How the huge energy of quantum vacuum gravitates to drive the slow accelerating expansion of the Universe

Abstract

We investigate the gravitational property of the quantum vacuum by treating its large energy density predicted by quantum field theory seriously and assuming that it does gravitate to obey the equivalence principle of general relativity. We find that the quantum vacuum would gravitate differently from what people previously thought. The consequence of this difference is an accelerating universe with a small Hubble expansion rate H ∝ Λe −β √ GΛ → 0 instead of the previous prediction H = 8πGρ vac /3 ∝ √ GΛ 2 → ∞ which was unbounded, as the high energy cutoff Λ is taken to infinity. In this sense, at least the "old" cosmological constant problem would be resolved. Moreover, it gives the observed slow rate of the accelerating expansion as Λ is taken to be some large value of the order of Planck energy or higher. This result suggests that there is no necessity to introduce the cosmological constant, which is required to be fine tuned to an accuracy of 10 −120 , or other forms of dark energy, which are required to have peculiar negative pressure, to explain the observed accelerating expansion of the Universe.

Hiding the Cosmological Constant

“…This notion was anticipated by Wheeler [8], who called the resulting picture "spacetime foam." Note that I am not considering fluctuations of the cosmological constant itself, though they may also matter [9]. Rather, I am proposing that the effects of the cosmological constant may fluctuate in a way that averages to near zero.…”

Limitations on Standard Sirens tests of gravity from screening

“…While generally expected to be attributed to a cosmological constant arising from vacuum fluctuations, it has proven extraordinarily difficult to motivate the observed acceleration from quantum theoretical predictions [7,8] (however, see, e.g., Refs. [9][10][11][12][13][14]). Given the broad possibilities for modifying gravity, the cosmic large-scale structure was shown to be insufficient to exhaustively probe the vast available model space, being fundamentally limited by a dark degeneracy that is however broken by measurements of the cosmological propagation of gravitational waves [15,16].…”

Screening and degenerate kinetic self-acceleration from the nonlinear freedom of reconstructed Horndeski theories

“…Either the Universe turns out to be consistent with ΛCDM, which will motivate a more directed effort in tackling the cosmological constant problem (see, e.g., Refs. [70][71][72][73][74][75][76][77][78][79][80][81][82][83]). On the other hand, if recent observational tensions [3,84,85] persist then that will be strong evidence that the theory describing the Universe on cosmological scales requires revision and potentially will go beyond a cosmological constant.…”