Astrophysics has given empirical evidence for the cosmological constant that accelerates the expansion of the universe. Atomic, Molecular, and Optical Physics has proven experimentally that the quantum vacuum exerts forces - the van der Waals and Casimir forces - on neutral matter. It has long been conjectured [1] that the two empirical facts, the cosmological constant and the Casimir force, have a common theoretical explanation, but all attempts of deriving both from a unified theory in quantitative detail have not been successful so far. In AMO Physics, Lifshitz theory has been the standard theoretical tool for describing the measured forces of the quantum vacuum. This lecture discusses a version [2] of Lifshitz theory that also accounts for the electromagnetic contribution to the cosmological constant. Assuming that the other fields of the Standard Model behave similarly, gives a possible quantum-optical explanation for what has been called dark energy.

[1] Ya. B. Zel'dovich, Usp. Fiz. Nauk 95, 209 (1968).

[2] U. Leonhardt, Ann. Phys. (New York) 411, 167973 (2019).