In 2005, exactly one hundred years after its first formulation, Einstein's mass-energy equivalence was tested and shown to be correct to an accuracy of at least 4 parts in 10 000 000!

Measurements carried out at the ILL (in collaboration with the Massachussets Institute of Technology, MIT) made it possible to verify Einstein's equation directly with a precision 55 times more accurate than any previous measurements.

This represents the most accurate verification of the relation between mass and energy ever achieved.

M. Jentschel et al., ILL Annual Report 2005, p.50

Nature, 483-Decembre 2005