Combining the Constants

By: David Bradley

Professor Ted Haensch of the Ludwig Maximilians University, Germany explained how precision spectroscopy carried out on the superficially simple hydrogen atom can yield incredibly accurate values for the fundamental constants, such as the Rydberg constant, which determines the precise scale of atomic spectra and is one of the cornerstones of the system of fundamental constants. Moreover, such studies allow scientists to undertake what he described as stringent tests of the fundamental laws of nature.

Haensch explained that the scientific quest for ever-increasing precision has provide the impetus for some rather dramatic advances in the art of measuring the frequency of light. Laser technology, for instance, has advanced to the point at which femtosecond (billion billionth of a second) pulses are possible and exploited in devices that can compare optical frequencies with unprecedented precision. Again, one of the major draws for developing such advanced technology is the possibility of detecting changes in the fundamental constants as time passes.

By comparing the absolute frequencies of light produced by different fundamental sources at one point in time and then again several years later these precision tools should reveal whether there is any variation. The resonance of photons in the ultraviolet, the so-called sharp ultraviolet 1S-2S two-photon resonance was determined by researchers in 1999 and again in 2003 using the kind of ultra precise microwave frequency caesium atomic clock mentioned by Salomon (see "Timing is everything") for comparison.

Haensch discussed how these tools and measurements have set new laboratory limits for determining the possible slow variations of fundamental constants. By comparing optical resonances also in single ions of mercury and ytterbium with a caesium clock, researchers in different laboratories have now confirmed that any changes of the fine structure constant with time remains smaller than 2 x 10 E-15/year. Much more stringent limits can be expected from future comparisons of different optical atomic clocks.

Read on... Condensation Matters