Analysis of information sources in references of the Wikipedia article "Vacuum" in English language version.
...deals with the quantum vacuum where, in contrast to the classical vacuum, radiation has properties, in particular, fluctuations, with which one can associate physical effects.
Returning to the vacuum of a relativistic field theory, we find that both paramagnetic and diamagnetic contributions are present.QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See Carlos A. Bertulani (2007). Nuclear physics in a nutshell. Princeton University Press. p. 26. Bibcode:2007npn..book.....B. ISBN 978-0-691-12505-3.
The fundamental state of minimum energy, the vacuum, is not unique and there are a continuum of degenerate states that altogether respect the symmetry...
Returning to the vacuum of a relativistic field theory, we find that both paramagnetic and diamagnetic contributions are present.QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See Carlos A. Bertulani (2007). Nuclear physics in a nutshell. Princeton University Press. p. 26. Bibcode:2007npn..book.....B. ISBN 978-0-691-12505-3.