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Big Bang Theory
It took 9.2 billion years of cosmic evolution before our Sun and Solar System even began to form. Such a small event has led to so much.
Early on, only matter and radiation were important for the expanding Universe. After a few billion years, dark energy changed everything.
Our own galaxy, the Milky Way, is both completely normal and absolutely remarkable in a number of ways. Here's the story of our cosmic home.
Millennia ago, philosophers like Anaximander grasped that nature is the ultimate recycler.
On the largest cosmic scales, galaxies line up along filaments, with great clusters forming at their intersection. Here's how it took shape.
Astronomers claim to have found structures so large, they shouldn't exist. With such biased, incomplete observations, perhaps they don't.
Observations of an enormous cosmic structure, dubbed the "Big Ring," seem to violate the Copernican principle.
For every proton, there were over a billion others that annihilated away with an antimatter counterpart. So where did all that energy go?
One newly discovered, ancient star has a composition unlike any other. Explaining its existence is already blowing astronomers' minds.
Finding it at all was a happy accident. Examining it further may help unlock the secrets hiding within the earliest galaxies of all.
Today, the star-formation rate across the Universe is a mere trickle: just 3% of what it was at its peak. Here's what it was like back then.
Earth wasn't created until more than 9 billion years after the Big Bang. In some lucky places, life could have arisen almost right away.
As early as we've been able to identify them, the youngest galaxies seem to have large supermassive black holes. Here's how they were made.
For 550 million years, neutral atoms blocked the light made in stars from traveling freely through the Universe. Here's how it then changed.
Even after the first stars form, those overdense regions gravitationally attract matter and also merge. Here's how they grow into galaxies.
The first stars in the Universe were made of pristine material: hydrogen and helium alone. Once they die, nothing escapes their pollution.
The first stars took tens or even hundreds of millions of years to form, and then died in the cosmic blink of an eye. Here's how.
The Big Bang's hot glow faded away after only a few million years, leaving the Universe dark until the first stars formed. Oh, the changes!
Atomic nuclei form in minutes. Atoms form in hundreds of thousands of years. But the "dark ages" rule thereafter, until stars finally form.
The first elements in the Universe formed just minutes after the Big Bang, but it took hundreds of thousands of years before atoms formed.
In the early stages of the hot Big Bang, there were only free protons and neutrons: no atomic nuclei. How did the first elements form from them?
In the early stages of the hot Big Bang, matter and antimatter were (almost) balanced. After a brief while, matter won out. Here's how.
For a substantial fraction of a second after the Big Bang, there was only a quark-gluon plasma. Here's how protons and neutrons arose.
In the very early Universe, practically all particles were massless. Then the Higgs symmetry broke, and suddenly everything was different.
In the earliest stages of the hot Big Bang, equal amounts of matter and antimatter should have existed. Why aren't they equal today?
When the hot Big Bang first occurred, the Universe reached a maximum temperature never recreated since. What was it like back then?
Some 13.8 billion years ago, the Universe became hot, dense, and filled with high-energy quanta all at once. Here's what it was like.
Cosmic inflation is the state that preceded and set up the hot Big Bang. Here's what the Universe was like during that time period.
Bang bang all over the Universe.
If the Universe is expanding, and the expansion is accelerating, what does that tell us about the cause of the expanding Universe?