Page 14 - Unlikely Stories 1

Perils of Scanference

It shows possible and impossible zones for all world lines passing
through one point in space-time. That point is B , in the center lying
0
in a hypersphere of the present—three-dimensional space flattened
to a plane on the diagram; time, the fourth dimension, runs
perpendicular to it. The cones formed by the possible space-time to
which B could be connected flow into it from the past and away
0
from it into the future. That absolute perimeter is formed by the
speed of light, the limiting velocity in space-time. Any point outside
those cones is inaccessible to B : the latter can have no knowledge of
0
the former. Possible world lines are called time-like; impossible ones
are space-like, requiring faster than light movement through space-
time. Do you follow that?
Gen. Esel: For the moment.
Dr. Silberfisch: One particular world line we shall call A B C . You
0
0
0
can see that B could have been arrived at from other A points in its
0
past, and proceeded to other C points in its future. Of course, the
farther away that line gets from the vertical in this diagram, the faster
the movement between two points. Electromagnetic signals are
traveling on the surface of the cones: light from the most distant
interstellar objects, reaching us after billions of years, help us
establish the parameters of the past. But that is not relevant here.

Gen. Esel: Thank you. I don’t need a lecture in cosmology.
Dr. Silberfisch: Certainly. Now presuming we are at B , as I said, we
0
can imagine coming to it from any of several A possibilities close to
A0. Similarly, all the subsequent possibilities for B , its C future, if
0
you will, would be clumped around the only one we actually do
experience, called C . All other possibilities for B in the hypersphere
0
0
of C ’s present are simultaneously and automatically excluded, just as
0
going from one C point to another and from one A point to another
are impossible. Each present knows only one past, and can be the
only past known by its future—that is, until Gibbons came along.
Now, look at this second diagram.

13