232 Chapter 5 Our Ever-Expanding Universe
We have already seen that different curvatures of space cause the geometry of a trian-
gle to change (see Figure 5-5). On a flat surface, parallel lines remain parallel, meaning that
the edges of a triangle are straight and the angles of the triangle add up to 180 degrees. On
a closed (spherical) surface, parallel lines converge so that a triangle’s lines bend outward
and the angles of the triangle add up to something greater than 180 degrees. On an open
(saddle-shaped) surface, parallel lines bend apart so that a triangle’s lines bend inward and
the angles of the triangle add up to less than 180 degrees.
The lines of the triangle formed by our observations while looking at an area of tem-
perature fluctuation will conform to the curvature of space and thus determine how the
area we’re observing appears to us. If the universe is flat (W = 1), the image will appear
normal, and the area will measure 1 degree across. A closed universe (W > 1) would bend
the light coming from the area outward, magnifying the image and making the area look
1.5 degrees wide. An open universe (W < 1) would bend the light inward, demagnifying the
image and making the area look 0.5 degrees wide. The WMAP calculations showed that our
universe is indeed flat.
Because we now know that our W = 1, we can determine how much dark energy
makes up the universe. Early calculations showed that W
M
= 0.30, meaning that that the
universe is 30 percent matter. This includes the 5 percent that is normal, baryonic matter
and the 25 percent made up of dark matter. As for the rest of the makeup of the universe,
W
L
gives us how much dark energy makes up the universe. Since W = W
M
+ W
L
and we
know that W = 1 and W
M
= 0.30, simple math allowed astronomers to predict that W
L
=
0.70, meaning that 70 percent of the universe is dark energy. This was later proven by
WMAP when it determined that W
L
= 0.72.
Since only 5 percent of the total mass-energy density of the universe is the baryonic
matter with which we are familiar, 95 percent of the universe consists of things we don’t yet
understand.
Note Scientists project that if the rate of expansion continues to accelerate, we will
eventually enter what’s called a de Sitter universe, one in which everything has been
stretched out so far that there wont be matter in the sense that we know it. No more plan-
ets, stars, or even spread-out particles. The only thing left will be the cosmological constant.
The True Age of the Universe
Now we seem to have a better idea of what our universe really looks like and how it seems
to be changing over time: it is essentially flat and expanding outward. To get a deeper
understanding of what the universe looks like, though, we should also know how old it is.
We’ve talked a lot about the Big Bang, but when did it happen? The estimated age
of the universe (that is, the time since the Big Bang) is 13.7 billion years. This number
has been determined from theoretical calculations and has been verified numerically from
observations that WMAP provides. Other observations also help to confirm the age of the
universe. It makes sense that the universe has to be at least as old as the oldest thing in
it, right? Well, in 2009, the Swift Gamma-Ray Burst Mission observed a gamma-ray burst
that was 13 billion years old! This gamma-ray burst happened when a star that was roughly
200 times more massive than our Sun used up all its nuclear fuel and collapsed into a black
hole. When it collapsed, it created a hypernova, an explosion over 100 times more energetic

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