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The word uncertainty is used a lot in quantum mechanics. One school of thought is that this means there's something out there in the world that we are uncertain about. But most physicists believe nature itself is uncertain.
Intrinsic uncertainty was central to the way German physicist Werner Heisenberg, one of the originators of modern quantum mechanics, presented the theory.
Uncertainty - Principle - Properties - Particle - Time
He put forward the Uncertainty Principle that showed we can never know all the properties of a particle at the same time.
For example, measuring the particle's position would allow us to know its position. But this measurement would necessarily disturb its velocity, by an amount inversely proportional to the accuracy of the position measurement.
Was - Heisenberg
Was Heisenberg wrong?
Heisenberg used the Uncertainty Principle to explain how measurement would destroy that classic feature of quantum mechanics, the two-slit interference pattern (more on this below).
Quantum - Physicists - Slits - Particle - Velocity
But back in the 1990s, some eminent quantum physicists claimed to have proved it is possible to determine which of the two slits a particle goes through, without significantly disturbing its velocity.
Does that mean Heisenberg's explanation must be wrong? In work just published in Science Advances, my experimental colleagues and I have shown that it would be unwise to jump to that conclusion.
Velocity - Size - Uncertainty - Principle—always - Sense
We show a velocity disturbance—of the size expected from the Uncertainty Principle—always exists, in a certain sense.
But before getting into the details we need to explain briefly about the two-slit experiment.
Type - Experiment - Barrier - Holes - Slits
In this type of experiment there is a barrier with two holes or slits. We also have a quantum particle with a position uncertainty large enough to cover both slits if it is fired at the barrier.
Since we can't know which slit the particle goes through, it acts as if it goes through both slits. The signature of this is the so-called "interference pattern": ripples in the distribution of where the...
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