Cosmic Evolution: From the Big Bang to Dark Energy
The Future of the Universe
Cosmologists believe that the future of the universe depends on the density of its mass-energy. Two possible scenarios were initially considered: the Big Chill and the Big Crunch. However, the recent discovery of dark energy, responsible for the accelerating expansion, has introduced another possibility: the Big Rip.
- Big Chill: The Great Cooling. An open universe where matter-energy is insufficient to reach critical density, allowing gravity-free expansion.
- Big Crunch: The Great Contraction. A closed universe where the amount of matter and energy is sufficient to overcome the critical density, creating a gravitational pull so strong that it slows down the expansion and eventually reverses it, leading to a large contraction and reaching a point of singularity.
- Big Rip: The Big Tear. A universe close to critical density, but where the repulsive force of dark energy could overtake the force of gravity.
Structure of the Universe: Distances and Scales
Perhaps due to the action of dark matter, or for some reason still unknown, the more than 100 billion galaxies that make up the universe tend to gather in swarms called clusters. These clusters are grouped into superclusters, which are arranged in filaments, forming huge cosmic walls. The universe has a spongy and bubbly structure, where clusters of galaxies are arranged as filaments in the walls of the bubbles, supported by a kind of skeleton formed by cosmic dark matter.
Galaxies: Islands in the Universe. The Milky Way
Galaxies are vast accumulations of matter in the form of cosmic dust, nebulae, and stars, some of which have planetary systems. All of these galactic components are held together by strong gravitational forces generated among the masses. In galaxies, the space between the stars is not empty; it contains the interstellar medium, a mixture of gases and dust, which also includes a small fraction of organic compounds synthesized by a set of chemical reactions, making the interstellar medium a true cosmic laboratory. The Milky Way is a spiral galaxy that contains nebulae, cosmic dust, and between 100 billion and 300 billion stars. Our solar system, including the Sun, Earth, and other planets, is located in one of its arms, about 30,000 light-years from the galactic center.
The Echo of the Big Bang: Background Radiation
The expansion of the universe has caused the photons of light radiation to cool, reaching the current temperature. This entails a reduction in the intensity of radiation and, therefore, an increase in the wavelength to microwave frequencies, known as the cosmic microwave background.
Eras of Galaxies
Matter is organized into atoms of hydrogen, helium, and lithium, which formed a vast primordial nebula from which galaxies formed through gravitational instability. Perhaps the force of gravity acting on the initial fluctuations or irregularities in the density and temperature of the material generated during the inflation of the universe caused the primordial nebula to tear off in the form of filaments and clumps. These formations were the origin of large-scale structures, where galaxies gather in clusters, superclusters, and filaments, giving our universe its bubbly and fluffy appearance.
Dark Energy
Dark energy acts as a repulsive force against gravity and resembles a cosmological constant. Dark energy, of unknown nature, represents 74% of the matter-energy in the universe.
Dark Matter
Galaxies and all visible matter in the universe only account for 4% of the matter-energy density. It is possible that the seemingly empty regions are filled with a type of matter called dark matter. Its nature is not yet known because it does not emit or absorb electromagnetic radiation, making it undetectable. Its existence can only be inferred indirectly by its gravitational effects on galaxies. Dark matter forms an invisible web that serves as a kind of cosmic skeleton, entwining the clusters of galaxies and all the ordinary matter we can see.