Cosmology: Origin and Evolution of the Universe
**Modern Cosmology**
Cosmology studies the structure, origin, and development of the universe. Astronomy is the science of the stars, based on the information provided to us by the electromagnetic radiation that reaches us from them. Astrophysics applies the laws of physics to study the nature and behavior of stars. Mathematical models are a set of equations that describe physical systems and help to further study the properties of the system they describe.
Static and Infinite Model
In the early twentieth century, the accepted model was that the universe had no beginning or end. Einstein’s theory of general relativity predicted an expanding universe model, but he added the cosmological constant so that the model remained static and finite.
Hubble’s Discovery
Hubble proved that the universe is expanding. This means that at one time all galaxies were together, and there was a Big Bang, an explosion from an infinitely dense and hot immaterial point.
Dynamic and Infinite Model
In 1948, the steady-state model was proposed, supporting the expansion of the universe where a field is generated continuously.
**The Expansion of the Universe**
Hubble’s Law: v = HD
Measuring the speed of recession of galaxies: The light reaching Earth from the stars contains colors that can be separated by a spectroscope, resulting in a spectrum. Each spectrum consists of the seven colors of the rainbow, and they are superimposed on a series of dark absorption bands. These spectra are a kind of fingerprint; each chemical element has its own, and the position in which these bands are found is a characteristic of each element. Hubble measured the position of chemical elements in several galaxies and compared these spectra with those obtained in a laboratory with the same elements. He discovered that the absorption bands experienced redshifts; this is because the galaxies are moving away from each other.
**The Big Bang**
Since the universe is expanding, it was concluded that all galaxies were at one point that marked the origin of the universe. The Big Bang model suggests that all matter in the universe and the core components of everything we know were in the form of an immaterial point, infinitely dense and hot, with conditions that current physics cannot describe.
The Dawn of Time
In the middle of nowhere, there was an explosion that generated a speck of light, infinitely hot. Space was born inside, and the universe has continued to expand. The energy of the radiation was so intense that it became tiny particles of matter. As time and space expanded, the matter cooled and formed primordial clouds of hydrogen and helium, from which galaxies formed.
**Planck Era**
It is assumed that the temperature and density were so high that the four forces that govern the behavior of all elementary particles were grouped in a single “superforce.” Electrogravity and all matter were in the form of energy.
**Grand Unification Era**
Gravity separated from the three remaining forces.
**Era of Inflation**
The expansion and cooling of space-time allowed the separation of the strong nuclear force from the other two, which remained together. This caused a huge amount of energy to be released, causing the universe to dramatically increase in size. Growth was exaggerated because some regions grew more quickly than others.
**Electroweak Era**
The universe was in a vacuum, but when the forces began to separate, huge amounts of energy were released, transforming into a machine capable of materializing energy and forming particles. Einstein said energy and matter are equivalent, and this is what happened: photons materialized, resulting in particles of matter and antimatter. However, the balance did not last long, as the temperature decreased and the energy of the radiation was not sufficient to enable materialization.
**Hadronic Era**
The universe had cooled enough for the strong nuclear force to act as a powerful glue, allowing the emergence of stable partnerships that led to the formation of hadronic particles. These formed the cores of the first chemical elements.
**Leptonic Era**
The temperature did not allow quarks to form, but there was still energy for their materialization in lower-mass particles. However, a time came when the expansion and cooling of the universe decreased, so energy was no longer materialized. By the end of this era, antimatter had disappeared, resulting in radiant energy.
**Era of Nucleosynthesis**
The temperature reached a low enough level to allow the union between protons and neutrons, forming nuclei of hydrogen, helium, and lithium.
**Era of Atoms and Radiation**
All matter was in an ocean of light, forming a plasma, a state in which atomic nuclei are dissociated into electrons. The temperature was low enough to allow the electromagnetic force to associate, allowing stable nuclei of protons and electrons.
**Era of Galaxies**
The universe became transparent to radiation at the time that matter was organized into atoms, forming a vast primordial nebula from which galaxies formed. The force of gravity acted on these fluctuations, causing the matter of this nebula to clump together in the form of filaments. These formations were the origin of large-scale structures.
**Dark Energy**
The universe is accelerating its expansion because of an unknown dark energy. This acts as a repulsive force against gravity.
**Dark Matter**
Galaxies and all visible matter in the universe only account for 4% of the total. Regions as dense as empty ones may be full of dark matter. Its nature is unknown to us because it neither emits nor absorbs electromagnetic radiation, which would allow us to detect it. Dark matter forms an invisible material that serves as a sort of skeleton that holds galaxies together.
**Stars**
They are huge balls of hydrogen and helium gas. These gases are so hot that they reach such high temperatures that the star ignites and emits a great deal of energy.
**Nebulae**
These are gaseous clouds of hydrogen, helium, heavy chemical elements in the form of cosmic dust, and a certain amount of organic compounds.
**Formation of the Solar System**
The solar system is immersed in a giant bubble called the Local Bubble, formed by the explosions of several supernovae. The shock wave generated by the supernova that marked the death of a giant star at one end of the Milky Way could represent the birth of the solar system. This shock wave caused the compaction of an immense nebula that turned into a giant disk. The center of the disk shrank into a ball of gas, hydrogen, and helium, which compacted and heated until the Sun formed. In the peripheral regions of the turbulent disk, two processes formed:
- Coagulation: Cosmic dust particles collided and stuck to each other.
- Accretion of planetesimals: The force of gravity acted, causing the impact of bodies on others.