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. — The story of our cosmic history is one of an expanding and cooling Universe. As we progressed from a hot, dense, uniform state to a cold, sparse, clumpy one, a number of momentous events happened throughout our cosmic history. At the moment of the hot Big Bang, the Universe was…

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, the Universe was filled with all the particles, antiparticles, and quanta of radiation it had the energy to create. As the Universe expanded, it cooled: the stretching fabric of space also stretched the wavelengths of all the radiation within it to…

In the earliest stages of the hot Big Bang, there equal amounts of matter and antimatter should have existed. Why aren’t they equal today? — 13.8 billion years ago, at the moment of the Big Bang, the Universe was the hottest it’s ever been in history. Every single known particle exists in great abundance, along with equal amounts of their antiparticle counterparts, all smashing rapidly and repeatedly into everything around them. The spontaneously create themselves…

When the hot Big Bang first occurred, the Universe reached a maximum temperature never recreated since. What was it like back then? — When we look out at the Universe today, we see that it’s full of stars and galaxies, in all directions and at all locations in space. The Universe isn’t static, though; the distant galaxies are bound together in groups and clusters, with those groups and clusters speeding away from one…

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. — Looking out at our Universe today, we not only see a huge variety of stars and galaxies both nearby and far away, we also see a curious relationship: the farther away a distant galaxy is, the faster it appears to move away from us. This continues as far as we’ve…

Perhaps the most remarkable fact about the Universe at all is simply that it, and everything in it, exists. But what’s the reason why? — Perhaps the most remarkable fact about the Universe, if you think about it on a truly fundamental level, is that it exists at all. And yet, not only does it exist, but there’s matter within it, which obeys the same rules everywhere and at all times, and assembles according to…

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. Our Universe today is full of matter and radiation, and can be observed by us through a variety of means. Atoms have clumped and clustered together…

With LEDs bringing brighter nighttime lighting than ever before, and thousands of new satellites polluting the skies, astronomy needs help. — For nearly all of human history, once the Sun went down and the sky darkened, so long as you had a clear, moonless night, you’d be greeting with a spectacular, thrilling night sky: with thousands of stars, a clear view of the Milky Way, and several faint, fuzzy nebulae all…

Finding alien technology on the seafloor would be truly incredible. This extraordinary claim, however, is debunked by the actual evidence. — Perhaps the biggest question in all of the cosmos is that of life beyond Earth. With so many stars and planets, and with the raw ingredients for life found strewn all about the Universe, there are enormous numbers of proverbial lottery tickets out there: chances for life to arise, survive…