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one thing that human simply cannot stop
doing is trying to figure out where we
came from and why we exist that's like
our big thing that and getting really
inventive with fried foods but that's a
subject for another channel philosophers
and fry cooks are still working on those
questions but science can at least
answer one thing when the universe began
and right now we're pretty confident
that it all happened around 13.8 billion
years ago with the Big Bang figuring
that out hasn't been easy and our
estimates could still get better but
thanks to some useful tools and a lot of
math we're off to a really good start to
calculate the age of the universe
astronomers use two main tools or pieces
of evidence the first is pretty
intuitive they look for old stuff for
the most part that means looking at
really far away stuff see the universe
has been expanding ever since the Big
Bang so the very oldest objects have
been hurdling away from the earth for
billions of years and based on how far
an object is astronomers can get a rough
idea of how old it is so far using
photos like ones from the Hubble Space
Telescope researchers have been able to
find clusters of stars as old as
thirteen point two billion years but
they don't know the stars are old just
by looking at them to figure it out they
have to take into account some of the
cool weird ways that light behaves see
as the universe expands it also
stretches the light waves traveling
through it so if the star is moving away
from Earth its light will be stretched
and have a longer wavelength by the time
it gets to us business called redshift
by seeing how stretched or redshifted a
star's light is and doing some math
astronomers can get a rough idea of how
far and how old a star is but that isn't
the only tool they use because even
though we can detect some faraway
objects others are still really
difficult to observe over those large
distances mostly this just tells us that
the universe has to be at least thirteen
point two billion years old to refine
the estimate astronomers also use
measurements about the expansion of the
universe itself we've known the universe
was expanding since the late 1920s but
understanding how it's expanding is
what's especially useful knowing how
fast it's happening and how that speed
is changing really allows researchers to
work backwards from right now to find
out exactly when the universe was a tiny
seed of everything it's basically like
how a forensic scientist can study an
explosion site until you win the bomb
went off just with a much bigger bomb in
this case two major discoveries have
helped us understand this expansion the
first was type 1a supernovas which
formed from the explosion of a tiny
white dwarf star and some other
stellar companion in 2011 a team of
scientists when a nobel prize for using
them to prove that the universe's
expansion is getting faster these
supernovas are extremely bright and
their brightnesses are all pretty
uniform so one of them will look a lot
like any other this makes them really
good for calculating distances or what
astronomers call standard candles since
we know what their brightness is should
be at any given distance whether it's a
million or a billion light-years away
they're easy to use in measurements and
after years of measurements astronomers
noticed that the redshifts for these
supernovas was a lot smaller than they
should have been for galaxies so far
away that means that sometime after the
supernovas emitted their light they
actually got farther from Earth than
expected that can only be explained by a
universe that's expanding faster as the
years go on although we aren't positive
what's causing that to happen but it has
helped us understand when the Big Bang
happened before we knew that the
expansion of the universe was
accelerating our calculations about its
age could be pretty inaccurate
astronomers used to assume a constant
rate of expansion so if you're working
backwards from our current rate you'd
get a universe that's way too ya or if
you picked a bad standard candle you'd
get inaccurate measurements too for
example Hubble's original calculations
from the 1920s used a type of star
called a Cepheid variable as the
standard candle and that suggested the
universe was about two billion years old
which is definitely not right Sciences
process still type 1a supernovas aren't
the only way we've studied how the
universe is expanding the other way we
figured out the rate of expansion is
with the Cosmic Microwave Background or
CMB which is the energetic glow left
over from the Big Bang well it's not
wildly energetic it comes in at 2.7
Kelvin or about negative 270 degrees
Celsius but it's not 2.7 Kelvin
everywhere you look and that's super
useful to us those temperature
variations can tell us about the
movement of objects and the densities of
gases in the universe both of which are
used in calculating the universe's rate
of expansion and along with type 1a
supernovas these studies have allowed us
to get a much more precise picture of
how the universe has been growing since
it began
that's let us zero in on our current age
estimate 13.8 billion years and our
observations are just going to get
better from here on out we think 13.8
billion is pretty solid but don't be
surprised if you hear that number change
a little bit as we make better
observations it just means we're getting
better at science and speaking of CMB
brilliant org has a lesson in
astronomy unit that covers even more of
what that background radiation has
taught scientists about the universe and
it's really fun because each question
makes you an active problem solver
so let's see if we learned anything from
everything I was just telling you about
I'm gonna take the quiz here in the
studio but brilliant org also set up a
link so that you can test your knowledge
at home for free you can find that at
brilliant org slash scishow space
cosmology so like all brilliant quizzes
this one opens with giving you more
information about how to solve these
problems this quiz kind of starts with
explaining the CMB a little bit more
before we dive into answering questions
about it and one of the things that I
love about brilliant is that it's not
just text-based that you're working with
you have amazing images like this map
not only do they help me understand the
problem that I'm trying to solve but
they give context to everything that
they're talking about in this quiz and
that helps me make more sense of it but
also retain that information over the
long run and be excited about it so
check out the quiz for yourself and let
us know how you do in the comments below
this quiz is totally free for you to
play with so have at it and the first
200 people to sign up at brilliant org
slash scishow space will get 20% off of
their annual premium subscription and be
supporting scishow space so thank you
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you
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