York testing Einstein's theories:
the only Canadian university on NASA-Stanford experiment

By Susan Scott

Prof. Norbert Bartel, Department of Physics and Astronomy

It's difficult to predict whether Albert Einstein would be laughing or crying were he alive today. More than 80 years after the brilliant physicist discovered the theory of relativity, people are still testing it - and a York University astronomy professor is part of this experiment.

In fact, York is the only Canadian university on the research team led by the National Aeronautical and Space Administration (NASA) and Stanford University in California. The Americans are also represented on the team by Harvard University in Massachusetts. Their $1-billion project is called Gravity Probe B. Its mission: to test two previously unverified predictions of Einstein's general theory of relativity. York and Harvard's part of the mission was to identify a "guide star" and to use it to test the theory.

The first part of the mission has been accomplished by the York's threesome of Norbert Bartel, an astronomy professor, Ryan Ransom, graduate astronomy student, and Michael Bietenholz, senior research associate, together with the Harvard team. They identified a star called IM-Pegasi, one that has existed for years in relative obscurity until its elevation to celebrity status by the researchers.

So what were scientists trying to test and how does the guide star identified by York and Harvard researchers fit in? The story begins with the explanation of Einstein's two theories of relativity: special relativity and general relativity. Special relativity weaves space and time together but does not discuss gravitation. This theory says that no signal can be produced faster than the speed of light. It also leads to other phenomena such as changes in the mass and shape of a body with speed, and changes in clock-rates seen by different moving observers.

Bartel explains the clock experiment and others to prove special relativity have been tested over the years. However, Einstein's general relativity theory is another matter. If no signal travels faster than light, how did that explain a theory by Sir Isaac Newton, a physicist who introduced his ground-breaking theory of the universe 300 years ago. Newton stated that gravity is a force transmitted instantaneously over vast distances. So, Einstein had a problem. By 1916, Einstein had developed his space-time theory that gravity was a "field" not a "force" distorting time and space. So each planet in its course, which seems to us to be moving in an elliptic (oval) orbit around the Sun, is really following a straight line, called a geodesic, through curved space-time.

Fast forward to 1959 and another physicist, Leonard I. Schiff, who significantly advanced the debate about relativity. Schiff, based at Stanford University, developed the idea of more accurately testing Einstein's theory using a gyroscope (invented in 1852) in a satellite orbiting the Earth. The gyroscope to be used on the project, as Bartel describes it, is a "rotating ball, partly of metal, about the size of a billiard ball." The underlying principle of a gyroscope, according to Newton, is that rotating systems, free from disturbing forces, such as the impact of meteorites, should stay pointed in the same direction in space. For Newton, space and time were absolutes. A perfect gyroscope set spinning and pointed at a star would stay aligned forever. But, Einstein had a different idea. He believed space-time is indented and may even be warped. A gyroscope orbiting the Earth finds two distinct space-time processes - the geodetic effect and frame-dragging - gradually changing its spin direction.

The geodetic effect follows from Einstein's belief that the Earth indents space-time because of the mass of the Earth. The second effect, frame-dragging, follows from the rotating Earth which warps space-time around it. But, how to accurately test the geodetic effect and frame-dragging? That's where Gravity Probe B, and the team's guide star come in.

Bartel says the Stanford research team began working on plans for Gravity Probe B around 1960. Bartel says he's been involved with the planning for the Gravity Probe B project since the late 1980s when he worked at Harvard with the researchers now working on the project. As part of the Gravity Probe B project, the NASA-Stanford team developed six technical requirements necessary to test these two effects. One of these requirements was the presence of a "trustworthy guide star, a bright properly located star whose motion with respect to inertial (motionless) space is known."

Bartel and his team identified half a dozen "candidates". But, even guide stars are not perfectly "fixed" in the sky. They move around too, so Bartel says his team had to use an even more stable reference to "correct" for the movement of the guide star. What's a more stable reference? Quasars. Quasars are a type of galaxy that are very far away from Earth. While a star is about 300 light years away, quasars are "billions of light years away," explains Bartel. "They are really dim and cannot be seen even with the small telescope on board the Gravity Probe B satellite."

He explains the star also had to emit "radio waves" so that it could be detected by a radio telescope using a process called very-long-baseline interferometry (VLBI). VLBI is a way of combining the information from widely-separated radio telescopes to mimic a single, very large instrument - and give incredibly detailed results.

Finally, using VLBI they narrowed the field to one guide star called IM-Pegasi. Bartel explains that 15 telescopes, positioned around the world at locations in Europe, North America, Hawaii and Australia and all pointing to this star, measured and recorded data on the star's movement. All the data from the telescopes were fed to a central computer at the National Radio Astronomy Observatory in New Mexico. Bartel says this data recording will continue for another few years to measure accurately the star's position and movement. Recently, Bartel's team presented images of their observations of the star at this year's annual convention of the American Astronomical Society.

He says the Gravity Probe B satellite with the gyroscope is scheduled to be launched in October 2000 and will orbit the Earth to be used for the experiments for the next couple of years. Will the experiments prove Einstein's theory correct or not? "That's the $1-billion question," says Bartel.