272
NEGATIVE PRESSURES
PRODUCE REPULSIVE
GRAVITY
COSMIC INFLATION
IN CONTEXT
KEY ASTRONOMER
Alan Guth (1947–)BEFORE
1927 Georges Lemaître
proposes that the universe
arose from a single primordial
atom. This is later named the
Big Bang theory.1947 George Gamow and
Ralph Alpher describe how
the elements hydrogen and
helium were formed in the
early universe.1964 The cosmic microwave
background is discovered to
be a remnant of the Big Bang.AFTER
1999 Dark energy is found to
be accelerating the expansion
of the universe.2014 BICEP2 withdraws claims
of finding evidence of inflation.2016 LIGO detects
gravitational waves, offering
a new way to observe the
structure of spacetime.B
y the 1970s, cosmologists
were grappling with a variety
of puzzles thrown up by the
Big Bang theory. In an attempt to
solve them, Alan Guth proposed a
stage of rapid inflation in the early
universe, caused by the effects
predicted by quantum theory.The puzzles
One of the problems with the
Big Bang theory came from the
Grand Unified Theory (GUT),
which describes how the forces
of the universe (aside from gravity)
arose a fraction of a second after
the Big Bang. The GUT predicted
that high temperatures at this time
would create bizarre features, such
as so-called magnetic monopoles(particles with only one magnetic
pole). There are, however, none to be
found, which suggests the universe
cooled faster than expected.
A second problem arose from
the way space is amazingly “flat,”
meaning that it expands according
to “normal” Euclidean geometry (see
diagram opposite). A flat universe
would only have arisen if the density
of the early universe matched a
certain critical figure. Varying it
slightly one way or the other would
have resulted in curved universes.
The final issue was the horizon
problem. Light from the edge of the
observable universe has taken the
entire life of the universe to reach
Earth. As light’s speed is constant,
scientists know that it has notInflation explains many of the features of the
universe, but there is no evidence that it is correct.The first stage of the
universe after the Big
Bang may have been a
period of rapid expansion
called inflation.The Big Bang theory
predicts features
that are not seen in
the current universe.