By Gary Felder, Smith College
The first event we know of after the big bang was a brief period called inflation. During the universe’s inflation, the universe expanded so rapidly that two particles that were an atom’s width apart before inflation would have been much more than a thousand light-years apart when inflation ended, a tiny fraction of a second after it began.
After the Inflation
We don’t know a lot about what the universe was like before inflation, but we do know that right after inflation, it was a hot, dense collection of elementary particles that was expanding rapidly. Those particles included quarks, which in the universe today are the building blocks of protons and neutrons.
There were also electrons, and the quarks and electrons later went on to make up all the atoms in the universe today. There were also several more exotic types of particles such as antimatter, neutrinos, dark matter, and dark energy.
The Principle of Inertia
From the end of inflation until today, three main processes have determined much of what has happened throughout the history of the universe.
First, the universe was expanding—that is, it was getting less dense. Why did everything keep rushing away from everything else? Because everything already was rushing away from everything else and left to their own devices, things tend to keep going the way they’re going. That’s called the principle of inertia. The bottom line is that we don’t know what started the expansion, but once it was started it kept going by inertia.
A Change of Temperature
The second main process was that the universe was cooling down. Why was it cooling down? Because it was expanding. In general, when a gas expands, it cools. And matter behaves very differently at different temperatures. At the temperatures we’re familiar with, heating or cooling can cause transitions such as melting or boiling.
Similarly, at the high temperatures of the early universe, the state of matter changed repeatedly as the universe cooled. This cooling was the major factor driving the events that occurred throughout the early universe.
This article comes directly from content in the video series The Big Bang and Beyond: Exploring the Early Universe. Watch it now, on Wondrium.
Bonding Behaviour
And the third main process: Foremost among the changes caused by cooling was that bigger and more complicated structures formed over time. As inflation ended, what we had were elementary particles. Over time, quarks combined into protons and neutrons, protons and neutrons fused into nuclei, nuclei and electrons combined into atoms, and eventually, atoms came together and formed stars and galaxies.
All that bonding behavior was largely a result of the cooling temperatures. At very high temperatures, particles can’t stick to each other. The more the early universe cooled down, the larger the structures that could form. In short, expansion led to cooling and cooling led to particles combining.
A Brief but Rapid Period
With that in mind, let’s pick our story back up just after inflation, that brief period of extremely rapid expansion. After inflation, the expansion slowed down tremendously, but in those early seconds, the expansion was still much faster than it is today. As a result, changes happened extremely quickly.
Today, the effects of expansion are measured in billions of years, but in the early universe, the expansion was so rapid that the universe underwent a number of important changes within the first second after the big bang. One of the earliest of those changes had to do with quarks, the building blocks that make up the protons and neutrons inside atomic nuclei.
Today we never see quarks on their own; essentially, all the quarks in the universe today are bound up into protons and neutrons. But when quarks were first produced, the universe was too hot for those quarks to stick together. At the unimaginably high temperatures shortly after inflation, the quarks were all moving so fast that they simply bounced off each other.
That changed about a hundred-thousandth of a second after the big bang when the temperature dropped to about a trillion degrees. At a trillion degrees, the quarks combined into protons and neutrons, and there have been virtually no free quarks in the universe since then. As the early universe expanded and cooled, the rate of expansion was slowing, so the next big changes took place on the more familiar time scales of seconds and minutes.
Common Questions about the Consequences of the Universe’s Inflation
Right after the universe’s inflation, the universe was in a hot and dense state, which included elementary particles. These particles included quarks and electrons, which are the universe’s building blocks, as well as antimatter, neutrinos, dark matter, and dark energy.
After the universe’s inflation, three main processes happened at the same time. First, the universe was expanding and continued to do so because of the principle of inertia. Second, the universe kept cooling down because of the universe’s expansion. Thirdly, because of the cooling of the universe, different structures such as atoms that couldn’t exist previously were now able to exist.
Right after the universe’s inflation, the quarks that were free because they were moving very fast due to the high temperatures bounced off each other. But after about a small fraction of a second, with the universe’s temperature cooling down, the quarks combined into protons and neutrons.
