Humanity has long been fascinated by the question of how the universe began, with many ideas proposed over the millennia. Over the last century, researchers have developed a scientific model called the Big Bang, which postulates that the universe had a definite beginning just shy of 14 billion years ago. In this theory, the universe was once much smaller and hotter, and has been expanding since it began. In broad strokes, scientists are certain that the Big Bang is an accurate description of the beginning of the universe, but when they try to understand it in detail, there remain mysteries. A recent paper in the prestigious journal Physical Review Letters may shed some light on the sequence of events that preceded the Big Bang.
Many non-scientists do not understand exactly what a cosmologist means when they talk about the Big Bang. For instance, the Big Bang does NOT include the exact, precise moment when the universe began. What came before and what “pulled the trigger,” so to speak, is not a component of the theory of the Big Bang. Furthermore, not even the most knowledgeable cosmologist can definitively say what happened at the first instant of the universe. The Big Bang only describes times after that moment.
In addition, scientists have known for a very long time that the Big Bang as it was first proposed back in 1931 by a Belgian priest and cosmologist by the name of Georges Lemaître cannot be correct. His theory explained the expansion of the universe, but it didn’t explain why the universe seemed so uniform. His theory predicted that locations on opposite sides of our visible universe should be appreciably different, but observations show that the two sides are effectively identical. The problem was that in order for the two sides to be so similar they would have to have had been in contact, but the locations are so far apart that light hasn’t had time to go from one to the other. The should have never interacted with each other and thus their similarity was a real mystery.
It was in 1981 that physicist Alan Guth realized that he could explain the uniformity of the cosmos if the two sides actually were in contact immediately after the universe was created and then, for a split second, the universe expanded much faster than the speed of light. This expansion then caused the two locations of the primeval universe to change from being in to contact to forever being separated. Guth called his theory “cosmic inflation.”
In inflation theory, from about 10-36 to about 10-32 seconds after the Big Bang, an energy field of a special kind filled the universe. This field, called the inflaton field, is a repulsive form of gravity and this repulsion caused the expansion of the universe to accelerate, with sizes growing by a whopping 1026 times. During that split second, our visible universe grew from being much smaller than an atom to about the size of a grapefruit.
And, after that, the period of inflation – which is to say the period of accelerating expansion – stopped, and the universe continued to expand, but now slowing due to the effect of ordinary gravity. It is this ordinary expansion period that scientists call the Big Bang. Thus, astronomers can broadly break up the history of the universe into three parts: the moment of creation, the inflation period, and finally the Big Bang.
This theoretical triumvirate has been largely accepted since it was proposed about 40 years ago, but mysteries remained. For instance, during the period of inflation, the universe was cold, and no particles existed. During the Big Bang, the universe was hot and obviously full of particles that became the atoms that make up familiar matter. Since inflation was followed by the Big Bang, the transition from hot to cold and empty to full needed to be explained.
In the recent paper, researchers possibly solved the conundrum by essentially invoking a new kind of phase transition. The energy that drove the accelerating expansion of the universe during the inflation period converted into heat energy that created the hot bath of plasma that evolved into our familiar universe. In this transition, the inflaton field disappeared (thus turning off inflation) and heated up the universe, which led to us.
This work remains speculative and will certainly require substantial additional study to confirm, but the conversion of energy from one form to another allowed researchers killed two metaphorical birds with one stone. The work also highlights the fact that the details of how the universe came into play are actually pretty complex. It is highly likely that the final theory of the origins of the universe will be even more intricate.