The Universe

Basics

The Universe is all of space and time and their contents including planets, stars, galaxies, and all forms of matter and energy.
The Universe is believed to be around 13.8 billion years old, with the Big Bang theory explaining the creation of the Universe.
The size of the observable Universe is currently estimated to contain around 200 billion galaxies.

The Universe mainly consists of voids and filaments, predominantly made up of dark energy, dark matter, and baryonic matter.
Dark energy, constituting approximately 68% of the universe, is a form of energy hypothesised to permeate all of space, and is driving the acceleration of the expansion of the universe.
Dark matter, which makes up about 27%, does not interact with or emit light, and can only be detected indirectly through its gravitational effects.
Baryonic matter, accounting for about 5%, constitutes stars, galaxies, and life as we know it.

The Universe is expanding, a fact first observed by Edwin Hubble, meaning galaxies are moving away from us and each other.
This expansion is not steady but accelerating, possibly due to the presence of dark energy.
Depending on the balance of matter, dark matter, and dark energy, the universe could either continue to expand indefinitely (Open Universe), eventually slow and stop (Flat Universe), or eventually collapse in a “Big Crunch” (Closed Universe).

The Cosmic Microwave Background (CMB) is residual radiation from the Big Bang, and provides strong evidence supporting the Big Bang theory.
It was predicted by theory well before it was observed using radio telescopes.
The slight anisotropy (or differences in temperature) in the CMB gives us clues about the early distribution of matter in the Universe.

Galaxies are vast, gravitationally bound systems containing billions to trillions of stars, along with interstellar gas and dust.
Galaxies form into various shapes such as elliptical, spiral, and irregular compact.
Galaxy clusters are large collections of galaxies.
Superclusters, the largest structures in the Universe, are groupings of galaxy clusters, with our Milky Way galaxy being part of the Virgo Supercluster.

The Drake Equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.
Despite extensive searching (SETI programs), no evidence of extraterrestrial life has been definitively found.
The possibility of life on other planets, especially within our own galaxy, remains a subject of intense research and interest.