Stanford Today Edition: March/April 1997 Section: Features: The Relative Proof WWW: The Relative Proof
THE RELATIVE PROOF
Stanford Puts Einstein to the Test
By Robert Lee Hotz
Sometime before October 2000, as the last days of the 20th century count down, a sleek Delta II rocket will roar into a polar orbit from a seaside launch pad at Vandenberg Air Force Base. It will carry aloft a daring challenge to modern physics conceived more than 37 years ago by three naked Stanford scientists musing between laps at a men's swimming pool.
The result of that poolside encounter between William M. Fairbank, Robert Cannon and Leonard Schiff is methodically taking shape at Stanford today as a remarkable three-ton, trumpet-nosed spacecraft called Gravity Probe B. It is the focus of a unique $500-million NASA experiment designed to probe the invisible forces that weld together space, time and gravity.
In the generation since that poolside brainstorming session, a growing cadre of university scientists, engineers and students led by principal investigator Francis Everitt and program manager Bradford Parkinson has labored to create what is widely considered the most precise, sophisticated - and controversial - test yet of a scientific vision of gravity that has shaped our century's understanding of how the universe works: Albert Einstein's Theory of General Relativity.
The probe's aim sounds deceptively simple: Test the forces generated by the fabric of space as it spins around the wheeling carousel of Earth. From its orbit, the gravity probe will measure the influence of gravity with the most accurate gyroscopes ever designed - a million times more precisely than can be achieved on Earth.
On the accuracy of those meticulously calibrated measurements, Einstein's theory of gravity could stand or fall.
"If you ask the most extreme question - is this experiment manifestly a totally crazy idea? - the answer is that it became fairly obvious to us it was not manifestly crazy," says Everitt, who has been involved in the project since its inception in 1971. "There is a sense in which we all know that Einstein's theory must be wrong, or must be incomplete."
The question, Everitt explains, arises from the troubling incompatibilities between general relativity and quantum mechanics, the other leading theory that describes the physical laws governing the universe. General relativity operates on the broad scale of planets, galaxies and the forces that bind them, while quantum physics addresses the microworld of subatomic particles. They should mesh at some level; yet they do not, as best anyone can tell at this point in time.
"The way that it doesn't fit with quantum mechanics is extremely, frustratingly deep. One or the other of these theories must be radically fixed," he says.
"It is true that there is no very convincing alternative theory to Einstein's. It is also true that we know the theory must break down somewhere. The difficulty is that nobody knows where or how it will break down."
That is the conundrum that set Stanford scientists on a collision course with one of the most influential figures in the history of science.
MONUMENTAL RESEARCH EFFORT
Even before the assembly of the gravity probe, the research that has gone into it has spawned 59 doctoral dissertations, 20 master's degrees and six undergraduate engineering degrees at nine different universities. At Stanford alone, the project has drawn on the talents of students from 11 departments; 49 students are currently involved.
"There are a whole series of research projects where we are pressing the state of the art that are absolute naturals for students," says Parkinson, who is also a co-principal investigator on the project. "We have it all the way from students who have worked on theoretical physics issues to engineering problems like the construction of micro-thrusters."
So far, the relativity mission has spurred new technology ranging from significant improvements in spacecraft construction to an ingenious application of the Global Positioning System satellite navigation network to low-cost, automated landing systems for commercial airliners. Researchers expect to tease other side benefits from the probe in orbit, such as a geodetic map of Earth 100 times more accurate than any available today.
But it is the prospect of a new insight into the structure of Einstein's universe that galvanized the attention of the physics community.
"If Gravity Probe B flies, it will be a landmark in explaining something so fundamental," says Caltech physicist Kip Thorne, author of Black Holes and Time Warps: Einstein's Outrageous Legacy. "It will go down in the textbooks. I can see it forcing us back to the drawing boards. I think it is unlikely, but I by no means rule it out." And many scientific experts concur that much is riding on the outcome. "If they turn out to show [Einstein's] theory wrong, there will be an enormous impact on the whole foundation of physics," says Thorne.
Nobel laureate Sheldon Glashow called the gravity experiment a "must." Princeton mathematics professor Demetrios Christodoulou termed it "a fundamental physics experiment of the utmost significance." At the University of Chicago's Enrico Fermi Institute, astrophysicist S. Chandrasekhar said the experiment is of "central significance not only to the general theory of relativity but to a wide range of astrophysical phenomena."
Simply to definitively prove that Einstein is correct would be more than enough to justify the whole project in NASA's eyes.
"It would really change our perception of the universe," says NASA Gravity Probe B program manager Frank Giovane from Washington, D.C. "Everyone realizes it is of earth-shattering importance that we truly validate Einstein's theory."
In many ways, the Gravity Probe B project is unlike anything NASA - which has no division devoted to fundamental physics - has ever attempted. Unlike many astrophysics and astronomy satellites, designed as instruments of open-ended exploration, the relativity mission is designed to answer a single yes or no question. And it aims to validate a theory many scientists today already consider well proven.
It also is unique in another way: A university, not the space agency, has taken the prime role in a satellite mission. The project is managed directly by Stanford, with NASA retaining largely an oversight responsibility. Under contract to the university, Lockheed Martin Missiles and Space Co. is building the spacecraft and some of the experimental systems.
"For the most part, Stanford is in control of its scientific destiny," says Eugene W. Urban, a project scientist who is chief of the physics and astronomy division in the space sciences laboratory at the Marshall Space Flight Center in Huntsville, Alabama. "It is unusual," he adds.
In part, the arrangement evolved simply because so much of the project expertise is concentrated at Stanford, space agency officials said. But it also is a measure of trust.
It especially is a vote of confidence in Parkinson, who, prior to joining the Stanford faculty, was the U.S. Air Force officer most responsible for organizing and managing the development of the 24-satellite Global Positioning System (GPS), which has revolutionized the science of navigation around the world. For his role in orchestrating GPS, one aerospace expert called Parkinson "one of the unsung heroes of the space age."
Faith in its management, however, has not protected the relativity mission from all kinds of second thoughts about its scientific goals. In their pursuit, project scientists have already been subjected to unexpected tests of the limits of patience, tolerance and determination.
MECHANICS VS. POLITICS
For all its technical elegance, the project owes its existence as much to a grasp of fundamental political equations as to the mastery of abstruse relativity theory and orbital mechanics.
"I never had any idea I would get into the amount of political battling that I got into to keep the program going," Everitt says. "One is certainly not taught, when one is taught physics, that a significant period of your time would be spent in Washington, D.C."
Indeed, as Everitt speaks, he is not in his Stanford office, but in a hotel room near Capitol Hill in Washington, preparing to make the rounds of congresspeople, senators, staff aides and committee experts prior to a regular meeting at NASA headquarters on the project's status. There is no formal requirement that Everitt consult with anyone in Congress at the time of the NASA review, or even that he be present for the NASA meeting. But he considers it a prudent political exercise. "I would say it is like jogging - something you do to keep the body healthy," he says. In Everitt's view, such political common sense is in painfully short supply in the scientific community. If scientists today studied the men and women who oversee their federal funding with the same care given to analysis of technical data, Everitt says, researchers would not have so much trouble maintaining public support for their projects.
"Put yourself in the shoes of one of these congressional staff people," Everitt says. "They are desperately overworked. They are going to be seeing maybe 10 people in a day. There must be a reason they will decide you are one of the people they want to help. What constitutes that is a very subtle question, I would say. I think one of the factors is to actually realize the people you are talking to are real human beings."
Certainly, Everitt has done his best to make any encounter with him memorable. His curling mane of long hair evokes comparisons with Einstein's famous frizz. His cultured British accent lends a persuasive melody to his explanations of relativity's place in the federal budget. His air of aristocratic geniality invites confidence. "Knowing how well he had done in terms of working with Congress, you think of a guy in a sharp suit or the guys in Gucci loafers you see lobbying Congress," says Giovane at NASA. "That is not Francis. He looks like Einstein, maybe intentionally."
The project has been threatened with cancellation seven times - more times than almost any other project in the agency's history, NASA officials acknowledge. Yet it has survived where many other more widely supported projects have been scratched, due in no small measure to Everitt's political acumen.
As a study in the anthropology of science, the project illuminates the conflicts that arise from the competition for dwindling federal research funds and the manner in which the organizational structure of a research agency can affect the progress of science itself.
The Gravity Probe B scientists say part of the reason they have been forced to defend the project so often is that NASA itself has no natural home for a fundamental physics experiment like theirs, leaving it more vulnerable to advocates for other space science programs trying to preserve their own budgets.
"All the astrophysicists were very sympathetic," Everitt says wryly. "They would all love to see the program go, provided it goes after all their programs have gone."
Over the years it has been in development, the project has stirred enough uneasiness in some space science circles that it has been subjected to repeated formal, independent scientific reviews. In each instance, its scientific underpinnings have been endorsed, as the reports from NASA and the National Research Council show.
"The Gravity Probe B project has been reevaluated by the science community several times - more than any other project the agency has ever done - simply because of the gee-whiz nature of the science and the oh-gee-whiz of all the technical advances that have to be in place for this thing to work," says Urban at Marshall. "The precision of just about everything on this mission is unprecedented."
Nonetheless, skeptics believe that Gravity Probe B is a project - conceived only a few years after Sputnik was launched - that has outlived any early doubts about Einstein's theory.
It is, they contend, a project kept alive by skilled political maneuvers, draining scarce tax dollars from more deserving space science endeavors at a time of severe financial austerity. Indeed, even though the space agency today is emphasizing small, inexpensive science missions, Gravity Probe B remains one of the most costly space physics missions that has ever been undertaken.
In any case, the proposed test of relativity, critics argue, simply is too complex for its results to be believable and the probe's tolerances too unforgiving to perform as promised in the rigors of space.
The project's survival hung in the balance most recently last year, when NASA suspended $50 million in project funding while a panel of a dozen academics from the National Academy of Sciences led by Princeton Nobel laureate Val Fitch aired misgivings about the project's scientific merits.
When a majority of the scientists on the panel concluded that "GPB is well worth its remaining cost to completion," NASA restored the project's funding. Agency officials allocated $75 million in August to keep the project moving toward its launch date.
Despite its endorsement, the panel still had many reservations about the sheer complexity of the endeavor Stanford was undertaking. "Nevertheless, the extraordinary experimental requirements and the impossibility of ground tests of some critical systems at the necessary level of accuracy introduce significant risks," the panel warned.
"A majority of the task group believes that GPB has a reasonably high probability of achieving its design goals and completing the planned measurements. However, based on their experience with complex experiments on the ground, several members remain skeptical.
"The task group notes in any event, should the GPB experiment be completed successfully but yield results different from those predicted by general relativity, the scientific world would almost certainly not be prepared to accept them until confirmed by a repeat mission."
The questions that dog Gravity Probe B in some instances go beyond issues of technical competence to reflect the deep faith the scientific community at large has invested in Einstein himself. An internal NASA memorandum that surfaced in 1991 summed it up succinctly: "There is an unresolvable philosophical difference in how scientists view this mission."
George Keiser, a senior research associate who is the Stanford project's chief scientist, says, "General relativity is in some ways quite different from other aspects of physics because a large number of people have quite a bit of confidence in general relativity, partly because of Einstein's personality and partly because it is such an elegant theory.
"Einstein inspires trust. He was a brilliant physicist. He has such a reputation that any experiment which contradicts his theory immediately raises questions." To anticipate those questions, Keiser says, "what we have been trying to do is make sure we have enough cross-checks and to have a very high degree of confidence in our experimental results."
In an act of sustained genius that forms the raw material of a modern scientific legend, Einstein, between his 25th and his 38th birthdays, basically rebuilt the entire universe in his mind. He called his theory of gravity, published in 1916 when he was 37 years old, "the happiest thought of my life."
Overturning centuries of conventional wisdom about the fundamental laws of nature, Einstein conceived of a universe in which gravity is not a force so much as a distortion in the very fabric of space caused by a massive object - a sinkhole in the celestial quagmire. A planet or star churns that invisible fabric as it rotates, dragging space and time around it like a pinwheel.
It was the product of a thought experiment, he later wrote, in which he brooded on the plight of a man falling from a building.
"If one considers an observer in free fall, for example, from the roof of a house," Einstein wrote. "There exists for him during his fall no gravitational field - at least in his immediate vicinity."
From that deceptively simple starting point, he opened a door into a weird realm of black holes, time warps and superstrings.
Definitive tests of general relativity were beyond the science of his day, but his equations were so compelling to other scientists that his theory won almost immediate acceptance. So confident was he in the rightness of his insight that in a divorce settlement with his first wife he promised to split the proceeds from the Nobel Prize he felt certain it would help him earn. Indeed, in 1921 - three years after the divorce became final - he was awarded the Nobel Prize in physics.
In the years since, researchers have labored diligently in experiments of such bewildering complexity that it is easy to conclude that, in the matter of relativity, Einstein had the easy part.
To test general relativity, scientists have, among other things, pondered variations in the orbit of the planet Mercury, measured microwaves as they warp around the sun, bounced signals off Mars and the moon, monitored the radioactivity of superdense stars and studied the attractions between the stellar partners of a binary pulsar.
The Stanford experiment - decades in the making due to its unprecedented precision - entails the first direct measurements of several relativity effects.
A FAINT BREEZE CAN RUIN IT ALL
On one point at least, the project's backers and detractors agree: Gravity Probe B is science at its most fundamental.
The relativity mission entails some of the most sophisticated aerospace engineering and applied physics of the past two decades, yet at the center it is no more complicated than a spinning crystal ball.
At the heart of the relativity experiment are four supersensitive, superchilled gyroscopes, which fit into a block of fused quartz. Engineered to be almost completely free from disturbances, the gyroscopes will form an almost perfect space-time reference system as they orbit Earth within the supercooled probe. The rotor of each gyroscope is a polished sphere of electrically neutral quartz crystal about the size of a ping-pong ball.
To ensure the accuracy of the gyroscope, "you have to make the most perfectly spherical thing," said Rex D. Geveden, who oversees the gravity probe work at the science and applications project office at the Marshall Center.
As far as anyone knows, Stanford's quartz spheres are the smoothest, roundest objects ever made. Polished within 40 atomic layers of a perfect sphere, they are so smooth that if they were they the size of Earth, the tallest mountain would be barely six feet high.
Stanford researchers - among them Sasha Buchman, who is responsible for manufacturing and verifying the gyroscopes, and technician Thorwald van Hooydonk - were so successful that the gyro rotors they fabricated have been adopted by the National Institute of Standards and Technology as the density standard for the quartz materials from which they were sculpted.
Each rotor is suspended within a near-perfect vacuum in a housing that leaves only 5/10,000ths of an inch clearance. Jets of helium gas, traveling at the speed of sound, puff the gyros up to a speed of 10,000 rotations a minute. At that scale, even the most minute contamination would be disastrous to the experiment.
"If you get a particle of half a milli-inch, it can jam the whole gyro and it will come to a screeching halt," says co-investigator John Turneaure.
Once in orbit, the four gyroscopes - two spinning clockwise and two spinning counter-clockwise - are aligned with the star Rigel in the constellation Orion. A telescope aboard the probe will keep the gyroscopes precisely pointed toward the star. Therein lies the test.
Under the laws of motion that Newton formulated, the axis of each spinning gyroscope should stay pointed at the guide star indefinitely. But if the universe works as Einstein predicted, the gyroscopes should be pulled out of alignment ever so imperceptibly as space and time curve around the massive planet that is rotating below.
If Einstein is right, the gyroscopes should tilt slightly as they spin, in a movement called precession that is like the wavering circle described by a child's top as it twirls. The geodetic effect causing the precession is so slight that it would take 200,000 years for the axis of the gyroscope to drift in a complete 360-degree circle.
If the Stanford scientists can even measure the effect, that by itself will be no mean feat because it has to be done to within one-thousandth of an arc-second in a year - an accuracy equivalent to measuring the width of a human hair as seen from 10 miles away. (An arc-second is the unit of measurement based on the angle the sun moves through the sky in 15 seconds of time.)
The gyroscopes should also measure a previously undetected effect predicted by Einstein - the gravitomagnetic field generated by the spinning Earth. That effect should also cause the gyroscopes to tilt at the infinitesimal rate of 44 milli-arc-seconds a year.
With the probe traveling in a polar orbit as planned, the tilt caused by the geodetic effect would be at a right angle to the tilt caused by the gravitomagnetic effect, allowing both to be measured with sufficient precision to form a compelling test of general relativity.
"To say we are not nervous would be foolish," says Buchman. "One of the reasons this program took quite so long was all the tender loving care we put into development and testing to understand the system and get out all the bugs."
In 1993, NASA dropped a space shuttle mission that might have helped check out the equipment in space, but the gyros have proved themselves so far in more than 90,000 hours of ground tests.
The perfection of the spheres is only a first step, however.
The quartz rotors pose a second, equally daunting test of ingenuity: How can researchers measure the direction of spin of an unblemished sphere without disturbing it or being able to see it? For that matter, how can they keep the spheres from expanding as internal temperatures fluctuate, or protect them from variations in the surrounding magnetic fields?
To do so, the researchers have taken advantage of how materials behave at low temperatures.
Each sphere is coated with superconducting niobium and chilled to 2.5 degrees Kelvin, within a few degrees of absolute zero (minus 456 degrees Fahrenheit). That permits the balls to be suspended electrically.
Any changes in the tilt of the gyroscopes' spin axes can be measured indirectly by detecting changes in the direction of the magnetic field surrounding the spheres with superconducting sensors that do not exert any unwanted force on the rotors. The low temperatures also help to stabilize the onboard telescope and shield the entire experiment from outside magnetic interference.
To keep the gyroscopes at the proper temperature in space, the entire package of instruments will ride inside what essentially is a thermos bottle, called a dewar, brimming with 640 gallons of some of the coldest liquid known to science - superfluid helium. The dewar for Gravity Probe B - 10 feet long and 7 feet wide - is the largest ever designed for space flight.
"They need an extremely low magnetic field, lower than anything achieved on Earth. The temperature has to be held constant to ten 1/1,000th of a degree Kelvin," says Richard T. Parmley, who is guiding Lockheed's work on the dewar. "Everything has to be incredibly stable. As temperatures change, materials change. When you get down to these temperatures, things are incredibly stable."
But every solution creates a problem of its own.
When Stanford researchers conceived the idea of supercooling their probe, no one had ever used liquid helium in a satellite. To control so much liquid helium in orbit is yet another demanding challenge.
The helium is also used to power the 16 thrusters that keep the probe from rolling or pitching in orbit. If uncorrected, even the faint breeze stirred by the solar wind could blow the spacecraft off course. That is why it must be kept so precisely.
"We can't have any distur-bances," Parmley says. "The helium gas is a very smooth and undisturbing method of control."
There was simply no way to start with the kind of engineering sophistication demanded by the relativity mission. While the concept of the experiment was sound, in 1960 the technology did not exist to implement it. So the Stanford team worked up to it by designing, building and testing a series of prototypes of all the key elements of the spacecraft, in order to master their complexity.
"The real challenge," says Everitt, "is putting together all these different technologies and making them play together."
Asked to pick out the single most important innovation among the dozens that have gone into Gravity Probe B, Parkinson was momentarily at a loss for words.
His answer goes to the heart of the nature of a scientific endeavor:
"More than anything it is the continuity of people and the time - a handful of researchers who kept plugging away," he finally replies. "There are certain technology developments that take time, rather than lots of people. This project has been going at Stanford since the early 1960s. The persistence with which this has been pursued is amazing.
A review of project personnel records revealed the human capital invested in the experiment: Daniel DeBra has been working on the project for 29 years; Keiser, 14 years; Parkinson, 9 years; John Lipa, a quarter-century; and Everitt, 31 years, to name only a few.
"When they conceived this project, they thought it was a five-year deal, not a 30-year deal," Parkinson says. "When you are exploring the unknown, you can't predict how long it will take. Where it is taking you is not always obvious."
FOOLISH OR DAUNTING CHALLENGE?
In the months to come, the pace of the project will accelerate. The idea conceived so long ago takes its final form in the curious circuits, baffles, rotors and shielding of an operational spacecraft. In the not so distant future, technicians will marry the probe to the two-stage Delta rocket that will lift it high enough to make its final rendezvous with Einstein's theory. Once the probe reaches orbit, technicians and engineers will spend 40 days testing its systems to ensure that the probe survived the shake, rattle and roll of the rocket flight. Only then will the experiment com-\mence, revealing a corner of the fabric of space and time for human inspection.
It is easy enough to imagine a Stanford physics class a century from now poring over the results of Gravity Probe B. But what will be the lesson those students find in that text that once a group of Stanford researchers were foolish enough to try and rewrite Einstein or that a group of scientists and engineers set themselves one of the most daunting technical challenges of their day? For the ultimate importance of a project like Gravity Probe B may not be found in the telemetry beamed from orbit or from the formulas that measure the warp of space and time. Rather, it arises from the sheer difficulty of the scientific challenge the experiment posed and the manner in which it stirred the technical imaginations of the generation of men and women who labored to overcome it. ST
Robert Lee Hotz is an award-winning science writer for the Los Angeles Times.