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Cosmic alcohol once again confirms the constancy of a natural constant

Posted December 9, 2013
FOM PhD researcher Bagdonaite and FOM workgroup leader Ubachs visiting ALMA on the Chajnantor plateau in Chile. ALMA detected a methanol absorption line at 261 GHz. Credit: Fundamental Research on Matter (FOM)
A research team led by FOM workgroup leader Prof. Dr. Wim Ubachs and Dr. Rick Bethlem has once again demonstrated that the mass ratio between electrons and protons has remained the same over the past 7.5 billion years. The group, which published this conclusion last January in Science, has recently performed a wide range of measurements that confirm their earlier finding. The new results are published on 4 December in Physical Review Letters.

The mass of a proton is 1836.152672 times as big as the mass of an electron. That ratio, and with it the structure of all molecular material, has remained precisely the same for 7.5 billion years – at least within a margin of 100,000th of a percent. Ubachs and his colleagues concluded that when they observed methanol molecules outside the Milky Way last year, using the Effelsberg radio telescope.

Cosmic alcohol

Methanol (CH3OH, the simplest form of alcohol) is sensitive to changes in the proton-electron mass ratio. A small deviation would affect the structure of the molecule and the associated absorption spectrum. An absorption spectrum reveals precisely which radiation frequencies are absorbed by a particle. Each molecule has its own characteristic spectrum. The spectrum of methanol was found to be ideally suited for analysing the natural constant: if the proton-electron mass ratio changes, some lines in the methanol spectrum will strongly shift while others will remain the same (the so-called anchor lines).

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