bout fourteen billion years ago, the universe leaped into existence in a cataclysmic event called the Big Bang. Our universe began small and then expanded to its present cosmic dimensions. Scientists have long wanted to know the conditions of the universe in the earliest fractions of a second, but have been stymied by the billions of years of evolution in the interim. However, a group of researchers have employed a supercomputer that will allow them to turn back the clock and determine what the universe looked like at the moment of its birth.
The best current understanding of the nature of the universe shortly after it began is that it was a small, hot, and dense, sea of energy. This energy bath was nearly uniform throughout the cosmos of the time. However, because of the laws of quantum mechanics, there were tiny fluctuations in the distribution of energy, with certain locations having slightly more energy than normal and other locations having slightly less. The location and amount of energy variations were random.
Einstein’s equation E = mc2 tells us that mass and energy are equivalent, so those regions of small excesses of energy evolved into regions with a small excess of mass. And since gravitational forces are caused by mass, those regions had slightly stronger gravity than the regions that had less energy when the universe began. Over the billions of years, gravity then amplified the effect, with the regions with a small excess of mass gathering mass from regions those regions that started out with a small mass deficit.
The result is the universe we see today. Using powerful telescopes, astronomers have charted the location of galaxies from the neighborhood of our own Milky Way, out to locations many billions of light years away. They have observed that, on distance scales of a few hundred millions of light years, the cosmos has a “bubble-like” structure, with galaxies clustered on the surface of the bubbles, surrounding voids that are nearly devoid of galaxies. On larger scales, the universe looks uniform. If you imagine looking very closely at the foam on a mug of root beer, and then moving the mug away from you, you’ll have a good understanding of the structure of the universe. In our analogy, the galaxies are located on the membrane of the bubbles.
The problem for scientists trying to work out the distribution of energy shortly after the Big Bang is that they need to use modern day measurements to evaluate their predictions. And these modern-day measurements have nearly fourteen billion years of gravitational interactions that must be taken into account. It is rather difficult to calculate the effect of so many eons of gravity and remove it so the initial distribution of mass and energy can be worked out.
A group of Japanese researchers devised a method to disentangle the effect of gravity and determine the mass and energy distribution of the early universe. They used the supercomputer at the National Astronomical Observatory of Japan, located in Tokyo, to simulate 4,000 universes, each with a slightly different configuration of mass and energy. These simulations effectively let the mass of each simulated universe be affected by fourteen billion years of gravity. The researchers then devised algorithms that could reliably simulated take modern day measurements and determine the simulated universe’s initial conditions.
Similar techniques have been applied in the past to understand how galaxies assemble. However the advance in this recent result is that the “gravity removal” algorithms not only work on the universe as a whole, they also appear to be able to remove the effects due to cosmic inflation, which is a period in the history of the universe where the universe expanded at speeds faster than light for a tiny fraction of a second. Inflation theory is an unproved, but key, component of astronomers’ current understanding of the history of the universe. It explains the observed uniformity of the universe on the largest scales, and furthermore explains why the geometry of the universe is what we see.
The research group has not yet applied their gravity removal algorithms to data that describes the universe in which we live, however appropriate data has already been recorded by other research groups. One set of such data was recorded by a telescope at the Apache Point Observatory in Sunspot, New Mexico. This telescope is used by the Sloan Digital Sky Survey (SDSS) collaboration, and this group measures the location of incredibly distant galaxies – galaxies so far away that light has taken eleven billion years to get to us.
While the analysis will be challenging, this algorithm, combined with the SDSS data, might give us our first reliable glimpse of the birth of the universe and will give us a much better understanding of our cosmic origins. In doing so, astronomers might be able to answer one of the grandest questions of all – how the universe came to be.