Let us suppose we confine an electron in a volume v the we can know the uncertainity in its velocity. Now suppose we take a small volume d(v) and observe it . There are only two possibilities we find the electron or we do not find it . If we do not find it then we haven't interacted with the electron in any way but we have successfully reduced the confinement of electron to v - d(v) still keeping the uncertainity in velocity same thereby violating uncertainity principle . Thr key idea is measuring the positions the electron does not occupy and in a system there could be probability that the electron be absent from a space d(v). We are extracting information about electrons from thier absence rather than their presence.

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TopNewestInteresting question but I wonder if you've really reduced the confinement volume to \(V - dV.\) What happens after you stop observing, is the particle allowed to explore \(dV\) once again? – Josh Silverman Staff · 3 months, 1 week ago

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