[Bogie_smiles (OP)]

http://physicsworld.com/cws/article/news/2017/jul/20/roger-penrose-asks-if-a-cyclic-cosmology-is-lurking-in-ligo-noise

Roger Penrose asks if a cyclic cosmology is lurking in LIGO noise?


Cosmological noise: signals from both LIGO detectors
Correlated noise in the two LIGO gravitational-wave detectors may provide evidence that the universe is governed by conformal cyclic cosmology (CCC). That is the claim of Roger Penrose of the University of Oxford, who is proposing that the apparent noise is actually a real signal of gravitational waves generated by the decay of hypothetical dark-matter particles predicted by CCC.


Last month, physicists at the Niels Bohr Institute pointed out that some of the noise in the two LIGO detectors appears to be correlated – with a delay that corresponds to the time it takes for a gravitational wave to travel the more than 3000 km between the instruments.


Writing in a preprint on arXiv, Penrose argues that a significant amount of this noise could be a signal of astrophysical or cosmological origin – and specifically CCC.

Infinite aeons

First proposed over a decade ago by Penrose, CCC assumes that the universe consists of a succession of aeons. Each aeon begins with a big bang and proceeds into an unending future in which the universe expands at an accelerating rate. As this expansion becomes infinitely large, Penrose argues that it can be transformed back into the next big bang.


He says that a "reasonably robust implication of CCC" is that dark matter consists of particles called erebons – the name deriving from the Greek god of darkness Erebos. As dark matter goes, erebons are extremely heavy and have masses of about 10[size=0pt]–5[/size] g. This is roughly the Planck mass and on a par with a grain of sand and about 22 orders of magnitude heavier than a proton.

Near-instantaneous impulses

Penrose says that when an erebon decays, it deposits all its energy into a gravitational wave. While such waves have frequencies well above the detection capabilities of LIGO, their arrival at the detectors would be recorded as near-instantaneous impulses that could be mistaken for noise.About the authorHamish Johnston (hamish.johnston@iop.org) is editor of physicsworld.com

[evan_au]

If you were measuring correlation between the two LIGO detectors, you wouldn't do it in a time segment where a black hole collision was detected - because there is a correlated signal there from a "point source" in the sky.

I think that this correlation is very hard to achieve with just 2 detectors, because the noise bursts would be coming from all directions in the sky, and you get a very poor indication of direction when you have just 2 detectors. So you have to look for any events within ±10ms (the detectors are 3000km apart); this is likely to produce a lot of "false positives".

However, with another 2 gravitational wave detectors planned to come online in the next couple of years, it may well be possible to detect gravitational wave impulses coming from different directions in the sky. The extra detectors then allow you to eliminate coincidences from 19ms of this 20ms window.

Some researchers are trying to build gravitational wave detectors with a higher frequency response than LIGO, and these should also be useful for detecting fast events.

Detection of high-frequency gravitational wave impulses from across the sky may point to annihilation of new types of particle (or even "starquakes" on neutron stars), but it does not directly prove the ultimate fate of the universe.

[evan_au]

Near-instantaneous impulses

Wondering about this further....

My primitive understanding of gravitational waves is that they twist spacetime as they are passing through, and then untwist it back to the original geometry after they have passed.

This suggests that gravitational waves do not impart an impulse to the hanging mirrors (which would show up as a change in length after the gravitational wave has passed), but would return the mirror to their previous separation.

The current LIGO detectors have a bandwidth of about 1kHz, so this suggests that gravitational impulses much less than 0.5ms should not be detectable unless they caused some overload and nonlinear distortion in the measurement circuits and filters.
See: https://en.wikipedia.org/wiki/LIGO#A.2B

It would be good for the LIGO team to characterize the behavior of their detectors when presented with a high-amplitude impulse of short duration, to see if there are detectable distortion and noise at the output. The two LIGO detectors have a common design, and would produce a similar signature under overload conditions. But it is likely that gravitational wave detectors from an independent design team would have significantly different overload behavior than LIGO, making correlation less obvious.

In any case, I look forward to more rigorous tests when there are additional gravitational wave detectors.