Random article: Faddeev-Popov ghost

Things like this make me wonder if quantum physics isn’t all a hugely elaborate practical joke by scientists on the rest of us mere mortals. Negative probabilities? Seriously?

In physics, Faddeev-Popov ghosts (also called ghost fields) are additional fields which need to be introduced in the realization of gauge theories as consistent quantum field theories.

The Faddeev-Popov ghosts are sometimes referred to as “good ghosts“. The “bad ghosts” represent another, more general meaning of the word “ghost” in theoretical physics: states of negative norm‚ÄĒor fields with the wrong sign of the kinetic term, such as Pauli-Villars ghosts‚ÄĒwhose existence allows the probabilities to be negative.

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