Your statements touch upon two major lines of evidence for the Big Bang theory and the subsequent evolution of the universe. Let's break them down:
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Cooling Temperature Changes:
- As the universe expanded after the Big Bang, it underwent significant cooling. This cooling can be observed in the temperature of the cosmic microwave background (CMB) radiation, which is the remnant thermal radiation from the early stages of the universe. The CMB provides critical evidence for the Big Bang model as it shows a uniform temperature across the sky, with slight fluctuations that correspond to the density variations that eventually led to the formation of galaxies and large-scale structures. By analyzing the temperature changes and the spectrum of the CMB, scientists can trace the universe's expansion history. These temperature changes over time support the idea that the universe has been expanding and cooling since its inception.
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Ratio of Hydrogen and Helium:
- The primordial nucleosynthesis that occurred within the first few minutes after the Big Bang resulted in the formation of light elements, predominantly hydrogen and helium, along with trace amounts of lithium and beryllium. The observed ratios of hydrogen (about 75% by mass) and helium (about 25% by mass) in the universe are consistent with predictions from Big Bang nucleosynthesis models. Measurements of these elemental ratios in old stars and the interstellar medium provide strong evidence that these elements were indeed formed during the early expansion of the universe. The fact that these ratios closely match theoretical predictions reinforces our understanding of the processes that took place shortly after the Big Bang.
Together, these pieces of evidence enhance our understanding of the universe's origins and evolution, supporting the Big Bang theory as the leading explanation for the universe's formation and the distribution of elements in it.
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