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
"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
the 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.
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"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
[Text copied from
University of Illinois news release]