Plasma of quarks and gluons
Experimentation in particle physics - Recent results

Unlike the vacuum of classical physics, which is synonymous with nothingness or "nothing", the vacuum of quantum field theory is endowed with an extremely rich and complex structure that underlies all physics (cf. § 2.8 of ).

Since Dirac, we've known that the vacuum is made up of virtual particle-antiparticle pairs $\left(e^{+}\mathrm{ }{e}^{-},\mathrm{\hspace{0.17em}}q\overline{q}\right)$ of negative energy, which can appear through quantum fluctuation...