Quantum weirdness; new experiments (Introduction)

by David Turell , Wednesday, May 20, 2015, 19:52 (3475 days ago) @ David Turell

A review of current efforts to pierce the fog:-http://www.nature.com/news/quantum-physics-what-is-really-real-1.17585?WT.ec_id=NATURE-20150521-The entire article is very interesting, but no answers as yet:-"It is this sentiment that has led Maroney and others to develop a new series of experiments to uncover the nature of the wavefunction — the mysterious entity that lies at the heart of quantum weirdness. On paper, the wavefunction is simply a mathematical object that physicists denote with the Greek letter psi (?) — one of Maroney's funny squiggles — and use to describe a particle's quantum behaviour. Depending on the experiment, the wavefunction allows them to calculate the probability of observing an electron at any particular location, or the chances that its spin is oriented up or down. But the mathematics shed no light on what a wavefunction truly is. Is it a physical thing? Or just a calculating tool for handling an observer's ignorance about the world?-"The tests being used to work that out are extremely subtle, and have yet to produce a definitive answer. But researchers are optimistic that a resolution is close. If so, they will finally be able to answer questions that have lingered for decades. Can a particle really be in many places at the same time? Is the Universe continually dividing itself into parallel worlds, each with an alternative version of ourselves? Is there such a thing as an objective reality at all?-***-"But this is where the debate gets stuck. Which of quantum theory's many interpretations — if any — is correct? That is a tough question to answer experimentally, because the differences between the models are subtle: to be viable, they have to predict essentially the same quantum phenomena as the very successful Copenhagen interpretation. Andrew White, a physicist at the University of Queensland, says that for most of his 20-year career in quantum technologies “the problem was like a giant smooth mountain with no footholds, no way to attack it”.-"That changed in 2011, with the publication of a theorem about quantum measurements that seemed to rule out the wavefunction-as-ignorance models2. On closer inspection, however, the theorem turned out to leave enough wiggle room for them to survive. Nonetheless, it inspired physicists to think seriously about ways to settle the debate by actually testing the reality of the wavefunction. Maroney had already devised an experiment that should work in principle3, and he and others soon found ways to make it work in practice.-***-"Because Wiseman's model does not need a wavefunction, it will remain viable even if future experiments rule out the ignorance models. Also surviving would be models, such as the Copenhagen interpretation, that maintain there is no objective reality — just measurements.-"But then, says White, that is the ultimate challenge. Although no one knows how to do it yet, he says, “what would be really exciting is to devise a test for whether there is in fact any objective reality out there at all.'”