Contrary to what many students are taught, quantum uncertainty may not always be in the eye of the beholder. A new experiment shows that measuring a quantum system does not necessarily introduce uncertainty. The study overthrows a common classroom explanation of why the quantum world appears so fuzzy, but the fundamental limit to what is knowable at the smallest scales remains unchanged. Read more

Ed ~ "Don't get too excited: the uncertainty principle still stands"

It was in Copenhagen, in 1927, that Heisenberg developed his uncertainty principle, while working on the mathematical foundations of quantum mechanics. On 23 February, Heisenberg wrote a letter to fellow physicist Wolfgang Pauli, in which he first described his new principle. In his paper on the uncertainty principle, Heisenberg used the word "Ungenauigkeit" (imprecision). Read more

Lecture - 1 Introduction to Quantum Physics;Heisenberg's uncertainty principle

Researchers around the world now have a new method of investigating the smallest particles of nature, which are governed by the laws of quantum mechanics. In a recent study published in the journal Nature, NRC scientists reported a way to directly measure a photon's "wavefunction" - and thereby know everything there is to know about this quantum mechanical system. Read more

New 'Double Slit' Experiment Skirts Uncertainty Principle

An international group of physicists has found a way of measuring both the position and the momentum of photons passing through the double-slit experiment, upending the idea that it is impossible to measure both properties in the lab at the same time. What quantum physicist Aephraim Steinberg of the University of Toronto in Canada and his colleagues have now shown, however, is that it is possible to precisely measure photons' position and obtain approximate information about their momentum, in an approach known as 'weak measurement'. Steinberg's group sent photons one by one through a double slit by using a beam splitter and two lengths of fibre-optic cable. Then they used an electronic detector to measure the positions of photons at some distance away from the slits, and a calcite crystal in front of the detector to change the polarization of the photon, and allow them to make a very rough estimate of each photon's momentum from that change. Read more

In quantum mechanics, the Heisenberg uncertainty principle states precise inequalities that constrain certain pairs of physical properties, such as measuring the present position while determining future momentum; both cannot be simultaneously done to arbitrarily high precision. That is, the more precisely one property is measured, the less precisely the other can be controlled or determined. Read more