"Remarkably mirror matter is capable of simply explaining a large number of contemporary puzzles in astrophysics and particle physics ..."___ Robert Foot
People across the Northeast saw a great ball of fire sailing through the atmosphere last week. Some even reported hearing sonic booms.
At least one chunk of the fireball from space fell into a Pennsylvania cornfield – scorching the corn, local officials said. But they could find no sign of solid debris.
Most experts explained that it must have been a meteor – the flash of a space rock burning up in the atmosphere. But a rock small enough to burn up would not have damaged the corn, raising the suspicion that this was no ordinary meteor. Perhaps it wasn't a chunk of normal rock. Maybe it was made of "mirror matter."
If so, Australian physicist Robert Foot's timing couldn't have been better. Less than two weeks earlier, he posted a paper on the Internet describing a new explanation for the famous Tunguska explosion of 1908. Something hit Siberia then, toppling trees across an area of more than 800 square miles. Calculations indicate that such devastation required a shock wave from an explosion with the power of 1,000 atomic bombs.
Speculators have suggested everything from antimatter to a UFO as a cause of the Tunguska explosion, with a comet or meteorite the most common explanation. Yet a space rock exploding with that much energy must have weighed 100,000 tons. And no debris has been found, Dr. Foot notes. "It is a remarkable result that such a large amount of extraterrestrial material apparently vanished without leaving behind significant remnants," he writes in his paper, available at xxx.lanl.gov/abs/hep-ph/0107132.
On the other hand, the lack of debris would be just what you'd expect if the exploding rock was a "mirror meteorite," says Dr. Foot, of the University of Melbourne. "It seems to be an interesting candidate to explain the 1908 Tunguska explosion, as well as smaller similar events," he writes.
Mirror matter is strictly hypothetical, but if it exists, it could explain many other mysteries in physics and astronomy, Dr. Foot contends. Its existence was first hinted at in the 1950s, when scientists discovered that some subatomic particles seem to know the difference between left and right. (They would spin only in one direction and not the other, for example.) It seemed odd that nature would enforce such a distinction, so some scientists suggested that another set of unknown "mirror" particles existed, for which left was switched with right, restoring left-right balance in the universe.
If so, every particle would have a mirror partner, perhaps of the same mass (although some authorities say the mass could differ) but utterly invisible. Mirror particles could make mirror atoms, mirror stars, mirror planets and mirror people, but nobody would know about them because they couldn't be seen. Only their gravity could be felt by anything in the ordinary, non-mirror world.
OK, that all seems too bizarre to worry about. But in recent years some popular theories have suggested mathematical reasons why mirror matter might exist. And astronomers do, in fact, detect large quantities of "dark matter" in space that exerts gravitational effects but can't be seen. It could be mirror matter. You never know.
Furthermore, Dr. Foot points out, all the planets detected in distant stellar systems are merely inferred from their gravitational pull. You can't actually see them. Maybe they are mirror planets. And free-floating planets discovered recently may only appear to be free – perhaps they are in orbit around invisible mirror stars.
Proving any of that won't be easy, but Dr. Foot suggests that mysterious meteors may provide some evidence. Calculations show that it need not be true that mirror matter interacts with ordinary matter only through gravity. (If so, a mirror rock would just pass right through the Earth.) Mirror particles could possess a very small electrical charge, Dr. Foot calculates. And therefore a rock from space could interact with atoms in the atmosphere, heating up (giving off light) and even creating a shock wave (causing sonic booms).
Mirror rocks could get hot on the inside and explode, explaining the shock wave that leveled the trees around Tunguska. It would have left no chunks of debris because mirror matter is invisible.
Smaller meteor incidents without debris are common, Dr. Foot said. In Jordan, a few months ago, a crowd of people witnessed a meteor split in two and crash into the ground, one piece scorching a tree and the other scorching a rock. But no fragments were discovered at either scene.
And news reports of last week's fireball sound similar. "It is certainly possible that it may have been an object made of mirror matter," Dr. Foot commented via e-mail.
Dr. Foot advises digging below the impact sites of such events and analyzing the soil (or perhaps analyzing the burnt material) for the presence of mirror atoms. (He thinks they could be sorted out with a centrifuge.) So it might be possible to recover real mirror matter and prove its existence.
On the other hand, there may be problems with the mirror matter explanation. A mirror electrical charge big enough to cause mirror meteors might mess up physics elsewhere – in the sun, for example. The fact that the sun is shining limits how much charge mirror matter could have, certain spoilsport scientists will tell you.
Still, says Dr. Foot, the search for mirror matter should continue. It might even have "all sorts of practical applications," he says in his paper.
"Of course," he adds, "it is premature to speculate too much along these lines until it is actually discovered."
