A quantum enigma has been put to the test once again, but this time physicists have made the experiment smaller than it has ever been.
The classic double-slit experiment tests the behavior of light, electrons, atoms and some molecules as both particle-like and wave-like, a mysterious duality that has intrigued and puzzled scientists for more than a century.
Light or electrons are aimed at a solid plate with two parallel cuts in it, offering two choices: go through the slit on the left or the slit on the right. Subatomic particles will sometimes break the rules and go through both slits, just as a wave would.
The most bizarre aspect of this particle-wave duality is that it depends on how much an observer pays attention. The more carefully the observer measures whether it was the left or right slit, the more the object in question chooses a single slit, just as a particle would.
Now an international team of scientists has exhibited this quantum identity crisis using a single hydrogen molecule as their lab equipment.