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The beginning of everything.

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The Big Bang.

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The idea that the universe was suddenly
born and is not infinite.

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Up to the middle of the 20th century,
most scientists thought of the universe

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as infinite and ageless.

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Until Einstein’s theory of relativity gave
us a better understanding of gravity,

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and Edwin Hubble discovered that galaxies
are moving apart from one another

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in a way that fits previous predictions.

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In 1964, by accident, cosmic background
radiation was discovered,

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a relic of the early universe,

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which, together with other observational
evidence, made the Big Bang

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the accepted theory in science.

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Since then, improved technology like the
Hubble telescope

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has given us a pretty good picture of the
Big Bang and the structure of the cosmos.

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Recent observations even seem to suggest
that the expansion of the universe

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is accelerating.

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But how did this Big Bang work?

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How can something come from nothing?

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Let’s explore what we know.

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We can ignore the beginning part
for now.

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First of all, the Big Bang was not
an explosion.

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It was all space stretching
everywhere all at once.

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The universe started
very, very, very small

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and quickly expanded to the
size of a football.

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The universe didn’t expand into anything,
space was just expanding into itself.

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The universe cannot expand into anything
because the universe has no borders;

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there is, by definition, no “outside”
the universe.

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The universe is all there is.

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In this hot, dense environment, energy
manifested itself

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in particles that existed only for the
tiniest glimpses of time.

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From gluons, pairs of quarks were created,
which destroyed one another,

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perhaps after giving off more gluons.

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These found other short-lived quarks
to interact with,

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forming new quark pairs and
gluons again.

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Matter and energy were not just
theoretically equivalent,

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it was so hot they were practically
the same stuff.

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Somewhere around this time, matter
won over antimatter.

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Today, we’re left with almost all
matter and nearly no antimatter at all.

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Somehow, one billion and one matter
particles were formed

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for every one billion particles of
antimatter.

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Instead of one massive ultimate force
in the universe,

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there were now several refined versions
of it acting under different rules.

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By now the universe has stretched to a
billion kilometers in diameter,

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which leads to a decrease in temperature.

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The cycle of quarks being born and
converted back to energy

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suddenly stops.

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From now on, we work with what we have.

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Quarks begin forming new particles,
hadrons, like protons and neutrons.

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There are many, many combinations of
quarks that can form all sorts of hadrons,

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but only very few are reasonably stable
for any length of time.

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Please take a moment to appreciate that
by now, only one second has passed

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since the beginning of everything.

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The universe, which has grown to one
hundred billion kilometers,

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is now cold enough to allow most of the
neutrons to decay into protons

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and form the first atom, hydrogen.

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Imagine the universe at this point as an
extremely hot soup,

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ten billion degrees Celsius, filled with
countless particles and energy.

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Over the next few minutes, things cooled
and settled down very fast.

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Atoms formed out of hadrons and electrons,

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making for a stable and electrically
neutral environment.

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Some call this period the Dark Age,
because there were no stars

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and the hydrogen gas didn’t allow visible
light to move around.

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But what’s the meaning of visible light,
anyway, when there’s nothing alive yet

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that could have eyes?

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When the hydrogen gas clumped together
after millions of years and

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gravity put it under great pressure, stars
and galaxies began to form.

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Their radiation dissolved the stable
hydrogen gas into a plasma

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that still permeates the universe today
and allows visible light to pass.

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Finally, there was light!

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Okay, but what about the part
we didn’t talk about?

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What happened right at the beginning?

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This part can be defined as the Big Bang.

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We don’t know at all what happened here.

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At this point, our tools break down.

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Natural laws stop making sense,
time itself becomes wibbly-wobbly.

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To understand what happened here,
we need a theory that unifies

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Einstein’s relativity and quantum
mechanics, something countless

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scientists are working on right now.

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But this leaves us with lots of
unanswered questions.

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Were there universes before our own?

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Is this the first and only universe?

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What started the Big Bang, or did it
just occur naturally,

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based on laws we don’t understand yet?

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We don’t know, and maybe we never will.

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But what we do know is that the universe
as we know it started here

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and gave birth to particles, galaxies,
stars, the Earth, and you.

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Since were ourselves are made of
dead stars, we are not separate

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from the universe; we are part of it.

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You could even say that we are the
universe’s way of experiencing itself.

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So, let’s keep on experiencing it, until
there are no more questions to ask.