, step by step, down
to the present. It would be a lot of hard and very exacting work, but
the result would be worth it." He took a sip from his glass and added:
"Remember, you don't have to prove that the world today would be the way
you set it up. All you have to do is make sure that nobody else would be
able to prove that it wouldn't."

"Well, how could you present that?"

"As a play, with fictional characters and a plot; time, the present,
under the changed conditions. The plot--the reason the coward conquers
his fear and becomes a hero, the obstacle to the boy marrying the girl,
the reason the innocent man is being persecuted--will have to grow out
of this imaginary world you've constructed, and be impossible in our
real world. As long as you stick to that, you're all right."

"Sure. I get that." The plump man was excited again; he was about half
sold on the idea. "But how will we get the audience to accept it? We're
asking them to start with an assumption they know isn't true."

"Maybe it is, in another time-dimension," the colonel suggested. "You
can't prove it isn't. For that matter, you can't prove there aren't
other time-dimensions."

"Hah, that's it!" the sandy-haired man exclaimed. "World of alternate
probability. That takes care of that."

He drank about a third of his highball and sat gazing into the rest of
it, in an almost yogic trance. The plump man looked at the colonel in
bafflement.

"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,