by the body into the tissue, taking the tracer isotope with it.

As the radioactive substance emits positrons, these antimatter electrons immediately interact with their normal-matter equivalents and are converted to energy in the form of a pair of high-energy gamma ray photons. These shoot off in opposite directions until they reach the doughnutlike detector that is around the relevant section of the patient’s body. Here, the gamma rays interact with a substance called a scintillator, which is stimulated by the gamma ray photons into giving off a burst of lower-energy light.

This is the same approach that was taken when nuclear decay was first discovered—but then the scintillator had to be observed in a darkened room by eye or through a microscope. In the PET scanner, that ring also contains electronics designed to take a small amount of light and amplify it, converting the tiny flashes that appear simultaneously on both sides of the ring into a signal that can be registered on a computer and built into a “slice-by-slice” image of the cross section of the part of the body of interest.

The PET scanner is an example of using a seminatural source of antimatter. The antimatter is produced in a natural fashion from the breakdown of the atomic nucleus, but those unstable, short-lived isotopes are produced artificially using a device such as a cyclotron, which is a small particle accelerator (typically the size of an SUV) located at or near the hospital where the scanner is to be used.

A more dramatic possibility for a fully natural source of antimatter is that there could be a whole universe of it out there, if only we could get access to it. When matter initially formed after the big bang, there was no particular reason why it should be purely conventional matter. In the incredibly high-energy state immediately after the big bang, energy would constantly be converted into pairs of matter and antimatter particles. In principle, there should have been equal amounts of matter and antimatter, which then would eventually wipe each other out, leaving a universe full of energy alone.

That this didn’t happen is usually explained by assuming that very subtle differences in the properties of matter and antimatter meant that there was a tiny extra percentage of matter—everything else was then wiped out, leaving only this excess. This theory, devised by Andrey Sakharov, the Russian physicist better known for being a political dissident, suggests that as a little as one particle in a billion survived the vast matter/antimatter wipe-out. But that was enough.

Some have speculated, though, that instead of the antimatter being destroyed in those early days of existence, the universe in some way became segmented, and that there are vast pockets of antimatter out there—perhaps on the same scale as our own observable universe. If the two ever came into contact, the result would be an outpouring of energy that would make every supernova ever seen combined look like a match being struck.

On a more practical level, antimatter is usually made in the laboratory as the product of a high-energy collision, for instance by shooting protons at a metal target. The antimatter doesn’t come from the matter but rather from the energy of collision. Just as happened with the seething energy after the big bang, a large amount of energy can spontaneously convert into a pair of particles—one matter, one antimatter.

It’s Einstein’s E = mc
²
equation working in reverse. Here energy is being converted into matter. The newly created pair of particles tend to fly off wildly, and normally the antimatter half would very soon smash into a matter particle and disappear back into energy. When antimatter is produced in the lab, though, the antimatter particle is braked by sending it through a sea of charged particles, which absorb energy, slowing it down, before it can be captured in a magnetic field and stored. This is a delicate process—too much damping and the antiparticle will be annihilated in the braking medium, but get it just right and you’ve caught yourself an antiparticle.

Sadly for Dan Brown fans, if not for the survival of the world, the
Angels and Demons
scenario fails on practically every level. We can’t make enough antimatter, we can’t keep more than a tiny amount of charged antimatter in a trap, any store that could hold a usable amount would not be transportable, and we can’t keep uncharged antimatter at all. The antimatter bomb, or any other form of antimatter weapon, is not likely to emerge from CERN, nor to be a danger to anyone in the foreseeable future.

But the production of antimatter is a relatively mundane and small-scale aspect of CERN’s potential as a source of destructive power. Now that the Large Hadron Collider has been brought to its full capacity, it is generating energies with a concentration that has never before been produced by human beings. There is no danger that this will destroy the whole universe and start things over again in a repeat of the big bang—although the energy is remarkably high, it is infinitesimal in scale compared to the real big bang, and there have been plenty of natural cosmic events since the early days of the universe with much more energy—but there are two possibilities for the LHC to produce destructive materials that could result in devastation.

All the scientists involved at CERN are very clear that these apparent sources of danger are nothing to worry about. They play down the risks. But then, they would. To some outside observers there seems plenty of reason for fear. As we will see later, an attempt has been made to take out an injunction against CERN to prevent the scientists there from destroying the universe.

The most likely dangerous-sounding products of the Large Hadron Collider are tiny, particle-sized black holes. Let’s take a step back from the Hollywood image of a black hole for a moment and understand what one is before we start to worry about what it could do. If you believed Hollywood, the black hole would be like an unstoppable space vacuum cleaner, sucking in anything and everything in its path, capable of destroying an entire galaxy as it sucks more and more material into its inescapable gravity field, all the time increasing its gravitational strength.

Before looking at what the LHC could create, it’s worth noting that black holes are theoretical constructs. No one has seen one directly. They’ve certainly not been experimented on. All we have is theory and indirect observation. It’s strong theory, and it’s very probably true, but there are alternatives that would explain the phenomena we believe are caused by black holes without the real things existing. To be fair to black-hole supporters, though—and that’s the vast majority of astronomers and cosmologists—there is a better basis for black holes’ existence than there is for many other cosmological phenomena.

The reasoning behind our assumption that black holes exist is twofold. They seem to be an inevitable conclusion of certain physical processes, even though those processes don’t have to have ever happened in reality; and various observations from deep space seem to suggest that black holes are more than just speculation.

The physical processes that make black holes likely are those that define how stars change and develop through their lifetimes. We haven’t been around long enough to watch a single star go through this process, which usually takes billions of years, but we’ve observed enough stars in different stages of their development to make it very likely that these theories for how black holes could form are correct.

Remarkably, the idea of special stars that don’t let out light was dreamed up over two hundred years ago. John Michell, an astronomer and geologist from England born in 1724, was thinking one day about the concept of escape velocity—something that eventually would be a crucial factor for the space program. If you throw a ball in the air, it falls back down to Earth.