Hyperspace (32 page)

Cosmic rays were first discovered 80 years ago in experiments performed by the Jesuit priest Theodor Wulf atop the Eiffel Tower in Paris. From the 1900s to the 1930s, courageous physicists sailed in balloons or scaled mountains to obtain the best measurements of cosmic rays. But cosmic-ray research began to fade during the 1930s, when Ernest Lawrence invented the cyclotron and produced controlled beams in the laboratory more energetic than most cosmic rays. For example, cosmic rays, which are as energetic as 100 million electron volts, are as common as rain drops; they hit the atmosphere of the earth at the rate of a few per square inch per second. However, Lawrence’s invention spawned giant machines that could exceed that energy by a factor of 10 to 100.

Cosmicray experiments, fortunately, have changed dramatically since Father Wulf first placed electrified jars on the Eiffel Tower. Rockets
and even satellites can now send radiation counters high above the earth’s surface, so that atmospheric effects are minimized. When a highly energetic cosmic ray strikes the atmosphere, it shatters the atoms in its wake. These fragments, in turn, create a shower of broken atoms, or ions, which can then be detected on the ground by this series of detectors. A collaboration between the University of Chicago and the University of Michigan has inaugurated the most ambitious cosmic-ray project yet, a vast array of 1,089 detectors scattered over about a square mile of desert, waiting for the cosmic-ray showers to trigger them. These detectors are located in an ideal, isolated area: the Dugway Proving Grounds, 80 miles southwest of Salt Lake City, Utah.

The Utah detector is sensitive enough to identify the point of origin of some of the most energetic cosmic rays. So far, Cygnus X-3 and Hercules X-l have been identified as powerful cosmic-ray emitters. They are probably large, spinning neutron stars, or even black holes, that are slowly eating up a companion star, creating a large vortex of energy and spewing gigantic quantities of radiation (for example, protons) into outer space.

So far, the most energetic cosmic ray ever detected had an energy of 10
²⁰
electron volts. This figure is an incredible 10 million times the energy that would have been produced in the SSC. We do not expect to generate energies approaching this cosmic energy with our machines within the century. Although this fantastic energy is still 100 million times smaller than the energy necessary to probe the tenth dimension, we hope that energies produced deep within black holes in our galaxy will approach the Planck energy. With large, orbiting spacecraft, we should be able to probe deeper into the structure of these energy sources and detect energies even larger than this.

According to one favored theory, the largest energy source within our Milky Way galaxy—far beyond anything produced by Cygnus X-3 or Hercules X-l—lies at the center, which may consist of millions of black holes. So, because the SSC was canceled by Congress, we may find that the ultimate probe for exploring the tenth dimension may lie in outer space.

Historically speaking, there have been many times when physicists have solemnly declared certain phenomena to be “untestable” or “unprovable.” But there is another attitude that scientists can take concerning
the inaccessibility of the Planck energy—unforeseen breakthroughs will make indirect experiments possible near the Planck energy.

In the nineteenth century, some scientists declared that the composition of the stars would forever be beyond the reach of experiment. In 1825, the French philosopher and social critic Auguste Comte, writing in
Cours de philosophie
, declared that we would never know the stars other than as unreachable points of light in the sky because of their enormous distance from us. The machines of the nineteenth century, or any century, he argued, were not powerful enough to escape from the earth and reach the stars.

Although determining what the stars were made of seemed beyond the capabilities of any science, ironically at almost the same time, the German physicist Joseph von Fraunhofer was doing just that. Using a prism and spectroscope, he could separate the white light emitted from the distant stars and determine the chemical composition of those stars. Since each chemical within the stars emits a characteristic “fingerprint,” or spectrum of light, it was easy for Fraunhofer to perform the “impossible” and to determine that hydrogen is the most abundant element in the stars.

This, in turn, inspired poet Ian D. Bush to write:

Twinkle, twinkle little star
I don’t wonder what you are,
For by spectroscopic ken,
I know that you are hydrogen.
⁶

Thus although the energy necessary to reach the stars via rockets was far beyond anything available to Comte (or, for that matter, anything available to modern science), the crucial step did not involve energy. The key observation was that signals from the stars, rather than direct measurement, were sufficient to solve the problem. Similarly, we can hope that signals from the Planck energy (perhaps from cosmic rays or perhaps an as yet unknown source), rather than a direct measurement from large atom smashers, may be sufficient to probe the tenth dimension.

Another example of an “untestable” idea was the existence of atoms. In the nineteenth century, the atomic hypothesis proved to be the decisive step in understanding the laws of chemistry and thermodynamics. However, many physicists refused to believe that atoms actually exist. Perhaps they were just a mathematical device that, by accident, gave the correct description of the world. For example, the philosopher Ernst
Mach did not believe in the existence of atoms, other than as a calculational tool. (Even today, we are still unable to take direct pictures of the atom because of the Heisenberg Uncertainty Principle, although indirect methods now exist.) In 1905, however, Einstein gave the most convincing, although indirect, evidence of the existence of atoms when he showed that Brownian motion (that is, the random motion of dust particles suspended in a liquid) can be explained as random collisions between the particles and atoms in the liquid.

By analogy, we might hope for experimental confirmation of the physics of the tenth dimension using indirect methods that have not yet been discovered. Instead of photographing the object we desire, perhaps we should be satisfied with a photograph of its “shadow.” The indirect approach would be to examine carefully low-energy data from an atom smasher, and try to see if ten-dimensional physics affects the data in some way.

The third “untestable” idea in physics was the existence of the elusive neutrino.

In 1930, physicist Wolfgang Pauli hypothesized a new, unseen particle called the
neutrino
in order to account for the missing component of energy in certain experiments on radioactivity that seemed to violate the conservation of matter and energy. Pauli realized, though, that neutrinos would be almost impossible to observe experimentally, because they would interact so weakly, and hence so rarely, with matter. For example, if we could construct a solid block of lead that stretched several light-years from our solar system to Alpha Centauri and placed it in the path of a beam of neutrinos, some would still come out the other end. They can penetrate the earth as though it doesn’t even exist, and, in fact, trillions of neutrinos emitted from the sun are always penetrating your body, even at night. Pauli admitted, “I have committed the ultimate sin, I have predicted the existence of a particle that can never be observed.”
⁷

So elusive and undetectable was the neutrino that it even inspired a poem by John Updike, called “Cosmic Gall”:

Neutrinos, they are very small.

They have no charge and have no mass

And do not interact at all.

The earth is just a silly ball

To them, through which they simply pass,

Like dustmaids down a drafty hall

Or photons though a sheet of glass.

They snub the most exquisite gas,

Ignore the most substantial wall,

Cold-shoulder steel and sounding brass,

Insult the stallion in his stall,

And scorning barriers of class,

Infiltrate you and me! Like tall

And painless guillotines, they fall

Down through our heads into the grass.

At night, they enter at Nepal

And pierce the lover and his lass

From underneath the bed—you call

It wonderful; I call it crass.
⁸

Although the neutrino, because it barely interacts with other materials, was once considered the ultimate “untestable” idea, today we regularly produce beams of neutrinos in atom smashers, perform experiments with the neutrinos emitted from a nuclear reactor, and detect their presence within mines far below the earth’s surface. (In fact, when a spectacular supernova lit up the sky in the southern hemisphere in 1987, physicists noticed a burst of neutrinos streaming through their detectors deep in these mines. This was the first time that neutrino detectors were used to make crucial astronomical measurements.) Neutrinos, in 3 short decades, have been transformed from an “untestable” idea into one of the workhorses of modern physics.

Taking the long view on the history of science, perhaps there is some cause for optimism. Witten is convinced that science will some day be able to probe down to Planck energies. He says,

It’s not always so easy to tell which are the easy questions and which are the hard ones. In the 19th century, the question of why water boils at 100 degrees was hopelessly inaccessible. If you told a 19th-century physicist that by the 20th century you would be able to calculate this, it would have seemed like a fairy tale.… Quantum field theory is so difficult that nobody fully believed it for 25 years.

In his view, “good ideas always get tested.”
⁹

The astronomer Arthur Eddington even questioned whether scientists were not overstating the case when they insisted that everything should be tested. He wrote: “A scientist commonly professes to base his
beliefs on observations, not theories.… I have never come across anyone who carries this profession into practice.… Observation is not sufficient.… theory has an important share in determining belief.”
¹⁰
Nobel laureate Paul Dirac said it even more bluntly, “It is more important to have beauty in one’s equations than to have them fit experiment.”
¹¹
Or, in the words of CERN physicist John Ellis, “in the words of a candy wrapper I opened a few years ago: ‘It is only the optimists who achieve anything in this world.’ ” Nonetheless, despite arguments that uphold a certain degree of optimism, the experimental situation looks bleak. I share, along with the skeptics, the idea that the best we can hope for is indirect tests of ten-dimensional theory into the twenty-first century. This is because, in the final analysis, this theory is a theory of Creation, and hence testing it necessarily involves re-creating a piece of the Big Bang in our laboratories.

Personally, I don’t think that we have to wait a century until our accelerators, space probes, and cosmic-ray counters will be powerful enough to probe the tenth dimension indirectly. Within a span of years, and certainly within the lifetime of today’s physicists, someone will be clever enough to either verify or disprove the ten-dimensional theory by solving the field theory of strings or some other nonperturbative formulation. The problem is thus theoretical, not experimental.

Assuming that some bright physicist solves the field theory of strings and derives the known properties of our universe, there is still the practical problem of when we might be able to harness the power of the hyperspace theory. There are two possibilities:

1. Wait until our civilization attains the ability to master energies trillions of times larger than anything we can produce today

2. Encounter extraterrestrial civilizations that have mastered the art of manipulating hyperspace

We recall that it took about 70 years, between the work of Faraday and Maxwell to the work of Edison and his co-workers, to exploit the electromagnetic force for practical purposes. Yet modern civilization depends crucially on the harnessing of this force. The nuclear force was discovered near the turn of the century, and 80 years later we still do not have the means to harness it successfully with fusion reactors. The next leap, to harness the power of the unified field theory, requires a much greater jump in our technology, but one that will probably have vastly more important implications.

The fundamental problem is that we are forcing superstring theory
to answer questions about everyday energies, when its “natural home” lies at the Planck energy. This fabulous energy was released only at the instant of Creation itself. In other words, superstring theory is naturally a theory of Creation. Like the caged cheetah, we are demanding that this superb animal dance and sing for our entertainment. The real home of the cheetah is the vast plains of Africa. The real “home” of superstring theory is the instant of Creation. Nevertheless, given the sophistication of our artificial satellites, there is perhaps one last “laboratory” in which we may experimentally probe the natural home of superstring theory, and this is the echo of Creation!