Calgary, AB, Canada. Even with all relevant information in hand, quantum mechanics shows that certain experimental outcomes cannot be perfectly predicted ahead of time.

This inability to accurately predict the results of experiments in quantum physics has been subjected to a long debate, but a new paper suggests quantum theory is close to optimal in terms of its predictive power.


Many of the predictions we make in everyday life are vague, and we often get them wrong because we have incomplete information, such as when we predict the weather.

Deeper down, there has been a long debate since Einstein and his co-workers over the inability to accurately predict the results of experiments in quantum physics.

In fact, physicists have speculated whether quantum mechanics is the best way to predict outcomes.

The current discussion has consequences beyond physics, affecting evaluations of scientific method and the potential limits on scientific observation and the generation of data, information, and knowledge (e.g., bioinformatics).Researchers from the Institute for Quantum Information Science (IQIS) at the University of Calgary, along with researchers from the Perimeter Institute (PI) for Theoretical Physics (Waterloo, Canada) and the Eidgenössische Technische Hochschule Zürich (ETH Zürich) have published their results in the Physical Review Letters. Their research looks at measurements on members of maximally entangled pairs of photons that are sent into an apparatus in which each photon can take one out of two possible paths.

This approach is based on the important expriment performed by Otto Stern and Walther Gerlach in 1922. The Stern-Gerlach apparatus deflected particles in a manner that illuminated basic principles of quantum mechanics. Derivations of the Stern-Gerlach apparatus have been used to demonstrate intrinsically quantum properties in atoms and electrons, showing how the system being measured is affected by the act of measurement.

"In our experiment, we show that any theory in which there is significantly less randomness is destined to fail: quantum theory essentially provides the ultimate bound on how predictable the universe is," says Dr. Wolfgang Tittel, associate professor and GDC/AITFIndustrial Research Chair in Quantum Cryptography and Communicationat the University of Calgary. Dr. Renato Renner, Professor at the ETH in Zürich adds: "In other words, not only does God play dice, but his dice are fair."

Randomness in quantum theory is one of its key features and is widely known, even outside the scientific community, says Tittel. "Its appeal is its fundamental nature and broad range of implications: knowing the precise configuration of the universe at the big bang would not be sufficient to predict its entire evolution, for example, in contrast to classical theory."