Experimental Relativity: Irwin Shapiro

Albert Einstein (1955-1879)

It was from the sessions on experimental relativity that I learned (to my complete satisfaction) the answer to the question I'd posed to Harry Woolf. The theory of relativity has entered the Space Age. It is most appropriate to the Einstein Year that the technology required for detecting the exceedingly feeble 1st and 2nd order effects of General Relativity has finally caught up with the predictions of theory.

The instruments of the famous Eddington eclipse expedition of 1919 appear by comparison to have been held together with Scotch tape and paper clips. On that occasion teams of poorly funded astronomers, toting little more than what we today might call box cameras, traveled to Brazil and West Africa to find evidence for the bending of light in a gravitational field. Their amounted to two serviceable images, only one of which could be successfully exploited by Arthur Eddington (through a laudable albeit notorious violation of strict scientific method), to announce the triumph of General Relativity.

Stepping out on the brink of the 80's, we were given previews of magnificent space operas involving at least 24 space crafts, two of them circling, and two more stationed on, Mars. Radio telescopes around the world were already poised to monitor the cross-hatched radio signals they were expected to beam back to astronomers on earth. We were shown previews of the Jupiter and Venus probes, already launched and slated to occult later this year; this is a new method for measuring the deflection of light by gravitational fields to a very high degree of precision. Methods employing occultation in space eliminate atmospheric interference in signal transmission. Many new directions are opening up for the detection of gravity waves. They are more than just a prediction of General Relativity, they are intrinsic to the shape of the theory: the tensor equations that equate gravitation with the bending of space-time are hydrodynamic in character. Space-time actually behaves like a liquid in which one expects to find both waves and turbulence.

Yet to date gravity wavefronts haven't been detected. However Irwin Shapiro displayed some very interesting calculations by John Taylor, which indicate that this situation may be about to change. Peaks of radio emissions from pulsars circling each other in binary pairs have been statistically analyzed. The graph of a faint parabolic decay in these emissions is show in the paper of Taylor, Fowler and McCulloch (Nature, 277, 1979). Shapiro interpreted this as evidence for gravity waves.

Taylor's graph grows by about 2 points a year. It seems a bit far-fetched to deduce the presence of a phenomenon as universal as gravitational waves, on the basis of 20 points in 12 years. However, when I visited with Phillip Morrison at MIT in 1993, he said that Taylor's parabola continues to follow its predicted trajectory year after year. He was convinced by that evidence. I wouldn't dream of contesting the opinions of Philip Morrison in his own field. As for Black Holes, he was still stating at that late date, "I'll be convinced when I see one."
(A joke. Regretfully, Dr. Morrison died a few weeks before the revision of the article was initiated in April 2005).

This report presents only a small selection of the advances in experimental relativity discussed at the Symposium. The 'symphonic scores' of these experiments are as elaborate as any contemporary piece of Boulez or Stockhausen. Most of the GR experiments are "piggy-backed" onto the large projects of exploration of the Space Program, and involve little extra technical work from the ground crews. Therefore their cost is minute in comparison to the Himalayan fiscal landscape of NASA.

The opportunity to be able to employ the sophisticated technology of orbiting space laboratories is balanced by a number of serious disadvantages. Owing to the expenses and security risks involved in routine NASA launches, the scientists who design the experimental GR packages are not allowed to be anywhere near their own equipment before it goes into launch. This means that it is impossible to eliminate or even reduce systemic errors.

It was therefore all the more gratifying to learn that all of the GR experiments performed in outer space from 1974 to 1979 have shown "a remarkable verification of the predictions of the theory." One can think of no more fitting birthday present to late Albert Einstein, than this simple comment of Irwin Shapiro's at the end of his talk.

Cosmology: Sciama’s visit to Cygnus X-1

Irwin Shapiro survey of experimental relativity was finished. The moment the discussion period opened the stocky English cosmologist Dennis Sciama rose up out of a chair near the front of the auditorium. Waving his arms he uttered the 'good news' in the apocalyptic tones befitting his subject. The affinities of cosmology to grand opera derive in their common goals:

1. To reveal, beneath the raw data of experience, the eternal invariants that govern the cosmos, or the eternal truths of love and fate.
2. To provide simple, gratifying answers to deep questions about our place in the universe and the direction in which we are headed .
   

Providentially for some, cosmology is a subject in which almost all relevant information is either inaccessible or unknowable. Given this state of affairs (similar to what one finds in homonid paleontology) its practitioners tend to make sweeping generalizations on the basis of a few scattered observations, with only a minor concern for confirmation through prediction. It's impossible to perform cosmological experiments since there's not much that is predictable (The Microwave Background Radiation is a notable exception).

Thus, although there are 8 commonly accepted solutions of the Einstein Field Equations it is exceedingly difficult to imagine experiments that would decide between them. Cosmology is therefore divided between Observation and Theory, with little activity in the domain of Prediction. Karl Popper would probably have concluded that Cosmology is "insufficiently falsifiable" to
quality as a science.

These inherent limitations tend to put cosmologists on the defensive. Since they lack the data needed to back up their hypotheses they are known to take cover behind the argument that the data is also insufficient to prove them wrong. Add to this the indisputable fact that their more earthbound (when not hidebound) colleagues, the physicists, have a tendency to cavort about with superior notions of the "purity" of their science, the cosmologists run the risk of falling foul of the perennial witch hunts mounted against the so-called 'pseudo-sciences' (normally the social sciences, but sometimes hapless 'reconstructive sciences' like geology and cosmology). Let a cosmologist make a slip of the tongue and people will start calling him an astrologer behind his back - worse than a truck driver! This snobbery merely increases the cosmologist's tendency to take refuge in dogmatism.

I hope that my thumbnail sketch of the science has put us in a better position to understand why Dr. Sciama accompanied his pronouncements with so many rhetorical flourishes. It also explains the mixture of weary skepticism and cautious interest they aroused. Sciama told us that the hitherto unclassifiable object at the center of the Galaxy Cygnus X-1, a pathological radio wave and X-ray source, is indeed a Black Hole. He presented no new findings to back up this assertion. In my conversations with several delegates afterwards, no-one would commit himself beyond stating that the evidence from radiation coming from the galaxy is consistent with the presence of a Black Hole (Since then, there are many candidates for Black Holes, including a few at the center of our own galaxy. The evidence is strong though not conclusive: there is still something hypothetical in the very existence of Black Holes).
Sciama then went on to say that because the object at the center of Cygnus X-1 is a Black Hole, the first- and second-order effects of General Relativity (normally so faint that they are barely detectable even with the most advanced technology) will be biblical in grandeur. Orbital shifts, like the shift in the perihelion of Mercury, the 43'' of arc that gave GR its initial boost, should be of the order of 100 degrees or more, almost one-third of a complete rotation. Gravity waves, to date undetected, will be visible in gargantuan vortices and turbulence.

Sciama's final announcement was that investigations were underway for the evidence of a "dual world" inside Cygnus X-1, in which the properties of space and time would be interchanged! All of these revelations were very exciting, and if they hadn't been presented with such chiliastic eloquence they might have been even more so. One way or another, Sciama's thunderous Toccata and Fugue launched the scientifically technical part of the ECS.

Black Hole phrenology

Many aspects of modern cosmology were touched on at the ECS. Here I relate only my impressions of talks given by Stephen Hawking and Martin J. Rees. Hawking's paper was read by Alan Lapedes standing beside Hawking's wheelchair on the stage. After summarizing recent developments in the field the talk transmitted, on a higher technical level, the substance of Hawking's article on the disintegration of Black Holes that appears in the Scientific American of February 1977. The talk was organized around 3 topics:

1. The Cosmological Censorship Hypothesis
2. The No Hair property
3. The surface temperature of a Black Hole.
   

The Cosmological Censorship Hypothesis (CCH) is a classic "cover-up" with which the history of the sciences is replete: the ether, phlogiston, epicycles. These are used to shore up a theory in trouble by postulating entities, which, by their very nature, cannot be observed. The CCH states that although a complete breakdown of causality occurs in the interior of a Black Hole, the universe outside the Hole remains causal, because this chaos, (along with matter, strong and weak forces light and everything else), remains trapped within it under the force of gravity.

The usefulness of this hypothesis lies in the fact that one can continue to use the equations of General Relativity to describe the "Large-Scale Structure of Space-Time" (the standard textbook on the subject by Hawking and Ellis) - including the existence of Black Holes !!!

The history of the sciences has shown that such ad hoc entities will eventually be discarded as unscientific, or, in the terminology of Karl Popper, as metaphysical rather than physical. As a holding action the "invisibility of chaos" may be useful, yet eventually it will be obliged to brave the light of day, if only to be given a shave by Occam. A Black Hole is said to "have no hair" because it is completely described by a finite number of parameters. Hawking cited 3: its mass, angular momentum and electric charge. However when the floor was open for discussion Claudio Teitelboim announced that he'd discovered a fourth parameter, its internal spin. Strangely there is no mention of his announcement in Some Strangeness in the Proportion, where it does however appear indirectly in a statement by John Archibald Wheeler in his talk "... there is another feature of the Black Hole. Claudio Teitelboim tells us, its spinor spin. "

The inclusion of internal spin does not rob the Black Hole of its miniscus of Absolute Perfection. Still I find it hard to believe that in this fatally flawed world there's anything that can get away with a paltry 4 parameters. A single atom requires over a hundred of quantum numbers to do it justice - and the list gets larger each year! .

Objections were raised from the floor of the auditorium against the endowment of barren beauty to objects anyone has yet to see. According to the No Hair principle, the Black Hole ingests it surroundings whole, like a python devouring a pig. All of its complexity is absorbed and nothing returned: matter, antimatter, electrons, mesons, quanta, quarks, neutrinos... Whatsoever be their strangeness in proportion previous to being ingested, they now serve only to fatten the 4 parameters.

Yet Hawking's own discovery discovered, Hawking Radiation coats the Black Hole with a tiny amount of hair! A sort of adolescent fuzz, nothing more. The Uncertainty Principle, the mainstay of Quantum Theory, sees to it that even the eternal glory of a Black Hole eventually undergoes disintegration.

Eternal Life and the baryon number

It was pointed out that this means that one abandon a fundamental principle of particle physics, the Conservation of Baryon Number: the quantitative difference between matter and anti-matter is an invariant in all interactions and processes of decay. Yu'val Ne'man asked if there might be some way of interpreting the equations to save baryon number conservation. Hawking's reply (through Lapedes): "I find it interesting that people have such an emotional attachment to baryon conservation. This may be because most people do not believe in eternal life. They would like to hope that the particles, which make up their bodies would live forever."

The jest crystallizes the very style of contemporary physics. Scientists have been condemned throughout modern history for mocking the existence of a soul. Now it appears that they have as little use for matter! The viability of the law of baryon conservation seems to depend upon whom one is talking with at a particular moment. The full quotation from Ne'man reads: "We owe a lot to baryon number. We owe our existence to the conservation of baryon number. Otherwise we would be floating in the universe as E=mc²! "

Fields and Particles

Today's physics community appears to be polarized into particle-ites and field-ites, with many shades of opinion falling between the extremes. The issues are quite difficult and involve as much philosophy as they do science. Its a pity that the physicists rarely bother to consult with the philosophers, though I do sympathize with their aversion to walking over to the ugliest building on campus, to climb 5 stories to a gloomy attic holding a few offices filled with oversized furniture, unfriendly secretaries and virtually no social amenities, not even a lounge with free tea and coffee. The reason for this sad parsimony is simple: nobody has figured out a way to turn existentialism into a thermonuclear bomb.

As Abraham Pais pointed out in his engaging account of the birth of modern physics there does not exist, even at this late date, any satisfactory definition, either ontological or epistemological, of the autonomous field in empty space.
If there were any place on earth to take a poll of the range of opinion in the field/particle debate, it would seem to be the ECS. At one extreme I found the physics professor from some SUNY campus who maintained that fields were nothing more than convenient devices for making calculations. At the other extreme stood Hawking himself, taking undisguised relish in tossing every principle of particle conservation onto the junk-heap of antiquated science and relying exclusively on entities implicit in the mathematics of field equations. One should also include the mathematicians at the Symposium, S.S. Chern and Tullio Regge, avid to replace everything physical, both fields and particles, by shopping lists of symmetry principles. Quote from Tullio Regge: "We must not forget, however, that physics, so to speak, is geometry plus an action principle."

Isaac Rabi resuscitates the media

The profundity, sophistication, and intellectual intensity of the field/particle debate (which shows no sign of cooling down after a century) should be contrasted with the manner in which it was viewed by the paparazzi responsible for covering it: on Thursday afternoon, March 18th, Isidor Isaac Rabi, Nobel prizewinner and crusty octogenarian, hoisted himself up painfully from his chair to tell the audience once more that only the things one sees in the laboratory are real. There was a certain amount of, well, I wouldn't call it demagoguery to his delivery, rather something in his tone of voice like that of a teacher scolding his recalcitrant students. To paraphrase his critique, the physics community must re-enter the laboratories to discover what one brings into it: the real reality that everyone really knows is really there. His is a perspective not too keen on distinguishing particles from fields.

One gets a glimpse into Rabi's world-view by the comment he once made to the effect that Oppenheimer's "failure" as a physicist was due to "overeducation" in the humanities: "It seems to me that in some respects Oppenheimer was overeducated in those fields, which lie outside the scientific tradition, such as his interest in religion, the Hindu religion in particular, which resulted in a feeling for the mystery of the universe which surrounded him almost like a fog... " (In "Who Got Einstein's Office?", p. 147.)

With the dying away of Rabi's final word one saw a dozen journalists rise up out of their seats and dash like a coherent wave packet out of the auditorium to the Press Room. Curious myself to see what could have roused them after 5 days of collective indolence I went back there myself shortly afterwards to see what all the fuss was about. I was astonished to find them all hard at work. One of them racked his brains to come up with a original headline of the genre: Leading Scientist Cries Back To The Laboratories! Another one was flipping the pages of the science encyclopedias to note down all of the distinctions and accolades bestowed upon the sage by a grateful humanity. A seasoned hack gave us the following advice: "Just write something like , 'He made advances in understanding the molecular structure of matter '. You can always say that about a physicist."

From the entrails of a debate over the most challenging ontological dilemma of the 20th century, the "reality" of the mathematical constructs (fields, tensors, Schrodinger wave functions, space-time), which have undermined the 'tangible' magnitudes (matter, time, space, momentum) that we are accustomed to encountering in daily life, the press corps had been roused from its slumbers once and only , when the perennial mugwump arose to pound his wooden ideas on the "real" floor on which he stood. In the final analysis, the newsmen did not even take the time to appreciate what merit there was in Rabi's rebuke:
".... I think Hilbert was once asked, in a certain mathematical colloquium, what he thought of a paper. And he said "Kreide" (chalk). And this is just a slight reminder that there is a real world "

The Cosmological Principle: Martin Rees is miffed

With the delivery of the paper by Martin J. Rees "The Size and Shape of the Universe", we move away from the Hawking Plenum of Gravitation to enter a more nebulous yet equally challenging Empyrean of Observational Cosmology.
For observational purposes the knowable universe is limited to the photosphere, the 14 billion or so light-years that a light signal travels from the instant of the Big Bang to earth-bound observers in the present. It is the cosmologist's version of Rabi's laboratory. Through a combination of the Postulate of Special Relativity, which limits the transmission of signals to the speed of light, and the Hubble Law of the expansion of the galaxies, the photosphere falls short of the potential universe (Note: Inflationary Theories and the hypothesis of dark energy have since put new wrinkles into this simplified model.)

The cosmologist enters this laboratory with a small number of ground rules which he considers essential to his science. Looking deep into the universe he is also looking back in time: light from a star one billion light years away from us takes one billion years to reach us. The astronomical scale is almost impossible to grasp in intuitive images: our Sun, dominating the daytime sky, is but a single star. Yet at a great distance a galaxy of a trillion stars is a speck of light invisible to the naked eye.

In order to organize the data coming in from a volume of such inconceivable magnitude, cosmology requires a postulate, suggested by the evidence, but which in fact is deemed necessary for the subject to qualify as a science: The universe is homogeneous. In his follow-up commentary, Jim Peebles referred to it as the "Copernican argument":

"... that the view of the universe from most galaxies that seem to be equally good homes for observers would be quite different from our own galaxy , [...] seems unreasonable ." One of the consequences of this assumption is that the universe that lies beyond the boundary of the photosphere, parts of which will become visible over billions of years, will have the same large-scale features as those that we can now see. And the same must have been true in the past, most of which is unknown. The combination of the Homogeneity Principle with the Principle of Isotropy (that the universe looks the same in every direction), is commonly known as the Cosmological Principle. Quoting from Jim Peebles classic text "Principles of Physical Cosmology", (pg. 15):

The Cosmological Principle fulfills the same function for Cosmology as the Uniformitarian Principle for geology, which allows one to reconstruct the past of the Earth from processes at work in the present. There isn't any way of proving" such a principle yet (following Lyell, the founder of the science), it is deemed necessary if geology is to stake its claim as a real science.

The problem is that there is a crucial difference between the metaphysics of geology and cosmology: one uses the Cosmological Principle to look backwards in time and uncovers the Big Bang! Catastrophism, the opposing view dear to organized religion that early geologists had to contend with, contends that the world we live in was formed by special moments of creation, such as the 7 days of Genesis and the Deluge.

Its correlative in cosmology is the Big Bang. That the Big Bang was a true historical event is confirmed, both observationally through the microwave background radiation, and theoretically through the singularity theorems of Hawking and Penrose which show that all solutions of Einstein's field equations must have a temporal singularity. By a curious combination of circumstances, the Cosmological Principle, a pragmatic simplification of the problems of back- reconstruction , leads inexorably to the biggest catastrophe of all time! The Big Bang is (by definition) the greatest singular event in the history of the cosmos. The catastrophe scenarios of geology are puny in comparison: the asteroid that hit the earth 65 million years ago and killed off the dinosaurs; Brown's hypothesis, that the Earth spontaneously flips its poles every few million years; Velikovsky's "Worlds in Collision", etc. Compared to the Big Bang they are little more than random eye-blinks of an elephant relative to the stampeding of its herd.

Catastrophism combined with the Cosmological Principle may sometimes provide an iron-clad defense to your normally over-defensive cosmologist: any regularity in the universe is evidence for homogeneity. Any irregularity is a left-over from the Big Bang.

A few examples of this kind of reasoning cropped up at the Symposium. The autogestion of the galaxies as "islands" in the oceans of interstellar gas was explained by minute fluctuations in the distribution of matter, to the order of 1 part in 10,000. The preponderance of matter over anti-matter was explained in the same way. On the other hand, the uncanny regularity of the distribution of matter in every direction, the so-called isotropy of the observed universe, was justified by the homogeneity principle; ("homogeneity" implies "isotropy", not the other way around) as was the hypothesis of a unique value for Hubble's
constant throughout the length of the cosmos.

Despite my dubious accreditation as a lowly journalist, when the floor was opened after Rees' talk I stood up and expressed the views just presented: namely that a combination of the Big Bang and the Homogeneity Principle made it possible to give an 'explanation' for anything. Rees stared at me for a few minutes, and then acknowledged that the observed isotropy of matter is "a complete mystery".

I was grateful for the attention paid to my question. Neither my question nor Rees' reply appear in the text of Some Strangeness in the Proportion. I am not upset that only the questions of official delegates appear in the transcript. I do think it a bit odd, however, that it would not carry the replies of invited speakers!
Over the remainder of the Symposium, Rees continued to give me dirty looks. Once he even banged into me as I was entering and he was leaving the auditorium. Clearly my question had troubled him. The next day he sent around a colleague who, coming directly to the point, asked me what my academic status was. I told him I was a philosopher of science at Columbia University.

Such rudeness was gratifying to my ego, but it was also unnecessary. Serious cosmologists do in fact worry about this unsatisfactory situation. My question was not designed to put Rees on the spot before the assembled world “Nobeliat”! What it reveals is that all of us, professionals like Rees, and yours truly amateur, were grappling with the unsolved difficulties that would lead to Alan Guth's proposal of the inflationary scenario in 1981. What renders the observed homogeneity even more troublesome is the fact that, by Special Relativity widely separated parts of the universe are not causally connected. No one has the slightest idea of what holds the whole picture together. One appears to have a situation (familiar to Quantum Theory which is built on oxymorons) of being obliged to depict the Big Bang as a "homogeneous catastrophe "!

Summary of cosmology

A summary of the state of cosmology as presented at the Einstein Centennial Symposium:

1. The microwave background radiation at 3° Kelvin has brought back a kind of fixed reference frame that recalls, yet is quite different from the electromagnetic ether.
2. General Relativity has survived all falsification challenges by a wide margin.
3. Irwin Shapiro and John Taylor think that they may have detected the presence of gravity radiation in the energy bursts of binary pulsars
4. Dennis Sciama wants us to believe that a Black Hole has been uncovered in Cygnus X-1 .
5. Claudio Teitelboim announced the discovery of a new Observable in Black Holes, the Internal Spin
6. The Cosmological Censorship Hypothesis is God's way of fabricating a "cover-up" to the acausality inside a Black Hole.
7. The observed homogeneity of the distribution of matter in the universe is baffling, and does not in fact simplify the task of observational cosmologists.
8. Everyone now accepts, standard model of the Big Bang with essential modifications on the way. Cosmology is, and always has been, a Paradise ofcontradiction. Yet one need not agree with Immanuel Kant's "proof" in the Critique of Pure Reason that cosmology is a worthless pursuit for serious minds. If nothing else, it keeps bright people off the streets and out of trouble. Banning the cosmologists from science is akin to Plato's expulsion of the poets from his Republic. It isn't possible to uproot Mankind's unslakable thirst for knowledge about the origins, structure and future of the universe in which He finds Himself. Nor is there any good reason for doing so. He will probably continue to be thoroughly lost, but at least He feels a little better.