Archives
Examination of radiation left from birth of universe could alter theories
James E.
Kloeppel, Physical Sciences Editor
217-244-1073; kloeppel@illinois.edu
|
Released
4/2/07
CHAMPAIGN, Ill. —
Using relic radiation from the birth of the universe, astrophysicists
at the University of Illinois have proposed a new way of measuring the
fine-structure constant in the past, and comparing it with today.
By focusing on the absorption of the cosmic microwave background by
atoms of neutral hydrogen, the researchers say, they could measure the
fine-structure constant during the “dark ages,” the time
after the Big Bang before the first stars formed, when the universe
consisted mostly of neutral hydrogen and helium.
The fine-structure constant characterizes the strength of the electromagnetic
force, which is one of the four fundamental forces in physics. But,
the fine-structure constant may not be constant. Recent observations
of quasars – starlike objects billions of light-years away –
have found a slightly different value for the fine-structure constant.
“If the fine-structure constant does vary over time and space,
we could use it as a probe of new physics beyond the standard model
and beyond general relativity,” said Benjamin Wandelt, a cosmologist
at Illinois, who developed the proposed measurement technique with
graduate student Rishi Khatri.
A varying fine-structure constant also could help explain the mysterious
dark energy that pervades the universe, Wandelt said, and help constrain
what kind of theory would unite the four fundamental forces into a “theory
of everything.”
Using light from quasars, astronomers can look for variations in the
fine-structure constant from the present up to 5 billion years ago.
Using the spectra of neutral hydrogen, astronomers can peer much further
back in time.
“There is a void from about 300,000 years after the Big Bang,
when radiation that formed the cosmic microwave background was emitted,
to about 500 million years later, when the first stars formed,”
Wandelt said. “Our measurement technique could probe the fine-structure
constant during this period, known as the dark ages.”
When a neutral hydrogen atom absorbs a photon of light from the cosmic
microwave background, the electron flips its spin, causing a slight
difference in its spectrum.
The telltale fingerprint of this atomic transition at a wavelength of
21 centimeters can serve as a sensitive search for past values of the
fine-structure constant, said Wandelt and Khatri, who describe their
measurement technique in a paper accepted for publication in the journal
Physical Review Letters, and posted on its Web site.
While most radio telescopes are too small to look for variations in
the fine-structure constant, there are new instruments in the design
or construction phase – including the Long Wavelength Array and
the Low Frequency Array – that will provide the first limits when
brought on line.
“The measurements would be tricky, but not impossible,”
Wandelt said.
Editor’s note: To reach Benjamin Wandelt, e-mail: bwandelt@illinois.edu.
