What Was Before the Big Bang?

The question predates modern cosmology by at least 1,600 years. Fourth-century theologian St. Augustine wrestled with the question of what existed before God created the universe. He concluded that the Biblical phrase "In the beginning" implied that God had made nothing previously. Moreover, Augustine argued that time and the universe had been created simultaneously [source: Villanova University].

In the early 20th century, Albert Einstein's theory of general relativity led to similar conclusions. Mass warps time, making time run a tiny bit slower for a human on Earth's surface than a satellite in orbit. Based on Einstein's work, Belgian cosmologist Rev. Georges Lemaître proposed in 1927 that the universe started as a singularity and expanded through the Big Bang [source: Soter and Tyson].

According to Einstein's theory of relativity, time only came into being as the primordial singularity expanded toward its current size and shape. However, this is one cosmological quandary that won't stay dead. The advent of quantum physics and a host of new theories resurrected questions about the pre-Big Bang universe.

Some astrophysicists speculate that our universe is the offspring of another, older universe. This story, they believe, is written in the cosmic microwave background (CMB), the relic radiation left over from the Big Bang.

Cosmic Microwave Background

Astronomers first observed the CMB in 1965, and it quickly created problems for the Big Bang theory. These problems were addressed (for a while) in 1981 with the inflation theory, which entails an extremely rapid expansion of the universe in its first moments. This theory accounts for temperature and density fluctuations in the CMB but dictates that those fluctuations should be uniform.

However, recent mapping efforts suggest that the universe is lopsided, with more fluctuations in some areas than in others. Some cosmologists see this observation as supporting evidence that our universe "bubbled off" from a parent universe, according to California Institute of Technology researcher Adrienne Erickcek [source: Lintott].

Chaotic Inflation Theory

In chaotic inflation theory, this concept goes even deeper: an endless progression of inflationary bubbles, each becoming a universe, and each of these birthing even more inflationary bubbles in an immeasurable multiverse [source: Jones].

Other models revolve around the formation of the pre-Big Bang singularity itself. If you think of black holes as cosmic trash compactors, they stand as prime candidates for all that primordial compression. Our expanding universe could theoretically be the white hole output from a black hole in another universe.

A white hole is a hypothetical body that acts in the opposite manner of a black hole, giving off energy and matter rather than sucking it in. Some scientists propose that our universe may have been born inside a black hole, and every black hole in our universe could each contain separate universes as well [source: Choi].

The Big Bounce

Long ago, medieval religious philosophers in India taught that the universe goes through an endless cycle of creation and destruction. Some contemporary scientists have arrived at a similar idea. They believe that instead of a hot Big Bang, the universe expands and contracts in a cycle, bouncing back each time it shrinks to a certain size.

In the Big Bounce theory, each cycle begins with a small, smooth universe that gradually expands, becomes clumpier and more warped over time, and eventually starts to collapse and smooth itself out before starting anew [source: Davis].

For the Big Bounce idea to work, it has to find a way around the singularity theorems developed by British physicists Roger Penrose and Stephen Hawking. These theorems suggest that a contracting universe would shrink all the way down to a singularity, similar to a massive dying star condensing to form a black hole. Big Bounce models depend on the idea of negative energy counteracting gravity and reversing the collapse, driving the universe and space-time apart again and again [source: Wolchover].

As we delve deeper into the mysteries of the cosmos, we confront an array of theories and possibilities. From the cosmic microwave background to the theories of quantum mechanics and general relativity, our understanding of the universe is constantly evolving. The concept of dark energy, the mysterious force driving the universe's expansion, adds another layer of complexity to our understanding.

As the universe expands, distant galaxies move away from us, and the cosmic horizon — the limit of the observable universe — changes.

This expansion is driven by dark energy, a mysterious force that makes up about 68% of the entire observable universe. The nature of dark energy, quantum fluctuations, and the quantum vacuum are all areas of active research that could shed light on the universe's history and its ultimate fate.

String theory, another fascinating area of research, suggests that the fundamental building blocks of the universe are not point-like particles, but rather one-dimensional strings. This theory could potentially unite the principles of quantum mechanics and general relativity, providing a quantum theory of gravity.

As we continue to explore the far reaches of the universe, from the very beginning to the far future, we must constantly rethink our understanding of the cosmos. From the hot, dense state of the early universe to the cold, empty space between distant galaxies, our journey to understand the universe is far from over.