Einstein's time-strain measured with the highest accuracy worldwide

Speed ​​of lithium ions at speeds up to 20, 000 kilometers per second determined

Dye laser (orange) with pump laser (green) © Sascha Reinhardt, Sergei Karpuk, Christian Novotny, Guido Saathoff
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Time-stretching is one of Einstein's most intriguing aspects of Einstein's theory of relativity because it eliminates the notion of an absolutely valid time: moving clocks tick slower. In the experiment, time expansion was first observed by Ives and Stilwell in 1938 using the Doppler effect. Now physicists have succeeded in measuring the time dilation with unprecedented accuracy.

They used an approach that combines the storage and cooling of lithium ions and the measurement of their optical frequencies with a frequency comb. "The study of time-stretching is not only important for fundamental physics, but has for satellite-based positioning with GPS and many other applications in communication technology a very practical function, " said Professor Gerhard Huber of the University of Mainz. Together with scientists from Heidelberg, Garching and Winnipeg, he reports about the experiment in the scientific journal Nature Physics online.

Since its introduction in 1905, the special theory of relativity of Albert Einstein has been the basis for all descriptions of physical processes. An essential principle of this theory is that the speed of light always remains constant, regardless of whether an observer moves at his own speed or not.

Measurement 100, 000 times more accurate

However, the time in this concept is no longer constant, but slowed down in a moving system such as a rocket in space. This time dilation or time dilation was first measured in 1938 and determined with an accuracy of one percent. The work now published by Nature Physics is 100, 000 times more accurate than this first measurement. "This is a spectacular accuracy, which is also necessary if we want to test the basics of physics, ie the standard model, " says Huber.

Two lasers are on

Presentation of the laser system Sascha Reinhardt, Sergei Karpuk, Christian Novotny, Guido Saathoff

About 20 years ago, the Mainz nuclear physicist, together with Professor Dirk Schwalm from the Max Planck Institute for Nuclear Physics in Heidelberg (MPIK), began this research work on the newly installed TSR storage ring of the MPIK. At relativistic speeds - that's up to six percent of the speed of light or up to 20, 000 kilometers per second - lithium ions are stored as a fine beam and excited with lasers on their optical resonances. These very sharp resonances work like atomic clocks moving with the ions. display

The laser excitation is done with two lasers, which are sent to the ion beam behind and opposite. If both lasers excite the same ions, the proper time of these clocks as well as their speed in the storage ring can be accurately measured. Only with the knowledge of the optical frequencies can the factor of the time expansion, which at the same time describes the mass increase, be determined from the experiments and compared with the known value in the special relativity theory of Einstein. The exact frequency measurement was done in Garching near Munich with an optical frequency comb in collaboration with the team around Professor Theodor H nsch, who was awarded the Nobel Prize in 2005 for the development of this pioneering method.

Special relativity confirmed

"Within a measurement accuracy of one to ten million, the special relativity theory could be confirmed at the TSR storage ring in Heidelberg, " summarizes Huber. The measurement thus joins the series of the review of the so-called standard model of physics, which describes the elementary particles and the forces acting between them, and also the test of the Lorentz invariance, ie the G Existence of special relativity, including. "However, the accuracy achieved so far is not enough to detect deviations."

The employees from Mainz, Sergei Karpuk and Christian Novotny, are now working on an experiment at much higher speeds, which can be achieved at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt with the storage ring ESR. In the first tests, the ions reached up to 34 percent of the speed of light here.

(idw - University of Mainz, 23.11.2007 - DLO)