Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by infinities that erupt when theorists try to prod their calculations into new domains. Getting rid of these nagging infinities has probably occupied far more effort than was spent in originating the theories.

What's that mean?

if haply your dates of life were conterminant

Whereas in classical physics mass and energy are distinct concepts, on relativistic scales, they become indistiguishable and are replaced by mass-energy.