The Einstein Test
By Frank Kuznik
If the gods of physics smile upon Francis Everitt, sometime before the end of this decade four near-perfect quartz spheres spinning away in supercooled isolation 400 miles above Earth will experience an infinitesimal change in the direction of their spin. It will be a change so absurdly small- the width of a hair is huge by comparison- that for a long time it was thought impossible to measure. No less audacious is what Everitt hopes to prove-or disprove-by quantifying this minuscule movement: Einsteinís general theory of relativity.
Itís an undertaking that, not surprisingly, has been decades in the making, and it has drawn some of the brightest thinkers in the fields of physics and engineering. It has also attracted its share of criticism, both from the scientific community and from NASA, which is providing most of the funding. Nonetheless, project director Everitt has managed to counter every challenge with compelling evidence of the programís merit. To put it plainly, Everitt is poised to either confirm or overthrow the entire foundation of modern cosmology.
Dramatic as the venture is, youíd never guess as much from a quick look around the projectís main offices. The effort is headquartered in an oversized construction trailer--a "modular pavilion" in Caliorniaspeak--wedged into a corner of a parking lot adjacent to Stanford Universityís science and engineering buildings. The trailer hums with a lively mix of physics and engineering professors and graduate students. The former are mostly congenial middle-aged men in sport shirts who wax enthusiastic about magnetic torques and gyroscopic drift rates the way most men do about sports; the latter are socially awkward savants in T-shirts and shorts quietly hunched over computer screens. A total of 100 Stanford staff and students work on the program, which is called Gravity Probe B (Gravity Probe A was a 1976 experiment in which scientists tested the general theory of relativity by comparing the rates of two ultra-precise clocks, one launched into space and one kept on the ground.)
The guts of the GP-B project are crammed into two nearby lab and office buildings, with most of the testing and assembly of the payload being done in what was the first electron linear accelerator, now a series of clean rooms and a maze of equipment, wires, and computers predominantly labeled PROPERTY OF THE U.S. GOVERNMENT. Albert Einstein hovers over the entire scene like an ethereal guru, his visage gazing out from pictures on the walls, books covers, GP-B T-shirts, stationary, even the office phone list. A life-size Einstein poster confronts you when you walk in the back door of the trailer. A stand-up cutout of Einstein sits on a shelf in Francis Everittís office, looking over the GP-B directorís shoulder as he talks to visitors.
Everitt is 58; he wears his black and silver hair down to his shoulders, and he sports a bushy Einsteinian mustache. Speaking in an authoritative British accent, he says, "If you ask me to speculate-Will we confirm or will we deny general relativity? -I must say Iím an experimentalist; all Iím interested in is the truth."
Isnít that rather too modest?
"Well, surely itís the right kind of scientific modesty in this circumstance," he replies. "If I were completely modest, or if any of us were completely modest, we wouldnít do an experiment of this kind. But on the other hand, you know, we are undertaking a rather difficult enterprise, which seems worthwhile from many different points of view."
In a nutshell, what the experiment will attempt to do is measure two effects that Einsteinís general relativity theory predicts. That theory contradicts Newtonís vision of gravity as a force instantaneously traversing great distances and redefines it as a field that warps the space-time fabric. If space and time are woven together the way Einstein envisioned, then the shape of that fabric should be affected by the gravitational forces exerted by rotating bodies. A comparatively small body like Earth wonít affect the space-time fabric very dramatically; nonetheless, GP-B will try to determine if Earth is exerting the two primary effects Einstein hypothesized. The first is the geodetic effect, the degree to which a planetís mass bends space-time. The second is frame-dragging, the degree to which a planetís rotation drags space-time around. Both should be observable in fractions of a milliarc-second, aptly described by one graduate student as "a gnatís whisker of a measurement."
The instrument the GP-B team has devised to detect these effects is basically a large thermos bottle, with 400 gallons of supercooled helium surrounding a nine-foot-long cylindrical "probe." The probe consists of a telescope, which keeps the instrument precisely pointed at a guide star, and four gyroscopes, each a fused quartz sphere about the size of a Ping-Pong ball and ground to specifications better than one one-millionth of an inch. Each gyro will be positioned in a quartz housing containing a superconducting loop. Any change in the direction of a gyroís spin will produce a change in the direction of the sphereís magnetic field that the loop will detect. The entire payload provides a high-vaccuum, lead-shielded environment with a temperature near absolute zero. The idea is that if the gyros are sufficiently isolated from such factors as heat, electrical charges, and magnetic fields, any change that occurs in their spin direction can be attributed to the curvature of Einsteinís postulated space-time fabric.
GP-B began as a conversation in the late 1950s between three Stanford scientists: Leonard Schiff, William Fairbank, and Robert Cannon. "The original idea was Leonardís," says Cannon, the only on of the three still alive. "He thought it was only a gedanken experiment-something you think through but never physically do. Fairbankís contribution was to suggest we do this at zero degrees Kelvin, where everything is supposed to be perfect. Mine was to say we should go into orbit, where we could probably get the gyrosí weight down to about a millionth of their Earth weight."
Francis Everitt arrived at Stanford in 1962 as Fairbankís protégé. Over the next five years a working model of the experiment began to emerge, but the problems seemed insurmountable. How could one stabilize an extremely sensitive gyroscope in an orbiting satellite, then keep it near absolute zero for the year or more the experiment would take? How could it possibly be kept free of disturbing outside influences during that time? And assuming all that could be done, how could one ultimately measure submicroscopic changes in the direction of its spin? Everitt recalls the reaction of one contractor NASA hired to check out the projectís feasibility: "These guys have got to be kidding."
The solutions evolved over the next two decades (see "The Methuselah Project," February/March 1987). Of considerable help was the development of a system the instrument uses to compensate for even the faintest trace of drag from the Earthís atmosphere. The system relies on a quartz sphere (identical to one of the gyros) that is kept shielded from external accelerations in a cavity near the spacecraftís center of mass. Because it is so well isolated, the sphere follows an ideal gravitational orbit; the spacecraft, sensing the reference sphereís position, will continually apply thrust forces to "chase after" the sphere, and thus end up moving in a near-perfect orbit itself.
More than a dozen technologies and engineering methods have emerged from the GP-B program, as well as 44 Ph.D.ís, five engineering degrees, and 12 masterís degrees. With most of the conceptual and technical hurdles behind them and the launch of the instrument tentatively scheduled for 1998, the project team is now working on refining individual components-for example, nudging the quartz gyroscopes--already the roundest object ever made--a few ten-millionths of an inch closer to perfect sphericity, and integrating them into a working whole.
That approach is itself noteworthy. Space hardware is often designed and built direct from drawing board to finished product, using components and systems with some flight history. GP-B doesnít have that luxury-nor does it have any margin for error. "This is not a straightforward engineering task," says John Turneaure, a co-principal investigator on the project. After working out the design concept, the team developed small portions of the hardware and demonstrated that each would work. Next, they put these pieces together in small groups for subsystem testing and finally assembled the subsystems in order to test the workings of the complete instrument.
In practical terms that means the team has had to build, test, and refine two prototypes of the GP-B probe that will never even fly in space. A scaled-down version of the probe, designed to test the gyroscopesí performance in low gravity, is scheduled to fly on the shuttle in 1995.
Then thereís the nightmarish "Gravity Probe B Error Tree" to consider. Thatís a poster that shows 177 boxes representing factors that could affect GP-Bís final measurements. On a mission where a random gas molecule in the instrument or too much sloshing of the liquid helium could queer the whole thing, the tolerances for each of those 177 factors must be excruciatingly fine to guarantee valid results. Says science mission project manager Jeremy Kasdin, whose office displays the poster, "The idea is to make sure weíve tracked all the errors, understand them, and can drive them down." But always there is the overarching question: What if the gyroscopes get rocked by a disturbance no one had foreseen?
Everitt has obviously fielded this question before. He fairly leaps to the board in his office and launches into an hour-long lecture on the checks, cross-checks, and redundancies built into GP-B, as well as the years he and his colleagues have spent considering the possible effects of everything from cosmic rays to micrometeoroids--at the end of which he say, "So Iíve really just given you flavors, rather than a detailed argument of why I think the results of this experiment will be very believable."
This, when you talk to the GP-B team, is the hope they profess. Not to overthrow Einstein. Not to lay the foundation for a new theory of the universe. "Iíd like to see experimental results with very low uncertainty and internal consistency which other scientists will believe," says John Turneaure.
But thatís just the problem, say some critics of GP-B, who contend that the vast majority of the scientific community already believes the theory of general relativity. Itís been supported increasingly by sophisticated astronomical observations, say these critics; GP-B is a risky, one-shot experiment that canít be corroborated by another, so why not spend our money in a potentially more productive area?
To which Everitt and his team reply that, accepted or not, Einsteinís theory needs revision. For one thing, it doesnít square with quantum mechanics. Furthermore, while Einsteinís theory of special relativity, which weaved space and time together and produced the famous equation E=mc2, is well verified, his theory of general relativity isnít. Though a few observations confirm certain aspects of general relativity (see "The Case for Einstein,"), important aspects of the theory have yet to be tested by traditional scientific experimentation. Given a chance to do that--to achieve some results that are unprecedented in their precision and others that are altogether unique--why not try?
Everitt sums up his position with a classic bit of British understatement: "Hereís all we can say: That weíre pressing into a new and interesting area where we know eventually something has to be found. We do not know whether GP-B will find that something. But nobody at the moment has any much better ideas about where to find something, so maybe letís press on."
NASAís support for GP-B has run hot and cold. At one time then-administrator James Fletcher reportedly told a subordinate arguing for the program, "Weíve got the technology from it, letís just cancel it." Today more people seem to echo the sentiments of Charles Pellerin, formerly NASAís astrophysics director who says, "Iíd like to see it happen. But Iíve also created forums where we have discussions about it, because I feel the most important thing was to get the truth on the table, and letís all make decisions based on truth."
Thatís meant an endless series of review committees trooping through Stanford, most skeptical about GP-B when they started, almost all laudatory by the time they finished. Perhaps the most threatening group was convened early last year. "This was the committee to end all committees," says program manager Brad Parkinson, a co-principal investigator on the project and, before that, one of the founders of the Global Positioning System. "Everyone who had ever breathed a strong word against us was put on this committee."
The preliminary draft of the committeeís report came down hard against continuing the project. Essentially, the committee was concerned about the possibility that GP-B might yield results differing from earlier experimental tests of general relativity. In such an instance, said the report, it would be hard to conceive of an alternative theory that could account for the discrepancy. In response, Everitt swung into action, sending copies of the draft to over a dozen of the worldís top gravitational physicists. They in turn bombarded the head of the committee with glowing reviews of GP-B. Robert Reasenberg of the Harvard-Smithsonian Center for Astrophysics: "...a scientific and technological tour de force...This superb work offers NASA the opportunity for a significant success..." John Wheeler of Princeton: "...it will cast a brilliant light on marvels of new technology and of new measurement technique destined to have beneficial impact all across the spectrum of human endeavor." And so on.
The committeeís final report ended up backing the project. So did NASAís Space Science and Applications Advisory Committee when it met a few months later. But when the most recent NASA budget got to Congress, GP-B, along with several other research programs, hadn't made the cut.
"I thought our troubles were over--it was really a surprise to me that we were canceled this year," Everitt says with a sigh. "GP-B has been canceled six times since 1980, all in different ways by different people, never by the same person twice for the same reasons."
As a result, Everitt has had to become a lobbyist. Arguably the best known face from Stanford on Capitol Hill, he spends a good chunk of time in Washington every year persuading Congressmen and committee staffers to put GP-B back in the NASA budget. And he has an expert partner in Parkinson, who was nicknamed "Silver Tongue" for his lobbying efforts inside the Department of Defense when he was selling the Global Positioning System.
The two have done an impressive job. For on thing, the latest threat has been overcome, with the program being restored for fiscal year 1993. Says David Gilman, NASA program manager for GP-B, "To show you how strong Congressional support has been, the [previous] two times Congress restored funding for GP-B itís been an outright gift to NASA. Itís really exceptional when that happens."
Still, living and dying every year by the NASA budget sword takes a toll. "I think weíre used to the turmoil," says Parkinson, "but itís a nuisance and a hell of a lot of work for us. And it always puts you in ĎThe Perils of Pauline,í with a train hurtling down the track toward you. Itís a tough problem not to lose your nerve." Everitt seems more disconcerted than nervous. Asked how he would define his job, he smiles wanly and says, "Iím not quite sure what I consider myself. Sometimes I consider myself to be a traveling salesman."
He pauses for a reflective moment. Everittís in classic nutty professor attire today--dress shoes, baggy suit pants, and black long-sleeved Gravity Probe B T-shirt with Einsteinís calm, disheveled visage. He takes off his glasses and says, "I think the thing that kept me going through the dark times was that we were both in the process of inventing some new technology and knowing that if we pulled the experiment off, we would be doing something very fundamental, which seems to me an ideal match. Of course, I never imagined it would take us this long."
When and if GP-B finally get off the ground, the only thing that might rival its results for sheer drama is the projectís 40-year history of technical hurdles, political mayhem, and impossible dreams come true.
The Case for Einstein
While a number of competing theories of gravity have been knocked out of the ring, the theory of general relativity has yet to be irrefutably verified. Still, several observations and experiments over the years have given weight to what physicists consider the most beautiful and profound scientific theory of this century: