Gravitational Waves, potentials and limits of a discovery

by Jonathan Tennenbaum* The February 11 announcement of the first successful detection of gravitational waves by the LIGO Observatory in the United States is joyous news, and a welcome contrast to the rather depressing panorama of world events in the preceding period. This breakthrough provides a good occasion to reflect upon the strengths and weaknesses of science in our present era. Let us look at first at the strong side. Thanks to decades-long efforts of physicists, astronomers and engineers of countries around the world, a revolutionary new type of instrument has been created for exploring the Universe – an instrument able to “see” a form of radiation whose physical nature and characteristics are fundamentally different from those of electromagnetic waves and cosmic rays, which have been the basis for practically all astronomical observations until now. In the long term this breakthrough promises to have a comparable impact on the development of astronomy, as the emergence of optical telescopes four centuries ago. Indeed, now that LIGO has provided a “proof of principle” for the detection of gravitational waves, more measuring stations can be added, on the Earth and later in space, creating more and more powerful “gravitational telescopes”. A great deal of information is available concerning how the first gravitational wave signal was detected, and concerning the presumed source of the signal at an estimated distance of 1.3 billion light years from the Earth. The signal, which lasted only about two-tenths of a second, was identified through the analysis of data from two independent detectors located in the U.S. states of Louisiana and Washington. The relevant signal was recorded in the morning of September 14 last year, but the formal announcement was made only after a painstaking process of analysis and efforts to reduce the probability of error to as close to zero as possible. Happily, in contrast to many developments in modern physics, which are virtually inaccessible to people who lack specialized knowledge and mathematical training, the basic ideas behind the LIGO are relatively simple and can be understood by a much wider audience. This includes the principle of interferometry; the method of comparing signals from interferometers at distant locations; and the basic strategy for how to “pick out” the extraordinarily weak signal of a gravitational wave from raw data containing large amounts of noise caused by a variety of physical mechanisms and sources inside and outside the detectors. A crucial role was played by the use of physical models to predict the characteristics of the gravitational wave signals that would be generated by relevant types of astrophysical events. As a simple analogy: it is much easier to identify the voice of a specific person in a crowded and noisy room, if we know in advance what the voice sounds like and what the person is saying. [caption id="attachment_6819" align="alignnone" width="1321"] Fitting a LIGO interferometer in one frame is extremely difficult because of the size of the instrument. In this photo, all of LIGO Hanford’s Y-arm is seen stretching off into the desert, but less than half of the X-arm fits into the photo. The mid- and end-stations are labeled, but the arm is so long that the perspective of the shot distorts the distance between them. (Caltech/MIT/LIGO Lab)[/caption] For readers with a basic knowledge of physics and astronomy I would very much recommend the article “LIGO and the Detection of Gravitational Waves“ by Barry C. Barish and Rainer Weiss, two of the leading scientists in the project (http://www.fcaglp.unlp.edu.ar/~observacional/papers/PDFs/obs_grav-waves_…). This article, written back in October 1999, explains the basic approach and strategy behind the design of LIGO. The “official” scientific report on the first observation of gravitational radiation, just published in Physical Review Letters (116, 2016), can be found at the address:http://www.ligo.org/science/Publication-GW150914/index.php). It is important to point out, that although the successful detection of gravitational waves was a brilliant achievement of technical ingenuity, no new scientific discovery was involved. At most, the detection of gravitational waves can be seen as a welcome corroboration (although not a proof) of the scientific theories which were the basis for designing the LIGO observatory and for processing and interpreting the data. This includes above all the General Theory of Relativity and Einstein’s original 1916 prediction of the existence of gravitational waves. On the other hand we have reason to expect that future gravitational astronomy will lead to the discovery of anomalies that do not fit into present physical theories. How will the scientific community react to such anomalies? This question brings up the weaker side of science in our present era. There is unfortunately a great discrepancy between the spectacular development of technology over the last 100 years, and the relative lack of progress at the fundamental level of physics. The last true revolution in physics occurred nearly a century ago, with the discoveries of quantum mechanics and the theory of relativity. Despite a vast development of theoretical physics over the last 100 years, the basic foundations of present-day physics were already established by the 1930s and have remained essentially the same since then. The clearest symptom of stagnation at the fundamental level is the tendency for many scientists to overestimate the scope of validity of present-day scientific theories and to make exaggerated claims concerning how much we really know today (with any degree of certainty) about our Universe. This tendency is particularly strong in astrophysics and in cosmology — two fields most directly concerned with gravitational waves and the future interpretation of data obtained from detection of gravitational waves. It is not uncommon to hear astrophysicists and cosmologists describe details of the birth and age of the Universe, about what happened in the first billionths of a second after the Big Bang — when the Universe supposedly consisted a plasma of quarks and gluons etc. — as if they were talking about established facts. Sometimes the impression is given, especially in presentations to general audiences, that most of the fundamental questions about the origin and development of the Universe have already been answered; and that only details remain to be worked out. It is not sufficiently emphasized that the various assertions concerning the history of the Universe, concerning black holes, dark matter, quarks and gluons etc. all have a strongly hypothetical character; they are derived from theoretical models which involve far-reaching assumptions having only a limited basis in empirical reality. Terms such as “Standard Model” or “consensus view” tend to distract attention from the fact, that the some of the most distinguished scientists in the relevant fields have rejected these theoretical models and assumptions. In their book “A Different Approach to Cosmology” the celebrated astronomers Fred Hoyle, Geoffrey Burbidge and Jayant Narlikar made fun of the conformist behavior of scientists, with a picture of a crowd of geese all running in the same direction. Speaking at a conference in 2005 Geoffrey Burbridge described the situation with reference to theories of the origin of the Universe: “I hope that by now that I have provided enough evidence for a reasonable person to conclude that there is no particularly compelling reason why one should so strongly favor a standard model universe … apart from the fact that it is always easier to agree with the majority rather than to disagree. This sociological effect turns out to be actually extremely powerful in practice, because as time has gone on young cosmologists have found that if they maintain the status quo they stand a much better chance of getting financial support, observational facilities and academic positions, and can get their (unobjectionable) papers published…” The French astrophysicist Jean-Claude Pecker warned against the hubris of modern cosmologists: “And we would pretend to understand everything about cosmology, which concerns the whole Universe? We are not even ready to start to do that. All that we can do is to enter in the field of speculations. So far as I am concerned, I would not comment myself to any cosmological theory… Actually, I would like to leave the door wide open.” A similar situation applies to a certain extent to the subject of black holes. The presumed source of the signal detected by LIGO last September is a pair of black holes orbiting each other, losing energy by radiating gravitation waves and collapsing into a single object. The form of the resulting signal was predicted with the help of mathematical models, and the prediction was used in looking for the “signature” of a gravitational wave within the noisy raw data generated by LIGO. The fact that a signal with exactly the expected form was found, adds to the existing body of astronomical evidence for the real existence of black holes in our Universe. But the famous cosmologist Stephen Hawkings, for example, believes that their physical nature differs fundamentally from what is predicted by “standard theory”. In a 2014 paper Hawkings writes: “There are no black holes – in the sense of regimes from which light can’t escape to infinity.” The Indian physicist Abhas Mitra, head of Theoretical Astrophysics at the famous Bhabha Nuclear Research Center, states in a 1999 paper: “Thus we confirm Einstein’s and Rosen’s idea … (that) Schwarzschild Singularities (i.e. Black Holes – JT) are unphysical and cannot occur in Nature.” Mitra considers that the “candidate black holes” identified by astronomers are simply massive compact objects of a certain type. In an interview with the Times of India Mitra remarked: “Many Nobel laureates too have been struggling to resolve this paradox (the so-called Black Hole Information Paradox of Hawkins – JT), but they want to keep black holes alive. …You see, black hole is one of the biggest physics paradigms for almost 100 years with thousands of celebrity professors, researchers, Nobel Laureates having personal stake. … If my papers were wrong, they would have torn me apart and feasted like vultures on me. … Many Indian academicians desire that maybe someday somebody from the West would do that and they would be relieved of their moral guilt of ignoring me.” The purpose of this commentary is not to take sides in scientific controversies. Our main point is this: Scientists must never forget that the real Universe is not constrained to follow the laws of physics as we know them today. On the contrary, we can be sure that every real process in Nature involves physical principles which Man has not yet discovered. In the progress of human knowledge we are always at the beginning! Thus, when attempting to interpret data from the detection of gravitational waves, scientists must keep in mind that present-day physical theories will inevitably become obsolete in the future, as a result of new, fundamental scientific revolutions. The most important task of the emerging gravitational astronomy is exactly to help lay the basis for such revolutions — rather than merely filling in facts in some “standard theory” which future generations of physicists will laugh at.

• From the Web site: http://www.physicaleconomy.com/node/37