# Blue Origin — The origins of the universe > A clear, serious guide to the Big Bang: what happened in the first moments of the universe, the evidence behind it, and the questions that remain open. Ask us anything. Blue Origin (blueorigin.si) is an independent, English-language educational website about the Big Bang and the early universe. It summarises the standard cosmological model in plain language, cites the main lines of evidence, lists the open questions, and answers readers' questions personally by email. ## Key facts - Age of the universe: 13.8 billion years (Planck 2018: 13.787 ± 0.020 Gyr) - Cosmic microwave background temperature: 2.725 K, released ~380,000 years after the Big Bang - Planck time: 10⁻⁴³ s, the earliest moment current physics can describe - Cosmic inflation: ~10⁻³⁶ to 10⁻³² s, expansion by a factor ≥ 10²⁶ - Primordial nucleosynthesis: 10 s to 20 min, ~75% hydrogen and ~25% helium by mass - First stars: ~100–200 million years after the Big Bang - Composition today: ~5% ordinary matter, ~27% dark matter, ~68% dark energy ## Frequently asked questions ### What is the Big Bang? The Big Bang is the scientific model describing how the universe expanded from an extremely hot, dense early state about 13.8 billion years ago. It is not an explosion in space but the expansion of space itself, and it is supported by the observed expansion of the universe, the cosmic microwave background and the abundance of light elements. ### How old is the universe? About 13.8 billion years. The most precise value, 13.787 ± 0.020 billion years, comes from the Planck satellite measurements of the cosmic microwave background published in 2018. ### What was there before the Big Bang? Nobody knows. In the standard model, time as we measure it begins with the Big Bang, so "before" may not be a meaningful question. Several hypotheses exist, such as eternal inflation, a bouncing universe or quantum gravity scenarios, but none is confirmed by observation. ### What is the cosmic microwave background? The cosmic microwave background (CMB) is light released about 380,000 years after the Big Bang, when the universe cooled enough for atoms to form and became transparent. Stretched by expansion, it now reaches us as microwaves with a temperature of 2.725 kelvin, uniform across the whole sky. ### What is the evidence for the Big Bang? Three independent observations: distant galaxies recede faster the farther they are (Hubble–Lemaître law, 1929); the cosmic microwave background fills the sky at 2.725 K (discovered 1965); and the measured amounts of hydrogen, helium and deuterium match what a hot early universe would have produced in its first minutes. ### What is cosmic inflation? Inflation is a proposed period of extremely rapid expansion between roughly 10⁻³⁶ and 10⁻³² seconds after the Big Bang, during which space grew by a factor of at least 10²⁶. It explains why the universe is so uniform and flat, but the field that drove it has not been identified. ### What are dark matter and dark energy? Ordinary matter is only about 5% of the universe. Dark matter, about 27%, is matter detected only through its gravity. Dark energy, about 68%, is whatever causes the expansion of the universe to accelerate. The nature of both is unknown. ## Pages - [Home](https://blueorigin.si/): timeline of the first moments, evidence, open questions, ask-us and contact forms - [Sitemap](https://blueorigin.si/sitemap.xml) ## Contact Questions and corrections via the forms on https://blueorigin.si/#ask and https://blueorigin.si/#contact.