A rapidly moving mirror that turns virtual photons into real ones is the first experimental evidence of the dynamical Casimir effect.
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.
It occurs when a mirror moves through space at relativistic speeds. Here's what happens. At slow speeds, the sea of virtual particles can easily adapt to the mirror's movement and continue to come into existence in pairs and then disappear as they annihilate each other.