How to Destroy the Universe (20 page)

Inflation not only dug the Universe out of a gravitational hole by stopping it collapsing on itself, it also
planted the seeds from which galaxies would later grow. As is often the case, it all comes down to quantum physics. Ordinary empty space is filled with virtual quantum particles constantly popping in and out of existence. But as the first quantum physicists discovered in the early years of the 20th century, subatomic particles can equally well be thought of as waves. In the embryonic Universe, these waves introduced tiny irregularities in the density of matter from point to point across space. Before they could pop out of existence again, as is usually the case with such quantum fluctuations, inflation blasted them up from the quantum realm and stretched them out, quite literally, to astronomical proportions. It was the gravity of these now cosmic-sized density fluctuations that sucked in the material from which galaxies grew, and within each galaxy then formed stars, planets and—on at least one planet orbiting an average yellow star in a fairly typical galaxy—there emerged life.

The history of the Universe after the era of inflation, about 10-
³⁶
seconds (one billion-billion-billion-billionth of a second) after the Big Bang is reasonably well understood. The radiation from the Big Bang fireball was stretched out and diluted by the expansion of space to form a kind of relic echo of the Big Bang, called the cosmic microwave background
radiation (CMB). The CMB dates from when the Universe was just 300,000 years old. Before this time matter existed as a sea of positively charged protons and negatively charged electrons. These particles scattered the radiation from the Big Bang this way and that. However, at 300,000 years the temperature of the Universe dropped sufficiently for protons and electrons to combine into electrically neutral atoms. At this point interactions between radiation and matter ceased, and the radiation was free to stream out through space as the CMB. This ghostly microwave glow still pervades space today, and numerous spacecraft have been sent into orbit to study it. Space missions are the best way to investigate the CMB because a great deal of the microwave radiation from space is masked by microwave emission from water in Earth's atmosphere. A small quantity of the CMB does make it through: about one percent of the static on an untuned TV is, in fact, the echo of creation. Spacecraft have measured the minuscule fluctuations and ripples in the CMB and from it extracted a picture of the post-Big Bang universe. But the physics of the Universe leading up to inflation is something of an undiscovered country. It is believed that the Big Bang was a quantum event—analogous to the creation of virtual particles in empty space—which caused space and time to appear where before there was nothing at all.

Only a theory of “quantum gravity” can address this, the ultimate question of creation, and at present such a theory seems a long way away. Other forces in nature have been quantized successfully. However, Einstein's theory of general relativity—our best theory of gravity—seems exceptionally difficult to cast in quantum language, being riddled with so-called divergences where the predicted values of physical quantities become unphysically infinite. String theory and M-theory are contenders to furnish us with a theory of quantum gravity, but they're yet to deliver on this promise.

Up to about 10
^-43
of a second after the Big Bang, quantum gravity was wrapped up with quantized versions of the other three forces of nature—electromagnetism, and the strong and weak nuclear forces—to form a kind of all-encompassing superforce that physicists have modestly termed “the theory of everything.” The end of the Universe's quantum gravity era was marked by a phase transition where gravity split away to become a separate force in its own right, leaving the other three bundled together as a so-called “grand unified theory.” A number of different models for grand unified theories exist, but at present these are very poorly tested.

Another phase transition brought about the end of the grand unified phase of cosmic history—at around 10
^-36
seconds after the Big Bang. This is the same event at which inflation is believed to have taken place. The grand unified phase transition saw the strong force—the force responsible for binding together the nuclei of atoms—peel away from the rest of the group. Now just electromagnetism and the weak nuclear force (the force responsible for radioactive decay of nuclei) remained unified, as the so-called electroweak theory. This theory is well-established, having been confirmed by experiments. Finally, the electroweak symmetry itself broke apart at around a trillionth (10
^-12
) of a second after the Big Bang to leave the four forces of nature as the separate and distinct entities that we see today.

The Universe is the ultimate physics laboratory, providing a stage on which to test out theories of high-energy particle physics through the effects they've had on cosmic structure and the microwave background radiation. But the particle physics processes that happened before inflation are beyond the reach of even the most powerful telescopes. And this is where particle accelerators come in. These are colossal machines that accelerate beams of subatomic particles to extraordinarily high speeds and then smash them together. The idea is to recreate the superheated conditions of the Big Bang in order to study the processes
that governed this step in the Universe's birth and development. Particles crash together and are split into their constituent components, such as quarks (each proton and neutron particle is made up of three of these smaller quarks), and the behavior of these fragments can then be studied to unravel the laws governing their behavior.

The world's first particle accelerator was switched on at the University of California, Berkeley, in 1931. It had a collision energy of 1 mega electronvolt (MeV). An electronvolt (eV) is a unit of energy defined as the total kinetic energy gained by an electron when it's accelerated through an electric potential difference of 1 volt. There are now 26,000 accelerators in operation around the world. The biggest and most powerful is the Large Hadron Collider (LHC) at the CERN research center on the border between France and Switzerland. Its maximum collision energy will be 574 tera electron-volts (TeV) per particle—574 million times more powerful than the 1931 machine.

Particle accelerators work using a tube dotted with a sequence of electrified sections connected to an alternating voltage. Electrically charged particles—such as electrons, protons, or whole atomic nuclei—are placed at one end of the tube. The first tube section is then charged with the opposite polarity to the particles so that they are attracted toward it. As they pass by, the
polarity is reversed so that they are repelled onwards and accelerated further. This process is repeated all the way along the accelerator tube so that fast moving particles emerge at the other end. Modern accelerators also incorporate magnets to curl the particles around into a giant ring. This means that the particles can be looped round over and over, gathering more speed with every circuit. The LHC at CERN is a vast underground ring accelerator 27 km (17 miles) in circumference. At full power, particles in the beam complete 11,245 circuits of the ring per second.

One of the principal reasons the LHC's sprawling complex of magnets, computers, scientific experiments and heavy duty engineering was put together was to look for a single subatomic particle of nature: the Higgs boson. It's the only missing particle in what has become known as the standard model of particle physics, which explains all of the interactions between the four forces of nature as they stand today as well as the electroweak unified theory. Also known as the “God particle,” the Higgs was proposed in 1964 by the British physicist Peter Higgs as a way for all the other particles of nature to have acquired their different masses. His idea was that space is filled with a sea of Higgs bosons, which cluster around other particles, so making those particles massive. Different kinds of
particles interact with the Higgs to differing degrees and this is why the particle types all have different masses—while some remain massless.

Finding the Higgs has had to wait for a particle accelerator with the power of the LHC. That's because the higher the mass of a subatomic particle is, the higher the collision energy required to create it experimentally. The precise mass of the Higgs isn't known, but the bulk of the range in which that mass is thought to lie was above what could be reached with the collision energies of previous accelerator machines. Not everyone is convinced the Higgs exists. Cambridge physicist Stephen Hawking has placed a bet that the LHC won't find it. If he wins, this would mean a substantial rewrite of the laws of particle physics. Then again, Hawking has placed a number of scientific wagers in the past and his hit rate has been less than impressive.

The LHC will crash together subatomic particles so hard that the density of matter generated in the collisions may well be high enough to form microscopic black holes. This has prompted fears from the public that one of these black holes could “escape from the lab” and devour Earth. One group in Hawaii even went so far as to file a lawsuit against CERN to try to prevent
them from switching the accelerator on. CERN's designers, and other physicists, insist that the accelerator is safe. They say that any miniature black holes formed would rapidly evaporate away by Hawking radiation (see
How to make energy from nothing
). Also, the high-energy cosmic rays from deep space that regularly pummel Earth pack much more energy that the LHC collisions. If there really were a danger, the planet would have been destroyed long ago.

• Sound waves

• Wave properties

• The decibel scale

• Ultrasound and infrasound

• The brown note

• The Doppler effect

• Shock waves

• Louder than bombs

Bang your fist on a desk and you create sound—a mechanical vibration that travels through solids, liquids and gases. We use it to communicate, as a tool, and as a weapon. It's used extensively in the animal kingdom, while sounds generated in the rest of the natural world are some of the loudest on record. The eruption of the volcano Krakatoa in 1883, for example, was heard nearly 5,000 km (3,000 miles) away. But there was another cataclysm during Earth's prehistory that was even louder still.

Sound is essentially a pressure wave traveling through matter. All matter has pressure inside it due to the thermal motion of its atoms and molecules. The pressure inside a sealed container of gas is caused as the molecules of the gas beat against the container walls. Heat the gas up and their beating becomes more vigorous, and the pressure rises. Pressure is defined as the force per unit area acting on a surface, and it's usually measured in Pascals, after the 17th-century French mathematician Blaise Pascal, who carried out much of the initial research in this area.

Sound is a momentary increase in this pressure. Strike the skin of a drum and the downward movement of the drum skin compresses the air that it's moving into. With nothing to contain it, this compression spreads out through the air as a wave. Close to the drum the compression is greater and the sound is thus louder; as you get further away the wave has spread out, so the degree of compression is less and the sound is quieter. Unlike water waves, which are transverse waves (that is, the displacement caused by the wave is at right angles to its direction of motion), sound waves are longitudinal (the displacement is parallel to the direction of motion, rather like waves on a stretched spring).

Physicists describe sound waves, and all other kinds of waves, using four principal quantities. The first is the speed of the waves. This is determined by the properties of the medium that the sound is traveling through. In particular, it is fixed by the density (with the sound speed decreasing as the density gets higher) and the stiffness (increasing with the degree to which the medium resists being compressed). The second quantity is the frequency of the sound. This is simply the number of wave crests passing a fixed reference point every second. It is measured in cycles per second (also known as hertz, after German physicist Heinrich Hertz). The frequency of a sound is determined by its source—strike a drum once per second and it will give out sound pulses at a frequency of 1 Hz. Rig the drum up to a machine that can strike it 100 times per second and you get sound with a frequency of 100 Hz. We hear the frequency of a sound as its pitch—for example, a middle octave A note is characterized by a frequency of 440 Hz.

The next property is wavelength. This is just the distance between two successive wave crests. It is given by dividing a sound wave's speed by its frequency. And finally, there's the amplitude of the wave. This is the size of the displacement it produces as it passes. Thinking for a moment in terms of water waves, the amplitude is simply the height of the wave crest. Of
course, sound is a longitudinal wave so the amplitude is more like the amount of compression of the medium that the wave causes as it travels by. We hear the amplitude as the loudness, or volume of the sound.

Scientists measure the loudness of a sound on the decibel scale. This is a direct measure of the sound wave's amplitude. It is gauged logarithmically, scaled so that a decibel increase of 40 corresponds to an increase in the amplitude of the sound wave by a factor of 100. Thus, 60 corresponds to 1,000; 80 to 10,000; and so on. Leaves rustling in a breeze come in at about 10 decibels, rain falling is about 50, a loud concert is about 115 and a shotgun blast at close range 170. The threshold of pain begins at about 130 dB.