How to Destroy the Universe (26 page)

We've had the weak force, so it's probably no surprise that the final force of nature is known as the strong force. It too operates exclusively within the nuclei of atoms, and it's responsible for binding the protons and neutrons inside atomic nuclei together. But it soon emerged that the true picture was even more complex. Experiments in the 1960s revealed that the particles in the nucleus are not fundamental entities but are instead made of smaller particles, known as quarks. Each proton and neutron in an atomic nucleus is in fact a cluster of three of these quarks, bound together by the strong force. Whereas electrons and protons carry electrical charge, each quark carries a so-called “color charge.” Color comes in three types—red, green and blue—and each can be either positive or negative. Quantum color has nothing to do with color in the real world. It is just a name given to a quantity that is hard to think about—unlike electric charge, color charge exists purely at the quantum level and we thus have no intuitive grasp of it.
Color charge generates a field through which the strong nuclear force is mediated. Whereas the electromagnetic field is carried by photons, the color field is carried by a new kind of particle known as a gluon—of which there are eight different sub-varieties. The theory of color charge is known as quantum chromodynamics, or QCD. It was developed in the 1960s and '70s and was confirmed by experiments in particle accelerators soon after. As its name suggests, the strong force is the most powerful of all the forces of nature, coming in at about 100 times stronger than electromagnetism.

Could any of these forces be used to build a working deflector shield? In science fiction, writers often invoke hand-wavy arguments by which a force field could work based on gravity. The basic idea is similar to a gravitational lens (see
How to see the other side of the Universe
), where space is curved by the gravity of a massive object to deflect a light beam (such as a laser blast), or any other inbound object for that matter. Gravitational lenses curve light inwards to focus it. A deflector shield would need to do the opposite and deflect the light away from the spacecraft. One way this could work is using a kind of anti-gravitating material, similar to the dark energy that is thought to pervade the Universe, making its rate of expansion get
progressively quicker. According to general relativity, dark energy would curve the space around the spacecraft and deflect incoming objects.

The problem with this idea is that no one knows how to capture and bottle dark energy. Something similar has been produced in laboratory experiments to investigate the Casimir effect (see
How to travel through time
), although only in minuscule amounts. And for the material to bend space enough to be useful, planet-sized amounts of the stuff would be needed. And that's the real problem—gravity is just too weak. What about the weak and strong nuclear forces? These are a no-go right from the off because their range is limited to within the atomic nucleus, which is about a trillonth of a millimeter across. That just leaves electromagnetism—which, it turns out, could be just the ticket.

Scientists at the UK's Defence Science and Technology (DSTL) Laboratory have figured out how to use electric fields to protect tanks from rocket-propelled grenade (RPG) attacks. Fired from a shoulder-mounted launcher, each of these missiles packs a shaped high-explosive charge that melts a mass of copper and then injects the molten material as a jet into the target. Capable of punching through 30 cm (12 in) of steel, these weapons cost just a few hundred dollars
and pose a lethal threat to tank crews. The DSTL believe high-strength electric fields could offer a solution. Their design uses a device called a supercapacitor. Capacitors are electrical components that can store up charge and then release it in a massive burst. They are used, for example, in camera flashes. Supercapacitors are a new design that takes advantage of nanotechnology—engineering on tiny length scales of just a billionth of a meter—to store thousands of times more charge than has previously been possible. Electric armor works by using a computer monitoring system that can discharge a supercapacitor into the metal body of an armored vehicle the moment it detects an RPG launch. This momentarily sets up a huge electromagnetic field around the vehicle, deflecting any inbound metal objects away. The team believe the armor could not only make tanks safer, but also lighter and more maneuverable as they would be able to dispense with much of their heavy steel plating.

Electromagnetic shields aren't confined to planet Earth. British physicist Ruth Bamford has worked out how to surround a spacecraft with a magnetic field that can repel high-energy radiation particles. These particles spew from the surface of the Sun and can cause severe radiation sickness and even death in astronauts. This is something of a show-stopper if, for example,
over the coming decades we want to send crewed missions to Mars. One solution is to clad spacecraft with layer upon layer of lead shielding to block this radiation. But lead shielding is extremely heavy and so adds significantly to the weight that has to be blasted into space, making the cost prohibitive. Most of the dangerous particles are electrically charged. Ruth Bamford's idea exploits this fact by replacing bulky lead shielding with a magnetic bubble surrounding the spacecraft, which—just as Earth's magnetic field keeps us safe from cosmic radiation—bats these harmful particles away from the spacecraft and back off into space.

This isn't an entirely new idea, but it was previously thought that an enormous magnetic bubble was required—about 20 km (12 miles) across—demanding a huge electromagnet and power-generation equipment just as bulky as the lead shielding that it's meant to replace. Bamford's calculations now indicate that a bubble just 100 m (300 ft) in diameter would do the trick. The machinery needed to create this could practically fit inside an astronaut's hand luggage and, most importantly, can be built with existing technology. Dr. Bamford's idea may not be quite up to fending off Klingon invaders just yet. But it's one small step in the right direction.

• The dismal science

• The futures market

• Sharing the wealth

• Quantum games

• Prediction markets

At first sight, physics and economics sound like they have about as much in common as space flight and potatoes. But an increasing number of researchers are discovering that powerful economic insights can be gained by applying the laws and principles of physics to the movement of money. This field of science now has its own name: econophysics.

Economics is the science of trade. It governs the exchange of goods and services between people, businesses and nation states. Specialists in other scientific disciplines sometimes refer to it as the “dismal science” because they say it has none of the perceived beauty of the “natural” sciences such as chemistry, biology and, of
course, physics. But in the mid-1990s that disdain began to evaporate and physicists started applying their knowledge of the fundamental behavior of the natural world and the techniques of physics to try to solve problems in economics and finance.

The application of math to economics goes back much further, as far as the 17th century. Powerful mathematical methods—such as differential calculus, a branch of math dealing with how quantities change with time—were employed from the end of the 19th century to allow economists to draw up precise models of how economic systems behave in response to particular inputs. A simple example is supply and demand. As the available quantity of a product or service decreases, so people are prepared to pay more for it—this is “demand.” Likewise, the more a manufacturer or service provider can charge for a product, the more of it they're willing to sell, in order to maximize profit—this is “supply.” Plot these on a graph of price against quantity and demand is a downward sloping curve, while supply is an upward sloping curve. Where they cross is called the “equilibrium point”—and it is toward this point that the actual price of particular goods or services will converge.

There are also vastly more complex cases. For example, Elliott wave theory tries to explain the movements of financial markets in terms of waves of optimism and
pessimism in the eyes of investors. These swings create ripples in the prices of stocks and shares, which mathematical economists try to predict. Meanwhile, if you're a hedge fund manager, complex mathematical analysis is all in a day's work. Hedge funds trade in a range of commodities—investing in shares that look set to perform well and “short selling” stock they believe will fall. The analysis enables the fund manager to literally “hedge his bets”—spreading the investment in such a way that no matter how the market performs the fund continues to grow.

One such market commodity that hedge funds deal with is known as “futures.” Here, traders don't buy actual shares in a company but rather they buy the option to buy shares for a fixed price at a certain date in the future. If at that time the actual value of the shares is more than the fixed price then the trader can exercise the option and sell the shares straight away for an immediate profit. If, on the other hand, the price of the actual stock is less then the trader can decline to buy, but loses whatever they paid for the option. The behavior of the futures market is notoriously hard to predict. Traders attempt to rein in this variance by using a formula known as the Black–Scholes equation. This is a fiendishly complicated mathematical relationship linking the price of a stock and the price of the
option to buy that stock, taking into account other economic parameters such as interest rates and the market volatility. Solutions to the equation reveal what the maximum price of an option should be for a buyer to make a profit, and what the minimum price is that a seller should offer.

In 1996, physicist Kirill Ilinski at the University of Birmingham in the UK invoked quantum physics to improve on this revered formula. He used the mathematics for the theory of quantum electrodynamics (QED)—the quantum model of electromagnetic fields, which describes the behavior of electrically charged subatomic particles. Rather than using the formulae to compute the behavior of positive and negative electrical charges, he switched these quantities for positive and negative amounts of money: credit and debt. He swapped the electromagnetic field—which in QED mediates the interaction between positive and negative charges—for a so-called “field of arbitrage,” which contains all of the information about pricing and interest rates, and thus mediates how credit and debt interact.

Quantum theories like QED obey the uncertainty principle. This means they cannot predict the exact outcome of an experiment, only the probability of each possible outcome. Ilinski used this to model the unpredictability of the stock exchange. And it seems to work.
The Black–Scholes equation emerged from his QED-based formalism, but only after some simplifications. In QED, empty space isn't really empty. Instead, it is full of “virtual particles” of the electromagnetic field, which randomly pop in and out of existence in accordance with quantum uncertainty. In the financial version of the theory, virtual particles of the arbitrage field also exist and play the role of random opportunities. But in the same way that other quantum effects conspire to quickly damp out virtual particles in QED, virtual opportunities in arbitrage are also extremely short-lived.

Ilinski says this can be interpreted as the presence of speculators in his model. Speculators anticipate price changes and act quickly when an opportunity arises, rapidly erasing the chance for others to benefit from it. In the absence of speculators, Ilinski recovered the standard form of the Black–Scholes equation. But leaving speculators in, via their QED counterparts, gives an extended version of the formula that makes it possible to hedge deals against the actions of these market traders.

It is sometimes said that in any economy 20 percent of the people own 80 percent of the wealth. Now physics is shedding light on this too. One of the first people to
carry out a mathematical analysis of the distribution of wealth in a population was the French engineer Vilfredo Pareto. In 1897, he figured out that—in Europe at least—money was distributed according to what's known as a power law. In other words, the number of people with more than a given amount of wealth,
W
, was proportional to 1 /
W
^e
—where the “power”
e
, Pareto found, is a number varying between 2 and 3. It meant, essentially, that the number of people with a lot of money was very small. Since then, economists have realized that Pareto's law only applies for large values of
W
, corresponding to the top three percent of the population. The bank balances of everyone else must follow a different rule.