The History of the Universe: From the Big Bang to the Mysteries of the Early Galaxies

Cosmology, as a discipline that studies the evolution of the universe as a whole, has embarked on a wonderful journey for us about how the universe evolved from an extreme state to the present scene of diversity. In the field of cosmology, the most widely recognized theory is the Big Bang theory. This theory describes the formation of the universe in detail, from a short but violent explosion to a long transformation. According to this theory, the expansion process of the universe is not blindly expanding outwards, but has experienced three different expansion states within a fixed time frame: constant velocity, deceleration and acceleration.

The origin of the universe can be traced back to a tiny, extremely dense, extreme temperature divergence, just a few millimeters across, like a super black hole. About 13.7 billion years ago, this tiny point of divergence experienced a seismic explosion that we call the Big Bang.

The term "big bang" was first coined by British astronomer Fred Hoyle. Hoyle advocated the Steady State Theory, a cosmological model opposed to the Big Bang. In his 1949 BBC program, he used the "viewpoint of the big bang" to describe the theory of Lemaitre et al. The supporting evidence for the big bang theory includes Hubble's law, cosmic microwave background radiation, element abundance, evolution and distribution of galaxies, etc. Hubble's law states that distant galaxies and galaxy clusters are moving away from our line of sight and receding faster at greater distances. The cosmic microwave background radiation is an important evidence, which clearly supports the existence of the big bang, especially when scientists draw the black body radiation curve according to its spectrum, most people begin to believe in the big bang theory.

After this explosion, the universe began to expand rapidly and cool down, entering the starting point of evolution from a state of extremely high temperature and high density. In the early days of the universe, it was dark matter that dominated the expansion, and this stage is decelerating expansion. And the later period to the present, is the accelerated expansion dominated by dark energy. This variation allows us to describe the evolution of the universe over time as a bell-shaped picture, showing the changes in the rate of expansion at different stages.

Below we outline the history of the universe in seven key phases, starting with the first billion years of the universe, with a special focus on the first three minutes of upheaval that formed the building blocks of much of our present-day universe. The first stage is the period of big inflation. In the extremely short 1e-34 seconds after the birth of the universe, the temperature is extremely high, and matter exists in the form of the most basic particles. What followed was the post-inflation period, in the first 1e-32 seconds of the universe, space expanded rapidly, the temperature dropped to about 1e27K, and electrons and neutrons began to form at this stage. Then, there is a period of rapid cooling, the first 1e-6 seconds of the universe, the temperature is about 1e13K, quarks combine to form protons and neutrons. Then, there is the first three minutes of the universe, at a temperature of about 1e8K, during which nuclei of hydrogen and helium appear. The fifth stage is the formation of hydrogen and helium nuclei, which are also the earliest major elements in the universe. In the short time that followed, most of the elementary particles had formed. However, as time went on, the universe evolved more and more slowly, gradually transforming into the rich and diverse universe we know. The sixth stage saw the birth of the first generation of stars, and this stage was long

For billions of years, the temperature dropped to 70K, and the matter aggregated into molecular clouds due to gravity, and the first generation of stars was born in these regions. The seventh stage occurred between 1 billion and 13.8 billion years ago, when the temperature gradually dropped to 3K. The stars evolved, and due to the presence of heavy elements, the second generation of stars and planetary systems like our solar system began to form. With the existence of planets, the environment suitable for the development of life began to be formed.

However, the appearance of the first stars in the history of the universe has brought new puzzles and challenges. According to the observations of the EDGES project, scientists have discovered that the first batch of stars were born about 180 million years after the Big Bang formed the universe. This discovery challenges our established understanding of the universe model and raises new possibilities. The findings show that the timing of the emergence of these early stars matches some theories' predictions, but not others. In addition, the study also pointed to a higher-than-expected rate of early hydrogen uptake, which could mean problems with theories about the temperature of the early universe. It could be that the primordial gas was cooler than expected, or that the background radiation was warmer than expected. The discovery could also mean that early galaxy formation and star formation processes may have diverged from our current understanding. Therefore, these results need further research and verification. Scientists hope to confirm the findings of the EDGES telescope through other independent methods, and further explore the meaning and impact behind these observations.

These explorations will continue to lead us to a deeper understanding of the origin and evolution of the universe, and at the same time reveal that our understanding of the universe still needs to be continuously updated and expanded. It's been a journey full of surprises, challenges, and opportunities, and we're at the forefront of cosmic mysteries, looking forward to unraveling more and revealing more about our universe.