The Big Bang is the leading theory for the creation of the universe. By studying various cosmological effects, and based on our understanding of quantum physics, scientists suggest that the universe began as a singularity – a single point of seemingly infinite density and temperature – and expanded to its present-day scale. By measuring this rate of expansion, we can place the point of the Big Bang at 13.82 billion years ago.
The first milestones we can talk about in anything resembling scientific language is known as the Planck epoch, a period that lasted until 10-43 seconds after the Big Bang. To put that number into perspective, it looks like this when written in full: 0.000000000000000000000000000000000000000001 seconds.
The force is strong…
During the Plank epoch (named after the German physicist Max Planck), the universe was unimaginably hot and dense – around the size of a single subatomic particle and 1032 Kelvin. The four fundamental forces that we know today – gravity, strong and weak nuclear forces and electromagnetism – were one and the same force, described as a single superforce.
Gravity breaks free
Within the first brief moments of its creation, the universe underwent some fundamental changes. As it expanded and cooled, the force of gravity separated out, while the three other forces were unified as the electronuclear force. This period – from 10-43 seconds to 10-36 seconds after the Big Bang – is known as the grand unification epoch.
The Big Bang
Next comes the inflationary epoch, when the universe underwent extremely violent expansion. In an almost imperceptibly short period of time (from 10-36 to 10-33 seconds after the Big bang), the universe grew from one nanometer in diameter to roughly 10.6 light years – or 62 trillion miles. It was filled with a hot quark-gluon plasma, ten thousand trillion trillion degrees in temperature and with a mass of 1,075 g/cm3. That’s the equivalent of all the matter in the Milky Way galaxy compressed into the space of a single Hydrogen atom!
From theory to reality
Up until this point – around 10-32 seconds after the Big Bang – everything is theoretical but untested. However, the next major event, which occurred 10-11 seconds after Big Bang, is completely within our understanding because this is the epoch that has been recreated at the CERN Large Hadron Collider.
The electroweak epoch occurred when the temperature fell low enough for electromagnetism and weak nuclear force to become separated. During this process, the subatomic building blocks of everything we see today – the quarks and electrons – acquired mass. The most common theory for this process is known as the Higgs mechanism, and the search for the associated Higgs particle was one of the key goals for the Large Hadron Collider project.
One trillionth of a second after Big Bang
There is now one final step needed to arrive at the protons and neutrons – the building blocks of the elements – and the first elements themselves. The quark epoch began around a trillionth of a second after the Big Bang, when the quarks had cooled enough to become glued together by the strong nuclear force to form protons and neutrons. The simplest element, hydrogen, is made from a single proton. So after only one trillionth of a second in the life of the universe, the first chemical element had made an appearance.
Three minutes and counting
The period described above is known as the very early universe and it all took place within a single picosend of the Big Bang. After three minutes, the universe was cold enough for the protons and neutrons themselves to stick together to form helium. With two protons and one or two neutrons in its nucleus, helium is the second simplest chemical element. With just three minutes on the cosmological clock, the universe had the four distinct forces that we know today – gravity, strong and weak nuclear forces, and electromagnetism – and was composed of about 75% hydrogen (by mass) and 25% helium.
Ten billion years later…
While the universe was now in its its basic state, it took another billion years for the first stars to appear, and around ten billion for the universe to appear much as it looks today.