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

Qingdi Wang, Zhen Zhu, William G. Unruh

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−βG√Λ→0 instead of the previous prediction H=8πGρvac/3−−−−−−−−√∝G−−√Λ2→∞ 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.

https://arxiv.org/abs/1703.00543

https://phys.org/news/2017-05-…s-expansion-universe.html

And the plot thickens!!!

'**Blurred times' in a quantum world.**

**Combining these principles from quantum mechanics and general relativity, the research team headed by ?aslav Brukner from the University of Vienna and the Institute of Quantum Optics and Quantum Information demonstrated a new effect at the interplay of the two fundamental theories. According to quantum mechanics, if we have a very precise clock its energy uncertainty is very large. Due to general relativity, the larger its energy uncertainty the larger the uncertainty in the flow of time in the clock's neighbourhood. Putting the pieces together, the researchers showed that clocks placed next to one another necessarily disturb each other, resulting eventually in a "blurred" flow of time. This limitation in our ability to measure time is universal, in the sense that it is independent of the underlying mechanism of the clocks or the material from which they are made. "Our findings suggest that we need to re-examine our ideas about the nature of time when both quantum mechanics and general relativity are taken into account", says Esteban Castro, the lead author of the publication.Read more at: https://phys.org/news/2017-03-blurred-quantum-world.html#jCp**

# Entanglement of quantum clocks through gravity

http://www.pnas.org/content/114/12/E2303.full.pdf