(January 25, 2016) How
did the universe begin? And what came before the Big Bang? Cosmologists have
asked these questions ever since discovering that our universe is expanding.
The answers aren't easy to determine. The beginning of the cosmos is cloaked
and hidden from the view of our most powerful telescopes. Yet observations we
make today can give clues to the universe's origin. New research suggests a
novel way of probing the beginning of space and time to determine which of the
competing theories is correct.
The most widely accepted theoretical scenario for the
beginning of the universe is inflation, which predicts that the universe
expanded at an exponential rate in the first fleeting fraction of a second.
However a number of alternative scenarios have been suggested, some predicting
a Big Crunch preceding the Big Bang. The trick is to find measurements that can
distinguish between these scenarios.
One promising source of information about the universe's
beginning is the cosmic microwave background (CMB) - the remnant glow of the
Big Bang that pervades all of space. This glow appears smooth and uniform at
first, but upon closer inspection varies by small amounts. Those variations
come from quantum fluctuations present at the birth of the universe that have
been stretched as the universe expanded.
The conventional approach to distinguish different scenarios
searches for possible traces of gravitational waves, generated during the
primordial universe, in the CMB. "Here we are proposing a new approach
that could allow us to directly reveal the evolutionary history of the
primordial universe from astrophysical signals. This history is unique to each
scenario," says coauthor Xingang Chen of the Harvard-Smithsonian Center
for Astrophysics (CfA) and the University of Texas at Dallas.