Maybe I can play the same game with the other known force, which was, at that time, known as the electromagnetic force -- we know of others today, but at that time that was the only other one people were thinking about.
Talvez eu possa jogar o mesmo jogo  com a outra força conhecida, que era, naquela altura, conhecida  como a força eletromagnética, hoje conhecemos outras  mas, naquela altura, era a única força  em que as pessoas pensavam,