Galaxy observations show no change in fundamental physical constant(Forwarded)

Media Relations
University of California-Berkeley

18 April 2005

Galaxy observations show no change in fundamental physical constant
By Robert Sanders, Media Relations

BERKELEY -- A fundamental number that affects the color of light emitted
by atoms as well as all chemical interactions has not changed in more
than 7 billion years, according to observations by a team of astronomers
charting the evolution of galaxies and the universe.

The results are being reported today (Monday, April 18) at the annual
meeting of the American Physical Society (APS) by astronomer Jeffrey
Newman, a Hubble Fellow at Lawrence Berkeley National Laboratory
representing DEEP2, a collaboration led by the University of California,
Berkeley, and UC Santa Cruz. Newman is presenting the data, recorded by
the DEIMOS spectrograph on the Keck II telescope in Hawaii, and an
update on the DEEP2 project at a 1 p.m. EDT press conference at the
Marriott Waterside Hotel in Tampa, Fla.

The fine structure constant, one of a handful of pure numbers that
occupy a central role in physics, pops up in nearly all equations
involving electricity and magnetism, including those describing the
emission of electromagnetic waves -- light -- by atoms. Despite its
fundamental nature, however, some theorists have suggested that it
changes subtly as the universe ages, reflecting a change in the
attraction between the atomic nucleus and the electrons buzzing around it.

Over the past few years, a group of Australian astronomers has reported
that the constant has increased over the lifetime of the universe by
about one part in 100,000, based on its measurements of the absorption
of light from distant quasars as the light passes through galaxies
closer to us. Other astronomers, however, have found no such change
using the same technique.

The new observations by the DEEP2 survey team use a more direct method
to provide an independent measure of the constant, and show no change
within one part in 30,000.

"The fine structure constant sets the strength of the electromagnetic
force, which affects how atoms hold together and the energy levels
within an atom. At some level, it is helping set the scale of all
ordinary matter made up of atoms," Newman said. "This null result means
theorists don't need to find an explanation for why it would change so
much."

The fine structure constant, designated by the Greek letter alpha, is a
ratio of other "constants" of nature that, in some theories, could
change over cosmic time. Equal to the square of the charge of the
electron divided by the speed of light times Planck's constant, alpha
would change, according to one recent theory, only if the speed of light
changed over time. Some theories of dark energy or grand unification, in
particular those that involve many extra dimensions beyond the four of
space and time with which we are familiar, predict a gradual evolution
of the fine structure constant, Newman said.

DEEP2 is a five-year survey of galaxies more than 7-to-8-billion-light
years distant whose light has been stretched out or redshifted to nearly
double its original wavelength by the expansion of the universe. Though
the collaborative project, supported by the National Science Foundation,
was not designed to look for variation in the fine structure constant,
it became clear that a subset of the 40,000 galaxies so far observed
would serve that purpose.

"In this gigantic survey, it turns out that a small fraction of the data
seems to be perfect for answering the question Jeff's asking," said
DEEP2 principal investigator Marc Davis, professor of astronomy and of
physics at UC Berkeley. "This survey is really general purpose and will
serve a million uses."

Several years ago, astronomer John Bahcall of the Institute for Advanced
Study pointed out that, in the search for variations in the fine
structure constant, measuring emission lines from distant galaxies would
be more direct and less error-prone that measuring absorption lines.
Newman quickly realized that DEEP2 galaxies containing oxygen emission
lines were perfectly suited to provide a precise measure of any change.

"When the contradictory results from absorption lines starting showing
up, I had the idea that, since we have all these high redshift galaxies,
maybe we can do something not with absorption lines, but with emission
lines within our sample," Newman said. "Emission lines would be very
slightly different if the fine structure constant changed."

The DEEP2 data allowed Newman and his colleagues to measure the
wavelength of emission lines of ionized oxygen (OIII, that is, oxygen
that has lost two electrons) to a precision of better than 0.01
Angstroms out of 5,000 Angstroms. An Angstrom, about the width of a
hydrogen atom, is equivalent to 10 nanometers.

"This is a precision surpassed only by people trying to look for
planets," he said, referring to detection of faint wobbles in stars due
to planets tugging on the star.

The DEEP2 team compared the wavelengths of two OIII emission lines for
300 individual galaxies at various distances or redshifts, ranging from
a redshift of about 0.4 (approximately 4 billion years ago) to 0.8
(about 7 billion years ago). The measured fine structure constant was no
different from today's value, which is approximately 1/137. There also
was no upward or downward trend in the value of alpha over this
4-billion-year time period.

"Our null result is not the most precise measurement, but another method
(looking at absorption lines) that gives more precise results involves
systematic errors that cause different people using the method to come
up with different results," Newman said.

Newman also announced at the APS meeting the public release of the first
season of data (2002) from the DEEP2 survey, which represents 10 percent
of the 50,000 distant galaxies the team hopes to survey. DEEP2 uses the
DEIMOS spectrograph on the Keck II telescope in Hawaii to record
redshift, brightness and color spectrum of these distant galaxies,
primarily to compare galaxy clustering then versus now. The survey, now
more than 80 percent complete, should finish observations this summer,
with full data release by 2007.

"This is really a unique data set for constraining both how galaxies
have evolved and how the universe has evolved over time," Newman said.
"The Sloan Digital Sky Survey is making measurements out to about
redshift 0.2, looking back the last 2-3 billion years. We really start
at redshift 0.7 and peak at 0.8 or 0.9, equivalent to 7-8 billion years
ago, a time when the universe was half as old as it is today."

The survey also has completed measurements that could shed light on the
nature of dark energy -- a mysterious energy that permeates the universe
and seems to be causing the universe's expansion to accelerate. The team
now is modeling various theories of dark energy to compare theoretical
predictions with the new DEEP2 measurements.

As Davis explained it, the amount of dark energy, now estimated to be 70
percent of all the energy in the universe, determines the evolution of
galaxies and clusters of galaxies. By counting the number of small
groups and massive clusters of galaxies in a distant volume of space as
a function of their redshift and mass, it is possible to measure the
amount by which the universe has expanded to the present day, which
depends on the nature of dark energy.

"Basically, you count the clusters and ask, 'Are there a lot, or a
few?'" Davis said. "That's all it amounts to. If there are very few
clusters, that means the universe expanded quite a ways. And if there
are a lot of clusters the universe didn't expand as much."

Davis currently is comparing DEEP2 measurements with predictions of the
simplest dark energy theory, but hopes to collaborate with other
theoreticians to test more exotic dark energy theories.

"What they are really trying to get at is how the dark energy density is
changing as the universe is expanding," said UC Berkeley theoretical
physicist Martin White, a professor of astronomy and of physics who has
worked with Davis. "If the dark energy density is Einstein's
cosmological constant, then the theoretical prediction is that it
doesn't change. The holy grail now is to get some evidence that it's not
the cosmological constant, that it is in fact changing."

IMAGE CAPTION:
[http://www.berkeley.edu/news/media/r.../expansion.gif
(13KB)]
While the Sloan Digital Sky Survey (left) looks at galaxies in the
nearby universe, the DEEP2 Galaxy Redshift Survey is a smaller survey of
much more distant galaxies. Their distance from us (7 billion light
years or more) means that the light we see today left these galaxies
when the universe was less than half as old as it is today, and is so
faint that the world's largest telescope, the Keck, is needed to study
them. The magnified regions show that as the universe evolved, galaxies
became more densely clustered even as these clusters moved farther apart
with the expansion of the universe. The strength of these effects
depends on cosmological parameters, allowing the study of dark energy by
comparing groups and clusters of galaxies at low and high redshift.
(Credit: Brian Gerke, UC Berkeley)