energy and mass again

Just a further thought.
Einstein said that energy and mass are equivalent. What if they are the same, just one on thing, which we have not successfully identified and characterised? This would make the search for what provides mass redundant.
It occurs to me that the great edifice of modern physics is, like the Ptolemaic system in its later manifestations, an elaborate mathematical model that works well enough with observation, whilst remaining founded on a totally false premise.