Atomic clocks prove the stability of a fundamental physical constant
Are the fundamental constants really constant? Recent investigations carried out at the Physikalisch-Technische Bundesanstalt (PTB) have shown that one essential fundamental constant – namely the mass ratio of protons to electrons – can have changed only by a maximum of one part in a million over the age of our solar system (i.e. extrapolated over approx. 5 billion years). Previously, scientists deemed the possible changes to be twice as high. To obtain this result, physicists from PTB compared caesium and ytterbium atomic clocks with each other for 7 years. Their results, together with those of a similar experiment carried out at the British metrology institute NPL (National Physical Laboratory), have been published in the current issue of the journal Physical Review Letters.