The Big Bang.

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

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

as infinite and ageless.

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

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

in a way that fits previous predictions.

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

a relic of the early universe,

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

the accepted theory in science.

Since then, improved technology like the Hubble telescope

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

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

is accelerating.

But how did this Big Bang work?

How can something come from nothing?

Let’s explore what we know.

We can ignore the beginning part for now.

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

It was all space stretching everywhere all at once.

The universe started very, very, very small

and quickly expanded to the size of a football.

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

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

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

The universe is all there is.

In this hot, dense environment, energy manifested itself

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

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

perhaps after giving off more gluons.

These found other short-lived quarks to interact with,

forming new quark pairs and gluons again.

Matter and energy were not just theoretically equivalent,

it was so hot they were practically the same stuff.

Somewhere around this time, matter won over antimatter.

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

Somehow, one billion and one matter particles were formed

for every one billion particles of antimatter.

Instead of one massive ultimate force in the universe,

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

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

which leads to a decrease in temperature.

The cycle of quarks being born and converted back to energy

suddenly stops.

From now on, we work with what we have.

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

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

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

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

since the beginning of everything.

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

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

and form the first atom, hydrogen.

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

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

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

Atoms formed out of hadrons and electrons,

making for a stable and electrically neutral environment.

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

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

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

that could have eyes?

When the hydrogen gas clumped together after millions of years and

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

Their radiation dissolved the stable hydrogen gas into a plasma

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

Finally, there was light!

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

What happened right at the beginning?

This part can be defined as the Big Bang.

We don’t know at all what happened here.

At this point, our tools break down.

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

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

Einstein’s relativity and quantum mechanics, something countless

scientists are working on right now.

But this leaves us with lots of unanswered questions.

Were there universes before our own?

Is this the first and only universe?

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

based on laws we don’t understand yet?

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

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

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

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

from the universe; we are part of it.

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

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

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