clifford_a-_pickover_surfing_through_hyperspacebookfi-org

136 surfing through hyperspace
Figure 5.8 A 2-D human on a Mobius strip universe. If the human travels around
the strip, his internal organs will be reversed.
sphere, he returns to his starting point. If he looks ahead, he sees his own back.
If you lived in a hyperspherical universe, you too could return to your starting
point after a long time. If the hypersphere were small, you'd see your own back
while looking forward. As alluded to in the section on extrinsic geometry
(Chapter 1), some cosmologists have suggested that our universe is actually a
large hypersphere. The universe may be finite but with no boundary, just as a
sphere's surface is finite, but has no edge. In other words, our universe may be a
4-D sphere with a 3-D surface having a circumference of the order of 1000 billion
light-years. (One light-year is the distance traveled by light in one year—
about 5,900,000,000,000 miles.) According to this model, what we perceive as
straight, parallel lines may be large circles intersecting at two points fifty billion
light-years away in each direction on the hypersphere (in the same way that longitude
lines on a globe actually meet at the poles.)
If our universe is curved, our space can be finite and still have no edge. It
simply curves back on itself. This means that if we fly far through space, we
could never encounter a wall that indicates that space goes no further. There
could be no sign that reads:
GO BACK. SPACE ENDS HERE.
The idea that our universe could be the surface of a hypersphere was suggested
by Einstein and has startling implications. 1 As an analogy, again consider
a 2-D Flatland on the surface of a sphere. If an inhabitant started to paint Flatland's
surface outward in ever-widening circles, he would reach the halfway
point when the circles would begin to shrink with the Flatlander on the inside;
eventually he would paint himself into a little place of the universe, at which