cosmological constant problem


  • Roughly, the vacuum energy is calculated by summing over all known quantum-mechanical fields, taking into account interactions and self-interactions between the ground states,
    and then removing all interactions below a minimum “cutoff” wavelength to reflect that existing theories break down and may fail to be applicable around the cutoff scale.

  • In cosmology, the cosmological constant problem or vacuum catastrophe is the substantial disagreement between the observed values of vacuum energy density (the small value
    of the cosmological constant) and the much larger theoretical value of zero-point energy suggested by quantum field theory.

  • In addition, some of the proposals are arguably incomplete, because they solve the “new” cosmological constant problem by proposing that the actual cosmological constant is
    exactly zero rather than a tiny number, but fail to solve the “old” cosmological constant problem of why quantum fluctuations seem to fail to produce substantial vacuum energy in the first place.

  • Because the energy is dependent on how fields interact within the current vacuum state, the vacuum energy contribution would have been different in the early universe; for
    example, the vacuum energy would have been significantly different prior to electroweak symmetry breaking during the quark epoch.

  • Depending on the Planck energy cutoff and other factors, the quantum vacuum energy contribution to the effective cosmological constant is calculated to be between 50 and as
    much as 120 orders of magnitude greater than observed,[1][2] a state of affairs described by physicists as “the largest discrepancy between theory and experiment in all of science”[1] and “the worst theoretical prediction in the history of

  • Luongo and Muccino have shown that this mechanism permits to take vacuum energy as quantum field theory predicts, but removing the huge magnitude through a counterbalance
    term due to baryons and cold dark matter only.

  • Around 1987, Steven Weinberg estimated that the maximum allowable vacuum energy for gravitationally-bound structures to form is problematically large, even given the observational
    data available in 1987, and concluded the anthropic explanation appears to fail; however, more recent estimates by Weinberg and others, based on other considerations, find the bound to be closer to the actual observed level of dark energy.

  • [24][25] From light front quantization insight, the origin of the cosmological constant problem is traced back to unphysical non-causal terms in the standard calculation,
    which lead to an erroneously large value of the cosmological constant.

  • Were the vacuum energy precisely zero, as was once believed, then the expansion of the universe would not accelerate as observed, according to the standard Λ-CDM model.

  • [3] History The basic problem of a vacuum energy producing a gravitational effect was identified as early as 1916 by Walther Nernst.

  • The model assumes that standard matter provides a pressure which counterbalances the action due to the cosmological constant.

  • [28] In 2021, Nikita Blinov and Patrick Draper confirmed through the holographic principle that the CKN bound predicts the measured cosmological constant, all while maintaining
    the predictions of effective field theory in less extreme conditions.

  • However, this calculated vacuum energy density is many orders of magnitude bigger than the observed cosmological constant.

  • [12][13] 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 lead to huge differences in the resulting cosmologies.

  • This view treats the cosmological constant as simply another fundamental physical constant not predicted or explained by theory.

  • [14] Cutoff dependence The calculated vacuum energy is a positive, rather than negative, contribution to the cosmological constant because the existing vacuum has negative
    quantum-mechanical pressure, while in general relativity, the gravitational effect of negative pressure is a kind of repulsion.

  • Nevertheless, many physicists argue that, due in part to a lack of better alternatives, proposals to modify gravity should be considered “one of the most promising routes
    to tackling” the cosmological constant problem.


Works Cited

[‘1. Calculated based on the Hubble constant and the dark energy density parameter ΩΛ.
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