Zero (27 page)

Rockets bring their own supply of stuff to push against. Rocket fuel burns in the engine and is sent out the back of the rocket, driving the spaceship forward, just as the rush of air out of a balloon sends it flying around the room. But tossing away fuel is an expensive and cumbersome way to go places, and even modern improvements on the chemical engine, such as engines that use electricity to throw stuff out the back of a rocket, are unable to provide the fuel efficiency to send probes to distant stars in a reasonable amount of time. To get even to the nearest star, you would need an enormous amount of fuel to jettison out the back of the rocket—a tremendous waste.

Physicist Marc Millis heads NASA's Breakthrough Propulsion Project and hopes to overcome this problem with the physics of zero. Unfortunately, the zeros of black holes—singularities—look like unlikely candidates in the short term. Not only is it extremely difficult to create a naked singularity that a wormhole needs, but it also appears that even a naked singularity will tear space travelers to shreds. In 1998 two physicists from the Hebrew University in Jerusalem showed that even a spinning or charged black hole—with a nice, ring-shaped singularity—will kill an astronaut, thanks to mass inflation. As you fall toward the singularity, the black hole's mass appears to grow and grow to infinity. The gravitational tug is so strong that you'd be torn apart in a fraction of a second. Wormholes would be hazardous to your health.

Even if the zeros at the center of black holes don't provide an easy way to travel through space, the zero of quantum mechanics provides an alternative: the zero-point energy might be the ultimate fuel. It is here that the mainstream of physics ends and the fringe begins.

According to Millis, astronauts might harness the energy in the vacuum to push a spaceship, just as mariners harnessed the wind to drive a frigate. “I'm making an analogy to the Casimir effect, where you can push plates together with a noticeable radiation pressure from the vacuum,” he says. “If there were any way to get asymmetric forces out of that, where you get force in one direction and not the other, you'd get a propulsive force.” Unfortunately, so far the Casimir effect seems to be symmetric; both plates collapse and pull each other together. The action of one has an equal and opposite reaction on the other. But if there were some sort of quantum sail, a one-way mirror that reflected virtual particles on one side but let them pass unhindered through the other, the vacuum energy would push the whole object toward the unreflective half of the sail. Millis admits that nobody has any clue how to do this. “There are no theories how to engineer the device,” he says sadly.

The problem is that the laws of physics say you can't get something for nothing; just as the frigate lowers the speed of the wind, the quantum sail would have to lower the energy of the vacuum. How can you modify nothing?

Harold Puthoff, the director of the Institute for Advanced Studies in Austin, Texas, believes that a quantum sail would simply alter the properties of the vacuum. (Puthoff is best known for his 1974 paper in
Nature
that purported to prove that Uri Geller and other psychics could view objects remotely—without their eyes. This conclusion was not in the mainstream of science.) “The vacuum decays to a slightly lower state,” says Puthoff. If so, then quantum sails are just the beginning; it would be possible to make engines that run solely on zero-point energy. Their only drawback would be that the fabric of the universe would fall apart. Slowly. “We'd never make a dent. It's like scooping up cupfuls of water from the ocean,” says Puthoff.

It might also destroy the universe.

There is no question that the vacuum has energy; the Casimir force is witness to that fact. But is it possible that the energy of the vacuum is truly the lowest possible energy? If not, danger might be lurking in the vacuum. In 1983 two scientists suggested in
Nature
that tinkering with the energy of the vacuum might cause the universe to self-destruct. The paper argued that our vacuum might be a “false” vacuum in an unnaturally energetic state—like a ball perched precariously on the side of a hill. If we give the vacuum a big enough nudge, it might start rolling down the hill—settling into a lower energy state—and we would not be able to stop it. We would release a huge bubble of energy that expands at the speed of light, leaving a vast trail of destruction in its wake. It might be so bad that every one of our atoms would be torn apart during the apocalypse.

Luckily, this is an extremely unlikely scenario. Our universe has lasted billions of years, and it's improbable that we are living in such a precarious state; cosmic-ray collisions would probably already have “sparked” the vacuum with enough energy to cause such a disaster were it possible. This hasn't stopped some believers—physicists included—from picketing high-energy laboratories like Fermilab; they believe that a high-energy collision could cause a spontaneous collapse of the vacuum. Even if those concerns were valid, it seems all but impossible to propel a spaceship with zero-point energy. However, Puthoff believes he has a way to extract energy from the void.

In theory, scientists can get energy from the Casimir effect even at absolute zero in the bleakest part of the vacuum of space. Two plates generate heat when they smack together—heat that can be converted to electricity. Alas, the plates have to be pried apart again, which requires more energy than was initially produced; most scientists believe that this fact kills the idea of making a perpetual-motion machine that runs on vacuum energy. But Puthoff thinks he sees several ways around this dilemma. One is to use plasmas instead of plates.

A plasma, a gas of charged particles, is just like a metal plate as far as the Casimir effect is concerned. A conducting, cylinder-shaped gas would be compressed by the zero-point fluctuations just as plates are forced together. The collapse would heat the plasma, releasing energy. Unlike metal plates, plasmas could be made easily with a bolt of electricity, according to Puthoff, and instead of having to pry the plates apart again, the plasma “ash” is discarded. Puthoff gingerly claims to have gotten out 30 times more energy with this method than was put in. “There's some evidence; we've even got a patent,” he says. However, Puthoff's device is one in a long line of “free energy” machines—none of which, in the past, have withstood scientific scrutiny. It is unlikely that his device to harness the zero-point energy will be any different.

According to quantum mechanics and general relativity, the power of zero is infinite, so it's no surprise that people are hoping to tap its potential. But for the time being, it appears that nothing will come of nothing.

[ZERO AT THE EDGE OF SPACE AND TIME]

M
odern physics is a struggle of two titans. General relativity holds sway in the realm of the very, very big: the most massive objects in the universe, such as stars, solar systems, and galaxies. Quantum mechanics rules the domain of the very, very small: atoms and electrons and subatomic particles. It would seem that these two theories could live in harmony together, each dictating the rules of physics for different aspects of the universe.

Unfortunately, there are objects that lie in both realms. Black holes are very, very massive, so they are subject to the laws of relativity; at the same time, black holes are very, very tiny, so they are in the domain of quantum mechanics. And far from agreeing, the two sets of laws clash at the center of a black hole.

Zero dwells at the juxtaposition of quantum mechanics and relativity; zero lives where the two theories meet, and zero causes the two theories to clash. A black hole is a zero in the equations of general relativity; the energy of the vacuum is a zero in the mathematics of quantum theory. The big bang, the most puzzling event in the history of the universe, is a zero in both theories. The universe came from nothing—and both theories break down when they try to explain the origin of the cosmos.

To understand the big bang, physicists must marry quantum theory with relativity. In the past few years they have begun to succeed, creating a monster theory that explains the quantum-mechanical nature of gravity, allowing them to peer at the very creation of our universe. All they had to do was banish zero.

The Theory of Everything is, in truth, a theory of nothing.

General relativity and quantum mechanics were bound to be incompatible. The universe of general relativity is a smooth rubber sheet. It is continuous and flowing, never sharp, never pointy. Quantum mechanics, on the other hand, describes a jerky and discontinuous universe. What the two theories have in common—and what they clash over—is zero.

The infinite zero of a black hole—mass crammed into zero space, curving space infinitely—punches a hole in the smooth rubber sheet. The equations of general relativity cannot deal with the sharpness of zero. In a black hole, space and time are meaningless.

Quantum mechanics has a similar problem, a problem related to the zero-point energy. The laws of quantum mechanics treat particles such as the electron as points; that is, they take up no space at all. The electron is a
zero-dimensional
object, and its very zerolike nature ensures that scientists don't even know the electron's mass or charge.

This seems like a silly statement. It has been nearly a century since scientists measured the electron's mass and charge. How could physicists not know something that has been measured? The answer lies with zero.

The electron that scientists see in the laboratory—the electron that physicists, chemists, and engineers have known and loved for decades—is an impostor. It is not the true electron. The true electron is hidden in a shroud of particles, made up of the zero-point fluctuations, those particles that constantly pop in and out of existence. As an electron sits in the vacuum, it occasionally absorbs or spits out one of these particles, such as a photon. The swarm of particles makes it difficult to get a measurement of the electron's mass and charge, because the particles interfere with the measurement, masking the electron's true properties. The “true” electron is a bit heavier and carries a greater charge than the electron that physicists observe.

Scientists might get a better idea of the true mass and charge of the electron if they could get a little closer; if they could invent a tiny device that could get a short distance inside the cloud of particles, they would be able to see more clearly. According to quantum theory, as the measuring device gets past the first few virtual particles on the rim of the cloud, scientists would see the mass and charge of the electron go up, and as the probe gets closer and closer to the electron, it would pass more and more virtual particles, so the observed mass and charge go up and up. As the probe approaches zero distance from the electron, the number of particles it passes goes up to infinity—so the probe's measurements of the mass and charge of the electron also go to infinity. According to the rules of quantum mechanics, the zero-dimensional electron has infinite mass and infinite charge.

As with the zero-point energy, scientists learned to ignore the infinite mass and charge of the electron. They don't go all the way to zero distance from the electron when they calculate the electron's true mass and charge; they stop short of zero at an arbitrary distance. Once a scientist chooses a suitably close distance, all the calculations using the “true” mass and charge agree with one another. This is a process called renormalization. “It is what I would call a dippy process,” wrote physicist Richard Feynman, even though Feynman won his Nobel Prize for perfecting the art of renormalization.

Just as zero punches a hole in the smooth sheet of general relativity, zero smooths and spreads out the sharp point charge of the electron, covering it in a fog. However, since quantum mechanics deals with zero-dimensional particle-points such as the electron, technically all particle-particle interactions in quantum theory deal with infinities: they are singularities. When two particles merge, for instance, they meet at a point: a zero-dimensional singularity. This singularity makes no sense in quantum mechanics or in general relativity. Zero is the wrench in the works of both great theories. So physicists simply got rid of it.

It is not obvious how to get rid of zero, as zero appears and reappears throughout time and space. Black holes are zero-dimensional, as are particles such as the electron. Electrons and black holes are real things; physicists can't simply will them away. But scientists can give black holes and electrons an extra dimension.

This is the reason for
string theory,
which was created in the 1970s when physicists began to see the advantages of treating every particle as a vibrating string rather than as a dot. If electrons (and black holes) are treated as one-dimensional, like a loop of string, instead of as zero-dimensional, like a point, the infinities in general relativity and quantum mechanics miraculously disappear. For instance, the renormalization trouble—the infinite mass and charge of the electron—vanishes. A zero-dimensional electron has an infinite mass and charge because it is a singularity; as you get closer and closer to it, your measurements zoom off to infinity. However, if the electron is a loop of string, the particle is no longer a singularity. This means that the mass and charge don't go off to infinity, because you are no longer passing an infinite cloud of particles as you approach the electron. Furthermore, as two particles merge, no longerdo they meet at a point-like singularity; they form a nice, smooth, continuous surface in space-time (Figures 54,55).

Figure 54: Point particles create a singularity…

Figure 55:…string particles don't.

In string theory different particles are really the same type of string, just wiggling in different ways. Everything in the universe is made up of these strings, which are about 10
^-33
centimeters across; comparing the size of a string to the size of a neutron is like comparing the size of a neutron to the size of our solar system. From the perspective of beings as large as we are, the loops look like points because they are so tiny. Distances (and times) smaller than the size of the loops no longer matter; they don't make any physical sense. In string theory, zero has been banished from the universe; there is no such thing as zero distance or zero time. This solves all the infinity problems of quantum mechanics.

Banishing zero also solves the infinity problems in general relativity. If you imagine a black hole as a string, no longer do objects fall through a rip in the fabric of space-time. Instead, a particle loop approaching a black-hole loop stretches out and touches the black hole. The two loops tremble, tear, and form one loop: a slightly more massive black hole. (Some theorists believe that the act of merging a particle to a black hole creates bizarre particles such as
tachyons:
particles with imaginary mass that travel backward in time and move faster than light. Such particles might be admissible in certain versions of string theory.)

Removing zero from the universe might seem like a drastic step, but strings are much more tractable than dots; by eliminating zero, string theory smooths out the discontinuous, particle-like nature of quantum mechanics and mends the gashes torn in general relativity by black holes. With these problems patched over, the two theories are no longer incompatible. Physicists began to think that string theory would unify quantum mechanics with relativity; they believed that it would lead to the theory of quantum gravity—the Theory of Everything that explains every phenomenon in the universe. However, string theory had some problems. For one thing, it required 10 dimensions to work.

For most people, four dimensions are one too many. It is easy to see three of them: left-right, front-back, and up-down represent the three directions we can move in. The fourth arrived when Einstein showed that time was similar to these three dimensions; we are constantly moving through time like a car that's speeding down a highway. The theory of relativity shows that just as we can change how quickly we rush down a highway, we can change the rate at which we move through time—the faster we go through space, the quicker we move through time. To understand Einstein's universe, we have to accept the idea that time is the fourth dimension.

Four is reasonable—but 10? We can measure four dimensions, but what happened to the other six dimensions? According to string theory, they are rolled up like little balls, too tiny to see. When you pick up a piece of paper, it seems two-dimensional. It has length and breadth, but it doesn't seem to have any depth at all. Nevertheless, if you take a magnifying glass and gaze at the edge of the piece of paper, you begin to see that it has a wee bit of depth. You need a tool to help you see it, but that third dimension is there, too tiny to see under normal conditions. The same is true with those extra six dimensions. In everyday life they are way too tiny to see; they are too small to detect even with the most powerful equipment that we could possibly manufacture in the near future.

What do these six extra dimensions
mean
? Nothing, really. They don't measure anything that we are accustomed to, like length, breadth, width, or time. They are simply mathematical constructs that make the mathematical operations in string theory work in the manner that they have to. Like imaginary numbers, we can't see them or feel them or smell them, even though they are necessary for doing calculations. Though it is a strange concept physically, it is the predictive power of the equations that interests scientists, rather than their comprehensibility—and an extra six dimensions do not constitute an insurmountable problem, mathematically. Spotting them might. (Ten seems small nowadays. In the past few years physicists realized that the many competing varieties of string theory are actually, in a sense, the same thing. Scientists realize now that these theories are dual to each other just as Poncelet realized that lines and points were dual to each other. Scientists now believe that there is a monster theory that underlies all of these competing theories: the so-called M-theory, which lives in 11 dimensions, not 10.)