Gruber Prize for LIGO team’s gravitational waves

The 2016 Gruber Cosmology Prize of $500 000 award citation reads:

The Gruber Foundation proudly presents the 2016 Cosmology Prize to Rainer Weiss, Kip Thorne, Ronald Drever, and the entire LIGO team for pursuing a vision to observe the universe in gravitational waves, leading to a first detection that emanated from the collision of two black holes. 

This remarkable event provided the first glimpse into the stronggravity regime of Einstein’s theory of general relativity that governs the dynamics of black holes, giving direct evidence for their existence, and demonstrating that their nature is consistent with the predictions of general relativity.

The first detection of gravitational waves was a major technical achievement, but it’s the identification as from a collision of a pair of black-holes that’s given by Gruber as its cosmological significance.  If not black-holes, then would theoretician Kip Thorne still merit the prize?  The “first glimpse” into Einstein’s general relativity was of course gained from “pulsars”, rapidly-pulsing radio wave emitters which were quickly identified with neutron stars of highly compact neutron matter.  The collision of two such objects has long been predicted to give a mega-burst of gravitational radiation.

Science normally demands an observation is reproducible – waiting for further detections or even a spectrum  of wave sizes and periods would normally be required.  Moreover, a study back in 2002 established that the late-stage part of the wave pulse (‘ring-down’ modes) would be needed to provide strong evidence for black-holes [Abramowicz et al., Astron & Astrophys.] – the LIGO signal was not strong enough for this.  So the LIGO team fell back on saying neutron stars cannot be as big as 30 times the sun’s mass and ignoring possibilities of other condensed-matter astrophysical objects of similar size.

The cosmological significance of the LIGO detection was thus the first detection of compact objects of around 30 times the sun’s mass, spiralling in to touch each other and then coalescing in the way predicted by Landau and Lifshitz in the 1960s.  But condensed-matter objects generally, whether the ‘horizonless’ variety or exotic black-holes.  The analysis and computational methods (‘post Newtonian’ expansions) have been advanced since then, but as leading theorists have just shown (Ruffini et al.), the results are close to the Landau-Lifshitz modelling.   As long as the nature of the binary compact objects remains uncertain, there’s no living theoretician to share the prize with Weiss, Drever and the LIGO team.

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