"One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence."
So begin Christopher Wilson from Chalmers University in Sweden and friends in their marvellously readable paper about a rather extraordinary piece of science.
This maelstrom of quantum activity is far from benign. Physicists have known since 1948 that if two flat mirrors are held close together and parallel with each other, they will be pushed together by these virtual particles.
The reason is straightforward. When the gap between the mirrors is smaller than the wavelength of the virtual particles, they are excluded from this space. The vacuum pressure inside the gap is then less than outside it and this forces the mirrors.
This is the static Casimir effect and it was first measured in 1998 by two teams in the US.
But there is another phenomenon called the dynamical Casimir effect that has never been seen.
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