The Big Bang theory is more than just a hypothesis—it is supported by evidence, though we still do not fully understand every stage of the universe’s early evolution. 

Singularity at the beginning?

Most commonly, people imagine the universe began from a singularity, an infinitely dense point from which everything evolved. However, this idea is only one of many hypotheses about how everything began. 

What might have existed before this singularity—or even if there was a “before”—is still unclear. 

We do not even need something like a singularity to be sure that we can not say anything about time point zero because any time you have a lot of energy in a small space you need a theory that reconciles particle physics with gravity, a theory of quantum gravity, which we have not yet discovered.

Planck time

The earliest moments of the universe, from zero to 1/10⁴³ seconds, area called the Planck Time. During this period, the laws of physics break down, leaving us unable to explain what occurred.

GUT era

After the Planck Time the universe entered the GUT (Grand Unified Theory) era, lasting approximately 1/10³⁵ seconds. 

The GUT explains how the four ground forces we know as gravity, electromagnetism and the strong and weak nuclear force worked together under extreme conditions. This era marked a time when the electromagnetism, weak force, and the strong force acted as one force governed by this theory (Click here to learn more about the fundamental forces). 

Some physicists believe that gravity was included in this unified force during the Planck Time. We would need the theory of everything (TOE) to bring gravity in.

Cosmic inflation

Next came the cosmic inflation, an astonishingly rapid expansion of the universe that stretched it from a minuscule point to the size of a beach ball in about 1/10³⁴ seconds. While we observe its effects, the cause of this sudden acceleration remains a mystery. Physicists try to develope an explanation with dark energy.

Quark era

After inflation, the quark era began. The strong force separated from the force described by the GUT, leaving electromagnetism and the weak force together, the electroweak force. 

Quarks and gluons were moving around freely, a state possible only in the extreme conditions of the early universe. 

This era lasted until about a microsecond after the Big Bang. At the 1/10¹⁰ seconds mark, the electroweak force split into electromagnetism and the weak force. 

Around this time, something must have happened, causing most of the universe’s antimatter annihilate with matter, leaving a slight excess of matter-enough to form the universe as we know it.

BigBang Nucleosynthesis

Roughly a tenth of a millisecond after the Big Bang, during the Big Bang nucleosynthesis, the first protons, neutrons and mesons formed. 

By around 100 seconds, as the universe cooled to a billion degrees, protons and neutrons combined because there was not enough energy for the quarks to escape the strong force, binding the nucleus together. They formed nuclei, starting with deuterium (a proton boned to a neutron forming heavy hydrogen) and progressing to the nucleus of helium, lithium and beryllium. 

This process lasted about 30 minutes, leaving a universe composed mostly of hydrogen and helium nuclei.

Surface if last scattering

The next major phase was the surface of last scattering, which occurred about 300 000 years after the Bang Bang.  During this period, the universe cooled enough for nuclei to capture electrons, forming neutral atoms. This decoupling of matter and radiation allowed light to travel freely, creating the cosmic microwave background (CMB) we observe today.

Following this, the Dark Age began- a period when the universe cooled further, and matter began condensing into clumps.

Cosmic Dawn

 Around 100 million years after the Big Bang, the Cosmic Dawn commenced. When regular matter tried to clump drawn by its own gravity, but pressure often countered this process.

Luckily, we have a kind of matter in the universe, so exotic that we have not even been able to re-create it. It is known as dark matter because it does not interact with light, it does not emit radiation, but it exerts a gravitational pull. This allowed dark matter to form the first structures in the universe, creating gravitational wells into which regular matter eventually fell, leading to the formation of stars and galaxies.

Era of Galaxies

As stars formed, the era of galaxies started. Their light ionized the neutral hydrogen gas, creating giant bubbles of ionized gas. This process continued for about a billion years. 

Over the next 13 billion years, stars continued to form, galaxies grew, supermassive black holes emerged, and elements combined to complex molecules and, eventually, living matter. So, here we are…