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ROWE: There's a mystery at
the very heart of the universe.
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We don't know how old
the cosmos is.
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OLUSEYI: Understanding
the age of the universe
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is fundamental to understanding
the universe at all.
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It's at the heart
of everything.
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ROWE: It's more than just
celebrating a birthday.
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PLAIT: We want to know
how much mass is in it,
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how much energy is in it,
how it behaves.
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We have to have this number
nailed down.
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MINGARELLI:
The age of the universe
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enables us to not only
understand where we came from,
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but potentially,
the fate of the universe,
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what will happen millions and
billions of years from now.
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ROWE: But our quest to discover
the age of the universe is
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starting a war.
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SUTTER: Usually Nature
just whispers to us.
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Now Nature is screaming
in our ear
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that we're doing something
wrong, and that's exciting.
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ROWE: We think the universe
started with a bang.
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Everything that has ever
existed is squashed up
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in this space smaller
than a pinhead,
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and all of a sudden,
space just starts expanding
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everywhere at once.
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ROWE: The idea that
the universe grew from
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a ball smaller than a pinhead
is hard to understand,
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but figuring out
when it happened
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sounds like it should be
more straightforward.
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It seems like a simple
question right?
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But it turns out,
getting
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the age of the universe is
pretty tricky.
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ROWE: Scientists have
just a single fact
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as their starting point --
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the universe is expanding.
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When people realized
the universe was expanding,
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they thought they finally had
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a way to estimate the age of
the universe.
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Take the universe now
and run it backwards in time.
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Things get closer and closer
until they come
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to a single point.
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That time to that point is
the age of the universe.
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ROWE: The expansion rate is
so important,
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it's been given its own name --
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the Hubble constant.
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SUTTER: The Hubble constant
is the present day
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expansion rate of
the universe.
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It is a key ingredient
to understanding
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the entire expansion history
of our universe and its age.
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ROWE: Scientists
discovered a strange
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radio signal
permeating the cosmos.
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It's the remnants of ancient
light from the early universe.
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We call it the cosmic
microwave background, or CMB
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for short.
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The cosmic microwave
background radiation is
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simply the afterglow
of our Big Bang,
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the way the universe looked
when it was 400,000 years old.
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ROWE: The European Space Agency
launched the Planck satellite.
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Using sensitive
radio receivers,
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the orbiter studied the sky in
every direction,
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measuring tiny changes in
the temperature and polarization
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of the radiation signal.
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The CMB has all
these variations
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in temperature, and they're not
randomly generated.
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They are there because of
physical processes
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that occurred
when the universe
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was in its primordial
fireball phase.
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ROWE: The red blobs are
where matter was hottest,
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and the blue areas are
where matter was cooler.
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The smallest red blobs
are where
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hot material was packed
tightly together.
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That's where material in
the universe would have
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been denser, and that's
where galaxies would
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preferentially form.
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It's so cool to get to look at
those blueprints and study them
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and see how
that baby universe
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later grew up into the universe
we see around us today.
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ROWE: Although it doesn't
look like much,
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hidden within this picture
is almost everything
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we can know about the universe.
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In a complex process using
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different mathematical models,
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cosmologists figured out how
the ancient cosmos
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captured in the CMB
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became the universe
we see today.
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They worked out how
the universe got from
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small to big and how fast
that expansion happened.
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PONTZEN: The data from
the cosmic microwave background
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is absolutely the gold
standard for cosmology.
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It's beautifully clean, we can
understand it really well,
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and we have
a lot of confidence
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that what we learn from it
is pretty robust.
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ROWE: By running
the expansion backwards,
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we get an age...
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13.82 billion years.
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Job finished!
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But it's not quite
a slam dunk.
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The figure must be verified.
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We don't make
a single measurement
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using a single technique.
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We make multiple measurements
via multiple techniques.
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ROWE: Another group
of scientists use
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a totally different method
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to calculate
the age of the cosmos,
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measuring objects
that we can see
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in our universe to determine
how far away they are and how
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fast they're moving away from
us as the universe expands.
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The most direct and most
accurate measurements
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are using what is known
as parallax.
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Parallax is the apparent shift
in an object relative
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to the background
when it's viewed
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from two different locations.
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So if I look at my thumb with
one eye, and then I close it
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and look at the other eye,
it looks like my thumb moves.
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If I move my thumb
closer to my face,
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then the distance it moves
back and forth changes.
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It appears to move back
and forth more.
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That parallax difference
as we move the thumb closer
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and farther from the face
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is the way we measure
distances to distant objects.
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ROWE: Using parallax,
we can measure
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the distance to bright stars
called cepheids
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in the Milky Way.
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NANCE: Cepheids
are stars that burn 100,000
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times brighter than our sun,
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so they're extremely bright,
and they pulsate, meaning they
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get brighter and dimmer over
a regular time period.
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ROWE:
Cepheids that pulsate at
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the same rate have
the same brightness.
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They're known
as a standard candle.
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A standard candle is something
that is a standard, meaning
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we know how intrinsically
bright it is.
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So all we have to do
is measure
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the brightness that we appear
to perceive on Earth,
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and then you solve
for the distance.
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So imagine that
you're on the street.
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By looking down the street,
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you'll see that the street
lights get dimmer and dimmer
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the farther away they are,
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but that's not
their intrinsic brightness.
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Their intrinsic brightness
is the same.
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So by seeing how faint
the farthest away ones are,
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you can understand how far
away they are from you.
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ROWE: We can use
standard candles to measure
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the distance to stars
farther away.
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But there's a big problem --
throughout the universe,
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there's a competition between
the expansion pushing things
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apart and gravity pulling
things together.
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In the Milky Way,
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there's so much matter
that gravity wins.
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Even looking at galaxies in
our neighborhood,
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the expansion is tiny,
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but at cosmic scales of very
different galaxies,
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matter is more spread out,
and expansion wins,
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so we can only measure expansion
over massive distances.
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The way we start to measure
distances to things that
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are farther and farther away
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is to use something we call
the distance ladder.
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NANCE: Each category of object
that we observe
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is on a separate rung
of this ladder.
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Measuring the distance to one
will then inform us how far
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away the second rung is
and then the third rung.
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So each rung depends on
the previous rung, and from
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stacking these together, we can
start to measure things very,
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very far away from us.
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ROWE: Using parallax
to measure cepheid stars in
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the Milky Way
gives us a benchmark.
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We can then use
their standard brightness
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to measure cepheids
in other galaxies.
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The next rung is a brighter
standard candle called
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Type 1A supernovas.
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They can be seen
in galaxies farther away.
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Finally, we can measure light
from distant elliptical
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galaxies, and by looking
at how red the light is,
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we can work out how fast
they're moving away from us.
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So those three things
give us the nearby universe,
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the somewhat far away universe,
and the very distant universe,
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rung by rung.
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ROWE:
March 2021.
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Scientists measure
the light from 63
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giant elliptical galaxies,
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the farthest rung of
the distance ladder.
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They hope to get the most
accurate measurement of
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the Hubble constant to date
and a precise age
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for the universe.
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Their calculations make
the universe
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13.3 billion years old,
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not too far away from
the figure of
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13.82 billion years
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given by the cosmic
microwave background,
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a difference of around 6%.
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That sounds trivial, but that
equates to hundreds of millions
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of years of cosmic history
that either happened
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or didn't happen.
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PLAIT: 50 years ago,
when we weren't quite as good
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at measuring everything about
the universe,
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we would have been
thrilled to
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have our numbers
agreeing to this level.
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But nowadays, having
a difference like this,
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it's unacceptable.
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ROWE: Clearly, the two
techniques do not agree.
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Cosmologists split into
two camps.
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We had hoped that these two
methods were like building
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a bridge from either side
and then meeting in the middle.
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But they're not.
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Now we know that something is
going on
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we don't understand.
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00:10:01,239 --> 00:10:02,505
BULLOCK: Even though
these measurements
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are roughly the same,
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00:10:03,942 --> 00:10:06,910
it's really dangerous to just
accept them and assume that
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everything's fine,
because in science,
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usually, the initial really big
discoveries start off
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as small differences,
but then you pull
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on that thread,
and something wonderful emerges.
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ROWE:
So does a simple question,
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how old is the universe,
unravel everything?
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ROWE: The universe
is expanding outwards.
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00:10:37,309 --> 00:10:41,011
The rate it's growing is
called the Hubble constant,
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00:10:41,013 --> 00:10:44,814
and it's the key to working out
the age of the universe.
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00:10:44,916 --> 00:10:47,217
So the Hubble constant might
just seem
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00:10:47,319 --> 00:10:51,154
like some academic number that
doesn't mean anything,
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but that number contains
information about
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the composition,
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00:10:57,162 --> 00:11:00,430
the evolution, and the fate
of the universe.
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00:11:01,466 --> 00:11:02,832
ROWE:
It's an important number,
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00:11:02,934 --> 00:11:04,501
but there's a problem.
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00:11:04,503 --> 00:11:08,338
Our best measurement methods
don't match.
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00:11:08,407 --> 00:11:10,507
It's incredibly frustrating
to not
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00:11:10,509 --> 00:11:12,509
know how old the universe is.
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00:11:12,511 --> 00:11:14,444
It's even more frustrating
to know that
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there's two experiments,
which are excellent experiments
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that we firmly believe in,
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00:11:19,217 --> 00:11:20,884
that completely disagree
with each other.
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00:11:20,886 --> 00:11:24,654
My hair fell out a long time
ago over this kind of stuff.
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00:11:24,756 --> 00:11:27,424
This has been
the number-one question
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00:11:27,526 --> 00:11:29,259
for over half a decade.
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00:11:30,328 --> 00:11:33,763
ROWE: There must be something
wrong with one of the methods.
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00:11:33,865 --> 00:11:36,232
PONTZEN: There's a definite
sense in the community
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00:11:36,234 --> 00:11:39,135
that whichever camp
you happen to fall into,
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00:11:39,237 --> 00:11:41,805
the problems lie on the other
side of the fence.
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00:11:41,940 --> 00:11:43,840
So if you're mainly working
with the cosmic
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00:11:43,942 --> 00:11:46,309
microwave background,
you probably think
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00:11:46,411 --> 00:11:49,212
something is up
with the distance ladder.
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00:11:49,347 --> 00:11:51,748
ROWE: If there's a problem
with the distance ladder,
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00:11:51,850 --> 00:11:53,817
there's a prime suspect.
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00:11:53,885 --> 00:11:57,053
The ladder relies on stars
that have a predictable
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00:11:57,122 --> 00:11:59,923
brightness called
standard candles.
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00:11:59,925 --> 00:12:04,561
But there's evidence that
these stars are not always
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00:12:04,662 --> 00:12:05,962
the same brightness.
248
00:12:06,064 --> 00:12:10,266
So if you expect an object to
have a particular brightness,
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00:12:10,302 --> 00:12:12,068
and it has
a different brightness,
250
00:12:12,170 --> 00:12:15,905
then whatever conclusion
you draw that relies on
251
00:12:15,907 --> 00:12:17,107
the brightness
of that object is
252
00:12:17,242 --> 00:12:18,908
gonna be off somewhat.
253
00:12:18,910 --> 00:12:21,644
Think of the stars
like streetlights.
254
00:12:21,746 --> 00:12:24,948
If one light is broken
and dimmer than the others,
255
00:12:25,050 --> 00:12:27,650
you might think
it's farther away.
256
00:12:27,752 --> 00:12:30,320
PONTZEN: The concern with
the distance ladder is that
257
00:12:30,421 --> 00:12:33,723
if any of the single rungs
is not perfect,
258
00:12:33,725 --> 00:12:36,059
then the entire ladder might
be out of whack
259
00:12:36,161 --> 00:12:38,061
by the time you get
to the top.
260
00:12:38,163 --> 00:12:40,363
ROWE: What we need is
a fresh approach
261
00:12:40,465 --> 00:12:42,665
to measuring the age of
the universe.
262
00:12:42,734 --> 00:12:45,635
SUTTER: We're hoping we could
bring in a tie breaker,
263
00:12:45,737 --> 00:12:47,837
a referee,
a brand new method
264
00:12:47,939 --> 00:12:50,306
that didn't care about
any of this or any
265
00:12:50,308 --> 00:12:54,511
of that, and tell us what is
the Hubble constant.
266
00:12:54,613 --> 00:12:57,313
ROWE:
We may have just found one.
267
00:12:57,415 --> 00:13:01,217
This observatory
doesn't have a telescope.
268
00:13:01,319 --> 00:13:03,920
It's hunting
for an invisible wave,
269
00:13:03,922 --> 00:13:07,891
a disturbance in spacetime
itself, caused
270
00:13:07,893 --> 00:13:12,228
by massive objects
accelerating or colliding.
271
00:13:12,230 --> 00:13:14,464
It's known as LIGO.
272
00:13:14,533 --> 00:13:17,033
MINGARELLI:
LIGO stands for the Laser
273
00:13:17,035 --> 00:13:20,136
Interferometer Gravitational
Wave Observatory,
274
00:13:20,238 --> 00:13:23,840
and it is a ground-based
gravitational wave detector.
275
00:13:23,975 --> 00:13:27,544
ROWE: A perfectly stabilized
beam of laser light bounces
276
00:13:27,612 --> 00:13:30,947
in a five-mile-long,
L-shaped tunnel.
277
00:13:31,049 --> 00:13:34,450
As a gravitational wave passes
through the detector,
278
00:13:34,519 --> 00:13:36,286
space stretches,
279
00:13:36,288 --> 00:13:39,722
forcing the light to travel
a tiny bit farther.
280
00:13:39,824 --> 00:13:43,960
You're bouncing a laser
over an incredible distance
281
00:13:44,062 --> 00:13:47,664
and trying to measure as
spacetime itself
282
00:13:47,732 --> 00:13:49,666
gets stretched and deformed
283
00:13:49,734 --> 00:13:52,769
whether that lazar had to
travel a tiny bit further
284
00:13:52,804 --> 00:13:53,903
or a tiny bit shorter,
285
00:13:53,905 --> 00:13:57,340
and a tiny bit here is
the width of a single atom
286
00:13:57,442 --> 00:13:59,709
over miles
and miles of distance.
287
00:14:00,912 --> 00:14:04,414
ROWE: LIGO has already detected
colliding black holes,
288
00:14:06,051 --> 00:14:09,719
but it's also received
a signal from something
289
00:14:09,721 --> 00:14:11,621
less massive.
290
00:14:11,623 --> 00:14:14,624
Neutron stars are
the densest thing in
291
00:14:14,626 --> 00:14:16,759
the universe other than
black holes.
292
00:14:16,828 --> 00:14:19,863
They're the last stopping point
before you would collapse
293
00:14:19,965 --> 00:14:22,131
all the way to form
a black hole.
294
00:14:22,133 --> 00:14:24,834
ROWE: They're the size of
Washington, D.C.,
295
00:14:24,936 --> 00:14:28,238
but they can have
the mass of two suns.
296
00:14:28,306 --> 00:14:32,942
A collision between neutron
stars is incredibly powerful.
297
00:14:33,044 --> 00:14:35,845
It's one of the most energetic
events in the universe, and it
298
00:14:35,947 --> 00:14:38,815
distorts the fabric of
spacetime very strongly,
299
00:14:38,817 --> 00:14:41,351
because their gravity
is so strong.
300
00:14:41,386 --> 00:14:43,119
ROWE: But unlike
black hole mergers,
301
00:14:43,121 --> 00:14:46,522
neutron star collisions can
also send out light.
302
00:14:48,326 --> 00:14:52,161
In 2017, LIGO sent out
an alert -- more than
303
00:14:52,230 --> 00:14:57,066
70 telescopes on Earth and in
space swung into action.
304
00:14:57,135 --> 00:15:00,336
This binary neutron star
merger was the first time
305
00:15:00,438 --> 00:15:02,538
we had witnessed
gravitational waves
306
00:15:02,641 --> 00:15:04,507
and light waves coming from
the same event.
307
00:15:07,345 --> 00:15:09,612
It was groundbreaking.
308
00:15:09,714 --> 00:15:13,716
ROWE: This event is ideal
for Hubble constant hunters.
309
00:15:13,718 --> 00:15:15,718
The light tells us how fast
310
00:15:15,820 --> 00:15:18,588
the colliding stars
are moving away from us.
311
00:15:18,590 --> 00:15:22,592
Gravitational waves
give us the distance.
312
00:15:22,594 --> 00:15:26,229
If we know how far away it is
and how fast it's moving,
313
00:15:26,364 --> 00:15:28,331
that's the Hubble constant.
314
00:15:28,333 --> 00:15:32,435
PONTZEN: Having neutron star
mergers added to your arsenal
315
00:15:32,437 --> 00:15:34,137
of ways of measuring
316
00:15:34,238 --> 00:15:36,806
the universe's expansion
is great, because it's
317
00:15:36,808 --> 00:15:38,308
completely independent.
318
00:15:38,410 --> 00:15:40,810
It uses physics that's not
related to either
319
00:15:40,912 --> 00:15:44,047
of the two competing methods
we have so far.
320
00:15:44,115 --> 00:15:45,815
ROWE:
Sounds perfect.
321
00:15:45,917 --> 00:15:47,717
The result?
322
00:15:47,852 --> 00:15:49,352
So this brand-new
measurement that
323
00:15:49,454 --> 00:15:51,154
were hoping would be
a tie breaker...
324
00:15:53,525 --> 00:15:57,060
ended up coming right in
between these two extremes.
325
00:15:58,129 --> 00:16:00,830
Thanks for the help.
326
00:16:00,932 --> 00:16:04,233
ROWE: But it might not be
as bad as it sounds.
327
00:16:04,336 --> 00:16:07,203
The number of neutron star
collisions where
328
00:16:07,205 --> 00:16:11,507
we have detected gravitational
waves and light...one.
329
00:16:12,644 --> 00:16:15,044
We shouldn't be at all
disheartened by the fact
330
00:16:15,113 --> 00:16:17,413
that this hasn't
actually decided
331
00:16:17,415 --> 00:16:20,149
the problem, because there's
a huge margin for error
332
00:16:20,251 --> 00:16:22,218
when you have just one object.
333
00:16:22,320 --> 00:16:24,821
We would like
something like 100 events
334
00:16:24,956 --> 00:16:27,357
like this neutron star merger.
335
00:16:27,458 --> 00:16:29,959
That might seem like
a huge improvement we need,
336
00:16:30,028 --> 00:16:31,427
but actually,
it's very feasible that
337
00:16:31,429 --> 00:16:33,830
in the next decade,
we'll get there.
338
00:16:33,832 --> 00:16:37,266
ROWE: Gravitational waves
may give us a precise age of
339
00:16:37,368 --> 00:16:39,569
the universe,
but there is a chance
340
00:16:39,637 --> 00:16:42,939
they'll tell us the problem
isn't with our measurements,
341
00:16:43,041 --> 00:16:45,408
but with our understanding
of the cosmos.
342
00:16:45,510 --> 00:16:48,244
If we keep getting different
answers for the Hubble constant,
343
00:16:48,313 --> 00:16:50,646
especially depending on
the method we use,
344
00:16:50,715 --> 00:16:52,515
that's a big clue that
we don't
345
00:16:52,517 --> 00:16:54,817
understand something
fundamental about
346
00:16:54,919 --> 00:16:56,219
the universe's evolution,
347
00:16:56,320 --> 00:16:58,154
its makeup,
something important.
348
00:16:59,624 --> 00:17:02,825
ROWE: Our search for the age of
the universe just might
349
00:17:02,827 --> 00:17:06,429
destroy our model of how
we think the cosmos works,
350
00:17:07,432 --> 00:17:10,633
plunging physics
into chaos.
351
00:17:20,545 --> 00:17:23,112
ROWE: We don't know
the age of the universe.
352
00:17:23,214 --> 00:17:26,716
We had hoped that the results
from our experiments would be
353
00:17:26,718 --> 00:17:31,120
like building a bridge,
starting at opposite ends
354
00:17:31,122 --> 00:17:33,056
and meeting in the middle.
355
00:17:33,157 --> 00:17:34,857
As time goes on,
356
00:17:34,959 --> 00:17:38,127
as the evidence accumulates,
357
00:17:38,129 --> 00:17:40,930
these two sides of the bridge
are not gonna meet.
358
00:17:40,932 --> 00:17:44,133
Something has to give.
359
00:17:44,135 --> 00:17:46,235
ROWE: Some believe the problem
lies in the way
360
00:17:46,337 --> 00:17:49,906
we've interpreted the picture
of the early universe,
361
00:17:49,908 --> 00:17:54,343
the pattern hidden in
the cosmic microwave background.
362
00:17:54,412 --> 00:17:56,612
We're really confident in
the data that we have from
363
00:17:56,714 --> 00:17:59,215
the CMB, but it's actually
an indirect
364
00:17:59,317 --> 00:18:01,250
measurement of
the universe's age.
365
00:18:01,319 --> 00:18:04,320
It depends on our model of
the universe being right.
366
00:18:04,422 --> 00:18:08,958
It could be, it could very well
be that our fundamental
367
00:18:09,060 --> 00:18:11,928
cosmological model
that we've used
368
00:18:11,930 --> 00:18:15,832
to successfully describe
the universe is coming up short,
369
00:18:15,834 --> 00:18:17,733
that there's something
wrong in there,
370
00:18:17,869 --> 00:18:20,536
that that engine is broken.
371
00:18:20,638 --> 00:18:24,941
ROWE: That engine is
the standard cosmological model.
372
00:18:25,076 --> 00:18:27,510
Based on our knowledge of
particle physics
373
00:18:27,512 --> 00:18:29,212
and general relativity,
374
00:18:29,214 --> 00:18:31,414
it's like an instruction manual
375
00:18:31,416 --> 00:18:33,316
for how the universe works.
376
00:18:33,418 --> 00:18:36,953
Rewriting it is
a radical suggestion.
377
00:18:37,054 --> 00:18:40,123
For the most part,
it matches what we see,
378
00:18:40,125 --> 00:18:43,326
but it does struggle
with one thing.
379
00:18:43,394 --> 00:18:46,829
As the universe expands
away from the Big Bang,
380
00:18:46,964 --> 00:18:51,134
the intuitive thing you would
expect is for gravity to start
381
00:18:51,235 --> 00:18:52,735
pulling it back together again.
382
00:18:52,737 --> 00:18:55,404
So over time, gravity
would just reverse that
383
00:18:55,406 --> 00:19:00,009
and pull everything back in,
back to a single point.
384
00:19:00,011 --> 00:19:03,513
But what we see in
the data is completely opposite.
385
00:19:03,648 --> 00:19:06,215
What we see is that
the universe is not only
386
00:19:06,217 --> 00:19:07,817
continuing to expand,
387
00:19:07,919 --> 00:19:10,920
but it's speeding up faster
and faster all the time.
388
00:19:10,922 --> 00:19:13,122
To explain
this weird phenomenon,
389
00:19:13,257 --> 00:19:15,258
the cosmological model
relies on
390
00:19:15,359 --> 00:19:18,661
the existence of
a strange, unknown force --
391
00:19:18,730 --> 00:19:20,463
dark energy.
392
00:19:20,565 --> 00:19:22,832
Dark energy is
the most perplexing
393
00:19:22,934 --> 00:19:25,535
and mysterious thing I've
encountered in my research.
394
00:19:25,670 --> 00:19:28,204
PLAIT: Dark energy is a term
that we slap
395
00:19:28,206 --> 00:19:30,806
on this idea that
the universal expansion
396
00:19:30,808 --> 00:19:33,109
is accelerating.
397
00:19:33,111 --> 00:19:35,244
That's about all
we know about it.
398
00:19:35,313 --> 00:19:36,646
We don't know
what's causing it.
399
00:19:36,747 --> 00:19:37,813
We don't know
how it behaves.
400
00:19:37,815 --> 00:19:39,015
We don't know what
it was like in
401
00:19:39,017 --> 00:19:40,650
the past or what it's like
in the future.
402
00:19:40,718 --> 00:19:43,819
So we just call it
dark energy.
403
00:19:43,955 --> 00:19:47,857
ROWE: It's invisible --
it fills the whole universe
404
00:19:47,959 --> 00:19:50,960
and pushes galaxies apart.
405
00:19:51,029 --> 00:19:53,062
In some sense,
it's like a spring,
406
00:19:53,164 --> 00:19:56,332
a contracted spring, and you
let it go, and it wants to push
407
00:19:56,334 --> 00:19:58,334
everything away.
408
00:19:58,336 --> 00:19:59,735
ROWE: And things
get stranger.
409
00:19:59,837 --> 00:20:04,807
Dark energy doesn't dilute as
the universe expands.
410
00:20:04,909 --> 00:20:07,043
HOPKINS:
As empty space gets created
411
00:20:07,144 --> 00:20:10,913
or expands, the dark energy
associated with that
412
00:20:10,915 --> 00:20:12,014
stays the same.
413
00:20:12,050 --> 00:20:14,617
It basically populates
all this empty space.
414
00:20:14,619 --> 00:20:16,352
Imagine I'm draining
a bucket of water,
415
00:20:16,421 --> 00:20:19,622
and water just magically
appears out of nowhere.
416
00:20:19,624 --> 00:20:21,757
That's like how
dark energy behaves
417
00:20:21,826 --> 00:20:23,926
as the universe is expanding.
418
00:20:23,928 --> 00:20:25,795
ROWE: Dark energy
plays an important
419
00:20:25,797 --> 00:20:28,431
role in the standard
cosmological model.
420
00:20:28,433 --> 00:20:31,367
If our understanding of it
is wrong,
421
00:20:31,469 --> 00:20:33,035
then so too is the model,
422
00:20:33,037 --> 00:20:37,406
which means the age of
the universe we get from the CMB
423
00:20:37,408 --> 00:20:39,442
is wrong, too.
424
00:20:39,510 --> 00:20:41,644
TEGMARK: Since nobody has a clue
what dark energy is,
425
00:20:41,746 --> 00:20:42,945
there are a lot of
different theories.
426
00:20:43,047 --> 00:20:46,849
But the biggest question of
all is simply, is it constant?
427
00:20:47,952 --> 00:20:51,320
PONTZEN: Our standard assumption
about dark energy is that
428
00:20:51,422 --> 00:20:53,256
it's pushing apart the universe
429
00:20:53,357 --> 00:20:55,358
with the same strength
throughout the history
430
00:20:55,459 --> 00:20:56,659
of the universe.
431
00:20:57,729 --> 00:21:02,231
ROWE: Now physicists are
wondering if that idea is wrong.
432
00:21:02,233 --> 00:21:06,702
Maybe, in the early universe,
dark energy acted differently.
433
00:21:06,704 --> 00:21:10,339
Hey, you know that whole dark
energy thing that's messing
434
00:21:10,441 --> 00:21:11,807
with the universe today?
435
00:21:11,809 --> 00:21:15,745
Maybe it messed with
the universe back then.
436
00:21:15,813 --> 00:21:19,515
THALLER: It could be that dark
energy really has affected
437
00:21:19,650 --> 00:21:22,118
the rate of expansion a lot
more than we thought.
438
00:21:22,220 --> 00:21:25,521
This is gonna throw a big
monkey wrench into our idea of
439
00:21:25,523 --> 00:21:26,889
how old the universe is
440
00:21:26,891 --> 00:21:29,025
and what it was like
at different eras.
441
00:21:29,027 --> 00:21:34,230
ROWE: The theory is called
new early dark energy.
442
00:21:34,232 --> 00:21:38,034
DE RHAM: So the idea behind
new early dark energy is that
443
00:21:38,036 --> 00:21:41,604
dark energy was present during
the very early periods
444
00:21:41,606 --> 00:21:44,173
of the universe,
but in a very different state.
445
00:21:44,208 --> 00:21:48,210
Just like you can think of
water being present in
446
00:21:48,346 --> 00:21:50,313
two states,
447
00:21:50,315 --> 00:21:54,450
it can be liquid water if
the environment is quite hot,
448
00:21:54,519 --> 00:21:56,852
or it can be frozen water
449
00:21:56,954 --> 00:21:59,121
if the environment is colder.
450
00:21:59,123 --> 00:22:01,223
PLAIT:
We call that a phase change.
451
00:22:01,326 --> 00:22:03,225
Maybe in the early universe,
452
00:22:03,227 --> 00:22:05,728
dark energy underwent
a phase change, as well.
453
00:22:05,730 --> 00:22:09,231
It was different before then
and acts differently now.
454
00:22:09,233 --> 00:22:13,169
ROWE: According to the theory,
this more energetic state of
455
00:22:13,270 --> 00:22:15,538
early dark energy
pushed apart
456
00:22:15,606 --> 00:22:18,708
the early universe
much faster than we thought.
457
00:22:18,710 --> 00:22:22,712
PONTZEN: So that speeds things
up in the opening moments of
458
00:22:22,814 --> 00:22:24,013
our universe,
459
00:22:24,015 --> 00:22:27,616
which starts to actually bring
things back into agreement
460
00:22:27,618 --> 00:22:29,819
when you look at
interpreting both
461
00:22:29,821 --> 00:22:32,254
the cosmic microwave
background and the distance
462
00:22:32,323 --> 00:22:34,023
ladder measurements.
463
00:22:34,025 --> 00:22:36,559
PLAIT: One of the things
that we see in the universe
464
00:22:36,627 --> 00:22:39,061
is that things change with time,
density changes,
465
00:22:39,163 --> 00:22:40,629
matter changes,
energy changes.
466
00:22:40,631 --> 00:22:42,431
Why not dark energy?
467
00:22:42,533 --> 00:22:45,368
ROWE:
Adding new early dark energy
468
00:22:45,469 --> 00:22:48,337
to the early universe
changes the standard model.
469
00:22:48,406 --> 00:22:52,742
The CMB gives a higher figure
for the expansion of
470
00:22:52,810 --> 00:22:54,944
the universe, and finally,
471
00:22:55,045 --> 00:22:58,047
an age that matches
the one given by
472
00:22:58,149 --> 00:23:00,616
the distance ladder method.
473
00:23:00,718 --> 00:23:04,320
If you think about that bridge
analogy, where the two parts
474
00:23:04,422 --> 00:23:07,623
just don't meet,
the early dark energy adjusts
475
00:23:07,625 --> 00:23:11,427
the angle of the early
universe part of the bridge,
476
00:23:11,429 --> 00:23:14,930
and it just gets them to
actually meet in the middle.
477
00:23:14,932 --> 00:23:19,135
ROWE: It's still controversial,
but new dark energy may be
478
00:23:19,237 --> 00:23:22,037
detected in detailed
measurements of
479
00:23:22,139 --> 00:23:24,306
the cosmic microwave
background.
480
00:23:24,308 --> 00:23:26,709
SUTTER: I mean,
in one sense, like,
481
00:23:26,844 --> 00:23:28,511
do we really need
to overcomplicate
482
00:23:28,613 --> 00:23:30,413
the universe here?
But you know what?
483
00:23:30,415 --> 00:23:34,116
The universe is under
no obligation to be simple.
484
00:23:34,118 --> 00:23:38,087
ROWE: But there's one thing
physicists can agree on.
485
00:23:38,089 --> 00:23:41,123
Dark energy truly is
a can of worms we've just
486
00:23:41,258 --> 00:23:43,959
opened, and there may be some
big changes coming up.
487
00:23:44,061 --> 00:23:46,262
ROWE: There is a more
radical possibility.
488
00:23:46,330 --> 00:23:51,434
Maybe we need to ditch dark
energy altogether and question
489
00:23:51,436 --> 00:23:56,205
one of the most famous theories
of all, general relativity.
490
00:23:56,340 --> 00:23:57,606
Is it possible?
491
00:23:57,708 --> 00:24:00,643
Did Einstein make
a colossal mistake?
492
00:24:09,754 --> 00:24:12,154
ROWE: In trying to work out
the age of the universe,
493
00:24:12,223 --> 00:24:15,558
physicists have started
a revolution,
494
00:24:15,659 --> 00:24:18,727
a revolution that could
overturn everything we thought
495
00:24:18,829 --> 00:24:21,530
we knew about how
the universe works,
496
00:24:21,532 --> 00:24:24,366
including the bedrock
of modern physics,
497
00:24:24,468 --> 00:24:26,969
Einstein's theory of gravity,
498
00:24:27,038 --> 00:24:28,804
general relativity.
499
00:24:28,906 --> 00:24:31,407
Underlying everything,
500
00:24:31,542 --> 00:24:34,543
all of cosmology,
is general relativity,
501
00:24:34,612 --> 00:24:39,014
but maybe we need a completely
new understanding
502
00:24:39,016 --> 00:24:40,850
of gravity.
503
00:24:40,952 --> 00:24:43,953
ROWE:
Gravity is a strange force.
504
00:24:44,088 --> 00:24:46,322
It's always attractive.
505
00:24:46,424 --> 00:24:49,458
The Earth pulling on us
gives us our weight.
506
00:24:49,560 --> 00:24:53,729
The force of gravity
acts over huge distances.
507
00:24:53,731 --> 00:24:57,867
The sun tugs on objects
throughout the solar system.
508
00:24:57,969 --> 00:25:00,870
The Milky Way pulls on
other galaxies.
509
00:25:00,938 --> 00:25:04,640
PONTZEN: On the one hand,
gravity is incredibly familiar
510
00:25:04,742 --> 00:25:07,042
to us, you know, the apple
falling from the tree
511
00:25:07,144 --> 00:25:08,644
and all of that stuff,
512
00:25:08,746 --> 00:25:11,347
and we also know that gravity
behaves in a very
513
00:25:11,448 --> 00:25:13,816
predictable way
throughout our solar system
514
00:25:13,918 --> 00:25:16,619
from all the spacecraft
and things we've sent out.
515
00:25:16,621 --> 00:25:20,556
But when it comes to how it
behaves on incredibly tiny
516
00:25:20,658 --> 00:25:23,125
scales and also on incredibly
517
00:25:23,227 --> 00:25:25,961
large scales,
covering the whole universe,
518
00:25:26,030 --> 00:25:29,064
it's possible that we just
don't yet have the right
519
00:25:29,133 --> 00:25:31,634
picture of what's going on.
520
00:25:31,736 --> 00:25:34,069
ROWE: Einstein's model
of gravity has remained
521
00:25:34,138 --> 00:25:36,705
largely the same for
100 years.
522
00:25:36,807 --> 00:25:39,742
So much of modern physics
is really standing on
523
00:25:39,843 --> 00:25:41,310
Einstein's shoulders,
524
00:25:41,379 --> 00:25:43,412
but at the same time,
525
00:25:43,514 --> 00:25:46,615
we can't ever take
anything for granted.
526
00:25:46,617 --> 00:25:50,419
ROWE: Claudia de Rham works on
a theory called massive gravity.
527
00:25:50,421 --> 00:25:52,621
It's based on a key part of
528
00:25:52,723 --> 00:25:56,625
Einstein's theory that says
gravity doesn't have mass.
529
00:25:56,627 --> 00:26:00,162
Once you understand that
general relativity is the theory
530
00:26:00,264 --> 00:26:01,630
of a massless particle,
531
00:26:01,732 --> 00:26:03,332
the immediate response
should be,
532
00:26:03,334 --> 00:26:05,701
well, what if it was massive?
533
00:26:05,703 --> 00:26:08,070
ROWE: The theoretical particle
that carries
534
00:26:08,138 --> 00:26:10,906
gravity is called
the graviton.
535
00:26:10,908 --> 00:26:13,742
If gravitons
don't have any weight,
536
00:26:13,778 --> 00:26:16,745
then there's nothing to slow
them down as they speed
537
00:26:16,847 --> 00:26:18,113
through the universe.
538
00:26:18,182 --> 00:26:21,216
They can act over
infinite distances,
539
00:26:21,218 --> 00:26:23,552
just like photons of light.
540
00:26:23,654 --> 00:26:28,123
So one galaxy on this side of
the universe can actually pull
541
00:26:28,225 --> 00:26:31,226
on a galaxy that's right on
the other side of the universe.
542
00:26:31,329 --> 00:26:35,064
ROWE: But if gravity
has weight, things change.
543
00:26:35,132 --> 00:26:36,398
DE RHAM: In some sense,
544
00:26:36,400 --> 00:26:39,335
if we attach a little backpack
to our graviton particle,
545
00:26:39,437 --> 00:26:45,808
its effect is to slowly slow
it down just enough so as to
546
00:26:45,943 --> 00:26:49,144
make its effect
on very large distances
547
00:26:49,246 --> 00:26:53,749
being a tiny little bit
weaker, and that's our way to
548
00:26:53,818 --> 00:26:55,351
switch off the effect of
549
00:26:55,419 --> 00:27:00,022
gravity on huge
cosmological distances.
550
00:27:00,024 --> 00:27:04,059
ROWE: If gravity is a little bit
weaker, a galaxy on this side
551
00:27:04,128 --> 00:27:05,961
of the universe can't pull on
552
00:27:06,063 --> 00:27:08,330
one on the other side of
the cosmos.
553
00:27:08,332 --> 00:27:12,234
It has a huge effect on
the expansion of the universe.
554
00:27:13,838 --> 00:27:17,606
PONTZEN: If the force of gravity
actually just switches off at
555
00:27:17,708 --> 00:27:19,141
large distances,
556
00:27:19,210 --> 00:27:22,711
then you no longer have to
counter the fact that
557
00:27:22,713 --> 00:27:23,878
everything is pulling
558
00:27:23,914 --> 00:27:26,115
everything else together,
because it isn't anymore.
559
00:27:26,250 --> 00:27:29,218
So that would quite naturally
explain why
560
00:27:29,320 --> 00:27:32,354
the expansion of our universe
would be speeding up.
561
00:27:32,423 --> 00:27:38,127
ROWE: This acceleration is what
we see in the universe today.
562
00:27:38,262 --> 00:27:42,531
Currently, we use
dark energy to explain it.
563
00:27:42,666 --> 00:27:45,167
OLUSEYI: So,
if the graviton has mass,
564
00:27:45,236 --> 00:27:48,837
that means that we can
get out of the universe
565
00:27:48,939 --> 00:27:51,807
what we see without the need
for dark energy.
566
00:27:51,909 --> 00:27:54,410
DE RHAM: What if actually
what we were observing
567
00:27:54,412 --> 00:27:58,414
is simply
the first sign of gravity
568
00:27:58,416 --> 00:28:01,116
switching off
at very large distances.
569
00:28:01,118 --> 00:28:04,420
Maybe we're just observing
the first effect of
570
00:28:04,422 --> 00:28:06,422
the graviton having a mass.
571
00:28:06,424 --> 00:28:09,224
ROWE: Without dark energy
to deal with,
572
00:28:09,226 --> 00:28:12,461
the universe is a lot easier
to explain.
573
00:28:12,529 --> 00:28:15,564
SUTTER: Maybe we don't need
these complicated physics.
574
00:28:15,633 --> 00:28:19,134
Maybe it's just all the normal
ingredients of the universe,
575
00:28:19,136 --> 00:28:22,504
but operating under
a different set of rules.
576
00:28:22,506 --> 00:28:27,009
ROWE: Claudia hopes her theory
will soon be put to the test.
577
00:28:27,011 --> 00:28:30,813
Around 2037,
578
00:28:30,815 --> 00:28:33,749
we'll have a new
gravitational wave detector,
579
00:28:33,818 --> 00:28:37,920
the Laser Interferometer
Space Antenna, or LISA.
580
00:28:39,223 --> 00:28:43,225
It'll be bigger than LIGO
and will orbit the Earth.
581
00:28:43,327 --> 00:28:45,127
When LISA get out there
in space,
582
00:28:45,262 --> 00:28:47,563
we'll even have a bigger
handle on
583
00:28:47,664 --> 00:28:51,033
gravitational waves evolving
throughout the whole universe,
584
00:28:51,035 --> 00:28:54,303
and so it will allow us to go
very deep in our understanding
585
00:28:54,305 --> 00:28:55,704
of gravity.
586
00:28:55,706 --> 00:29:00,209
ROWE: LISA is a system of three
satellites arranged in a giant
587
00:29:00,211 --> 00:29:05,314
triangular formation,
1.5 million miles apart.
588
00:29:06,450 --> 00:29:08,217
It should pick up
very low
589
00:29:08,352 --> 00:29:13,422
frequency gravitational waves
from more ancient events,
590
00:29:13,424 --> 00:29:17,960
perhaps even shockwaves from
the birth of the universe.
591
00:29:18,095 --> 00:29:21,029
If the graviton
has mass,
592
00:29:21,031 --> 00:29:24,433
then the waves will arrive
more slowly than predicted,
593
00:29:24,435 --> 00:29:28,437
but until we receive those
signals, all bets are off.
594
00:29:28,506 --> 00:29:32,040
It's a big deal to propose
a difference in gravity,
595
00:29:32,109 --> 00:29:35,144
but then again,
we don't know.
596
00:29:35,212 --> 00:29:36,411
OLUSEYI:
I'm making no bets.
597
00:29:36,413 --> 00:29:40,315
The universe has proven itself
to be so deceptive.
598
00:29:40,417 --> 00:29:43,152
So I'm gonna wait until it
tells me what it is.
599
00:29:45,523 --> 00:29:47,756
ROWE: The question of
the age of the universe
600
00:29:47,858 --> 00:29:50,159
opens Pandora's box,
601
00:29:50,260 --> 00:29:52,761
and the expansion rate
of the universe
602
00:29:52,830 --> 00:29:55,297
holds another secret,
603
00:29:55,299 --> 00:29:59,868
our ultimate fate --
how the universe will end.
604
00:30:11,215 --> 00:30:13,515
ROWE: We know exactly how
the Earth will end.
605
00:30:15,719 --> 00:30:18,720
In around 5.4 billion years,
606
00:30:18,823 --> 00:30:21,123
the sun will turn
into a red giant,
607
00:30:21,125 --> 00:30:24,459
expanding to 1,000 times
its current size.
608
00:30:26,330 --> 00:30:28,063
The Earth will
be destroyed.
609
00:30:30,034 --> 00:30:32,267
Humans, if we still exist,
610
00:30:32,303 --> 00:30:34,937
will have long deserted
our home planet.
611
00:30:37,208 --> 00:30:39,408
But how will
the universe end?
612
00:30:40,945 --> 00:30:43,412
MINGARELLI: The age of
the universe enables us to
613
00:30:43,414 --> 00:30:46,114
not only understand
where we came from,
614
00:30:46,217 --> 00:30:48,951
but potentially,
the fate of the universe.
615
00:30:48,953 --> 00:30:52,221
What will happen millions and
billions of years from now?
616
00:30:53,224 --> 00:30:55,357
ROWE: If scientists
confirm the value
617
00:30:55,426 --> 00:30:56,725
of the Hubble constant,
618
00:30:56,827 --> 00:31:00,028
the elusive figure that tells
us just how fast the universe
619
00:31:00,030 --> 00:31:02,364
is expanding,
it will tell us the age of
620
00:31:02,466 --> 00:31:06,568
the universe, and it will help
us predict its end.
621
00:31:06,637 --> 00:31:08,604
SUTTER: Measuring
the Hubble constant is
622
00:31:08,606 --> 00:31:10,939
measuring the expansion
rate today,
623
00:31:11,041 --> 00:31:14,610
right now, it's like checking
your speedometer at one moment.
624
00:31:14,745 --> 00:31:16,712
But just because
it's your speed now,
625
00:31:16,714 --> 00:31:19,114
it doesn't mean it was
the same speed when you left
626
00:31:19,116 --> 00:31:21,917
your home or the same speed
when you'll be on the freeway.
627
00:31:21,919 --> 00:31:25,220
ROWE: How the expansion
changes over time
628
00:31:25,322 --> 00:31:27,522
will control the fate of
the cosmos.
629
00:31:27,625 --> 00:31:29,358
MINGARELLI: So depending on
the Hubble constant,
630
00:31:29,426 --> 00:31:31,727
the universe could
continue to expand.
631
00:31:31,829 --> 00:31:35,330
It could accelerate
its expansion rate,
632
00:31:35,332 --> 00:31:37,733
or it could be
decelerating.
633
00:31:38,836 --> 00:31:41,837
ROWE: At the moment,
galaxies are racing apart.
634
00:31:43,140 --> 00:31:45,841
A continually expanding
universe will
635
00:31:45,943 --> 00:31:49,011
cool down as it spreads out.
636
00:31:49,013 --> 00:31:53,315
Another name for this eternal
expansion is the Big Freeze,
637
00:31:53,450 --> 00:31:56,118
because as everything
gets spread out,
638
00:31:56,253 --> 00:31:59,621
the density is lower, and
there's no more opportunities
639
00:31:59,723 --> 00:32:01,323
for temperature differences.
640
00:32:01,325 --> 00:32:04,626
Everything just gets colder and
colder and colder and colder,
641
00:32:04,728 --> 00:32:09,631
slowly, eternally approaching
absolute zero.
642
00:32:09,633 --> 00:32:11,967
ROWE:
The more matter is spread out,
643
00:32:12,036 --> 00:32:14,770
the less chance there is for
star formation.
644
00:32:14,805 --> 00:32:18,507
And so the universe's
continued expansion means our
645
00:32:18,509 --> 00:32:23,612
night sky and every night sky
in the universe will inevitably
646
00:32:23,614 --> 00:32:26,415
continue to get darker
and darker and darker as things
647
00:32:26,417 --> 00:32:29,551
move further away
and as stars die off.
648
00:32:29,620 --> 00:32:33,755
SUTTER: Eventually,
all the stars will go out,
649
00:32:33,857 --> 00:32:36,425
and there'll just be
the leftovers,
650
00:32:36,427 --> 00:32:40,128
which we call the degenerates,
black holes,
651
00:32:40,130 --> 00:32:42,364
white dwarfs, rogue planets.
652
00:32:42,433 --> 00:32:46,034
It's gonna be
a very, very sad place.
653
00:32:46,036 --> 00:32:48,303
ROWE: The last refuge
of any matter at all
654
00:32:48,305 --> 00:32:50,305
will be black holes.
655
00:32:50,307 --> 00:32:52,741
You've got a big black hole in
the middle of each galaxy,
656
00:32:52,843 --> 00:32:56,712
over trillions of years,
everything in galaxies fall in,
657
00:32:56,714 --> 00:33:00,215
so finally, you're left with
big black holes over vast
658
00:33:00,217 --> 00:33:01,950
distances, separated
659
00:33:02,052 --> 00:33:04,519
almost universes away.
660
00:33:04,521 --> 00:33:07,956
MINGARELLI: So getting towards
the Big Freeze,
661
00:33:08,058 --> 00:33:10,959
black holes themselves
start to evaporate.
662
00:33:11,061 --> 00:33:14,463
There won't even be black
holes at the end of this
663
00:33:14,564 --> 00:33:16,298
accelerating universe.
664
00:33:16,300 --> 00:33:18,734
PLAIT:
All that's left is very,
665
00:33:18,869 --> 00:33:22,304
very low energy photons and
a little bit of matter dispersed
666
00:33:22,306 --> 00:33:25,140
throughout the universe,
and there's nothing left.
667
00:33:25,242 --> 00:33:26,441
That's it.
668
00:33:26,443 --> 00:33:29,111
THALLER: We call that
the heat death of the universe.
669
00:33:29,113 --> 00:33:31,813
There's no longer any place
that has more energy
670
00:33:31,815 --> 00:33:36,151
or more heat -- it's all just
thin, barely there photons.
671
00:33:36,220 --> 00:33:38,520
It's fascinating
scientifically,
672
00:33:38,622 --> 00:33:40,422
but from a human standpoint,
673
00:33:40,524 --> 00:33:42,824
not a lot of fun to
think about.
674
00:33:42,826 --> 00:33:44,393
ROWE: But if
the Hubble constant,
675
00:33:44,395 --> 00:33:48,430
the expansion rate of
the universe, keeps increasing,
676
00:33:48,432 --> 00:33:52,534
then the end of the universe
could be a lot scarier
677
00:33:52,636 --> 00:33:54,636
and come a lot sooner.
678
00:33:57,041 --> 00:33:59,708
One possibility
is that the expansion
679
00:33:59,843 --> 00:34:01,610
of the universe
will accelerate
680
00:34:01,712 --> 00:34:04,012
and continue
to accelerate forever,
681
00:34:04,014 --> 00:34:05,714
faster and faster and faster.
682
00:34:05,849 --> 00:34:08,950
And if that happens, we face
a scenario that we call
683
00:34:09,052 --> 00:34:11,253
the Big Rip,
where actually the whole
684
00:34:11,321 --> 00:34:14,222
of space essentially just
gets ripped to shreds.
685
00:34:15,826 --> 00:34:18,126
So the solar system
is gonna get ripped apart,
686
00:34:18,261 --> 00:34:21,563
then the sun and the planets
themselves will start to get
687
00:34:21,598 --> 00:34:22,930
ripped apart.
688
00:34:22,966 --> 00:34:26,168
And finally, it works its way
down to atoms, and atoms get
689
00:34:26,269 --> 00:34:28,370
ripped apart, and we're
starting to see effects on
690
00:34:28,405 --> 00:34:29,805
space and time.
691
00:34:31,041 --> 00:34:33,241
Space is ripped apart.
692
00:34:33,343 --> 00:34:34,676
Time comes to a stop.
693
00:34:37,047 --> 00:34:41,416
NANCE: So in this scenario,
time and space have no meaning.
694
00:34:41,518 --> 00:34:44,419
If everything is
infinitely far apart,
695
00:34:44,421 --> 00:34:48,523
then space
doesn't really exist.
696
00:34:48,525 --> 00:34:51,526
It's sort of beyond
our comprehension.
697
00:34:51,628 --> 00:34:54,229
ROWE: Working out
the expansion rate will
698
00:34:54,298 --> 00:34:57,432
tell us
which scenario we face,
699
00:34:57,434 --> 00:35:01,336
but for now, the lifespan of
the universe is unknown.
700
00:35:02,539 --> 00:35:07,509
Maybe we need to investigate
the other end of the timeline.
701
00:35:07,511 --> 00:35:09,611
But how can we get a fix on
702
00:35:09,613 --> 00:35:13,048
the age of the universe
without understanding
703
00:35:13,117 --> 00:35:14,549
its origin?
704
00:35:14,618 --> 00:35:17,319
BULLOCK: As you go back in time
towards the Big Bang,
705
00:35:17,321 --> 00:35:20,722
our knowledge of physics
really goes out the window.
706
00:35:21,959 --> 00:35:24,626
PLAIT: Temperatures off the
scale, pressure off the scale --
707
00:35:24,728 --> 00:35:27,963
the way everything behaved is
just so different that
708
00:35:28,064 --> 00:35:30,332
the rules we have now do
not apply.
709
00:35:31,401 --> 00:35:33,368
ROWE:
The biggest problem of all --
710
00:35:33,437 --> 00:35:37,105
what came just
before the Big Bang?
711
00:35:37,207 --> 00:35:40,942
Einstein's general relativity
predicts that all the matter
712
00:35:41,044 --> 00:35:42,744
and energy in the universe
713
00:35:42,846 --> 00:35:45,914
was concentrated down
to a single point,
714
00:35:45,916 --> 00:35:47,182
the Singularity.
715
00:35:47,184 --> 00:35:50,152
The Singularity is like
the part
716
00:35:50,220 --> 00:35:53,722
of those old maps
that says, "Here be dragons."
717
00:35:53,824 --> 00:35:57,425
Singularities are a problem.
We don't like them.
718
00:35:57,427 --> 00:36:00,228
This is where basically you
have a finite amount of matter
719
00:36:00,230 --> 00:36:02,130
in the universe,
but it's squeezed down
720
00:36:02,132 --> 00:36:05,233
into zero volume, so it would
be infinitely dense.
721
00:36:06,436 --> 00:36:09,304
SUTTER: Infinite densities don't
actually happen in nature.
722
00:36:09,439 --> 00:36:12,541
This is a sign that
our math is breaking down.
723
00:36:12,543 --> 00:36:13,808
This is a sign that we need
724
00:36:13,810 --> 00:36:17,512
to replace that with
a new understanding.
725
00:36:18,815 --> 00:36:21,416
ROWE: Many now believe
Einstein was wrong.
726
00:36:21,518 --> 00:36:25,053
There was no Singularity
begging the question,
727
00:36:25,155 --> 00:36:28,557
could the age of the universe
be infinite?
728
00:36:36,433 --> 00:36:38,567
ROWE: Scientists
investigating the age of
729
00:36:38,635 --> 00:36:42,137
the universe are struggling
to understand its origins.
730
00:36:43,207 --> 00:36:46,808
Could that be because
there was no beginning?
731
00:36:46,910 --> 00:36:50,111
Could the universe
be infinite?
732
00:36:50,214 --> 00:36:52,147
Because we think
we live and we die,
733
00:36:52,216 --> 00:36:54,049
we project that onto
the universe.
734
00:36:54,084 --> 00:36:56,218
But that may not
be the case.
735
00:36:56,353 --> 00:36:58,787
STRAUGHN: The idea
of an infinite universe is
736
00:36:58,789 --> 00:37:01,323
no more strange than the idea
of a singularity.
737
00:37:01,325 --> 00:37:03,959
And in fact, throughout
most of history,
738
00:37:04,060 --> 00:37:06,061
astronomers thought that
the universe was
739
00:37:06,129 --> 00:37:08,530
probably infinite.
740
00:37:08,632 --> 00:37:10,532
ROWE: The foundation
of our mathematical
741
00:37:10,634 --> 00:37:12,067
understanding of
the universe,
742
00:37:12,135 --> 00:37:15,637
Einstein's general relativity,
has a problem.
743
00:37:15,706 --> 00:37:18,940
It doesn't translate to
the world of the very tiny,
744
00:37:19,042 --> 00:37:23,411
which is why its laws break
down close to the Big Bang.
745
00:37:23,413 --> 00:37:27,015
General relativity does
a great job at describing things
746
00:37:27,017 --> 00:37:28,450
on scales that you and I are
747
00:37:28,518 --> 00:37:31,586
familiar with and things like
how planets move
748
00:37:31,588 --> 00:37:34,055
and how galaxies evolve,
all the big stuff.
749
00:37:34,124 --> 00:37:37,626
Quantum mechanics, on the other
hand, describes the world of
750
00:37:37,728 --> 00:37:40,729
the very small,
the world of the atoms.
751
00:37:40,831 --> 00:37:43,231
The problem is that
these two theories
752
00:37:43,333 --> 00:37:45,467
don't fit well
together at all.
753
00:37:46,536 --> 00:37:50,038
ROWE: A new theory known as
loop quantum gravity,
754
00:37:50,140 --> 00:37:54,109
brings quantum theory
and relativity together,
755
00:37:54,111 --> 00:37:56,945
and it makes a stunning
prediction.
756
00:37:57,047 --> 00:38:01,650
PONTZEN: So one possibility
is that the end of the universe
757
00:38:01,751 --> 00:38:04,853
could kind of match onto
the beginning of a new universe
758
00:38:04,955 --> 00:38:07,255
and create a cycle
of universes,
759
00:38:07,357 --> 00:38:09,024
one after the other.
760
00:38:09,026 --> 00:38:10,959
ROWE:
Nicknamed the Big Bounce,
761
00:38:11,061 --> 00:38:12,827
it predicts a universe that
762
00:38:12,829 --> 00:38:16,831
stops expanding and switches
into reverse.
763
00:38:16,833 --> 00:38:19,968
OLUSEYI: And the idea here is
that the universe can expand for
764
00:38:20,070 --> 00:38:22,070
a time, stop expanding,
765
00:38:22,138 --> 00:38:23,605
and then begin
to contract again.
766
00:38:23,607 --> 00:38:26,041
And some have suggested
that perhaps
767
00:38:26,142 --> 00:38:28,810
there's a cycle of expanding
and compressing.
768
00:38:28,812 --> 00:38:31,012
It bounces back over again.
769
00:38:31,014 --> 00:38:33,948
One of the appeals of
the bouncing model is
770
00:38:34,050 --> 00:38:36,851
that it allows us to get
beyond the Singularity.
771
00:38:36,953 --> 00:38:39,321
ROWE: A bit like
recycling on Earth.
772
00:38:39,423 --> 00:38:43,758
All the components get crushed
down and then reused,
773
00:38:43,827 --> 00:38:47,529
giving the cosmos
no beginning and no end.
774
00:38:47,664 --> 00:38:49,831
If the universe is cyclic,
775
00:38:49,933 --> 00:38:51,833
does the age even have
a meaning?
776
00:38:51,935 --> 00:38:54,869
STRAUGHN:
Age is a construct of humanity,
777
00:38:54,971 --> 00:38:56,438
because we need to count time.
778
00:38:56,506 --> 00:38:58,106
But if the universe
is infinite,
779
00:38:58,108 --> 00:39:01,042
maybe it doesn't matter in
the big scheme of things.
780
00:39:01,144 --> 00:39:03,545
ROWE: A contracting
and expanding universe
781
00:39:03,646 --> 00:39:06,514
messes with the concept
of age.
782
00:39:06,616 --> 00:39:07,949
But the very idea of
783
00:39:08,051 --> 00:39:12,120
an expanding universe provides
another cosmic curveball.
784
00:39:12,122 --> 00:39:14,456
It might not be alone --
it might
785
00:39:14,524 --> 00:39:18,927
be just one ageless universe
among many.
786
00:39:18,929 --> 00:39:23,331
It's an idea embedded in
the math of the Big Bang.
787
00:39:23,333 --> 00:39:26,334
The most popular theory
we have in astrophysics,
788
00:39:26,436 --> 00:39:30,004
what put the bang into
our Big Bang, is inflation.
789
00:39:30,006 --> 00:39:32,107
This idea that there was
a kind of dark energy
790
00:39:32,109 --> 00:39:34,709
on steroids that made our
universe double over and over
791
00:39:34,711 --> 00:39:36,811
not every seven billion years,
792
00:39:36,813 --> 00:39:39,714
but every split second,
793
00:39:39,716 --> 00:39:43,451
creating out of
almost nothing, a big bang.
794
00:39:43,553 --> 00:39:47,622
When the universe was just
a hundredth of a billionth
795
00:39:47,624 --> 00:39:51,059
of a trillionth of
a trillionth of a second old,
796
00:39:51,161 --> 00:39:54,662
it underwent a period of rapid
expansion called inflation.
797
00:39:54,731 --> 00:39:59,067
It doubled in size at least
90 times, going from
798
00:39:59,169 --> 00:40:02,303
the size of a subatomic
particle to that of
799
00:40:02,305 --> 00:40:03,638
a golf ball.
800
00:40:03,740 --> 00:40:06,608
TEGMARK: The problem with this
inflation is that
801
00:40:06,610 --> 00:40:07,742
it doesn't really stop.
802
00:40:07,844 --> 00:40:10,745
It just makes this ever bigger
space and says that,
803
00:40:10,814 --> 00:40:13,448
yeah, well, okay, there was
one region of space where
804
00:40:13,517 --> 00:40:16,618
this crazy doubling stopped
and galaxies formed,
805
00:40:16,620 --> 00:40:17,918
and that's us.
806
00:40:17,954 --> 00:40:20,522
But there's this vast realm
out there where inflation is
807
00:40:20,624 --> 00:40:22,056
still happening.
808
00:40:22,158 --> 00:40:24,726
ROWE: In the spots
where inflation stops,
809
00:40:24,828 --> 00:40:27,262
parallel universes form.
810
00:40:27,330 --> 00:40:30,231
This eternal inflation
means that
811
00:40:30,233 --> 00:40:32,934
new universes are popping into
existence all the time,
812
00:40:32,936 --> 00:40:35,236
but they're completely separated
one from the other.
813
00:40:35,338 --> 00:40:39,607
TEGMARK: Many of my colleagues
hate parallel universes.
814
00:40:39,609 --> 00:40:42,210
They just don't like the idea
that our universe is
815
00:40:42,212 --> 00:40:45,046
so big and most of it is
off limits for us.
816
00:40:45,115 --> 00:40:48,917
If you are willing to be a bit
more humble and accept
817
00:40:48,919 --> 00:40:51,352
that the reality might be
much, much bigger
818
00:40:51,421 --> 00:40:53,154
than we will ever see,
819
00:40:53,256 --> 00:40:56,858
then parallel universes
feel pretty natural.
820
00:40:58,528 --> 00:41:00,228
OLUSEYI: It's really interesting
how everything
821
00:41:00,330 --> 00:41:01,663
in the universe is
tied together.
822
00:41:01,764 --> 00:41:05,033
We can start with a simple
question like how old is
823
00:41:05,035 --> 00:41:08,636
the universe, and here we are,
questioning virtually
824
00:41:08,738 --> 00:41:10,104
everything about the universe.
825
00:41:11,107 --> 00:41:12,207
ROWE: Cosmology's
826
00:41:12,209 --> 00:41:15,410
century-long search for
the age of the universe
827
00:41:15,412 --> 00:41:18,847
forces us to question
our cosmological model,
828
00:41:18,949 --> 00:41:24,052
the nature of gravity,
and even time itself.
829
00:41:24,120 --> 00:41:26,554
The age of the universe
does bring up sort of
830
00:41:26,623 --> 00:41:30,725
profound philosophical
questions about how
831
00:41:30,827 --> 00:41:32,660
a universe can even start,
832
00:41:32,729 --> 00:41:35,563
how can you create something
from nothing?
833
00:41:38,068 --> 00:41:39,734
THALLER:
The vast majority of whatever
834
00:41:39,736 --> 00:41:43,705
the universe is,
is eternally hidden to us.
835
00:41:43,707 --> 00:41:46,708
So we answered the questions
how big, how old,
836
00:41:46,710 --> 00:41:50,345
and those very answers
show us that we don't
837
00:41:50,413 --> 00:41:52,947
even know if we've asked the
right questions to begin with.
76565
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