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 won’t 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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