University of Toronto physicists resolve a paradox of quantum theory
University of Toronto quantum physicists Jeff Lundeen and Aephraim Steinberg have shown that Hardy's paradox, a proposal that has confounded physicists for over a decade, can be confirmed and ultimately resolved, a task which had seemingly been impossible to perform. "For nearly a century, the widespread interpretation of quantum mechanics suggests that everything is uncertain until it is observed, and that observation inevitably alters reality," says Professor Steinberg. "However, in the 1990s, a technique known as 'interaction-free measurement' seemed to promise the ability to 'see without looking,' as a Scientific American article put it at the time. But when Lucien Hardy proposed that one could never reliably make inferences about past events which hadn't been directly observed, a paradox emerged which suggested that whenever one attempted to reason about the past in this way they would be led into error."
Over the course of nearly two years of work, Steinberg and then-student Jeff Lundeen, now a research associate at the National Research Council of Canada, built a complicated quantum optical experiment and developed new theoretical tools. In essence, they combined Hardy's Paradox with a new theory known as weak measurement proposed by Tel Aviv University physicist Yakir Aharonov, showing that in one sense, one can indeed talk about the past, resolving the paradox. Weak measurement is a tool whereby the presence of a detector is less than the level of uncertainty around what is being measured, so that there is an imperceptible impact on the experiment. "We found that all of the seemingly paradoxical conclusions in Hardy's Paradox can, in fact, be experimentally verified," says Steinberg, "but that the use of weak measurement removes the contradiction."
"Until recently, it seemed impossible to carry out Hardy's proposal in practice, let alone to confirm or resolve the paradox," he says. "We have finally been able to do so, and to apply Aharonov's methods to the problem, showing that there is a way, even in quantum mechanics, in which one can quite consistently discuss past events even after they are over and done. Weak measurement finds what is there without disturbing it."
Source: University of Toronto
- Physicists Resolve Confounding Paradox Of Quantum Theoryfrom Science DailyThu, 15 Jan 2009, 9:29:10 EST
- Paradox Lost - Quantum Physicists Say They Have Resolved Hardy's Annihilation Problemfrom Scientific BloggingWed, 14 Jan 2009, 22:49:05 EST
- Physicists resolve a paradox of quantum theoryfrom PhysorgWed, 14 Jan 2009, 14:35:19 EST
Latest Science NewsletterGet the latest and most popular science news articles of the week in your Inbox! It's free!
Check out our next project, Biology.Net
From other science news sites
Popular science news articles
- Actions on climate change bring better health, study says
- Cheater, cheater: UGA study shows what happens when employees feel excluded at work
- Infant solar system shows signs of windy weather
- Study: Antifreeze proteins in Antarctic fishes prevent freezing…and melting
- Plant variants point the way to improved biofuel production
- Ancient mammal relatives were active at night 100 million years before origin of mammals
- Walking fish reveal how our ancestors evolved onto land
- New DNA study unravels the settlement history of the New World Arctic
- Electric current to brain boosts memory
- Radio telescopes settle controversy over distance to Pleiades