Probe to test Einstein

After over 40 years of research, construction, and anticipation, and about $500 million spent, Gravity Probe B, the NASA experiment, will finally see launch early next year. GPB, as it is commonly called, will test Einstein's general theory of relativity, notably two effects called "space-time frame dragging" and "geodetic precession."

"We are trying to test, to a very high degree of accuracy, two new effects of Einstein's general theory of relativity," said Prof. Francis Everitt, co-principle investigator of GPB. "For this, we have a gyroscope in orbit and we will look for changes of direction of our gyroscope with respect to a star that is pointed at with a telescope. We actually have not one gyroscope, but four. What happens as the gyros moves through the space around the earth and also as the earth rotates, they move through the distorted space-time around the earth and gradually their direction of spin will change in the direction of the orbit, and as the earth rotates it drags space and time around with it, and we measure these effects."

A gyroscope is simply any body rotating around an axis. At the simplest level, they are toys on a string that don't topple when released; at the most complex, they function as navigational guidance instruments in airplanes, submarines, and here will serve to test one of the revolutions in science of the 20th century.

This experiment is on the scale of the legendary Michelson-Morely ether wind experiment in 1887. That test proved that unlike sound, light does not travel through a medium, a so-called "ether."

"GPB was originally proposed at Stanford by three professors, a theoretical physicist named Leonard Schiff, an experimental physicist Bill Fairbank, and an engineer Bob Cannon," said Parkinson. "When they proposed it, conceptually it's simple; in practice it's incredibly complex."

While the effect in space is greater by several magnitudes, it is still miniscule, which is one of the reasons the project has taken so long to perfect. The frame dragging is expected to change the gyroscope's direction of spin by 42 milliarc-seconds in one year. This is about the width of a human hair as seen from 10 miles away.

The implications of the results will be of great importance to the world of science. If the result differ from Einstein's predictions, there will be a flurry of activity.

"Much of what we understand about the whole universe is based on Einstein's theories, so if they're proven incorrect, there's a lot of fundamental physics that will have to be reassessed," said Cannon. "However, at this point in time, they are generally believed."

Problems arise when Einstein's general theory of relativity, an explanation on the scale of the grand cosmos, and quantum mechanics, an explanation on the scale of the atom, are attempted to be meshed. They should mesh at some level, yet they do not.

"Einstein's general theory of relativity cannot be quantized in any clear way," said Everitt. "When we get down to the quantum level, every theory must be quantized. There are some very deep technical problems with how to [combine relativity and quantum mechanics]. Somewhere, something has to break down. Either Einstein's theory breaks, or else there's something we don't understand about quantum mechanics. No one knows how to get beyond where we seem to be stuck now. Lots of people have interesting ideas, but we don't have the answer."

In fact, this very issue troubled Einstein. He did not agree with Bohr's interpretation of quantum theory and believed it must only be a temporary solution.

"Einstein understood [Grand Unification] and spent the last 40 years of his life trying to find the key," said Parkinson.

Grand Unification is the attempt to create a unified field theory which would combine all known fields, including electromagnetic, gravitational, and weak and strong nuclear. The unified field theory should explain all effects, gravitational and quantum. One of Einstein's greatest concerns was Bohr's explanation of Heisenberg's uncertainty principle. Einstein could not accept that "God would play dice," which is the implication of quantum theory.

According to the uncertainty principle, it is impossible to simultaneously know the precise values of two complementary components, such as velocity and position or energy and time of measurement. Bohr said that this is always the case.

In 1936, Einstein, Podolsky and Rosen introduced the famous E-P-R paradox. Simply, the paradox states that if two identical particles-having the same mass and velocity-are moved apart so far from each other that they can't interfere in any way, and the position of one and the velocity of the other is measured, then the precise position and velocity of the first are known. The uncertainty principle does not hold in this case.

The problem with an experimental test has been obtaining two identical particles. When I discussed this problem with my father, whose major in college was quantum mechanics, we came to conclusion that recent theoretical work by Steven Hawking and others that describe the quantum creation of an electron/positron pair could be used for testing the E-P-R paradox. After creation, the electron and positron fly away with the same speed, but exactly opposite directions. If we will measure the location of one of the particles and the velocity of the other, we will know the exact position and velocity of the first, as it has the same speed as the other, just in the opposite direction.

If the results of GPB confirm Einstein's prediction, his other theories should be reconsidered.

Over the 40 years of the program, much of the time has been spent inventing technology that was necessary for the probe. Various advanced technologies have come out of the GSB project, including tractor guidance, improved GPS navigation, and completely automatic landing of airplanes.

Now, the project has almost reached completion and everyone involved is anticipating the upcoming launch.

The world eagerly awaits the day that Einstein's predictions are verified or disputed. Either way, GPB has been a remarkable project spanning decades and involving hundreds of people. GPB will become another legacy Stanford's long history of challenging the unknown.

NOTE: Published article is an altered and condensed version of the article published in Stanford Daily.