Certain physical quantities—the fundamental electric charge, the masses of certain particles, the strengths of the basic forces of the Universe—are generally assumed to be constant in time and space. Some of our theories depend on that constancy, but it’s not an absolute certainty: it’s possible that in distant galaxies, the rules might be a little different. They can’t be drastically different, though: observations show that (for example) the hydrogen spectrum appears to be the same 12 billion years ago. A new observation has clarified the constancy of another relation: the ratio of the proton mass to the electron mass, one of the quantities that dictates the structure of all atoms. They found this by measuring the spectrum of methanol, the simplest type of alcohol.

New observations of methanol (also known as methyl alcohol) that absorbed light in a galaxy 7 billion years ago show that it behaves the same as molecules on Earth, to one part in 10 million. The spectrum of methanol depends sensitively on the ratio of the proton mass to the electron mass, considered in most theories to be one of the fundamental constants of nature. In other words, because the spectrum of methanol at a cosmologically significant distance is indistinguishable from that in the lab, at least one fundamental constant hasn’t changed measurably in at least 7 billion years. [Read more…]