Entropy is a measure of the disorder or randomness in a system. In the context of the early universe, it refers to the level of disorder or randomness in the distribution of matter and energy.
The higher the entropy of the early universe, the more evenly distributed matter and energy were. This means that it was more difficult for structures such as galaxies and stars to form, as they require a certain level of density and organization.
The decrease in entropy during the early universe is believed to be caused by the expansion of the universe. As the universe expanded, matter and energy became more spread out, leading to a decrease in entropy.
The arrow of time is a concept that describes the direction in which time flows, from past to present to future. The increase in entropy in the early universe is thought to be responsible for the arrow of time, as it is a result of the universe moving towards a state of maximum entropy.
Currently, there is no known way to reverse the increase in entropy in the early universe. This is due to the second law of thermodynamics, which states that the total entropy of a closed system will always increase over time. However, some theories suggest that the universe may eventually collapse in a "big crunch" scenario, which could potentially reverse the increase in entropy.