Cosmological constant problem

In cosmology, the cosmological constant problem or vacuum catastrophe is the disagreement in measured values of the cosmological constant. In general relativity, the value is measured by the vacuum energy density to be a small value. In cosmological constant, the zero-point energy suggested by c, is measured to be much larger.

Depending on the assumptions, the discrepancy ranges from 40 to more than 100 orders of magnitude, a state of affairs described by Hobson et al. (2006) as "the worst theoretical prediction in the history of physics."

The basic problem of a vacuum energy producing a gravitational effect was identified as early as 1916 by Walther Nernst.

The value was predicted to be either zero or very small, so that the theoretical problem was already apparent, and began to be actively discussed in the 1970s.

With the development of inflationary cosmology in the 1980s, the problem became much more important: as cosmic inflation is driven by vacuum energy, differences in modeling vacuum energy leads to huge differences in the resulting cosmologies.

The problem became increasingly central as an obstacle to theoretical progress during the later 1980s and the 1990s, and was variously dubbed an "unexplained puzzle", a "veritable crisis" and "the most striking problem in contemporary fundamental physics".

After the development of quantum field theory in the 1940s, the first to address contributions of quantum fluctuations to the cosmological constant was Zel’dovich (1967, 1968).

The vacuum energy in quantum field theory can be set to any value by renormalization. This view treats the cosmological constant as simply another fundamental physical constant not predicted by theory.

The value of the cosmological constant was first measured in 1998.

With the ability to measure the speed of gravity, its relation to the speed of light may soon provide confirmation of which theories and models best fit the cosmological constant.

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