The Big Bang Explained, takes you through an event that happened thirteen billion years ago to create the Universe and explains what happened at each point. We don’t know why and why aren’t clear why it took the initial form that it did but these are some of the unsolved mysteries of physics that makes it so compelling a subject for many.
10-43 seconds after the Big Bang
The first milestones we can talk about in anything resembling scientific language is known as the Planck Era, a period which occurred 10-43 seconds after the Big Bang. To put that number into perspective, it looks like this when written in full: 0.000000000000000000000000000000000000000001 seconds. This really isn’t a great deal of time at all and this number can be calculated because it is related to the strength of the gravitational force. It is so tiny, because gravity is so weak at this stage. We don’t know the reason for this either.
During the Plank Era, the four fundamental forces of nature that we know today – gravity, strong and weak nuclear forces and electromagnetism – were one and the same force. What has been described as a single superforce. A physicist would call this a very symmetrical situation.
Symmetry breaking events
As the universe rapidly expanded and cooled, it underwent a series of symmetry breaking events. The first at the end of the Planck Era, saw gravity separate from the other forces of nature, and so the perfect symmetry was broken. At around 10-36 seconds after the Big Bang, another symmetry breaking event occurred which market the end of the Grand Unification Era.
This new era saw the strong nuclear force – the force that sticks quarks together inside protons and neutrons – split from the other forces. At this point, the Universe underwent an amazingly violent expansion stage known as inflation, in which the Universe expanded in size by a factor of 1026. This is 100 million, million, million, million times in an unfathomably small space of time. It was over in 10-32. This was when subatomic particles entered the Universe for the first time, but they weren’t quite what we see today because none of them had any mass at all.
Large Hadron Collider clarity
Up until these eras’s detailed so far, everything is theoretical but untested. The next great symmetry-breaking event, which occurred 10-11 seconds after Big Bang, is completely within our reach, because this is the era being re-created at the CERN Large Hadron Collider. It is named electroweak symmetry breaking; at this point the final two forces of nature – electromagnetism and weak nuclear force – became 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 is one of the key goals for the Large Hadron Collider project.
Everything is clear
From this stage onwards, the experimental and theoretical ground is very firm. This is because we are able to perform experiments in particle accelerators to prove we understand the physics. The emergence of the familiar particles and forces we see in the Universe today happened as a result of a series of symmetry breaking events which began at the end of the Planck Era.
The concept of spontaneous symmetry breaking in the early Universe is exactly the same as for the transitions from water vapour to liquid water to ice. Complex patterns emerge without prompting – just as a result of falling temperature – and these patterns obscure the underlying symmetry of the initial state. So just as the seemingly infinite complexity of snowflakes masks the simple symmetry of oxygen and hydrogen atoms, so the array of forces of nature and subatomic particles we see as the building blocks of the Universe today obscures the symmetry of the early Universe.
1 millionth 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. This began around a millionth 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 millionth of a second in the life of the Universe, the first chemical element had made an appearance. 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.
There were also very, very small amounts of lithium, with three protons, and beryllium, with four protons – the third – and fourth – simplest elements. And this is pretty much where the process stopped. After three minutes the Universe had the four distinct forces that we know today – gravity, strong and weak nuclear forces, and electromagnetism, and was composed by about 75% hydrogen (by mass) and 25% helium.
This all explains the Big Bang process and the creation of the simplest chemical elements and of the successive symmetry breaking events in the early Universe.