Parallel Worlds (59 page)

tunneling
The process by
which particles can penetrate barriers that are forbidden by Newtonian
mechanics. Tunneling is the reason for radioactive alpha decay and is a
by-product of the quantum theory. The universe itself may have been created by
tunneling. It has been conjectured that one may be able to tunnel between
universes.

type I, II, III civilizations
The classification introduced by Nikolai Kardashev to rank
civilizations in outer space by their energy generation. They correspond to
civilizations that can harness the power of an entire planet, star, and galaxy,
respectively. So far, no evidence has been found for any of them in space. Our
own civilization corresponds probably to a type 0.7.

type Ia supernova
A supernova
that is often used as a standard candle to measure distances. This supernova
takes place in a double star system, where a white dwarf star slowly sucks
matter from a companion star, pushing it over the Chandrasekhar limit of i.4
solar masses, causing it to explode.

uncertainty principle
The principle
which states that you cannot know both the location and velocity of a particle
with infinite precision. The uncertainty in the position of a particle,
multiplied by the uncertainty in its momentum, must be greater than or equal
to Planck's constant divided by 2 n. The uncertainty principle is the most
essential component of the quantum theory, introducing probability into the
universe. Because of nanotechnology, physicists can manipulate individual atoms
at will and hence test the uncertainty principle in the laboratory.

unified field theory
The theory
sought by Einstein that would unify all the forces of nature into a single
coherent theory. Today, the leading candidate is string theory or M-theory.
Einstein originally believed that his unified field theory could absorb both
relativity and the quantum theory into a higher theory that would not require
probabilities. String theory, however, is a quantum theory and hence introduces
probabilities.

vacuum
Empty space.
But empty space, according to the quantum theory, is teeming with virtual
subatomic particles, which last only a fraction of a second. The vacuum is also
used to describe the lowest energy of a system. The universe, it is believed,
went from a state of a false vacuum to the true vacuum of today.

virtual particles
Particles that
briefly dart in and out of the vacuum. They violate known conservation laws but
only for a short period of time, via the uncertainty principle. The
conservation laws then operate as an average in the vacuum. Virtual particles
can sometimes become real particles if enough energy is added to the vacuum. On
a microscopic scale, these virtual particles may include wormholes and baby
universes.

wave function
A wave that
accompanies every subatomic particle. It is the mathematical description of the
wave of probability locating the position of any particle. Schrodinger was the
first to write down the equations for the wave function of an electron. In the
quantum theory, matter is composed of point particles, but the probability of
finding the particle is given by the wave function. Dirac later proposed a
wave equation which included special relativity. Today, all of quantum physics,
including string theory, is formulated in terms of these waves.

weak nuclear force
The force within
the nucleus that makes possible nuclear decay. This force is not strong enough
to hold the nucleus together, hence the nucleus can fall apart. The weak force
acts on leptons (electrons and neutrinos) and is carried by the W- and
Z-bosons.

white dwarf
A star in its
final stages of life, consisting of lower elements such as oxygen, lithium,
carbon, and so forth. They are found after a red giant exhausts its helium fuel
and collapses. Typically, they are about the size of Earth and weigh no more
than i.4 solar masses (or else they collapse).

WIMP
Weakly
interacting massive particle. WIMPs are conjectured to make up most of dark
matter in the universe. One leading candidate for the WIMPs are the sparticles
predicted by string theory.

wormhole
A passageway
between two universes. Mathematicians call these spaces "multiply
connected spaces"—spaces in which a lasso may not be shrunk to a point. It
is not clear if one may be able to pass through a wormhole without
destabilizing it or dying in the attempt.