Dating the universe
Having no elements heavier than lithium, these stars also produced the first heavy elements through stellar nucleosynthesis.
The Universe also contains a mysterious energy called dark energy, the density of which does not change over time.
The Big Bang model accounts for observations such as the correlation of distance and redshift of galaxies, the ratio of the number of hydrogen to helium atoms, and the microwave radiation background. During the Planck epoch, all types of matter and all types of energy were concentrated into a dense state, where gravitation is believed to have been as strong as the other fundamental forces, and all the forces may have been unified.
In developing the law of universal gravitation, Sir Isaac Newton built upon Copernicus's work as well as observations by Tycho Brahe and Johannes Kepler's laws of planetary motion.
Further observational improvements led to the realization that our Solar System is located in the Milky Way galaxy, which is one of many galaxies in the Universe.
and survive in modern languages, e.g., the German words Das All, Weltall, and Natur for Universe.
The same synonyms are found in English, such as everything (as in the theory of everything), the cosmos (as in cosmology), the world (as in the many-worlds interpretation), and nature (as in natural laws or natural philosophy).
After the initial expansion, the Universe cooled, allowing the first subatomic particles to form and then simple atoms.