Unveiling the Universe: Pre-Big Bang Theories & Quantum Gravity

"Imagine a universe, silent and devoid of life, with its last star gently dimming into oblivion. The universe will once again become lifeless, dark, and seemingly without purpose." These aren't lines from a dystopian novel, but rather, the words of physicist Brian Cox, from the BBC's TV series, "Universe." The extinguishing of the last star will mark the beginning of an eternally long, dark epoch, signaling the universe's end as we comprehend it. All matter will be swallowed by gigantic black holes, which will then dissolve into faint sparks of light. The universe will continue to expand until even this muted light becomes too faint to interact. All cosmic activity will halt. While this may seem like a gloomy outlook, many astronomers propose that a similar condition might have birthed the universe through the Big Bang. Let's delve deeper into this concept.

Understanding why it's illogical to question what existed before the Big Bang

Before we delve into what existed before the Big Bang, let's examine how the matter we encounter originated. If we're to understand the genesis of atomic and molecular matter, it's clear that none of this existed during the Big Bang or for hundreds of thousands of years afterwards. We have a comprehensive understanding of how the universe, once cool enough, evolved simpler particles into the first atoms, and how these atoms combined within stars to form heavier elements.

However, this explanation doesn't clarify whether everything originated from nothingness. Let's trace back even further to the first proton and neutron particles, which constitute the atomic nucleus. These particles emerged roughly one ten-thousandth of a second post-Big Bang. Prior to this, there were no tangible materials (in the typical sense of the term). Nevertheless, physics enables us to trace a timeline back to those physical processes that preceded stable matter.

At this juncture, we delve into theoretical physics, as we lack the means to generate sufficient energy in a laboratory to emulate the processes occurring during this period. One widely accepted theory is that everything was composed of a seething concoction of elementary particles known as quarks, the building blocks of neutrons and protons. Interestingly, during this period, matter and antimatter existed in roughly equal proportions. Each type of particle has an antimatter counterpart with an opposite (negative) sign. But how did these particles come into existence?

Did the Big Bang originate from nothing?

Quantum field theory suggests that even a vacuum, symbolizing empty space-time, is brimming with physical activity in the form of energy fluctuations. These fluctuations can give birth to particles that briefly appear before vanishing. While this might seem like a mathematical anomaly, scientists have confirmed their existence through numerous experiments.

At this point, one might wonder: From where does space-time itself originate? If we rewind even further to the "Planck epoch," one ten-millionth of a trillionth of a trillionth of a trillionth of a second post-Big Bang, space and time were subject to quantum fluctuations. To understand the Planck era, we require a comprehensive theory of quantum gravity, which combines quantum mechanics, governing the micro-world of particles, and general relativity, applicable on vast cosmic scales.

Quantum gravity

Currently we do not have a theory that explains quantum gravity, but various attempts have been made through string theory and loop quantum gravity. According to these theories, ordinary space and time are seen as emergent, that is, as waves on the surface of a deep ocean. What we experience as space and time are the product of quantum processes operating at the deepest microscopic level.

In short, in the Planck era our ordinary conception of space and time crumbles, so we can no longer rely on any cause-and-effect relationship. Nevertheless, all the candidate theories to explain quantum gravity describe something physical that was happening in the primordial era of the universe. A kind of quantum precursor to ordinary space and time. In short, until we make progress toward a solid "theory of everything," we will not be able to give a definitive answer. The most we can say with confidence is that physics, so far, has found no evidence for something coming from nothing.