Last month, a group of European astronomers,
using a massive radio telescope in Germany, made the most accurate
measurement of the proton-to-electron mass ratio
ever accomplished and found that there has been no change in the ratio
to one part in 10 million at a time when the universe was about half its
current age, around 7 billion years ago. When University of Arizona
astronomy professor Rodger Thompson put this new measurement into his
calculations, he found that it excluded almost all of the dark energy
models using the commonly expected values or parameters.
The research Thompson completed showed that a popular alternative to
Albert Einstein's theory for the acceleration of the expansion of the
universe does not fit newly obtained data on a fundamental constant, the proton to electron mass ratio. Thompson's findings, reported Jan. 9 at the American Astronomical Society
meeting in Long Beach, Calif., impact our understanding of the universe
and point to a new direction for the further study of its accelerating
expansion.
To explain the acceleration of the expansion of the universe,
astrophysicists have invoked dark energy – a hypothetical form of energy
that permeates all of space. A popular theory of dark energy, however,
does not fit new results on the value of the proton mass divided by the
electron mass in the early universe.
Thompson computed the predicted change in the ratio by the dark
energy theory (generally referred to as rolling scalar fields) and found
it did not fit the new data. UA alumnus Brian Schmidt, along with Saul Perlmutter and Adam Reiss, won the 2011 Nobel Prize in Physics for showing that the expansion of the universe is accelerating
rather than slowing down as previously thought. The acceleration can be
explained by reinstating the "cosmological constant" into Einstein's theory of General Relativity.
Einstein originally introduced the term to make the universe stand
still. When it was later found that the universe was expanding, Einstein
called the cosmological constant "his biggest blunder." The constant
was reinstated with a different value that produces the observed
acceleration of the universe's expansion. Physicists trying to calculate
the value from known physics, however, get a number more than 10 to the
power of 60 (one followed by 60 zeros) too large – a truly astronomical
number.
That's when physicists turned to new theories of dark energy to
explain the acceleration. In his research, Thompson put the most popular
of those theories to the test, targeting the value of a fundamental
constant (not to be confused with the cosmological constant), the mass
of the proton divided by the mass of the electron. A fundamental
constant is a pure number with no units such as mass or length. The
values of the fundamental constants determine the laws of physics.
Change the number, and the laws of physics change. Change the
fundamental constants by a large amount, and the universe becomes very
different from what we observe.
The new physics model of dark energy that Thompson tested predicts
that the fundamental constants will change by a small amount. Thompson
identified a method of measuring the proton to electron mass ratio in
the early universe several years ago, but it is only recently that
astronomical instruments became powerful enough to measure the effect.
More recently, he determined the exact amount of change that many of the
new theories predict.
If the parameter space or range of values is equated to a football
field, then almost the whole field is out of bounds except for a single
2-inch by 2-inch patch at one corner of the field. In fact, most of the
allowed values are not even on the field. "In effect, the dark energy
theories have been playing on the wrong field," Thompson said. "The
2-inch square does contain the area that corresponds to no change in the
fundamental constants, and that is exactly where Einstein stands."
Thompson expects that physicists and astronomers studying cosmology
will adapt to the new field of play, but for now, "Einstein is in the
catbird seat, waiting for everyone else to catch up."
The image at the top of the page shows the 10-meter South Pole Telescope
in Antarctica is located at the Amundsen-Scott Station, literally at
the geographic southern pole of our planet. (Daniel Luong-Van, National
Science Foundation). The 280-ton telescope has helped astronomers
unravel the nature of dark energy and zero in on the actual mass of
neutrinos — elusive subatomic particles that pervade the Universe and,
until very recently, were thought to be entirely without measureable
mass.
Source: The Daily Galaxy via University of Arizona
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