Why do we need electrons and protons

Proton mass to electron mass: the ratio is still considered constant

An important natural constant, namely the mass ratio of protons to electrons, can only have changed by a maximum of a millionth in around five billion years. So far, the maximum possible change was considered twice as high. Physicists from the Physikalisch-Technische Bundesanstalt in Braunschweig compared cesium and ytterbium atomic clocks for their measurement over a period of seven years. Their results were published in the journal Physical Review Letters, along with those of a similar experiment by the National Physical Laboratory in Great Britain.

Comparison of atomic clocks with cesium and ytterbium

A proton is about 1836 times heavier than an electron and, in addition to the electromagnetic force, is also subject to the so-called strong force, which is responsible for keeping the atomic nuclei together. If natural constants should not really be constant, but change over time, this would be noticeable, for example, as changes in the relative strength of these two basic forces - and this in turn would have an influence on the masses of the particles involved.

Nils Huntemann and his colleagues compared a cesium atomic clock with an optical clock in which an ytterbium ion serves as a clock. The mass of the electron determines the frequency of the optical atomic clock, while the proton mass influences the frequency of the cesium clock. If the mass ratio of the atomic building blocks were not constant, the clocks would deviate from one another in a predictable way over time. From their data, the researchers were able to calculate that the mass ratio of proton and electron shows no detectable change. Even the uncertainty remaining in the calculation would, extrapolated to five billion years - the age of our solar system - only make a change of one millionth of a part. Thus, the mass ratio can still be viewed as a universal and stable quantity.