The First Nuclear Clock Will Test if Fundamental Constants Change | Quanta Magazine

The new measurement is millions of times more precise than the others.

It marks the end of a marathon search for the exact laser frequency needed to induce the nuclear clock transition.

Researchers will now try to use the transition to observe whether the laws of physics vary over time, as predicted by many theories of fundamental physics.

Researchers observed that reversing the intrinsic angular momentum, or “spin,” of thorium-229 ’s outermost neutron seemed to take 10,000 times less energy than a typical nuclear excitation.

No other isotope has a nuclear transition in the energy range of conventional lasers, which can deliver the energy to trigger the transition reliably and precisely.

Researchers have found the energy needed to excite the nuclear clock transition in thorium-229 .

The state's energy is far more sensitive to variations in the fundamental constants than that of any atomic state.

Scientists will need to improve the precision of their measurements even further to notice changes more subtle than those already ruled out by conventional atomic clocks.