Brian Cox - What Caused The Big Bang?

The Big Bang, occurring nearly 14 billion years ago, marked the beginning of time and space. However, current cosmology suggests a phase called inflation existed before the hot, dense Big Bang. During inflation, the universe expanded exponentially fast, even from a size smaller than an atom to larger than the observable universe in a tiny fraction of a second. The energy driving this expansion then heated up space, creating the particles that form everything we see. The key questions remain: what started and stopped this inflation, and for how long did it last?

Big Bang cosmology takes us to the universe's origin, where conventional physics limits are reached. At T=0, the universe was a singularity with infinite density and temperature, marking the birth of matter, energy, and time itself. Before this moment, the concepts of time and space lose their meaning. The Big Bang was not an explosion in space, but the rapid expansion of space itself. The cosmic microwave background radiation is a relic of this era. The question of what was there before or at T=0 may not even make sense, as time might have originated with the Big Bang.

Several complex theories attempt to explain what caused the Big Bang. Quantum fluctuations suggest that even a vacuum buzzes with energy and random changes, potentially leading to the Big Bang's expansion. The Multiverse Theory proposes our universe is one of many, with the Big Bang being a transition between states. String Theory suggests the Big Bang resulted from the collision of higher-dimensional entities called 'branes.' Cosmic inflation posits a rapid exponential expansion shortly after the Big Bang, driven by a mysterious energy field that shaped the distribution of galaxies. The emphasis shifts from asking 'why' the Big Bang happened to 'how' the conditions and laws aligned for such an event.

For scientists, particularly physicists, the crucial question is 'how' the universe came to be. Precise measurements indicate the universe is 13.75 billion years old. What happened before the Big Bang remains unknown and is a subject of current research. At its beginning, the universe was extremely hot, dense, and small—everything we see was once compressed into a space smaller than an atom. As it expanded and cooled, complex structures like DNA, planets, stars, and people formed. Scientists explore these origins by observing stars and recreating early universe conditions in laboratories.

The Big Bang Theory leads us to intriguing concepts like repulsive gravity. While gravity is typically an attractive force, Einstein's equations allow for a repulsive form. This repulsive gravity, which pushes things apart, would occur when uniform energy is spread through a region of space, unlike the concentrated mass of planets or stars. If the very early universe was filled with a uniform bath of 'inflaton field' energy, it would have been subject to repulsive gravity, pushing everything rapidly outward. Thus, the 'bang' of the Big Bang might have been a spark of repulsive gravity.