What is casimir's trick. and its importance in particle physics
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Answer:
You must be referring to the Casimir Effect, an experiment with a vacuum chamber enclosing two sheets of very thin materials hanging vertically (to obviate gravity) suspended very close to each other, which causes them to move ever so slightly toward each other. At first it seemed as if some form of energy would appear inside the vacuum chamber that would push the two sheets toward each other, but then it was understood that it was just the ambient EMR, photons. A vacuum only means the absence of atoms, not photons. Photons are massless but they do have a bit of momentum owing to their kinetic EMR energy. Since there would be far more photons bouncing off the outside surfaces of the sheets than between them, the pressure would tend to make the sheets move toward each other. This principle of using photon pressure is the basis of what are called solar wind sails which use the blast of photons radiating from the Sun to push the attached vehicle away from the Sun. The significance of this would be to confirm the mass / energy equivalency principle, that even massless photons have a measurable momentum which can impact on matter.