Physical Constants Stay Constant

A clever astronomy observation has established that the physical constants of the Standard Model related to the electron mass, the Higgs field strength, the quark masses, the strength of the strong force, and Planck's constant, have been unchanged to a very high degree of precision for at least 7 billion years, subject to some fairly weak assumptions that are used to put a date on the observation (e.g. the constancy of the speed of light has to be assumed as part of a red shift calculation).

Of course, this is what scientists assume anyway.  But, finding a way to confirm the value of so many physical constants more or less directly, so distantly in the past, is a remarkable feat that quashes a variety of beyond the Standard Model theories.

On the other hand, the constants whose values have been observed to be constant are not necessarily those whose values would be expected to change over time, at least on those time scales. 

Many proposals for changing physical constants either suppose differing values in the extremely high energy environment of the first 0.5 billion years or less after the Big Bang (or even the first few hours or seconds after the Big Bang).  These formulas may formally be functions of temperature or entropy.  More than six billion years after the Big Bang, these physical constants would have long since reached equilibrium levels.

Others proposals for physical constants that vary over time involve physical constants related to gravity and the details of the particle composition of the universe (e.g. a dark matter proportion or Hubble's constant), which arguably arise from the structure of all of space-time and may evolve as the composition and dispersal of the universe changes over time.