SIGNS that the expansion of the Universe is accelerating may be an illusion.
Scientists think particles called axions might create the mirage by hijacking
light as it travels the cosmos.
Three years ago, cosmologists found that very distant supernova explosions
are fainter than they should be. This suggested that space had stretched more
than expected as the light sped towards Earth, so it had to travel farther. The
Universe appeared to be expanding faster and faster
(New Scientist, 11 April 1998, p 26).
With scientists struggling to explain what force could drive this
acceleration, a team in the US has now come up with an alternative explanation.
They say the light from distant supernovae is dim because some photons turn into
axions on their way to Earth.
Axions are hypothetical particles predicted by several leading theories of
particle physics. Even if they exist they'd be very difficult to detect because
they rarely interact with other matter. But Csaba Csáki of Los Alamos
National Laboratory in New Mexico says that if axions had a tiny
mass—10-21 times that of the electron—they would interact
with light in the tangled magnetic fields of intergalactic space. As photons
travelled to Earth, this interaction would persuade a fraction of them to flip
into axions themselves, making them undetectable.
With his Los Alamos colleague John Terning and Nemanja Kaloper of Stanford
University in California, Csáki has calculated that about a third of the
visible photons from the most distant supernovas would effectively vanish.
"We shouldn't just accept on face value that the Universe is accelerating,"
Csáki concludes. "There are alternative and viable explanations to the
supernova observations based on particle physics."