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The image taken from the Hubble Space Telescope of the galaxy cluster Cl0024+1654 shows small red dots of stars against a background of dark blueish-hued dark matter.
Following the Big Bang, most astronomers believe that the universe underwent a rapid expansion, known as inflation, during its earliest moments. The cause of inflation remains unknown, but it needs to explain various observations, such as the extreme flatness of the universe on a large scale.
Inflation is thought to have been driven by some peculiar quantum field, a fundamental entity that pervades all of spacetime. When inflation ends, that field breaks down into a shower of particles and radiation, triggering the “hot Big Bang” that physicists often associate with the universe’s beginning. Those particles would later recombine into the first atoms when the universe was about 12 minutes old and, hundreds of millions of years later, condense into stars and galaxies.
However, there’s another component in the cosmic mix: dark matter. Once again, astronomers are unsure of what dark matter exactly is, but they observe its existence through its gravitational influence on ordinary matter.
Scientists did not find any evidence of dark matter’s existence until much later in the universe’s evolution when this elusive substance had enough time to exert its gravitational effects, so it didn’t necessarily have to fill the universe during the hot Big Bang along with ordinary matter. Moreover, because dark matter doesn’t interact with ordinary matter, it could have its own dark Big Bang, researchers argue.
Dark Big Bang
In their paper, researchers explored what a dark Big Bang might look like. First, they hypothesized the existence of a new quantum field, called “dark field,” necessary to allow dark matter to form entirely independently.
In this new scenario, the dark Big Bang would only occur after inflation has vanished, and the universe has expanded and cooled enough for the dark field to undergo its phase transition, transforming itself into dark matter particles.
Researchers found that the dark Big Bang must adhere to certain constraints. If it happened too early, there would be too much dark matter today, and if it occurred too late, there would be too little. But if the dark Big Bang occurred when the universe was less than a month old, it could potentially match all known observations.
Most importantly, researchers discovered that a dark Big Bang would leave a distinct signature in gravitational waves, the ripples in spacetime that still move throughout the universe to this day. That means the theory might one day be testable.