Triumphant decades-long hunt for elusive gravitational waves
Yesterday, the 2017 Nobel Prize in Physics was awarded to Rainer Weiss, Barry C. Barish and Kip S. Thorne as representatives of the LIGO Scientific Collaboration and the Virgo Collaboration for the first direct detection on planet Earth of gravitational waves. The first two (out of a total of four by now) detection events, fittingly labelled GW150914 and GW151226 according to the dates of their respective observations, and announced to the international public at press conferences held on Feb 11, 2016 at Washington, DC, and on Jun 15, 2016 at San Diego, CA, happened more or less exactly 100 years after Albert Einstein (1879–1955) had predicted the existence of gravitational waves in a 1916 paper; Einstein (1916). His prediction was the result of a compelling mathematical derivation from the general theory of relativity which he had presented to the physics community only a few months earlier in November 1915; Einstein (1915). According to this theory, gravitational waves will be generated whenever astronomically huge mass distributions engage in dynamical processes entailing asymmetric relative acceleration. They will then propagate outwards at the speed of light, alternatingly stretching and squeezing the geometry of the spacetime fabric of the Universe in directions transverse to the direction of travel of the waves; cf. Misner et al (1973): Part VIII.
As the analysis of the available observational data by Abbott et al (2016a) revealed, the first event, GW150914, was triggered approximately 1.3 billion years ago (“in a galaxy far, far away …”) by two black holes of 36 and 29 solar masses that were trapped in a dance of inspiraling orbital motion and then merged to form a single black hole of 62 solar masses. Almost instantaneously, the enormous amount of 3 solar masses worth of energy was radiated away in the form of gravitational waves. Extremely fortunate for all of us, and the evolution of life on planet Earth in general, ultra-violent astrophysical events of this kind do not happen very frequently in our immediate vicinity.
The LIGO Scientific Collaboration and the Virgo Collaboration, which together comprise multicultural teams of more than 1,200 female and male scientists, engineers, technicians and software specialists from 15 different countries, can celebrate their triumph following some 40-odd years of highly diligent and focused research work. Throughout this period, researchers involved with the project must have been plagued with doubts more than once, worrying whether what they were up to really was a meaningful endeavour after all. Quite a few frustrating experiences concerning negative detection results had to be coped with, as they had to learn time and again that the sensitivity of their detectors still was not sufficiently high for their measurements to stand a chance of success. Therefore, in one way or another, the team members most likely felt hit by a massive lucky strike of fate when, eventually, all their past efforts proved worthwhile. However, it is probably not quite accurate to relate their case to the Israeli–US-American psychologist Daniel Kahneman’s famous qualitative equations (Kahneman 2011: 177)
success = talent + luck
great success = a little more talent + a lot of luck.
The teams have certainly been tempting their luck by well thought through planning, preparation, dedication, passion and perseverance. This common state of mind was quickly rewarded by a second detection event, GW151226, recorded only a few months after the first one; cf. Abbott et al (2016b), and with GW170104 and GW170814 two more detection events followed in the meantime.
The Laser Interferometer Gravitational-wave Observatory (LIGO) was built during the 1990ies at the two sites Hanford, WA, and Livingston, LA, this being a time when the US-American physicists Russell Hulse (born 1950) and Joseph Taylor Jr. (born 1941) had just been awarded the 1993 Nobel Prize in Physics for providing indirect evidence for the existence of gravitational waves, amounting to the annual inspiraling rates due to orbital energy loss of the binary pulsar neutron star system they had first observed in 1974. The two LIGO locations are to be found at nearly opposite ends of the North American continent, about 3,000 km (or 10 milli-lightseconds) apart. A third gravitational-wave observatory was built by the Virgo Collaboration near Pisa in Italy. At all of these sites, laser light beams are travelling up and down each of two about 4 km long underground vacuum tubes, bouncing off near-perfect mirrors at their respective ends. The vacuum tubes form L-shapes. When an incident gravitational wave generated by some astrophysical event is not propagating entirely in the plane spanned by the two tubes, relative changes in the tubes’ lengths of extremely tiny magnitudes can be measured. The maximum amplitude forecasted for such relative changes is 10e(-21). This corresponds to an accuracy of the width of a human hair when determining the distance between the Sun and the next nearest star about 4 lightyears away. Various technological upgrades of the LIGO and Virgo beam detectors were necessary to attain this impressive sensitivity. GW150914, GW151226, GW170104 and GW170814, the last event of which triggered for the first time also the Virgo beam detector, are now the four most accurate physical measurements wo/man-kind ever performed. Note that at least two beam detectors need to be in operation to exclude with near certainty that freak disturbances due to local environmental influences are responsible for a signal in any one of the measuring devices.
The British relativist Felix Pirani (1925–2015) settled a controversial debate during the 1950ies on whether gravitational waves were indeed a physical reality, i.e., whether this was a phenomenon that could transport energy from one astrophysical system to another. He provided a convincing theoretical argument as to how this energy transporting property could actually be measured in practice, by carefully monitoring the relative accelerations between freely suspended masses at the ends of two perpendicular tubes (in which, e.g., light beams are travelling up and down); see, e.g., Pirani (1956). It is on Pirani’s principle that the LIGO and Virgo beam detectors were designed.
My PhD supervisor, Reza Tavakol, once had me wondering when he said: “They don’t build cathedrals anymore.” What he was alluding to was the fact that very rarely in our modern times are people prepared to get involved in projects with a mid- or even long-term time horizon. Projects with foreseeable near-term (economical) benefits have been in fashion for quite some time. Of course, concerning timescales, the LIGO and Virgo projects do not quite compare to the building of, amongst others, the Cologne Cathedral, the completion of which took on the order of 1,000 years. However, it is quite remarkable that in this particular scientific enterprise an ever-increasing group of curious people (the first two publications in the Physical Review Letters bear the names of 1,004 authors, some of which deceased prior to the release of these papers) was prepared to invest a significant part of their lives and careers to pursuing one uniting big idea: a vision, one common goal, they all dreamed of realising one day. The teams’ outstanding strengths are diversity, multidisciplinarity, commitment, resilience and diligence. Of particular interest to social scientists, in this context, are the findings on characteristic idiosyncrasies of the international gravitational-wave community that the British sociologist Harry Collins obtained from analysing qualitative empirical data that he gathered over many decades by means of participating observations; Collins (2014).
In the cases of the LIGO Scientific Collaboration and the Virgo Collaboration, I think, we are looking at true “heroes groups” (and a benchmark case in (project) management) in the words that Stephan Sonnenburg used in his opening address to incoming first-year students at Karlshochschule on Sep 19, 2016. Perhaps it is worthwhile pointing out that Karlshochschule provides their students with the opportunity of gaining first small-scale experience of some of the qualities referred to above during the 0.3.1 IPRO: Introductory Company Project module. Taking a mid- or long-term perspective provides the foundation for obtaining sustainable rewards; on this issue, see, e.g., André Reichel’s blog entry on Jun 20, 2016 on Sustainability as a Key Idea for Change. The short-term perspective of mainstream economics regularly proves counter-productive in this respect.
Over the past few centuries, fundamental research in various disciplines has reliably (though, unfortunately, unpredictably) produced positive Black Swan events in the sense of Taleb (2007), leading to ground-breaking epistemological advances and unprecedented benefits for wo/man-kind. Be it the discoveries of the steam engine, electromagnetic induction, penicillin, or semiconducting materials, to name but a few important breakthrough instances: all of them had incredible spin-offs (pay-offs, in economical language), which could not possibly have been anticipated by anyone. And, as a matter of fact, most discoveries of the kinds described came about by sheer serendipity. According to the New York Times, the National Science Foundation (NSF) of the US of A alone, besides a number of other significantly contributing international organisations, supported the LIGO project with about $ 1.1 billion over more than 40 years. Without this support, the international public would not be in a position now to celebrate the joint LIGO and Virgo success.
The British cosmologist Peter Coles elaborates in his blog entry from Feb 13, 2016 on the pitfalls of “market-driven research,” which appears to be the present-day view taken by most national and transnational funding agencies. Of course, it is precious tax-payers’ money that these agencies are administering, but the acceptance of a certain degree of uncertainty as regards future outcomes of well-defined research projects seems paramount for great success stories in the long run. I guess the main points Coles makes apply well beyond the realms of the natural sciences.
The LIGO and Virgo measurements not only confirm Einstein’s prediction of the existence of gravitational waves travelling at the speed of light, but, in addition, they establish beyond reasonable doubt the reality of black holes (in binary systems) as veritable astrophysical objects. This is the best outcome one can possibly hope for when doing empirical research.
Wo/man-kind can now expect the construction over the coming decades of a world-wide grid of beam detectors. The prospect of factually performing gravitational-wave astronomy in the 21st Century has finally become tangible. There will then be available a new species of information flow, requiring intricate techniques of statistical data analysis for extracting information on the astrophysical processes generating gravitational waves.
Simply beautiful what people can achieve when they join their creative energies!
- Abbott B P et al (LIGO Scientific Collaboration and Virgo Collaboration) (2016a) Observation of Gravitational Waves from a Binary Black Hole Merger Phys. Rev. Lett. 116 061102 (1–16)
Also: Preprint arXiv:1602.03837v1 [gr-qc]
- Abbott B P et al (LIGO Scientific Collaboration and Virgo Collaboration) (2016b) GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence Phys. Rev. Lett. 116 241103 (1–14)
Also: Preprint arXiv:1606.04855v1 [gr-qc]
- Collins H (2014) Gravity’s Ghost and Big Dog: Scientific Discovery and Social Analysis in the Twenty-First Century (Chicago, IL: University of Chicago Press) ISBN–13: 9780226052298
- Einstein A (1915) Die Feldgleichungen der Gravitation Sitz.-Ber. Preuß. Akad. Wiss., Berlin 844–847
- Einstein A (1916) Näherungsweise Integration der Feldgleichungen der Gravitation Sitz.-Ber. Preuß. Akad. Wiss., Berlin 688–696
- Kahneman D (2011) Thinking, Fast and Slow (London: Penguin) ISBN–13: 9780141033570
- Misner C W, Thorne K S and Wheeler J A (1973) Gravitation (New York: Freeman and Co.) ISBN–10: 0716703440
- Pirani F A E (1956) On the Physical Significance of the Riemann Tensor Acta Phys. Polon. 15 389–405
Re-published: (2009) Gen. Relativ. Gravit. 41 1215–1232
- Taleb N N (2007) The Black Swan – The Impact of the Highly Improbable (London: Penguin) ISBN–13: 9780141034591