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

## TL;DR

This paper proposes a new perspective on quantum vacuum gravity, suggesting it leads to a naturally slow accelerating universe without the need for a cosmological constant or dark energy, potentially resolving the old cosmological constant problem.

## Contribution

It introduces a modified gravitational behavior of quantum vacuum energy that results in a slow acceleration, challenging previous assumptions and eliminating the need for fine-tuned dark energy.

## Key findings

- Quantum vacuum gravitates differently than previously thought.
- The universe's expansion rate is naturally slow, proportional to an exponential decay involving the cutoff scale.
- The model potentially resolves the old cosmological constant problem without fine-tuning.

## 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 $H\propto \Lambda e^{-\beta\sqrt{G}\Lambda}\to 0$ instead of the previous prediction $H=\sqrt{8\pi G\rho^{vac}/3}\propto\sqrt{G}\Lambda^2\to\infty$ which was unbounded, as the high energy cutoff $\Lambda$ 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 $\Lambda$ 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.