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How and when did our universe begin?
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How did it get to look like this?
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How will it end?
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Humans have been discussing these questions
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for as long as they've been around
without ever reaching much agreement.
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Today, cosmologists are working hard
to find the answers.
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But how can anyone hope to find
concrete answers to such profound questions?
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And how is it possible to explore and study
something as huge as the universe,
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most of which we'll never be able to reach?
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The answer is light.
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And although light from
distant parts of the universe
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can take billions of years to reach us,
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it carries six unique messages
that, when put together,
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can disclose an amazing amount
of information to astronomers
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who know how to look for it.
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Just as sunlight can be split up
into the familiar rainbow,
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splitting the light from distant objects
exposes different patterns of colors
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depending on its source.
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This distinctive light barcode
can reveal not only an object's composition,
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but also the temperature and pressure
of its constituent parts.
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There's even more we can
discover from light.
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If you've ever stood on a train platform,
you might have noticed
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that the train sounds different
depending on its direction
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with the pitch ascending
when it approaches you
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and descending when it speeds away.
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But this isn't because the train conductor
is practicing for a second career.
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Rather, it's because of something
called the Doppler effect
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where sound waves generated by
an approaching object are compressed,
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while those from a receding
object are stretched.
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But what has this to do with astronomy?
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Sound does not travel through a vacuum.
In space, no one can you hear you scream!
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But the same Doppler effect applies to light
whose source is moving at exceptional speed.
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If it's moving towards us,
the shorter wavelength
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will make the light appear to be bluer.
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While light from a source
that's moving away
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will have a longer wavelength,
shifting towards red.
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So by analyzing the color pattern
in the Doppler shift of the light
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from any object observed with a telescope,
we can learn what it's made of,
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how hot it is and
how much pressure it's under,
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as well as whether it's moving,
in what direction and how fast.
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And these six measurements,
like six points of light,
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reveal the history of the universe.
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The first person to study the light
from distant galaxies was Edwin Hubble,
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and the light he observed was redshifted.
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The distant galaxies were
all moving away from us,
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and the further away the were,
the faster they were receding.
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Hubble had discovered
our universe is expanding,
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providing the first evidence
for the Big Bang theory.
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Along with the idea that the visible universe
has been constantly expanding
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from a densely packed single point,
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one of this theory's
most important predictions
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is that the early universe consisted
of just two gases: hydrogen and helium,
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in a ratio of three to one.
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And this prediction can
also be tested with light.
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If we observe the light from a remote,
quiet region of the universe and split it,
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we do indeed find the signatures
of the two gases in just those proportions.
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Another triumph for the Big Bang.
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However, many puzzles remain.
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Although we know the
visible universe is expanding,
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gravity should be applying the brakes.
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But recent measurements of light
from distant dying stars
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show us that they're farther away
than predicted.
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So the expansion of the universe
is actually accelerating.
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Something appears to be pushing it,
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and many scientists believe
that something is dark energy,
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making up over 2/3 of the universe
and slowly tearing it apart.
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Our knowledge of the behavior of matter
and the precision of our instruments
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means that simply observing distant stars
can tell us more about the universe
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than we ever thought possible.
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But there are other mysteries,
like the nature of dark energy
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upon which we have yet to shed light.