How to Destroy the Universe (31 page)

inertia
The resistance of a body to moving or changing its existing state
of motion. To all intents and purposes inertia is the same thing as mass.

inflation
A colossal growth spurt, during which space is thought to have expanded by a factor of 10
²⁶
—a 1 followed by 26 zeroes—in a tiny fraction of a second shortly after the Big Bang.

Kepler's laws
Laws describing the motion of the planets worked out by German Johannes Kepler in 1605.

many worlds interpretation
An alternative to the Copenhagen interpretation of quantum theory, the many worlds interpretation ascribes the weird behavior of quantum particles to interference between parallel universes.

Newton's laws of motion
Three simple laws of motion formulated in the 17th century by British scientist Sir Isaac Newton.

Newton's theory of gravity
A theory that predicts the gravitational force that two or more massive bodies exert on one another. Although superseded by general relativity, it still gives a very good approximation for weak fields.

nuclear fission
The process of obtaining energy by splitting heavy atomic nuclei in two. It is the basis of all nuclear power stations in use today.

nuclear fusion
Reactions that generate energy by joining together light atomic nuclei, used in modern nuclear weapons. Fusion is the power source of the Sun.

optics
The study of the passage of light rays. It explains phenomena such as reflection, refraction (the bending of light) and diffraction (how light is spread out by narrow apertures).

phase transition
A process by which matter undergoes a fundamental shift from one state to another. Examples include the boiling of water to steam, and the spontaneous breaking of particle physics symmetries in the early Universe.

photoelectric effect
The basis for solar power, explained by Albert Einstein, who showed how some metals generate electricity when ultraviolet light falls on them.

plate tectonics
Earth's crust is divided into a number of pieces that jostle together. Their motion is governed by a field known as plate tectonics.

principle of least action
Perhaps the single most important concept in physics, which says that physical systems always follow the path of least resistance.

quantum entanglement
A pair of “entangled” quantum particles remain linked so that even when they are separated by a great distance, wiggling one will have an instantaneous effect on the other.

quantum theory
An often counterintuitive description of the world of subatomic particles. It says particles can sometimes behave like waves and, equally, waves sometimes act like particles.

radioactivity
The leaking of particles and radiation from the unstable nuclei of some atoms. Radioactivity takes three main forms: alpha particles, beta particles and gamma rays.

radio astronomy
The study of radio waves given off by far-away galaxies and cosmic gas clouds.

resonance
Like a tuning fork that's struck, all objects have a natural frequency.
When subjected to vibrations at this frequency they undergo violent oscillations. This effect is known as resonance.

Schrödinger's cat
A thought experiment based on the Copenhagen interpretation of quantum theory, which supposes that if a cat in a box lives or dies according to the behavior of a quantum particle then the cat must be alive and dead at the same time.

simple harmonic motion
Oscillating movement, such as that of a pendulum, a guitar string or a mass bouncing on a spring.

special relativity
A theory formulated in 1905 by Albert Einstein, which rewrote Newton's laws of motion for objects moving at close to light speed. The theory predicted distortions in space and time as well as the famous equation
E
=
mc
²
.

spontaneous symmetry breaking
How unified theories of particle physics broke apart as the Universe cooled to give the theories seen today. For example, the electroweak theory split into the weak nuclear force and electromagnetism.

star
A vast ball of gas composed mainly of hydrogen, illuminated by nuclear fusion reactions in its core. The closest example is our own Sun.

statistical physics
The analysis of systems in physics composed of many particles. It works by applying the mathematical laws of statistics to give the system's average large-scale properties.

string theory
An attempt to remove some of the mathematical anomalies that arise from treating subatomic particles as zero-dimensional dots by treating them instead as one-dimensional “strings.”

strong nuclear force
The force that glues together the quarks that protons and neutrons
are made of, and in turn binds these larger subatomic particles to form the nuclei of atoms.

subatomic particles
Matter is composed of atoms and molecules, which in turn are composed of subatomic particles, such as protons, neutrons and electrons.

superconductivity
Metals which, when cooled to within a smidgen of absolute zero temperature, lose all their electrical resistance. An electrical current in a loop of a superconductor will continue to circulate forever.

superfluid
Liquids that lose all their viscosity when cooled below a threshold temperature. An example is liquid helium.

supernova
A calamitous explosion that occurs when a massive star reaches the end of its life and throws off its outer layers. For a time, a supernova outshines the star's entire host galaxy.

thermodynamics
The physics of heat transfer and how that heat can be used to do useful work—for example, in engines.

uncertainty principle
It's one of the curiosities of quantum theory: the more accurately you measure one property of a subatomic particle, such as its position, the less accurately you are allowed to know other information about it, such as its speed. The principle was formulated in 1926 by German physicist Werner Heisenberg.

vacuum energy
Virtual particles mean empty space isn't as empty as you might think. The effect is called vacuum energy and the dark energy that dominates the Universe is one consequence of it.

virtual particles
Space is filled with a sea of virtual particles that can pop in and out of existence, so long as their energy and the time they exist for satisfy the uncertainty principle.

viscosity
The “stickiness” of a liquid. Water has low viscosity while syrup has high viscosity. The theory of viscosity is essential for understanding the drag forces that act on cars, ships and airplanes.

wave theory
Drop a stone in a pond and ripples carry the energy of the impact outward. Other forms of wave motion determine the physics of radiation and how sound travels from its source to your ear. Wave theory is the description of these processes.

weak nuclear force
One of two forces that operate within the nuclei of atoms. It is the force responsible for radioactive “beta” decay.

work
In physicist's parlance, work is the force applied to an object multiplied by the distance the object moves in response. It is measured in Joules, the same units as energy.