Page 3 - Nature Of Space And Time

when one goes to quantum theory. Lecture two will be about black holes and lecture three
will be on quantum cosmology.
The crucial technique for investigating singularities and black holes that was intro-
duced by Roger, and which I helped develop, was the study of the global causal structure
of spacetime.

Chronological
+
I
future (p)
.
+
Null geodesic in (p) which
I
does not go back to p and has
no past end point
Point removed
from spacetime
Time
Null geodesics through p
.
p generating part of
+
I (p)
Space
+
De ne I (p) to be the set of all points of the spacetime M that can be reached from p by
+
future directed time like curves. One can think of I (p) as the set of all events that can
be in
uenced by what happens at p. There are similar de nitions in which plus is replaced
by minus and future by past. I shall regard such de nitions as self evident.

.
+
I (S)
+
I (S)
q
+
I (S) q
.
+
I (S)
timelike curve

p

+
All timelike curves from q leave I (S)
.
+
+
I (S) can't be timelike I (S) can't be spacelike
.
_ +
One now considers the boundary I (S)of the future of a set S. It is fairly easy to
see that this boundary can not be time like. For in that case, a point q just outside the
boundary would be to the future of a point p just inside. Nor can the boundary of the

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