IF you think the world’s weird, science just proved it. Again. It seems the stuff we’re made of doesn’t actually decide what to be — and perhaps even when to be — until we look at it.
Australian physicists have been looking at subatomic particles. No, they haven’t shown we live in a Matrix. Nor have they found evidence of magic or miracles. The large-scale universe we live in is a completely different place, where particles and waves are real, predictable and solid. But in the infinitesimally small worlds of quantum theory, reality itself appears to be a problem. Physicists from the Australian National University put “the bizarre nature of reality” to the test in a new study published in the science journal Nature Physics. It found a famous experiment which appeared to determine that quantum objects don’t really have a substantial state until we attempt to measure them appears to hold up. “It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” ANU researcher Andrew Truscott said in a press release.
Mind-bending Matter
It’s a thought-twisting concept made famous by the parable of Schrodinger’s cat: When a cat is in a box, it’s neither alive nor dead because you cannot see it. Only the act of opening the box determines the condition of the cat. Please don’t try this experiment at home. Your cat is not suitably quantum in scale. Light, however, is. The mysterious behaviour light is the most widely known evidence of this quantum quackery: Photons are weird. You can see the effect yourself when shining a light through two narrow slots. The light behaves both like a particle, going through each slot and casting direct light on the wall behind it — and like a wave, generating an interference pattern resulting in more than two stripes of light. The problem puzzling physicists for decades has been: What makes a photon decide when to be one or the other?
Atomic logic
The ANU researchers tackled the subject by examining the behaviour of a single helium atom when passed through several sets of laser beams. The test was similar to that of the torch being shone through a grate: Would the atom travel in a straight line — as you’d expect from a particle. Or would it bend, as you’d expect from the interaction of waves? “Quantum physics predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” PhD student Roman Khakimov said in the report. Put simply — the helium atom was expected to behave like light — to pass through one grate like a particle, or both like a wave. In this experiment, a second set of laser “grates” would be randomly activated only after the atom had passed through the first one. The outcome?
The researchers found a wavelike interference pattern in the behaviour of the atoms once they passed through the second set of lasers. But if there was no second set of lasers, the atoms behaved as though they were particles and followed only one path. The upshot? “A future event causes the photon to decide its past,” associate professor Truscott said.
Decisions, decisions
The differences in the helium atom’s behaviour suggests it hadn’t “made up its mind” about being a wave or a particle until it was measured for the second time. Once it made that decision, this affected its past behaviour. “The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wavelike or particle-like behaviour was brought into existence,” Truscott said. It’s weird. But it is evidence validating the current stance of quantum theory. So how real is a measurement anyway? Often, the more you measure something the more you get. Take a coastline, for example — the smaller the ‘crinkly bits’ you measure, the bigger your beach gets. Reality checks are unreal.