"Maybe this alternate-probability time-dimension stuff means something
to you," he said. "Be damned if it does to me."

"Well, as far as we know, we live in a four-dimensional universe," the
colonel started.

The elderly man across from him groaned. "Fourth dimension! Good God,
are we going to talk about that?"

"It isn't anything to be scared of. You carry an instrument for
measuring in the fourth dimension all the time. A watch."

"You mean it's just time? But that isn't--"

"We know of three dimensions of space," the colonel told him, gesturing
to indicate them. "We can use them for coordinates to locate things, but
we also locate things in time. I wouldn't like to ride on a train or a
plane if we didn't. Well, let's call the time we know, the time your
watch registers, Time-A. Now, suppose the entire, infinite extent of
Time-A is only an instant in another dimension of time, which we'll call
Time-B. The next instant of Time-B is also the entire extent of Time-A,
and the next and the next. As in Time-A, different things are happening
at different instants. In one of these instants of Time-B, one of the
things that's happening is that King Henry the Seventh of England is
furnishing ships to Christopher Columbus."

The man with the odd clothes was getting excited again.

"Zees--'ow you say--zees alternate probabeelitay; eet ees a theory