It speaks to the impor­tance of dis­cov­er­ies in physics over the past few gen­er­a­tions that even the dis­in­ter­est­ed lay­man has heard of the field­’s cen­tral chal­lenge. In brief, there exist two sep­a­rate sys­tems: gen­er­al rel­a­tiv­i­ty, which describes the physics of space, time, and grav­i­ty, and quan­tum mechan­ics which describes the physics of fun­da­men­tal par­ti­cles like elec­trons and pho­tons. Each being applic­a­ble only at its own scale, one would seem to be incom­pat­i­ble with the oth­er. What the field needs to bring them togeth­er is kind of a “grand uni­fied the­o­ry,” a con­cept that has long since worked its way into pop­u­lar cul­ture. In the Big Think video above, physi­cist Michio Kaku explains this sci­en­tif­ic quest for what he calls “the God equa­tion” in about five min­utes. Such an equa­tion “should uni­fy the basic con­cepts of physics.” But gen­er­al rel­a­tiv­i­ty as con­ceived by Albert Ein­stein is “based on smooth sur­faces,” while quan­tum mechan­ics is “based on chop­ping things up into par­ti­cles.” The chal­lenge of bring­ing the two into con­cert has attract­ed “the great­est minds of the …