快猫短视频

CHANGING the speed of light gives physicists all sorts of headaches. Now
scientists in Argentina have found one more: electric charge might start to
appear as if from nowhere. But surprisingly, this may turn out to be a good
thing for theories of the early Universe.

Last year, two groups of researchers put forward theories of the Universe鈥檚
expansion that require the speed of light to have slowed since the big bang. One
argument in support of a changing light speed is the fact that temperature and
density are relatively uniform across the Universe. There鈥檚 no way such
far-flung corners of space can be causally connected
(see Diagram) unless light
once travelled faster than it does now
(快猫短视频, 24 July 1999, p 28).

Now Hector Vucetich, Susanna Landau and Pablo Sisterna at the University of
La Plata in Argentina say that if the speed of light isn鈥檛 constant, then charge
conservation鈥攁nother central tenet of physics鈥攚ill be violated. One
way to understand their proof is to think of light as a wave of oscillating
electromagnetic fields with an associated electric current shuttling charge back
and forth. If the speed of the wave falls, the associated current will deposit
charge faster than it picks it up, resulting in a net creation of positive
charge. 鈥淭his imposes strict limits on theories with varying light speed,鈥� says
Vucetich. 鈥淚t means they are almost impossible to get right.鈥�

The result may pose big problems for the theory put forward last year by John
Barrow of the University of Cambridge. This proposes that the speed of light
falls continuously as the Universe expands, meaning that it is still falling
today. If this is happening, then Vucetich鈥檚 result means either that the charge
on the electron must change, that electrons mysteriously disappear or that
neutrons are transformed into protons. Yet numerous experiments on charge
conservation have failed so far to pick up any such effects.

At first sight this looks like a blow for the speed change idea, but theories
in which the speed of light drops suddenly and then stays constant fare better.
Jo茫o Magueijo at Imperial College, London, and Andreas Albrecht at the
University of California, Davis, proposed last year that the speed of light was
greater immediately after the Universe was created, and fell to its current
value a fraction of a second after the big bang. Vucetich鈥檚 calculations predict
that this drop would have been accompanied by a sudden generation of excess
charge.

鈥淚t鈥檚 a good thing, too,鈥� says Magueijo. One of the mysteries of modern
physics is that there appears to be more matter than antimatter in the Universe.
It has been suggested that in the early Universe a process called baryogenesis
took place, creating excess matter and breaking the symmetry between matter and
antimatter. Magueijo suspects that excess charge generation might correspond to
baryogenesis of protons. 鈥淚t鈥檚 an intriguing idea,鈥� says his coauthor Albrecht.