Reality doesn’t exist until you look at it, pioneering quantum physics experiment finds

by Andrew Griffin

Reality doesn’t exist until it’s measured, at least for very small things, new research has found.

By replicating a famous experiment where an object is given a choice for how to behave, physicists found that the object doesn’t actually make its decision until it is seen. The finding proves one of the central parts of quantum theory, a branch of science that has been applied to make much of our modern technology.

Scientists gave an object a chance either to act like a wave or a particle, and looked to find out when the decision was made. While one might expect that it is either one or the other, quantum physics predicts that it will only act one way or the other when it is measured, after it has decided — and that was confirmed by the experiment.

To perform the test, scientists isolated a single helium atom. They then dropped it through a laser beam, and used a random number to decide whether a second set of beams were added that would interfere with the atom’s path.

But the researchers found that number wasn’t calculated until after the atom had passed through the crossroads of lasers and decided which way to go. Though the atom had already decided whether it would behave like a wave or a particle, it wasn’t decided which way it would go until it was measured, the research found.

"The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behavior was brought into existence," said associate professor Andrew Truscott, the scientist who led the experiment.

The test is known as the delayed-choice thought experiment, and was proposed by John Wheeler. When he came up with it in 1978, it seemed impossible that it could ever be put to the test — but researchers from the Australian National University were able to run a slightly varied version of it in tests.

"It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it," Truscott said.

Truscott and his team published their findings in Nature Physics.