How to Destroy the Universe (25 page)

Penrose's idea was rather like grabbing hold of a spinning merry-go-round and then jumping off with more
speed than you originally had. Only in this case it wasn't quite so simple. Anything entering the ergosphere would need to shed some mass while in there, which would then fall into the black hole. Penrose imagined that a futuristic civilization could use the process by using a rotating black hole as somewhere to dump its garbage. Shuttle craft would periodically carry garbage to the hole. Flying into the ergosphere and jettisoning this material would give the shuttle craft a kick, a bit like the way a rifle kicks back against your shoulder as it discharges a bullet. The fast-moving empty shuttles would then need to dock with some kind of giant dynamo structure that could convert their kinetic energy into usable electricity.

In theory it's possible to extract up to 29 percent of the energy locked away in the black hole in this way. Some physicists even believe the process could go some way to explaining the powerful jets of material that are seen spewing from the cores of some galaxies—most galaxies are already known to harbor enormous spinning black holes at their centers.

In the early 1970s, Cambridge University astrophysicist Stephen Hawking showed that even black holes that are not rotating give off energy. Hawking proved mathematically that black holes should emit particles,
effectively evaporating like a body at a temperature determined by the hole's mass. This seems to go against the idea that nothing which has crossed a black hole's event horizon can ever return to see the outside world again. However, Hawking used the rules of quantum theory—the physics of subatomic particles—to arrive at his result. General relativity makes no provision for quantum laws, so it shouldn't really be much of a surprise to find that quantum considerations can occasionally overturn its predictions.

Hawking's mechanism worked using an idea known as the uncertainty principle. Put forward by German physicist Werner Heisenberg in 1927, it basically says that it's impossible to know both the energy of a particle and the time at which you measure that energy. Instead there is a trade-off between the two so that high precision in the measurement of one translates into low precision in the measurement of the other. It means that pairs of particles—one matter and one antimatter can pop in and out of existence. Uncertainty allows the energy of a particle—or even of empty space at the quantum level—to vary in such a way that the size of the variations and the time they exist for satisfy Heisenberg's principle. Empty space, which you would normally expect to have zero energy, can suddenly gain energy by spawning particles, so long as these particles are gone again a short time later.

Hawking asked what happens to these “virtual particles” when they are created just outside a black hole's event horizon. He found that sometimes both particles get sucked over the horizon; sometimes the particles simply recombine and vanish before they get the chance to do anything; but sometimes one particle will fall over the horizon while the other has just enough energy to get away from the black hole's gravity. And
this creates a steady flow of particles away from the black hole. Meanwhile, the hole's mass—in the absence of any other matter falling in—steadily diminishes. US physicists Lois Crane and Shawn Westmoreland have even suggested that this energy output could be harnessed to run a spacecraft on tiny black holes that have been artificially generated using giant lasers.

Although energy that's extracted from around a black hole will have been mined from “empty space,” some people might argue that it's not strictly energy from nothing—because you need to have a black hole there in the first place. If that's your view then cosmologists have news for you. They say that our entire Universe may have been created from nothing—in the most literal sense of the word possible.

It was the day Einstein nearly got run over. He and his colleague the Russian–US physicist George Gamow were out walking in Princeton, New Jersey, one afternoon during the early 1940s. Gamow was explaining to Einstein how one of his students had just calculated that it's possible to make a star from nothing because its mass energy (as calculated from Einstein's formula
E=mc
²
) is exactly equal but opposite to its “gravitational potential energy.”

The gravitational potential energy of a star or planet is the energy required to assemble it if all its constituent parts were scattered an infinite distance apart. Another way to think of it is as the opposite of the energy that must be delivered to the star or planet in order to completely blow it apart. That energy is positive. And therefore the gravitational potential energy, which is equal yet opposite, must be negative. When Gamow told Einstein about his student's calculation the father of relativity is said to have stopped dead in his tracks. He and Gamow were crossing a road at the time and several cars had to swerve to avoid them. Einstein had realized that the calculation didn't just apply to stars but to the Universe at large as well.

Most cosmologists now believe this is how our Universe popped into creation, probably as a quantum event, much like the virtual particles flitting in and out of existence in empty space that give rise to Hawking radiation. Amazingly though, it wasn't just the matter that makes up the stars, planets and galaxies of our Universe that were created in the “Big Bang,” as the birth of the Universe has come to be known, but the very fabric of space itself. Before that—well, there was no “before that” because time was created in the Big Bang too, and asking what happened before time was created is like asking what's north of the north pole.

Of course, creating a Universe isn't something that would be remotely useful to you or me, nor is it something we're ever likely to be able to take a crack at. But a physicist in Germany has come up with a way to extract useful energy from empty space itself. It all comes down to the virtual particles we met back in the discussion about Hawking radiation. Back in the 1940s, a Dutch scientist called Hendrik Casimir worked out that these virtual particles would cause two metal plates placed a very short distance apart in a vacuum to move together. It's called the Casimir effect (see
How to travel through time
) and was verified experimentally in 1997. Dr. Thorsten Emig has found a way to extract useful energy from the effect via a ratchet-like device that uses the Casimir force to generate rotational motion in one direction, which can then be harnessed. Emig's design works by substituting the smooth plates of the standard Casimir experiment for corrugated ones, which introduces a lateral force that makes the plates slip past one another. By making the corrugations asymmetric, Emig keeps this slipping motion in one direction.

Emig believes the ratchet could generate enough energy to power tiny nanorobots—machines measuring just one ten-thousandth of a millimeter across, which have a host of applications in medicine and for engineering on the smallest scales. The work isn't just
another theoretical pipe dream: a real lateral Casimir force has already been measured by a team of experimental physicists working at the University of California. The energy for the virtual particles on which the Casimir effect relies is effectively borrowed from the vacuum of empty space—so Dr. Emig's device is, quite literally, mining useful energy from nothing.

• Field theory

• The forces of nature

• Quantum fields forever

• Raise shields!

• Electric armor

• Magnetic deflectors

No science fiction spacecraft would be complete without deflector shields to stave off attacks from hostile aliens. Now this idea is gaining traction in science fact. Physicists have come up with designs for force fields to guard real spacecraft against the harsh radiation in space that could otherwise hamper manned missions to planets such as Mars. Meanwhile, other scientists are developing electric shields for tanks and other military vehicles on Earth.

Fields are not solely the province of science fiction. Any kind of phenomenon in nature that's able to exert “action at a distance” does so through a field—a
distribution of mass or energy around an object that acts as the source. Perhaps the most familiar example is gravity. Any massive object creates a gravitational field around it that influences other massive objects passing through the field. This is why we have planets in orbit around the Sun—and why cricket balls thrown up into the air come back down to Earth again.

The behavior of a field in physics is given by an ominous-sounding mathematical entity, known as the field equation. Every theory has its own field equation (and, indeed, sometimes more than one) describing how the field works. The first theory of the gravitational field was put forward in the late 17th century by the English polymath Isaac Newton. The field equation in this theory was a relatively simple law, which said that the gravitational field of a body increases in proportion to the body's mass (so heavy things exert more gravity) and decreases with the distance squared from the source—so if you move twice as far away from an object, its gravitational field diminishes by a factor of four. Newtonian gravity was replaced in 1915 by a far more complex theory—the general theory of relativity—put forward by Albert Einstein. The theory ascribed gravity to bending of space. This in itself was a step up from Newtonian gravity because it explained how the field was being transmitted through space. The field equations of Einstein's theory (there are 10 of them) assert that gravitational interactions propagate
outward as ripples in space and time, traveling at the speed of light.

Gravity isn't the only player in physics. As far as we understand it, nature is home to a total of four fundamental forces. Gravity, as we've seen, is one. It's mediated by a long-range field that extends right across the Universe, causing far-flung galaxies to move under each other's influence. But despite this, gravity is really quite a feeble force. After all, it takes the entire mass of Earth to keep us humans stuck to the planet's surface. A much stronger force is electromagnetism, the theory of which was developed in the 19th century by British physicist James Clerk Maxwell. The electromagnetic force arises from the interaction between electric and magnetic fields. Maxwell's field equations are four mathematical expressions that describe how moving electric charges generate these fields and interact through them. According to Maxwell's theory, the fields themselves comprise electromagnetic waves—the same entities that light, X-rays and radio signals are made up of. Electromagnetism is much more potent than gravity, exerting a force that's 100 billion billion billion billion (a 1 followed by 38 zeroes) times stronger.

But change was in the air for Maxwell's theory too. In the early 20th century, physicists developing the new
discipline of quantum mechanics realized that electromagnetic waves aren't purely waves but can also be regarded to some extent as particles, which they called photons. In 1927, British physicist Paul Dirac worked out a quantum mechanical equation describing the dynamics of negatively charged electrons in the presence of an electromagnetic field. Dirac had taken the first steps toward constructing a theory of electromagnetism that was consistent with the quantum revolution. In the 1940s, the theory was refined and developed to yield a fully “quantized” version of Maxwell's electromagnetic theory, which was able to describe the behavior of electrically charged subatomic particles in electric and magnetic fields. Called quantum electrodynamics, or QED, it was the first example of a quantum field theory.

Quantum field theory is at the root of the final two forces of nature. These forces only operate within the nuclei of atoms and are thus inherently quantum—they do not exist in a non-quantized form. The first is known as the weak nuclear force. This is the force that's responsible for so-called “beta decay” of atoms—a kind of radioactive decay where an atomic nucleus converts some of its particles into either electrons or the electron's antiparticle, the positron. The weak force is mediated by a field made up of two particles—named
the
W
and
Z
. The
W
is electrically charged, like the electron, but can be either positive or negative; the
Z
is electrically neutral. The weak force is 100 billion times weaker than electromagnetism. In the late 1960s, a unified description encapsulating both the weak force and QED was put forward and confirmed by experiments. It is still missing one crucial component, the Higgs boson, which particle accelerators such as the Large Hadron Collider are currently hunting for.