Probing back to the origin of the universe involves a lot of estimation and guesswork. Imagine that the word ‘roughly’ is written before each date!
0: The Big Bang. Time and space are created.
10-43 seconds: Gravity separates from the three other fundamental forces (electromagnetism, and the weak and strong nuclear forces). This is the earliest time that theoretical physicists have probed so far. The strong force and electroweak forces become distinct soon after.
10-35 seconds: The universe expands, undergoing a spectacular acceleration known as inflation. This process takes tiny regions of space and blows them up into much larger volumes, ironing out any wrinkles in the process.
10-6 seconds: Particles gain mass. The electroweak forces break down into the electromagnetism and weak forces we observe today. Sub-atomic particles gain mass.
* 1 second: The first composite particles. Protons and neutrons form from a very hot soup of quarks and gluons.
3 minutes: The first elements (mostly hydrogen and helium) form. The universe expands and cools so fast that heavier elements don’t even have a chance to be created.
380,000 years: The universe’s temperature drops enough for the protons and neutrons to begin capturing electrons. Also, for the first time, light travels freely through space, and the fog of the early universe clears. This light is still detectable today as the cosmic microwave background.
30 million years: Stars first appear in the universe. Computer models suggest that the first stars may have formed at this point, along with the creation of heavy elements.
200 million years: The Milky Way forms. The Earth’s home galaxy was formed not long (well, in cosmic terms) after the first stars.
9 billion years: The Earth’s solar system forms. The disk of material left over after the formation of the Sun begins to get clumpy.
10 billion years: Life on Earth begins. The effect of harsh solar radiation and lightning on a primordial soup of organic material may have kick-started life.
11 billion years: Oxygen accumulates in the atmosphere of the Earth. The essential gas for animals to breathe appears for the first time.
13.5 billion years: Early humans evolve in Africa. Modern humans first appear on the continent and colonise the rest of the planet.
13.7 billion years: You check out this list. The origins of the universe are explained!