How does the change in temperature of the universe provide evidence for universe expansion that supports the Big bang theory

Question

The universe is cooling which according to the Big bang theory is expected to happen as a cosmos accumulates the universe is warming which according to the Big bang theory is expected to happen as the cost most disappears

Answer 1

The cooling of the universe is indeed a key piece of evidence supporting the Big Bang theory. Here's how temperature change relates to cosmic expansion and the Big Bang theory:

1. Initial Conditions: According to the Big Bang theory, the universe began as an extremely hot and dense point. As it expanded, it cooled down over time. This is a fundamental prediction of the theory: as the universe expands, the energy density decreases, leading to a drop in temperature.

2. Cosmic Microwave Background Radiation (CMB): One of the strongest pieces of evidence supporting the Big Bang theory is the existence of the Cosmic Microwave Background Radiation. This radiation is a remnant from the early universe, created about 380,000 years after the Big Bang when protons and electrons combined to form neutral hydrogen. At that time, the universe became transparent to radiation, and the energy from the hot plasma cooled as the universe expanded. The CMB is now observed as a uniform background radiation that has cooled to a temperature of about 2.7 Kelvin. This uniformity and specific temperature match predictions from the Big Bang theory, reinforcing the idea of an expanding universe.

3. Redshift of Galaxies: Observations show that distant galaxies are moving away from us, and their light is redshifted. This redshift provides evidence that the universe is expanding. As galaxies move away, the wavelengths of light they emit stretch, which leads to a decrease in temperature of their emitted light. This phenomenon aligns with the predictions of the Big Bang theory and helps to illustrate how the expansion of the universe causes a cooling effect.

4. Thermal History: The Big Bang theory posits that as the universe expands, it not only cools thermally but also undergoes phase transitions (such as the formation of protons, neutrons, and eventually atoms). This historical thermal evolution aligns with the current observations of the universe's temperature and structure.

In summary, the cooling of the universe is a natural consequence of its expansion, as described by the Big Bang theory. This cooling process, along with the evidence of the CMB and galaxy redshift, supports the notion that the universe has been expanding since its inception. The idea that the universe could warm as "cosmos disappears" doesn't fit well with the current understanding of cosmic evolution and the fundamental principles of thermodynamics and cosmology.