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2Physics Quote:
"Today’s most precise time measurements are performed with optical atomic clocks, which achieve a precision of about 10-18, corresponding to 1 second uncertainty in more than 15 billion years, a time span which is longer than the age of the universe... Despite such stunning precision, these clocks could be outperformed by a different type of clock, the so called “nuclear clock”... The expected factor of improvement in precision of such a new type of clock has been estimated to be up to 100, in this way pushing the ability of time measurement to the next level."
-- Lars von der Wense, Benedict Seiferle, Mustapha Laatiaoui, Jürgen B. Neumayr, Hans-Jörg Maier, Hans-Friedrich Wirth, Christoph Mokry, Jörg Runke, Klaus Eberhardt, Christoph E. Düllmann, Norbert G. Trautmann, Peter G. Thirolf
(Read Full Article: "Direct Detection of the 229Th Nuclear Clock Transition"

Sunday, April 23, 2006

Proton-Electron Mass Ratio

Spectra of Hydrogen and Mercury

New measurements of starlights suggest that the ratio of the proton's mass to the electron's mass has increased by 0.002% over 12 billion years. The spectra of hydrogen gas as recorded in lab is compared with spectra of light coming from hydrogen clouds billions of light years away when the universe was in its youth.

Molecular hydrogen absorbs light of specific wavelengths, and the resulting spectrum of "absorption lines" uniquely identifies Hydrogen atom by the 'bar' code made up of such lines. The positions of the lines depend on the ratio of the mass of the proton to the mass of the electron. Of course, one needs to carefully take into account the effect of the expansion of the universe which shifts these lines from higher (ultraviolet) to lower (visible) frequency.

The researchers have reported in Physical Review Letters this week that the mass-ratio of proton and electron (the ratio is about 1836 and is denoted by the letter mu) has increased by about 20 parts per million over the past 12 billion years. The proton-to-electron mass ratio figures in setting the scale of the strong nuclear force.

More studies of spectra of Hydrogen gas from distant galaxies are needed to confirm whether the mass ratio has indeed changed.

Here is the link to the abstract of the paper in Physical Review Letters.

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