New gravity theory may outdistance Einstein -- Part 3
by MIKE MARTIN, UPI Science Correspondent
STORRS, Connecticut, (UPI) -- Philip Mannheim says his theory of conformal
gravity, which may offer a better explanation of gravity in the far distant
universe than Einstein's general relativity, is filled with promise and fraught
with problems.
The theory holds promise, the University of Connecticut physicist explained,
because it solves big problems with general relativity that arise in deepest
space. For instance, it "precisely eliminates the need to introduce dark
matter," an as yet unobserved, unconfirmed, almost ghostly substance that
troubles many theorists. It also solves the so-called "cosmological constant"
problem, which troubled Einstein almost immediately after he introduced it in
his own equations to keep an expanding universe static and stable.
Yet conformal gravity also has difficulties of its own.
"The biggest problems for conformal gravity are mainly technical,"
Mannheim told UPI. "Its predictions result in difficult calculations which
all need yet to be done."
The theory may also suffer in the realm of the very small - the quantum
mechanical world - Mannheim noted. However, University of Michigan mathematician
Paul Federbush is using conformal gravity as a guide in his own work on quantum
gravity.
"My research so far in this direction is very preliminary," Federbush
told United Press International from his office in Ann Arbor. "I expect
any further progress, however, to be guided by the conformal gravity models
studied by Mannheim."
The most serious problem with conformal gravity, according to former Mannheim
co-worker Demos Kazanas, is its inability to predict the creation of large amounts
of deuterium, or "heavy hydrogen," during the Big Bang. Deuterium
was made only at the beginning of the universe and serves as a particularly
important marker of very early chemical activity in the cosmos.
Kazanas, an astrophysicist with NASA's Goddard Space Flight Center in Greenbelt,
Maryland, told UPI, "If Mannheim can get around the deuterium problem,
conformal gravity will find itself on a much more solid footing."
However, Kazanas said he believes, on a "gut level," that Mannheim
will ultimately be vindicated, but that working alone hinders his progress in
resolving the thorny problems that arise with any new theory.
Vindication could come soon.
According to Mannheim, recent Hubble telescope observations of distant supernovae
(exploding stars) may clearly distinguish conformal gravity from general relativity.
General relativity predicts that the universe is decelerating, or slowing,
at its farthest points.
Conformal gravity predicts that the farthest reaches of the universe are
accelerating, or speeding away from us. At these great distances, the gravity
from all the mass in our universe becomes repulsive, literally pushing away
the edges of space. In Einstein's universe, however, gravity is universally
attractive -- never repulsive.
Light accelerating away shifts toward the red end of the visible spectrum.
Therefore, if astronomers can observe bright light - from supernovae, perhaps
- at the very edge of the universe, and that light is red shifted enough, the
universe is indeed accelerating way out there and Mannheim's theory is closer
to correct.
The farthest supernova ever was discovered in April, 2001 by Adam Riess
of the Hubble Space Telescope Center.
"This new supernova is the first out at such huge distances where there
is a hope of distinguishing Einstein from Mannheim," University of Texas
astrophysicist Brad Schaefer told UPI from Austin.
A new satellite may peer even farther out.
"Within a few years, more very distant supernovae will be measured
with the new SNAP satellite in a strong test that can accurately distinguish
between Mannheim and Einstein," Schaefer said.
As to what may happen to physics without a viable alternative to general
relativity, "a growing number of astrophysicists are seriously worried,"
said Alison Campbell, an astronomer with the McDonald Observatory in Fort Davis,
Texas. "Those who have not yet taken the time to 'bone up' on conformal
gravity see only a void into which we jointly must step if we are to abandon
general relativity. We need are more people working on conformal gravity, to
see whether its promiseholds up under closer scrutiny."
Schaefer concurs.
"Mannheim's claims are at the forefront of science at its best. As for the question of whether Mannheim's gravity is a better description of nature than Einstein's gravity, we have to await the results of key experiments. By looking closely at the universe, nature will tell us whose predictions are correct."