"But," he said thoughtfully, "what happens if the monopolar field is generated upon a true square wave?"
"A true square wave is impractical."
"You mean because at the moment of transition, the wave front must assume, simultaneously, all values between zero and maximum?"
"Yes," she said, "and it is impossible to have any item operating under two values."
"That is an existent item," said Barden with a smile. "Bringing back H. G. Wells' famous point of whether an instantaneous cube could exist."
"This I do not follow."
"Look, Edith," said Tom patiently. "Any true square wave must have a wave front in which the rise is instantaneous, and assuming all values between zero and maximum for the duration of an instant. An instant is the true zero-time, with a time-quantum of nothing—the indivisible line that divides two adjoining events. Just as a true line has no thickness.
"Now," he went on, "generating the monopolar field on a true square wave would flop us from one field to the other in true no-time. At that instant, we would be existing in all values from maximum negative to maximum positive, at the same time at zero—but not truly assigned a real value. Therefore we should not stop.
"However," he went on, "that is an impossibility because the true instant of no duration is impossible to achieve with any mechanism, electrical or otherwise. However, the fields set up to make possible this square wave do permit the full realization of the problem. For a practical duration, however small, the value of the wave does actually assume all values from maximum negative to maximum positive!"
She looked at him with puzzlement. "I thought they taught you only this one science," she said.