The Cosmic Landscape (15 page)

And if the Laws of Physics can be different in other vacuums, so can all of science. A world with much lighter electrons but heavier photons would have no atoms. No atoms means no chemistry, no periodic table, no molecules, no acids, no bases, no organic substances, and of course, no biology.

The idea of universes with alternative laws of nature seems like the stuff of science fiction. But the truth is more mundane than it sounds. Modern medical technology routinely produces alternative universes inside MRI machines. The abbreviation MRI was not the original name for this technology: it replaced NMR, which stands for Nuclear Magnetic Resonance. But patients got scared by the word
nuclear
and wouldn’t go near the thing. So the name was changed to Magnetic Resonance Imaging to emphasize the magnetic aspects of the technology instead of the nuclear. In fact the nuclei that are involved in NMR are not uranium or plutonium nuclei as in nuclear warheads, they are the patient’s own nuclei that are ever so gently tickled by the magnetic field of the machine.

An MRI machine is basically a cylinder of empty space with a coil of wire surrounding it. An electric current through the coil creates a powerful magnetic field in the cylinder. It’s essentially a very strong electromagnet. The patient in the interior of the MRI machine is in a small private universe, where as we will see, the properties of the vacuum are slightly different from those on the outside. Imagine waking up one morning inside the machine, not knowing where you were. Something would seem amiss about the Laws of Physics. The most obvious thing you would notice is that iron objects would move in very odd ways, even presenting serious danger. If you happened to have a compass, it would rigidly lock into place along some particular direction.

It probably wouldn’t be a good idea to have a TV in the MRI machine, but let’s suppose you did. The picture would be distorted in bizarre ways. If you know how a television operates, you would trace the strange distortion to the motion of electrons. The strong magnetic field inside the cylinder exerts forces on the electrons that curve their trajectories from straight lines to corkscrew spirals. A theoretical physicist who knew about Feynman diagrams would say that something was different about the electron propagator. The propagator is not just a picture of an electron moving from one point to another, it’s also a mathematical expression that describes the motion.

The constants of nature would also be slightly unusual. The strong magnetic field interacts with an electron’s spin and even modifies the electron’s mass. Funny things happen to atoms in strong magnetic fields. The magnetic forces on the atomic electrons cause the atom to be slightly squashed in directions perpendicular to the field. The effects in a real MRI machine would be tiny, but if the magnetic field could be made much stronger, atoms would get squeezed into strands resembling spaghetti along the magnetic field lines.

The effects of the magnetic field can also be detected from small changes in the energy levels of atoms and, consequently, the spectrum of light they emit. There are changes in the precise manner in which electrons, positrons, and photons interact with one another. If the field were made strong enough, even the vertex diagrams would be affected. The fine structure constant would be a little different and depend on which way the electron moves.

Of course the field in the MRI machine is very weak, and the effects on the laws regulating charged particles are minute. If the field were very much stronger, the patient would feel funny. A field strong enough to seriously affect those laws would be absolutely fatal. The effects on atoms would have terrible consequences for chemical and biological processes.

There are two ways to view this, both of which are right. One is conventional: the Laws of Physics are exactly what they always were, but the environment is modified by the presence of the magnetic field. The other way to think about it is that the rules for Feynman diagrams have been changed and that something has happened to the Laws of Physics. Perhaps the most precise thing to say is:

The Laws of Physics are determined by the environment.

Fields, as we’ve seen, are invisible properties of space that influence objects moving through them. The magnetic field is a familiar example. Everyone who has played with magnets has discovered the mysterious action-at-a-distance forces they exert on paper clips, pins, and steel nails. Most people who have had a science course in school have seen the effect of a magnetic field on iron filings—tiny bits of iron—sprinkled on a surface in the vicinity of a magnet. The field assembles the filings into long filaments that look like hairy threads, lined up along the direction of the field. The filaments follow mathematical lines called
magnet lines of force
or
magnetic field lines.
The magnetic field has a direction at every point, but it also has a strength that determines how forceful the field is in pushing pieces of iron. In the MRI machine the field is more than ten thousand times stronger than the earth’s magnetic field.

The electric field is a slightly less familiar close relative of the magnetic field. It has no observable effects on iron filings, but it causes small bits of paper to move when there is some static electricity on them. Electric fields aren’t caused by electric current but by accumulations of static electric charge. For example, rubbing one material on another—your rubber shoe soles on the carpet, say—causes the transfer of electrons. One material becomes charged negatively, and the other positively. The charged objects create an electric field around them that, like magnetic fields, have both direction and strength.

Ultimately the Laws of Physics are variable because they are determined by fields, and fields can vary. Switching on magnetic and electric fields is one way to change the laws, but it is by no means the only way to modify the vacuum, or even the most interesting way. The second half of the twentieth century was a time of discovery of new elementary particles, new forces, and above all, new fields. Einstein’s gravitational field was one, but there were many others. Space can be filled with a wide variety of invisible influences that have all sorts of effects on ordinary matter. Of all the new fields that were discovered, the one that has the most to teach us about the Landscape is the
Higgs field.

The discovery of the Higgs field wasn’t an experimental discovery in the usual sense.
³
Theoretical physicists discovered that the Standard Model, without the Higgs field, is mathematically inconsistent. Without it the Feynman rules would lead to nonsensical results like infinite and even negative probabilities. But theorists in the late 1960s and early 1970s figured out a way to fix all the problems by adding one additional elementary particle: the Higgs particle.

Higgs particle, Higgs field—what’s the connection between particles and fields that leads us to call them by the same name? The field idea first appeared in the mid-nineteenth century in the form of the electromagnetic field. Michael Faraday imagined a field to be a smooth disturbance in space that affects the motions of electrically charged particles, but the field itself was
not
supposed to be made of particles. For Faraday, and Maxwell who followed him, the world was composed of particles and fields, and there was no doubt whatsoever about which was which. But in 1905 Albert Einstein, in order to explain Planck’s formula for heat radiation, proposed an outlandish theory. Einstein claimed that the electromagnetic field was really composed of a very large number of indivisible particles that he called photons. In small numbers, photons, or what are the same thing, light quanta behave like particles, but when many of them move in a coordinated way, the whole collection behaves like a field—a
quantum field.
This relation between particles and fields is very general. For each type of particle in nature, there is a field, and for each type of field there is a particle. Thus, fields and particles often go by the same name. The electromagnetic field (the collective name for electric and magnetic fields) could be called the
photon field.
The electron has a field. So, too, does the quark, the gluon, and each member of the cast of characters of the Standard Model, including the Higgs particle.

When I say that the Standard Model is mathematical nonsense without the Higgs field, I should qualify the statement. The theory without the Higgs field is mathematically consistent, but
only
if all particles move with the speed of light, like the photon. Particles that move with the speed of light cannot have any mass, so physicists say that the Higgs field is necessary in order to “give the elementary particles their mass.” In my opinion this is a poor choice of words, but I can’t think of a better one. In any case this is an important example of how the value of a field can influence the constants of nature.

Nobody has ever seen a Higgs particle, even in the indirect way that experimental physicists “see” particles. The difficulty isn’t in detecting them but is in producing them in the first place. The problem is not a fundamental one; to produce a particle as heavy as the Higgs, you simply need a bigger accelerator. But both the Higgs particle and Higgs field are so important to the success of the Standard Model that no one seriously questions their existence.
⁴
As I write this book, the construction of an accelerator is nearing completion in the European Organization for Nuclear Research (CERN) that should easily do the job of producing the Higgs particle.
⁵
Just about forty years will have passed from the time the Higgs particle was first discovered by theorists to the time of its detection.

If it were as easy to “switch on” the Higgs field as it is to switch on the magnetic field, we could change the mass of the electron at will. Increasing the mass would cause the atomic electrons to be pulled closer to the nucleus and would dramatically change chemistry. The masses of quarks that comprise the proton and neutron would increase and modify the properties of nuclei, at some point destroying them entirely. Even more disruptive, shifting the Higgs field in the other direction would eliminate the mass of the electron altogether. The electron would become so light that it couldn’t be contained within the atom. Again, this is not something we would want to do where we live. The changes would have disastrous effects and render the world uninhabitable. Most significant changes in the Laws of Physics would be fatal and therein lies a tale that we will return to repeatedly.

By varying the Higgs field, we can add diversity to the world; the laws of nuclear and atomic physics will also vary. A physicist from one region would not entirely recognize the Laws of Physics in another. But the variety inherent in the variations of the Higgs field is very modest. What if the number of variable fields were many hundreds instead of just one? This would imply a multidimensional Landscape, so diverse that almost anything could be found. Then we might begin to wonder what is not possible instead of what is. As we will see this is not idle speculation.

Whenever mathematicians or physicists have a problem that involves multiple variables, they think of a space representing the possibilities. A simple example is the temperature of the air. Imagine a line with a mark representing 0 degrees Fahrenheit, next to it a point representing 1 degree, another point at 2 degrees, and so on. The line is a one-dimensional space representing the possible values of the temperature. A point at 70 degrees would represent a beautiful, mild day; the point at 32 degrees, a freezing winter day. The temperature indicator on an ordinary household thermometer is exactly this kind of abstract space made concrete.

Suppose that in addition to a thermometer outside the kitchen window, we also have a barometer to measure the air pressure. Then we might draw two axes, one to represent temperature and one to represent atmospheric pressure. Again, each point, now in a two-dimensional space, represents a possible weather condition. If we wanted even more information—for example, how moist the air is—we might add yet a third dimension to the space of possibilities: humidity.

The temperature, pressure, and humidity combined tell us more than just the temperature, pressure, and humidity. They tell us something about the kinds of particles that can exist: in this case not elementary particles but droplets of water. Depending on the conditions either snowflakes, liquid drops, or sleet particles can move through the atmosphere.

The Laws of Physics are like the “weather of the vacuum,” except instead of the temperature, pressure, and humidity, the weather is determined by the values of fields. And just as the weather determines the kinds of droplets that can exist, the vacuum environment determines the list of elementary particles and their properties. How many controlling fields are there, and how do they affect the list of elementary particles, their masses, and coupling constants? Some of the fields we already know—the electric field, the magnetic field, and the Higgs field. The rest will be known only when we discover more about the overarching laws of nature than just the Standard Model. At the present time our best bet for these higher-level laws—our only bet—is String Theory. In chapters 7 and 8, we will see that String Theory has an unexpected answer to the question of how many fields control the local vacuum weather. From the current state of knowledge, it seems that it is in the hundreds or even thousands.