The Big Bang: What is it? Why study it? What happened before? How will it all end?

Approximately 13.8 billion years ago, the greatest event in all of existence occurred that literally created existence itself. This event is known as the Big Bang, and it’s responsible for the estimated septillion number of stars that are scattered across the vast reaches of the unknown, including the one our small, blue world orbits. However, other than knowing that the Big Bang occurred, there is still a septillion amount of information we still don’t know about the greatest event in the history of existence.

Here, Universe Today spoke with Dr. Gerald Cleaver, who is a Professor of Physics in the Department of Physics at the University of Baylor, about the various aspects of the Big Bang. These include what is the Big Bang, why we study the Big Bang, what we’ve learned about the Big Bang, what happened before the Big Bang, and how the universe might end? So, other than knowing the Big Bang occurred, what exactly is the Big Bang?

“The Big Bang is a scientific theory describing the sudden growth of our observable universe approximately 13.79 billion years ago (according to the best fit of recent parameters) when the universe was only 10^-43 seconds (s) old,” Dr. Cleaver tells Universe Today. “This expansion lasted about 10^-32 seconds and involved two stages, the pre-inflation stage from 10^-43 s to 10^-36 s, followed by the inflation stage from 10^-36 s to 10^-32 s. At the start of the Big Bang, the energy density of the universe was extremely high, on the order of 10¹⁹ GeV (Planck energy) per (10^-35 meter)³ (Planck volume). The temperature of the universe was around 10³² Kelvin (Planck temperature). The inflationary stage enlarged the length scale of the present observable universe be at least a factor of e⁶⁰ ~ 10²⁶.”

Essentially, the universe came into existence kicking and screaming where it was both extremely hot and extremely dense, but also started expanding very quickly, as in within a few millionths of a second after the Big Bang when quarks began clustering together to form protons and neutrons. Within minutes, these protons and neutrons also clustered to form nuclei. After this, however, was when matter started to form much more slowly, as it took another 380,000 years for electrons to begin orbiting these nuclei, thus creating the first atoms.

It is hypothesized these atoms consisted primarily of hydrogen and helium, which remain the most plentiful elements throughout the universe to this day. It took another 150-200 million years for the first stars to form from these hydrogen and helium elements, which resulted in the creation of oxygen, carbon, and iron being formed within these stars, later to be blasted throughout the cosmos after some of these stars explode as supernovae. While this paints a decent picture of the processes after the Big Bang, why is it so important to study the actual Big Bang?

“The further we examine and resolve remaining questions, especially finer details, of the Big Bang, the better we will understand how our universe came to be,” Dr. Cleaver tells Universe Today. “Hopefully, that knowledge will one day reach a level of completeness that enables humankind to accurately determine whether or not our universe is one among a multitude, the theoretical set of these often referred to as a multiverse. If cosmologists ever become convinced that it is, indeed, likely other universes do exist, we should seek to determine, if possible, the overarching physical laws that each and every universe obeys, even if their local physical laws differ.”

One of the most puzzling questions throughout the scientific and public communities is what happened before the Big Bang? There are several working hypotheses for what happened before the Big Bang, with one being known as the chaotic inflation theory, which calls for our universe being a part of a grander multiverse that popped out from another universe. Another hypothesis calls for our universe being the other end of a black hole, which we are referred to as a white hole. This could help explain what happens when you fall into a black hole, aside from Spaghettification, aka the noodle effect.

Dr. Cleaver tells Universe Today that while various theories of “pre-histories” exist regarding what happened before the Big Bang, noting some involve what’s known as string theory. One prediction calls for “a vast number of small cycles of pre-inflation growth”, where space expands before contracting again, followed by a massive expansion. The second prediction involves “branes” where inflation occurs followed by a slower rate of expansion until everything just stops and moves backwards from dark energy reversing its course, “as if time turned backwards”, which results in a Big Crunch, then finishes with a Big Bounce, both of which are discussed below.

While the universe might have started with a bang, the question remains as to how it will end? Currently, there are a myriad of hypotheses pertaining to how the universe will end: Heat Death or Big Freeze, Big Rip, Big Crunch, and Big Bounce. For the Heat Death/Big Freeze scenario, the universe is predicted to expand forever, resulting in heat throughout the universe to be evenly distributed and unusable. For the Big Rip scenario, the universe is predicted to be torn apart by dark energy getting stronger and stronger until the forces of attraction (dark matter) fail to keep everything together. For the Big Crunch scenario, as its name implies, the universe is predicted to collapse on itself until it turns into the most massive black hole in existence, with everything being sucked into it forever. For the Big Bounce, the universe is predicted to continue an endless cycle of expansion and contraction forever.

“Based on the (near) constant current low acceleration due to constant dark energy, I expect the observable universe to expand forever,” Dr. Cleaver tells Universe Today. “Around 100 billion years in the future, galactic clusters will become isolated from each other. Eventually, individual galaxies will become isolated, as well. With that, we would effectively be returning to the cosmology imagined by Einstein and physicists of the early 20^th century: that the only galaxy in existence was the Milky Way and the entire universe was not much larger than our Milky Way. Cosmologists have calculated that the dark energy is not strong enough to pull apart most galaxies. So, here it would stop.”

What new discoveries about the Big Bang will scientists make in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!