**What is Heisenberg’s Uncertainty Principle? How the sun shines and why the vacuum of space is not actually empty**

*By Alok Jha*

* The Observer, Saturday 9 November 2013*

The uncertainty principle is one of the most famous (and probably misunderstood) ideas in physics. It tells us that there is a fuzziness in nature, a fundamental limit to what we can know about the behaviour of quantum particles and, therefore, the smallest scales of nature. Of these scales, the most we can hope for is to calculate probabilities for where things are and how they will behave. Unlike Isaac Newton’s clockwork universe, where everything follows clear-cut laws on how to move and prediction is easy if you know the starting conditions, the uncertainty principle enshrines a level of fuzziness into quantum theory.

Werner Heisenberg’s simple idea tells us why atoms don’t implode, how the sun manages to shine and, strangely, that the vacuum of space is not actually empty.

An early incarnation of the uncertainty principle appeared in a 1927 paper by Heisenberg, a German physicist who was working at Niels Bohr’s institute in Copenhagen at the time, titled “On the Perceptual Content of Quantum Theoretical Kinematics and Mechanics”. The more familiar form of the equation came a few years later when he had further refined his thoughts in subsequent lectures and papers.

Heisenberg was working through the implications of quantum theory, a strange new way of explaining how atoms behaved that had been developed by physicists, including Niels Bohr, Paul Dirac and Erwin Schrödinger, over the previous decade. Among its many counter-intuitive ideas, quantum theory proposed that energy was not continuous but instead came in discrete packets (quanta) and that light could be described as both a wave and a stream of these.

Continue Learning: http://www.theguardian.com/science/2013/nov/10/what-is-heisenbergs-uncertainty-principle

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