It’s that t-229 can have its nucleus excited using far less energy than regular atomic clock nuclei.
That leads to ultra precise excitation using wavelengths that cancel out some of the fundamental forces within the atom.
That leads to us being able to monitor at a trillion to one ratio those forces based, in part, on mathematical ‘constants.’ In the excited state we can measure if there’s even the smallest variance in force, which in turn may mean that some ‘constants,’ aren’t.
However the real testing of that is in the future as they estimate that a 10 trillion to one ratio is needed.
Theory described a door, research defined the door and possibly what’s behind it, and experimentation just opened the door.