Notes on Relativity and Cosmology - Physics Department, UCSB

9.3. BEYOND THE HORIZON 251
Below, I have drawn in the curves of constant r so that you can visualize them
more easily. Note that larger r is farther from the center of the diagram, and in
particular farther out along the ‘flanges.’ One flange represents the left exterior,
and one represents the right exterior.
T 0
T
0
0
Y
0
X
0
X
0
Y
The most important thing to notice is that we can once again spot two lines
that 1) are the worldlines of light rays in the 3D flat space and 2) lie entirely
within the curved 2D surface. As a result, they again represent worldlines of
light rays in the black hole spacetime. They are marked with yellow lines on