YET another fundamental constant of nature may have changed over the last 12 billion years. If confirmed, the result could force physicists to radically rethink their theories and provide support for string theory, which predicts extra spatial dimensions.
This is not the first time such constants have been suspected of changing over the universe鈥檚 lifetime. Most famously, there has been controversy over the 鈥渇ine-structure constant鈥� alpha, which governs how light and electrons interact, with some claiming and others denying that it is changing (快猫短视频, 3 July 2004, p 6).
Now up for grabs is the ratio of the proton鈥檚 mass to that of the electron, known as mu, which is among the most mysterious of the constants. No one knows why the proton鈥檚 mass should be 1836 times that of the electron. Mu governs the strong nuclear force, which holds protons and neutrons together in atomic nuclei and is also responsible for binding the quarks that make up protons, neutrons and most other fundamental particles.
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鈥淯p for grabs is the ratio of the proton鈥檚 mass to that of the electron, among the most mysterious of constants鈥�
Researchers at the Free University in Amsterdam, the Netherlands and the European Southern Observatory in Chile have discovered evidence of variation in mu by comparing the spectrum of molecular hydrogen gas in the laboratory with what it was in quasars that emitted their light 12 billion light years ago. The spectrum depends on the relative masses of protons and electrons in the molecule. 鈥淲e concluded that the proton-electron mass ratio may have decreased by 0.002 per cent in the past 12 billion years,鈥� says team member Wim Ubachs (Physical Review Letters, vol 96, p 151101).
鈥淭his claimed result is very interesting if true,鈥� says Thibault Damour at the Institute of Advanced Scientific Studies (IHES) in Bures-sur-Yvette in France, who co-authored a 1996 paper that found no change in alpha.
Any change in mu would support theories that posit extra dimensions, because as these dimensions evolve, in a manner similar to our expanding 3D universe, the 鈥渃onstants鈥� would in fact vary over both space and time. Or, it could be that we still do not fully understand the proton, which may itself be evolving, leading to the observed variation.
鈥淓xtraordinary claims require extraordinary evidence, and this does not exist yet,鈥� says Victor Flambaum of the University of New South Wales, Australia. 鈥淭his result must be confirmed by other groups before a revolution in cosmology is needed.鈥�
