The Multiverse Contains Numerous Universes 219
The Multiverse Contains Numerous Universes
The theory of the multiverse hypothesizes that there are multiple universes outside of our
own. Some people hypothesize that hyperspace is a receptacle for the universe (that is, space
itself), and they believe that many universes are floating within hyperspace. There are many
different theories about how these so-called parallel universes were formed and how they
are related to our own universe. As the professor said, though, there is no scientific proof for
any multiverse theory, so the kinds of relationships that may exist between universes are
unknown. But many scientists nevertheless entertain the idea that the multiverse may form
a structure larger than the observable universe.
The cosmological principle posits that if viewed from a sufficiently large scale, the proper-
ties of the universe are the same for all observers. This means that there is no special place
in the universe, that the universe will have the same general appearance from any location,
and that the same laws of physics will apply at any location. If we extend our interpretation
of this principle, it would seem logical to assume that there could be countless other uni-
verses; the idea that our universe is unique is then illogical. In other words, if there were a
super-cosmological principle, the idea of the multiverse would not be at all far-fetched. But
philosophically, isn’t it more than a little strange to believe that other universes must exist?
Needless to say, this conjecture has its share of critics as well.
The Edge, Birth, and End of the Universe...
The degree that space bends is called curvature. When we say “space,” we mean everything
we consider to be in our universe: planets, stars, gas, comets, and even energy bends. In the
last chapter we talked about the potential shapes of our universe—let’s explore that idea a
bit more, revisiting the idea of positive curvature.
If the universe has positive curvature, a spaceship that aims for the edge of the universe
and continues proceeding “forward” will eventually return to its original location. Although
we can say that this will happen because space is curved, understanding what that really
means can be tricky. So let’s try to explore this idea.
Why Might Space Be Curved?
Curvature in three-dimensional space can be difficult to comprehend. Let’s begin by con-
sidering two-dimensional space instead. Two-dimensional space is like a world that exists
entirely on an infinite sheet of paper, as in Figure 5-1. The position of every object in this
world can be represented by using two coordinate axes.
Since that graph does not give us the feeling of “space,” let’s try to view our two-
dimensional model in three dimensions, as in Figure 5-2.
From this perspective, we can see the two-dimensional plane is a flat world, like a
board. If we assume that this world has two-dimensional inhabitants, it won’t matter to
them whether or not their world is bent in three dimensions. If the graph paper is curved,
folded, or crumpled up into a ball, it will make no difference to them, since the world that
is indicated by the x- and y-coordinates will remain the same. The inhabitants will not
notice the bending of that space—or at least they won’t notice without traveling very long

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