According to Einstein's theory of general relativity, a moving mass should create another field, called gravitomagnetic field, besides its static gravitational field. This field has now been measured for the first time and to the scientists' astonishment, it proved to be no less than one hundred million trillion times larger than Einstein's General Relativity predicts.

This gravitomagnetic field is similar to the magnetic field produced by a moving electric charge (hence the name "gravitomagnetic" analogous to "electromagnetic"). For example, the electric charges moving in a coil produce a magnetic field - such a coil behaves like a magnet. Similarly, the gravitomagnetic field can be produced to be a mass moving in a circle. What the electric charge is for electromagnetism, mass is for gravitation theory (the general theory of relativity).

A spinning top weights more than the same top standing still. However, according to Einstein's theory, the difference is negligible. It should be so small that we shouldn't even be capable of measuring it. But now scientists from the European Space Agancy, Martin Tajmar, Clovis de Matos and their colleagues, have actually measured it. At first they couldn't believe the result.

"We ran more than 250 experiments, improved the facility over 3 years and discussed the validity of the results for 8 months before making this announcement. Now we are confident about the measurement," says Tajmar. They hope other physicists will now conduct their own versions of the experiment so they could be absolutely certain that they have really measured the gravitomagnetic field and not something else. This may be the first empiric clue for how to merge together quantum mechanics and general theory of relativity in a single unified theory.

"If confirmed, this would be a major breakthrough," says Tajmar, "it opens up a new means of investigating general relativity and its consequences in the quantum world."

The experiment involved a ring of superconducting material rotating up to 6 500 times a minute. According to quantum theory, spinning superconductors should produce a weak magnetic field. The problem was that Tajmar and de Matos experiments with spinning superconductors didn't seem to fit the theory - although in all other aspects the quantum theory gives incredibly accurate predictions. Tajmar and de Matos then had the idea that maybe the quantum theory wasn't wrong after all but that there was some additional effect overlapping over their experiments, some effect they neglected.

What could this other effect be? They thought maybe it's the gravitomagnetic field - the fact that the spinning top exerts a higher gravitational force. So, they placed around the spinning superconductor a series of very sensible acceleration sensors for measuring whether this effect really existed. They obtained more than they bargained for!

Although the acceleration produced by the spinning superconductor was 100 millionths of the acceleration due to the Earth's gravitational field, it is a surprising one hundred million trillion times larger than Einstein's General Relativity predicts. Thus, the spinning top generated a much more powerful gravitomagnetic field than expected.

Now, it remains the need for a proper theory. Scientists can also now check whether candidate theories, such as the string theory, can describe this experiment correctly. Moreover, this experiment shows that gravitational waves should be much more easily to detect than previously thought.

Photo: the experimental apparatus. Credits: ESA