How to Destroy the Universe (12 page)

Everett threw out the notion of wavefunction collapse in favor of a new view that he called the relative state formulation, which became known as the many worlds interpretation. Rather than the wavefunction of a quantum system collapsing into just one of the many possibilities open to it, Everett suggested that there exist many universes where every possibility is played out for real. The particle's wavefunction doesn't just exist in our universe, but is spread out across this “multiverse” of many worlds. The question then becomes not how the wavefunction collapses in our one Universe, but which one of the many universes is the one we each subjectively happen to find ourselves in. Here's an
example. Let us say a particle has a very simple wave-function that spreads the particle's position between one of just two points in space. The set-up is such that the particle has a 30 percent chance of being in the first position and a 70 percent chance of being in the other. In the Copenhagen view, measuring the particle would force its wavefunction to collapse onto one location or the other, with relative odds 3:7. In the many worlds view, however, the particle really does exist at both locations—in 30 percent of all universes the particle is in the first position, while in the other 70 percent it's in the second position. Making a measurement picks which universe we're in, and we see the particle's position as it is in that universe.

In the Copenhagen interpretation, collapse of the wave function marks the transition from thinking of the particle's behavior as a wave (quantum behavior) to viewing it as a solid particle (classical behavior). An analogous process called decoherence happens in the many worlds interpretation. Whereas collapse of the wavefunction attributes this transition to the meddling fingers of the observer, decoherence puts it down to the inevitable interaction of a delicate quantum system with its classical environment. Prior to decoherence, the particle is in a purely quantum state. Quantum interference (see
How to be everywhere at once
) between
the different universes of the multiverse means that we view its behavior as a wave. But as soon as the delicate balance needed to maintain this quantum state is upset by outside forces, the system decoheres into a classical state. The universes of the multiverse then peel apart and we end up in just one of them.

The sprawling network of parallel universes that the many worlds interpretation relies on has made many scientists skeptical about the theory. In recent years, however, the meteoric rise of quantum computers (machines that harness the power of copies of themselves in parallel universes to carry out lightning-fast calculations—see
How to crack unbreakable codes
) have convinced many. But will it ever be possible to gather incontrovertible evidence as to whether parallel universes do or don't exist, and so prove which is right: Copenhagen or many worlds?

One scientist thinks such a proof is possible. Max Tegmark, a US physicist at the Massachusetts Institute of Technology, has come up with a macabre experiment that could tell between the two. He calls it “quantum suicide.” It's an outlandish twist on the old Schrödinger's cat thought experiment, where a cat is locked in a box with a phial of poison and a radioactive source. If the source emits a particle of radiation, the
poison is cracked open and the cat dies; otherwise it lives. Radioactive decay is a quantum process, meaning that the wavefunction of the radioactive source must be a mixture of decayed and not decayed. So—the reasoning goes—the cat must therefore be a mixture of both dead and alive at the same time before it's measured. Tegmark replaced the phial of poison in the experiment with a special kind of gun that fires automatically once every second. The gun is linked to a radioactive source. The default setting is for the gun to just click on an empty chamber each time—unless, that is, the source has emitted a particle of radiation in the last second, in which case the gun fires a live bullet. The source is chosen so that the probability of there being a decay event in any one-second interval is 50 percent. To anyone watching, the gun makes a random sequence of clicks and bangs, each interspersed with equal frequency. But according to Tegmark, and if the many worlds interpretation is correct, anyone brave enough to put their head in front of the barrel will see the gun click every time with 100 percent probability. It never fires a live round.

Tegmark's explanation is that in the many worlds view there are always universes in which the gun doesn't fire a live bullet. The wavefunction of the radioactive source is spread evenly across the multiverse—and, therefore, so is the final state of the human subject, including their very consciousness. Given that this
consciousness won't exist in universes where the gun fires a bullet, it must therefore always find itself in one of the 50 percent of universes where the gun just clicks. The experimenter must always perceive herself to end up in one of the universes in which she survives. From the point of view of an onlooker, however, the process wouldn't be too pretty. Copies of the experimenter and her consciousness exist in all the other universes in the multiverse. And in 50 percent of these universes the gun will fire live bullets. The onlooker will see it click and fire at random, so sooner or later they will see the experimenter shoot herself—quantum suicide. For this reason, the only way this method could really prove many worlds to a skeptic would be for the skeptic to put their head in front of the barrel—which, given their skepticism, is unlikely to happen.

The astute reader may be able to spot where Tegmark is going with all this. Anyone killed instantaneously (not rendered comatose or just critically injured) as a result of a quantum event can conceivably take advantage of the fact that (in the many worlds view) there exist parallel universes where the quantum event has the opposite outcome and they therefore survive. They will always find themselves in one of these universes, and could therefore achieve an immortality of sorts.

The quantum nature of the fatal event is crucial. For example, if you cross the road while fiddling with your iPhone and get hit by a bus load of commuters from the local park and ride there's nothing quantum about that, and you will be ground into the asphalt with 100 percent probability. Only when your death is triggered by the randomness of quantum physics will there be other universes where the randomness swings in your favor so that you can live. Tegmark points out that one such quantum killer is cancer, which begins with the mutation of a DNA molecule (molecules are made of atoms bonded together by quantum forces). He imagines a swarm of tiny nanorobots that could swim through your blood stream monitoring your DNA. As soon as they detected a cancerous mutation, the robots would kill you instantly—perhaps by remotely triggering a switch in your brain that instantly stopped all of your life processes. If he's right then by using this system you would never get cancer—quantum physics would provide a bizarre cure to this often fatal illness.

If you're going to enjoy your newfound longevity you'll need enough money put away for a lengthy retirement—to make your life not only long, but prosperous as well. And Tegmark has this taken care of too. Some lotteries now use quantum random number generators to pick the winning ticket. These use the randomness
of quantum processes—such as radioactive decay—to select their numbers. This makes them more secure than other methods, which sometimes use computer algorithms to generate a seemingly random sequence that can be predicted by someone who knows which algorithm is being used.

Quantum randomness is completely unexploitable. Until, that is, you remember the many worlds interpretation. If the lottery numbers are determined by a quantum event, yours will always be the winning ticket somewhere out there across the multiverse. Linking the same random-number generator to a quantum suicide gun rigged to kill you if you lose ensures that's exactly where you end up. Don't try this at home!

• Here nor there

• Measuring atoms

• Entanglement

• The quantum teleporter

• Beaming qubits

• Download yourself

It's the ultimate in personal transportation—a machine that can disassemble your body atom by atom and then beam all the information about you at the speed of light to a receiver, where you are promptly reassembled. If that sounds like the ramblings of a science nerd who's seen too much
Star Trek
then think again—teleportation has been verified experimentally.

The word “teleportation” was coined in 1931 by the independent British researcher Charles Fort. He spent many years of his life gathering and cataloging tales of the bizarre and the unexplained. While attempting to explain the reports of showers of stones, ice and
occasionally even live animals from the sky, Fort supposed that “teleportation exists, as a means of distribution of things and materials.”

But Fort also turned up mysterious accounts of human teleportation, such as that of Gil Pérez. The story goes that on October 24, 1593, the chief of the Guard at the Governor's Palace in the Plaza Mayor, Mexico City, noticed that one of his soldiers was not wearing the correct uniform. The dazed soldier said his name was Gil Pérez and that he was a guard at the Governor's Palace in the Philippine capital, Manila. While realizing he was no longer in the Philippines, Pérez had no idea how he had come to be in Mexico City. Probably the most famous teleportation legend is the story surrounding what has become known as the Philadelphia experiment. In 1943, during a supposed test of new “invisibility equipment,” the US Navy destroyer USS
Eldridge
is said to have disappeared from the Philadelphia Naval Shipyard to be spotted just moments later in waters off Norfolk, Virginia, by the crew of a passing merchant ship. The
Eldridge
allegedly teleported back to Philadelphia shortly after, where its crew suffered terrible after effects, including spontaneous human combustion and the melding of body parts with the ship. The US Office of Naval Research dismisses the experiment as an urban myth, probably arising from research on degaussing—the practice of passing currents around the hull of a ship to render it
impervious to magnetic mines. It may be no coincidence that the writers Robert Heinlein and Isaac Asimov—two of the most creative minds in science fiction—both worked at the Philadelphia Naval Yard between 1943 and 1945.

For many years, it was believed that the laws of quantum physics made teleportation impossible. In 1927, the German physicist Werner Heisenberg had put forward his so-called uncertainty principle, which turned out to be one of the cornerstones of physics. In a nutshell, it said that it is impossible to know everything about a quantum particle—precision in your knowledge of one of its properties must be traded off against imprecision in one of the others. One way to think of it is that the act of measuring one property of the particle disturbs it so much that you lose all accuracy in the other.

But if this was right, it meant that measuring the state of every atom and molecule inside an object in order to teleport it was going to be impossible. All you'd be allowed is a partial description, and what you got out the other end of the teleporter might bear little resemblance to what went in. The writers of the
Star Trek
TV show even went so far as to invent a fictional device that they called the “Heisenberg compensator” to give
them a retort to the flood of letters they received from science-savvy fans.

In a groundbreaking piece of research published in 1993, a team of scientists in the United States realized that you don't have to measure all the information about a quantum particle in order to transmit it. In effect, quantum theory lets you teleport information that you don't actually know. The idea works using a phenomenon known as quantum entanglement. This is where you take two subatomic particles and bring them together in just the right way so that their properties—such as speed, momentum, energy and so on—become linked. Two entangled particles taken to opposite sides of the Universe can appear to exhibit a kind of faster-than-light communication between each other, since measuring the state of one particle instantaneously fixes the state of the other all those billions of light years away. Albert Einstein was aware of quantum entanglement and used it to express his general disdain for quantum theory, famously calling it “spooky action at a distance.” William Wootters, one of the US team, likens the behavior of entangled particles to two boxes—one has a blue ball in it and the other has a black ball in it, but you don't know which ball is in which box. Take the two boxes to opposite sides of the Universe, and open one of them—and
what you see instantly tells you which ball is in the other box too.

Of course, quantum particles are specified by more than just one number, so as well as a blue ball and a black ball you might have some other pairs like a green ball and a red ball, a brown ball and a pink ball, and a white ball and a yellow ball. If you open one box and you find it to contain blue-red-pink-white then you know the other box is holding black-green-brown-yellow. You know this without having to make any measurements of (i.e. look inside) the second box. And this same sort of “oppositeness” in their properties is a fundamental relationship between pairs of entangled quantum particles. One property particles have, for example, is called quantum spin. It's very loosely analogous to rotational spin of everyday experience. However, in the quantum world spin can take just one of two values—called “up” and “down.” The two particles in an entangled pair will always have opposite quantum spin. But until a measurement is made it's impossible to say which has spin up, and which has spin down. What makes entanglement really weird—and slightly different from the boxes analogy—is that nature itself doesn't decide which is which until one of the particles is actually measured.