Ok, enough about Einstein for now, and back, briefly, to rock ’n’ roll. ;-)
The first known “secular” use of “rock” and “roll” in a recorded song dates to 1922 (!) and was recorded by Trixie Smith: “My Daddy Rocks Me (With One Steady Roll).” The soulful, bluesy recording can be found here, though the date given, 1938, is wrong, and the person depicted is evidently not Trixie Smith, but Bessie Smith.
I guess “rock” and “roll” was used previously in religious hymns, though one must suppose for an entirely different reason. :-) It is pretty obvious from the above-linked recording what THIS song means by “rock” and “roll.”