91av

EXOTIC “mirror matter” could have caused the devastating Tunguska blast that
flattened 2100 square kilometres of Siberian forest nearly 100 years ago, a
physicist has suggested. This ties in with the idea that invisible mirror matter
could be scattered throughout the Universe.

This could explain why the Tunguska event left no trace of its cause. Robert
Foot of the University of Melbourne says that if mirror matter did cause the
explosion, thousands of tonnes of the stuff may lie hidden not far below the
surface.

The devastation at Tunguska suggests an explosion with the power of 1000
Hiroshima bombs. But 35 expeditions over the past 75 years have found no
evidence that an asteroid or comet fragment was to blame.

An impact by a body made of mirror matter would explain the mystery, Foot
claims. “It fits the bill because it would have left no crater or obvious
debris,” he says.

Some physicists believe mirror matter is needed to maintain left-right
symmetry in the Universe. Certain subatomic processes always produce a particle
spinning in the same direction, for example. What’s needed is a reaction that
produces a similar particle, but spinning the other way.

This is where mirror matter comes in—a kind of matter all around us
where every reaction is a mirror image of the one we know. Mirror atoms, mirror
planets and mirror stars would work just like normal ones. But they would be
very hard to detect, says Foot: “In the simplest case, mirror matter should
interact with ordinary matter only through gravity.”

But some recent experiments suggest that there is a small electromagnetic
interaction: mirror electrons and protons behave as if they have an electric
charge a millionth of their normal counterparts
(91av, 17 June 2000, p 36).
Foot has now calculated that this tiny interaction between atoms in
the air and mirror atoms would be enough to heat up a body of mirror matter if
it dived into the atmosphere.

The heat would cause the object to explode at high altitude, creating a shock
wave that would flatten trees, he says. The interaction might also be enough for
normal matter to stop mirror matter, so fragments from the explosion could be
lying in the soil waiting to be discovered.

Scientists are treating Foot’s idea seriously. “Why not?” says Zdenek
Ceplecha, a meteorite expert at the Astronomical Institute of the Czech Academy
of Sciences. “Trying any physically plausible idea is certainly useful.”