Not surprisingly, dark matter aficionados are skeptical. He and David N. Spergel, also at Princeton, have written several papers proposing that dark matter particles interact strongly. Steinhardt says that summoning mirror matter isn't the most promising way to solve dark matter's problems. Another set of cosmic riddles may provide the strongest argument for mirror matter, assert Foot and Volkas. These puzzles all concern neutrinos, a ghostly class of subatomic particles that rarely interact with matter.
Most neutrinos pass through the Earth unimpeded and escape detection.
Consider the electron neutrino. Nuclear reactions deep in the sun create a steady supply of them, which astronomers have detected since the 1960s. However, solar physicists have faced a long-standing problem. The number of electron neutrinos detected is about half the predicted quantity. Part of the deficit may arise because some of the electron neutrinos have transformed into mirror electron neutrinos, suggest Foot and Mohapatra.