October 18, 2013
Heisenberg’s Hunch Was Correct, And Now Scientists Have Proof
John P. Millis, PhD for redOrbit.com - Your Universe Online
Students of physics are almost universally perplexed when they are first exposed to the paradoxical world of quantum mechanics. The reason the field is so difficult to wrap one’s mind around is that the behavior of quantum systems is fundamentally different from the macroscopic world in which we spend our lives.
One of the guiding principles of the quantum world is a set of statements known as Heisenberg's error-disturbance relations. Proposed by Werner Heisenberg in 1927, the thrust of the theory is that the very act of measuring a quantum system fundamentally changes it – that is, the act of simply observing the system causes irreversible and immeasurable disturbances.
For example an attempt to measure the position of a particle would have the consequence of changing its momentum. The best that can be accomplished is constructing a range of possibilities of the momentum derived from the position information. But the two quantities – position and momentum – cannot both be exactly known at the same time.
While the Heisenberg Uncertainty Principle is universally taught in physics departments across the world, a rigorous experimental verification of the relationship proposed by Heisenberg has remained elusive. According to Paul Busch, "While the slogan 'no measurement without disturbance' has established itself under the name Heisenberg effect in the consciousness of the scientifically interested public, a precise statement of this fundamental feature of the quantum world has remained elusive, and serious attempts at rigorous formulations of it as a consequence of quantum theory have led to seemingly conflicting preliminary results.”
But now Busch of the University of York, UK, Professor Pekka Lahti of the University of Turku, Finland and Professor Reinhard Werner of Leibniz Universität Hannover, Germany, have both provided a formal proof of the formulation. "We have shown that despite recent claims to the contrary, Heisenberg-type inequalities can be proven that describe a trade-off between the precision of a position measurement and the necessary resulting disturbance of momentum and vice-versa," adds Busch.
To evaluate the relationships between position and momentum, the team considered how simultaneous measurements of these quantities are calibrated. The errors in these measurements were re-imagined as the spreads in the distributions of the possible outcomes where either the position or the momentum of the particle is reasonably well known. They found that the spreads in the distributions for combined position and momentum measurements actually do obey Heisenberg's principle.
Concludes Werner, "Since I was a student I have been wondering what could be meant by an 'uncontrollable' disturbance of momentum in Heisenberg's Gedanken experiment. In our theorem this is now clear: not only does the momentum change, there is also no way to retrieve it from the post measurement state."