New Haven, Conn. Scientists studying the Big Bang say that it
is possible that string theory may one day be tested experimentally via
measurements of the Big Bangs afterglow.

Richard Easther, assistant professor of physics at Yale
University will discuss the possibility at a meeting at Stanford
University Wednesday, May 12, titled Beyond Einstein: From the Big Bang
to Black Holes. Easthers colleagues are Brian Greene of Columbia
University, William Kinney of the University at Buffalo, SUNY, Hiranya
Peiris of Princeton University and Gary Shiu of the University of
Wisconsin.

String theory attempts to unify the physics of the large
(gravity) and the small (the atom). These are now described by two
theories, general relativity and quantum theory, both of which are
likely to be incomplete.

Critics have disdained string theory as a philosophythat
cannot be tested. However, the results of Easther and his colleagues
suggest that observational evidence supporting string theory may be
found in careful measurements of the Cosmic Microwave Background (CMB),
the first light to emerge after the Big Bang.

In the Big Bang, the most powerful event in the history of
the Universe, we see the energies needed to reveal the subtle signs of
string theory,said Easther.

String theory reveals itself only over extreme small
distances and at high energies. The Planck scale measures 10^-35 meters,
the theoretical shortest distance that can be defined. In comparison, a
tiny hydrogen atom, 10^-10 meters across, is ten trillion trillion times
as wide. Similarly, the largest particle accelerators generate energies
of 10^-15 electron volts by colliding sub-atomic particles. This energy
level can reveal the physics of quantum theory, but is still roughly a
trillion times lower than the energy required to test string theory.

Scientists say that the fundamental forces of the Universe
gravity (defined by general relativity), electromagnetism, “weak”
radioactive forces and “strong” nuclear forces (all defined by quantum
theory) were united in the high-energy flash of the Big Bang, when all
matter and energy was confined within a sub-atomic scale. Although the
Big Bang occurred nearly 14 billion years ago its afterglow, the CMB,
still blankets the entire universe and contains a fossilized record of
the first moments of time.

The Wilkinson Microwave Anisotropy Probe (WMAP) studies the
CMB and detects subtle temperature differences, within this largely
uniform radiation, glowing at only 2.73 degrees Celsius above absolute
zero. The uniformity is evidence of inflation,a period when the
expansion of the Universe accelerated rapidly, around 10^-33 seconds
after the Big Bang. During inflation, the Universe grew from an atomic
scale to a cosmic scale, increasing its size a hundred trillion trillion
times over. The energy field that drove inflation, like all quantum
fields, contained fluctuations. These fluctuations, locked into the
cosmic microwave background like waves on a frozen pond, may contain
evidence for string theory.

Easther and his colleagues compare the rapid cosmic expansion
that occurred just after the Big Bang to enlarging a photograph to
reveal individual pixels. While physics at the Planck scale made a
“ripple” 10^-35 meters across, thanks to the expansion of the Universe
the fluctuation might now span many light years.

Easther stressed it is a long shot that string theory might
leave measurable effects on the microwave background by subtly changing
the pattern of hot and cold spots. However, string theory is so hard to
test experimentally that any chance is worth trying. Successors to WMAP,
such as CMBPol and the European mission, Planck, will measure the CMB
with unprecedented accuracy.

The modifications to the CMB arising from string theory could
deviate from the standard prediction for the temperature differences in
the cosmic microwave background by as much as 1%. However, finding a
small deviation from a dominant theory is not without precedent. As an
example, the measured orbit of Mercury differed from what was predicted
by Isaac Newton’s law of gravity by around seventy miles per year.
General relativity, Albert Einstein’s law of gravity, could account for
the discrepancy caused by a subtle warp in spacetime from the Sun’s
gravity speeding Mercury’s orbit.

Refer to http://www-conf.slac.stanford.edu/einstein/ for more information on
the “Beyond Einstein” meeting.