Tuesday, May 16, 2017

The accelerating expansion explained?

Seems to me that a lot of Chinese are doing interesting physics now.   This sounds interesting:

A group of physicists believe they may have cracked one of nature’s codes and finally explained what causes the accelerating expansion of the universe.
Qingdi Wang, a Ph.D. student at the University of British Columbia (UBC), has comprised a theory to bridge some of the incompatibility issues between the theory of quantum mechanics and Einstein’s theory of general relativity—two of the most successful theories that explain how the universe works.
Wang suggested that the universe is made of constantly fluctuating space and time.

“Space-time is not as static as it appears, it's constantly moving,” Wang said in a statement.
Astronomers discovered in 1998 that the universe is expanding at an increasing rate, which implies that space is not empty but rather filled with dark energy—likely from vacuum energy—that pushes matter away.

However, when the theory of quantum mechanics is applied to vacuum energy, it would predict that there is an extremely large density of vacuum energy, more than the total energy of all the particles in the universe. Also, Einstein’s theory of general relativity suggests that the energy would have a strong gravitational effect, which would likely cause the universe to explode.

However, physicists agree that the universe is expanding very slowly and the UBC team have made calculations that show that space is fluctuating wildly and at each point it oscillates between expansion and contraction.

As the universe swings from expansion to contraction, the two actions nearly cancel each other out, resulting in a small net effect that drives the universe to expand slowly at an accelerating rate.

“This happens at very tiny scales, billions and billions times smaller even than an electron,” Wang said.
The abstract to the paper is here, and it puts it rather more technically:
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 HΛeβGΛ0 instead of the previous prediction H=8πGρvac/3GΛ2 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 10120, or other forms of dark energy, which are required to have peculiar negative pressure, to explain the observed accelerating expansion of the Universe.

1 comment:

John said...

Thanks Steve,

More evidence for my long held opinion that scientific cosmology is cleverly disguised guessing ... or perhaps not so cleverly disguised. :)