It is common knowledge that protons are 1837 times heavier than electrons. Recent astronomical observations by Reinhold and others suggest that this ratio was even bigger in the past. If proven, this would require reconsideration of the most fundamental physical theories, including Einstein's theory of general relativity.

We have shown that the proton-to-electron mass ratio has not changed by more than 2.5 parts per million during the last 6 billion years. We used microwave spectra from the galaxy B0218+357, which is approximately 6 billion light years away from the Milky Way. These spectra include the famous ammonia transitions, which were used by Townes to build the first maser [Nobel Prize 1964]. The frequency of these transitions appears to be extremely sensitive to the mass ratio in question. Comparison of these ammonia lines with the microwave lines of other molecules revealed no relative frequency shift. This allowed us to place the most stringent limit on the space-time variation of the proton-to-electron mass ratio.

Victor Flambaum and Mikhail Kozlov