What was the Universe like before there were stars, galaxies, or even atoms? Today, the Universe is filled with billions of galaxies, stars, planets, gas clouds, and enormous structures spread across space. But about 13.8 billion years ago, the cosmos was in a much hotter, denser state. Over time, it expanded and cooled. Particles formed […]
Universe Timeline: From the Big Bang to Today Read Post »
If the universe is about 13.8 billion years old, how can scientists know what happened in its earliest history? They did not observe the Big Bang itself. No telescope captured an explosion taking place at a particular location in space. The Big Bang is also not the name for an explosion into empty space. In
How Scientists Know the Big Bang Happened Read Post »
If the first stars had not yet formed, how can we know what the universe looked like when it was only a few hundred thousand years old? The answer is microwave background radiation, more commonly called the cosmic microwave background (CMB). The CMB is ancient electromagnetic radiation that fills the universe. It was released when
What Is Microwave Background Radiation? The Universe’s Oldest Light Explained Read Post »
What Was the Universe Like Before Stars Existed? Today, the universe is filled with stars and galaxies. But there was a long period in cosmic history when none of them existed. About 380,000 years after the beginning of the universe’s expansion, the universe had cooled enough for electrons to combine with atomic nuclei, forming
What Was the Universe Like Before Stars Existed? Read Post »
If the early universe was unimaginably hot, how did the first atoms form? The answer begins with an important distinction: the universe did not start out filled with ordinary atoms. According to the modern Big Bang model, the universe has been expanding and cooling for about 13.8 billion years. In its early, hot state, matter
How Did the First Atoms Form? The Story of Hydrogen and Helium in the Early Universe Read Post »
Cosmic Inflation: How the Early Universe Expanded in a Fraction of a Second A second after the Big Bang, the universe was already expanding, cooling, and filled with an extremely hot mixture of particles and radiation. But if we move further back into cosmic history, we encounter an even more extreme possibility: cosmic inflation. Inflation
Cosmic Inflation: How the Early Universe Expanded in a Fraction of a Second Read Post »
What Happened One Second After the Big Bang? Inside the Newborn Universe One second seems almost meaningless on a human timescale. But one second after the Big Bang, the universe was already undergoing enormous physical changes. It was expanding and cooling from an extraordinarily hot, dense state. The temperature was around 10 billion kelvin, or
What Happened One Second After the Big Bang? Inside the Newborn Universe Read Post »
From Nothing to Everything? Understanding the Origin of the Universe How did everything we can see—galaxies, stars, planets and eventually life—come to exist? That question takes us to the origin of the universe, but answering it requires an important distinction. Scientists can describe a great deal about how the early universe evolved from an extremely
From Nothing to Everything? Understanding the Origin of the Universe Read Post »
What Happened Before the Big Bang? Exploring One of Science’s Biggest Questions If the universe had a beginning, what existed before it? It sounds like a simple question, but answering it is surprisingly difficult. When we ask what happened before the Big Bang, we are not simply asking what filled an empty space. We are
What Happened Before the Big Bang? Exploring One of Science’s Biggest Questions Read Post »