Answer: Temperature: One of the most significant observational differences between the early universe and the modern universe is the temperature. The early universe was much hotter than the modern universe. In fact, the temperature of the early universe was approximately 10^32 Kelvin, while the current temperature of the universe is about 2.7 Kelvin.
Composition: Another important difference is the composition of the universe. In the early universe, the majority of the matter was in the form of hydrogen and helium. However, as the universe expanded and cooled, these elements began to form stars, which in turn created heavier elements through nuclear fusion. As a result, the modern universe has a much wider variety of elements, including carbon, oxygen, and iron.
Density: The density of the universe has also changed significantly over time. In the early universe, the density was much higher, and the universe was more compact. However, as the universe expanded, the density decreased, and the universe became more diffuse. This change in density is also believed to have played a role in the formation of galaxies and other large-scale structures in the universe.
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