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I think the key conceptual hurdle is that the vacuum state is not nothing. Quantum field theory describes matter as excitations in quantum fields. These quantum fields are very strange things, and I don't know of any easy way to explain to a non-physicist what a quantum field is. The key thing is that the quantum fields fill all of spacetime. So a vacuum is ...

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I can think of two reasons why we need a lower bound, one statistical, one inuititive. First, the intuitive: The annihiliation/creation operators represent adding/removing particles (or excitations, or whatever). The vacuum state as lowest energy state represents obviously the empty state from which no further particles can be removed. It is also clear (in ...

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Second answer, what about the phenomenon of “Quantum Locking”? Right now it is being used to levitate superconductors over magnets, but I am sure you could exploit the phenomenon to transmit torque. Plus, you can put the superconductor on the vacuum side of the seal to keep it cold.

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John Rennie's answer is good already, but I want to add a single point: These fluctuations are very very short. In quantum mechanics you've got Heisenbergs uncertainty principle, which is often stated as $$\Delta x \cdot \Delta p \le \frac \hbar 2$$ and which means, that for any quantum object (think of an electron or a positron created in such a vacuum ...

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