Fear of Physics (16 page)

There is another way to describe this phenomenon. Light, as I have indicated earlier, is nothing other than an electromagnetic wave. Jiggle a charge, and the changing electric and magnetic fields will result in a light wave that travels outward. The light wave travels at the speed of light because the dynamics of electromagnetism are such that the energy carried by the light wave cannot be considered to have any “mass” associated with it. Put another way, the microscopic quantum-mechanical objects that on small scales correspond to what we call an electromagnetic wave on macroscopic scales, called
photons,
have no mass.

The reason magnetic fields cannot enter a superconductor is because when the photons corresponding to this macroscopic field enter inside and travel through the background of all the electrons in their coherent state, the properties of these photons themselves change. They act as if they had a mass! The situation is similar to the way you act when you are roller-skating on a sidewalk, as opposed to roller-skating in the mud. The stickiness of the mud produces much more resistance to your motion. Thus, if someone were pushing you, you would act as if you were much
“heavier” in the mud than on the sidewalk—in the sense that it would be much harder to push you. So, too, these photons find it much harder to propagate in the superconductor, because of their effective mass in this material. The result is that they don’t get far, and the magnetic field doesn’t permeate the material.

We are finally ready to talk about how all of this relates to the SSC. I said that it is hoped this machine will discover why all elementary particles have mass. Before reading the previous few pages, you might have thought that no two subjects could be more unrelated, but in fact it is likely that the solution to the elementary particle mystery is identical to the reason superconducting materials expel magnetic fields.

Earlier I said that electromagnetism served as a model for the force in nature that governs nuclear reactions such as those that power the sun, called the “weak” force. The reason is that the mathematical framework for the two forces is virtually identical, except for one important difference. The photon, which is the quantum entity corresponding to electromagnetic waves, which transmit electromagnetic forces, is massless. The particles that transmit the weak force, on the other hand, are not. It is for this reason that the weak force between protons and neutrons inside a nucleus is so short-range and that this force is never felt outside the nucleus, while electric and magnetic forces are felt at large distances.

Once this fact was recognized by physicists, it wasn’t long before they began wondering what could be responsible for this difference. The same physics responsible for the weird behavior of superconductors suggests a possible answer. I have already described how the world of elementary-particle physics, where special relativity and quantum mechanics work together, has a weird behavior of its own. In particular, I argued that empty space need
not really be empty. It can be populated by virtual-particle pairs, which spontaneously appear and then disappear, too quickly to be detected. I also described in chapter 1 how these virtual particles can have an effect on observed processes, like the Lamb shift.

Now it is time to put two and two together. If virtual particles can have subtle effects on physical processes, can they have a more dramatic effect on the properties of measured elementary particles? Imagine that a new kind of particle exists in nature that has a close attraction to particles of the same type. If one pair of such particles burps into existence, as virtual particles are wont to do, it costs energy to do this, so the particles must disappear quickly if energy is not to be violated. However, if these particles are attracted to each other, it may be energetically favorable not just to pop a single pair out, but rather to pop two pairs. But if two pairs are better than one, why not three? And so on. It could be, if one arranges the attraction of these particles just right, that the net energy required of a coherent system of many such particles is, in fact, less than that in a system in which no such particles are around. In this case, what would happen? We would expect such a coherent state of particles spontaneously to generate itself in nature. “Empty” space would be filled with such a coherent background of particles in a special single quantum state.

What would be the effect of such a phenomenon? Well, we would not necessarily expect to observe the individual particles in the background, because to produce one real such particle moving on its own might require an incredible amount of energy, just as it costs energy to try to kick an electron out of its coherent configuration in a superconductor. Instead, as particles move amid this background, we might expect their properties to be affected.

If we were to arrange this background to interact with the particles that transmit the weak force, called the W and Z particles,
and
not
with photons, then we might hope that this could result in the W and Z particles effectively acting as if they had a large mass. Thus, the real reason the weak force acts so differently from electromagnetism would be due not to any intrinsic difference but rather to this universal coherent background these particles move through.

This hypothetical analogy between what happens to magnetic fields in a superconductor and what determines the fundamental properties of “nature” might seem too fantastic to be true, except that it explains every experiment undertaken to date. In 1984, the W and Z particles were discovered and since then have been investigated in detail. Their properties are in perfect agreement with what one would predict if these properties arose due to the mechanism I have described here.

What is next, then? Well, what about the masses of normal particles, such as protons and electrons? Can we hope to understand these, too, as resulting from their interactions with this uniform, coherent quantum state that fills up empty space? If so, the origin of all particle masses would be the same. How can we find out for sure? Simple: by creating the particles, called Higgs particles, after the Scottish physicist Peter Higgs, which are supposed to condense into empty space to get the whole game going. The central mission of the Superconducting Supercollider is usually said to be to discover the Higgs particle. The same theoretical predictions that reveal so well the properties of the W and Z particles tell us that the Higgs particle, if it exists, should have a mass within a factor of 5 or so of these particles, and this range is what the design of the LHC is chosen to explore.

I should say that this picture does not require the Higgs particle to be a fundamental elementary particle, like the electron or
the proton. It could be that the Higgs is made up of pairs of other particles, like the pairs of electrons that themselves bind with one another to form a superconducting state in matter. And why does the Higgs exist, if it does? Is there a more fundamental theory that explains its existence, along with that of electrons, quarks, photons, and W and Z particles? We will be able to answer these questions only by performing experiments to find out.

I personally cannot see how anyone can fail to be awestruck at this striking duality between the physics of superconductivity and that which may explain the origin of all mass in the universe. But appreciating this incredible intellectual unification and wishing to pay to learn about it are two different things. It will, after all, cost up to $10 billion spread over ten years to build the LHC. The real issue of whether to build the LHC is not a scientific one—no properly informed individual can doubt the scientific worthiness of the project. It is a political question: Can we afford to make it a priority in a time of limited resources?

As I stressed at the beginning of this book, I believe that the major justification of the advances in knowledge likely at the SSC is cultural, not technological. We do not talk much about the plumbing facilities of ancient Greece, but we remember the philosophical and scientific ideals established there. These have filtered down through our popular culture, helping forge the institutions we use to govern ourselves and the methods we use to teach our young. The Higgs particle, if discovered, will not change our everyday life. But I am confident that the picture it is a part of will influence future generations, if only by exciting the curiosity of some young people, causing them perhaps to choose a career in science or technology. I am reminded here of a statement attributed to Robert Wilson, the first director of the large
Fermilab facility currently housing the highest-energy accelerator in the world. When asked whether this facility would contribute to the national defense, he is said to have replied, “No, but it will help keep this country worth defending.”

FOUR

You wake up one icy morning and look out the window. But you don’t see anything familiar. The world is full of odd patterns. It takes a second for you to realize that you are seeing icicles on the window, which suddenly focus into place. The intricate patterns reflecting the sun’s light then begin to captivate you.

Science museums call it the “aha” experience. Mystics probably have another name for it. This sudden rearrangement of the world, this new gestalt, when disparate data merge together to form a new pattern, causing you to see the same old things again in a totally new light, almost
defines
progress in physics. Each time we have peeled back another layer, we have discovered that what was hidden often masked an underlying simplicity. The
usual signal? Things with no apparent connection can be recognized as one and the same.

The major developments in twentieth-century physics conform to this tradition, ranging from the fascinating discoveries of Einstein about space, time, and the universe, to the importance of describing how oatmeal boils. In discussing these “hidden realities,” I don’t want to get caught up in philosophical arguments about the ultimate nature of reality. This is the kind of discussion that tends to confirm my general view of philosophy, best expressed by the twentieth-century philosopher and logician Ludwig Wittgenstein: “Most propositions and questions that have been written about philosophical matters are not false, but senseless.”
¹

Wondering, for instance, as Plato did, whether there is an external reality, with an existence independent of our ability to measure it, can make for long discussions and not much else. Having said this, I do want to use an idea that Plato developed in his famous cave allegory—in part because it helps me appear literate, but more important, because building upon it allows me to provide an allegory of my own.

Plato likened our place in the grand scheme of things to a person living in a cave, whose entire picture of reality comes from images—shadows cast on the wall—of the “real objects” that exist forever in the light of day, beyond the person’s gaze. He argued that we, too, like the person in the cave, are condemned only to scratch the surface of reality through the confines of our senses.

One can imagine the difficulties inherent in the life of the prisoner of the cave. Shadows give at best a poor reflection of the world. Nevertheless, one can also imagine moments of inspiration. Say that every Sunday evening before the sun set, the following shadow was reflected on the wall:

And every Monday evening, the image below replaced it:

In spite of its remarkable resemblance to a cow, this is really an image of something else. Week in and week out the same images would be cast upon the wall, relentlessly changing and reappearing with clockwork regularity. Finally one Monday morning, awaking earlier than normal, our prisoner would also hear the sound of a truck combined with the clatter of metal. Being a woman of extraordinary imagination, combined with mathematical talent, she had a new vision suddenly pop into her head: These were not different objects, after all! They were one and the same. Adding a new dimension to her imagination, she could picture the actual extended object, a garbage can: