EINSTEIN IN NEED OF UPDATE? CALCULATIONS SHOW THE SPEED OF LIGHT MIGHT CHANGE
In 1905, Einstein made major changes to laws of physics when he established
his theory of relativity. Now Einstein's laws might also undergo
significant changes.
Dimitri Nanopoulos, who holds the rank of Distinguished Professor of
Physics at Texas A&M University and heads the Houston Advanced Research
Center's Group for Astroparticle Physics, established, along with other
physicists, that the speed of light, instead of being the constant value of
186,282 miles per second, might change.
In 1905, Einstein established that light was the only object to have a
constant speed in all reference frames. This idea was the cornerstone to
his theory of relativity, and later to laws of physics.
"If the speed of light proves not to be constant any more, even by a very
small changeable amount, laws of physics - the theory of relativity
included - will have to undergo significant changes," says Nanopoulos.
Nanopoulos, who chairs the Theoretical Physics Division of the Academy of
Athens, is among the many physicists who are trying to establish the basis
of quantum gravity, a theory that has been dreamed of by physicists since
the 1920s.
While they were doing mathematical calculations, Nanopoulos and physicists
Nikolaos Mavromatos of King's College in London and John Ellis of the
European Center for Particle Physics (CERN) in Geneva, discovered a new
expression for the speed of light, which depends on its frequency.
"Through our calculations, we found that the speed of light is
frequency-dependent," says Nanopoulos. "But a change in the usual speed of
light value of 186,282 miles per second is noticeable only for light coming
from astronomical objects situated very far from Earth, which is why this
frequency dependence has not been noticed so far."
Physicists are setting up the theory of quantum gravity to put together two
major discoveries of physics in the 20th century: the theory of relativity
and quantum physics.
The theory of relativity explains both how space and time are related to
each other and how gravitation works. Quantum physics describes the
workings of the microscopic world, where laws of probability replace the
deterministic view used to describe our everyday world.
Until now, physicists have been considering many scenarios for quantum
gravity, but these scenarios have never been experimentally confirmed.
The hypotheses put forward by Nanopoulos and his collaborators has been
under experimental scrutiny, and the results obtained during the last few
months are encouraging.
"One way to experimentally test our hypothesis is to consider galaxies or
other objects in the sky that are very far from us," says Nanopoulos. "Then
we collect the photons (particles of light) simultaneously emitted by these
sources, and we look at differences of arrival times in a detector on earth
between photons of different frequencies. The photons of higher frequencies
should come later."
The frequency-dependent expression of the speed of light depends on the
gravitational constant, a quantity that is known since Newton established
his law of gravitation.
By using the differences in photon arrival times of six astronomical
sources, Nanopoulos and his collaborators estimated an upper bound of the
value of the gravitational constant from the data, and compared their
results with the expected value.
"We were amazed to see that if we use all these astronomical data, we find
very reasonable values for the gravitational constant," says Nanopoulos.
"That was our first surprise: the fact that, put together, a bunch of data
that had nothing to do with the gravitational constant, gave us values so
close to what we would expect to find."
A second experimental encouraging result about the frequency-dependence of
the speed of light was provided by the HEGRA (High Energy Gamma Ray
Astronomy) experiment, which is detecting photons from outer space, and is
situated in La Palma, Canary Islands.
The frequency-dependent expression of the speed of light was used to solve
a problem faced by three physicists: Tadashi Kifune, from the University of
Tokyo in Japan, Ray Protheroe, from the University of Adelaide in
Australia, and Hinrich Meyer, from the University of Wuppertal in Germany.
The problem occurred when HEGRA physicists detected very energetic photons
emitted by the galaxy Markarian 501.
"The most energetic of these photons were expected to interact with other
very low-energy photons from the infrared background radiation, which is a
radiation present since the early universe," says Nanopoulos. "When a very
energetic photon interacts with a low-energy photon, they have just the
right quantity of energy to create an electron-antielectron pair. But
physicists at HEGRA did not see any of the expected electron-antielectron
pairs, but did observe very energetic photons instead.
"By using the frequency-dependent expression of the speed of light, Kifune,
Protheroe and Meyer found that the combined energy of each type of photon
was not enough to create an electron-antielectron pair," adds Nanopoulos.
"That is why no electron-antielectron pair has been observed."
If by looking at more energetic photons, HEGRA never detects the expected
electron-antielectron pairs, this would provide further support of the new
hypothesis put forward by Nanopoulos and his collaborators.
"This frequency-dependence of the speed of light changes drastically our
view of the theory of relativity," Nanopoulos says. "It is also the first
time that we have a window of opportunity to study quantum gravity, and
thus scientifically study the origin of the Universe. It is a fantastic
thing that we can experimentally magnify such a tiny effect."
Nanopoulos says that if the frequency-dependence of the speed of light is
further confirmed by other experiments, the theory of relativity would
still be valid under certain circumstances.
"There is nothing wrong with Einstein's theory of relativity. If the energy
of an object is much smaller than 1019 proton masses or if the distance
between two objects is smaller than millions of light-years, Einstein's
equations are still valid," he says.