Understanding the Universe: Theories, Evolution, and Components
Origin of the Universe
Big Bang Theory:
Proposed by Lemaître (1927) and developed by Gamow (1948). All matter, space, and energy were initially concentrated at a single point (cosmic egg). A consequence of the instability was the large initial explosion and the beginning of the expansion of the universe. As the universe cooled gradually, elementary particles connected via electromagnetic and nuclear forces to form atoms. Thus came matter, space, and time. As the universe expanded and cooled, the material scattered in all directions, eventually clumping together to form astronomical structures.
Superstring Theory:
This theory posits the existence of microscopic entities that vibrate (strings), creating energy links located at the heart of matter and in higher-dimensional spaces beyond the four known dimensions (space and time).
Evolution of the Universe
Theory of the Big Crunch:
The universe will continue to expand, but ever more slowly, until the gravitational attraction of galaxies reverses the process. Galaxies will begin to approach each other slowly, then faster and faster, until they reach the initial situation before the explosion. This would be the end of the world.
Big Rip Theory:
Galaxies will separate increasingly faster, so that the universe will expand forever because of the existence of so-called dark energy, of unknown nature, which acts against gravity. Eventually, galaxies, stars, and even atoms could fall apart as the universe reaches its end.
Energy of the Universe
The theory of relativity validates the Big Bang. It allows us to explain phenomena that occur at cosmological scales (space and time). Quantum mechanics predicts phenomena that occur on a microscopic scale (forces that exist in the nuclei of atoms). Both theories are widely accepted, but it is known that they cannot both be entirely correct since there are points of conflict. There are currently efforts (S. Hawking) working on a new theory that unifies the previous two and allows us to better predict the behavior of both the microscopic particles and the universe as a whole. This unifying theory would demonstrate that the four fundamental forces (gravitational, electromagnetic, weak nuclear, and strong nuclear) of the universe are actually different manifestations of the same force.
The Observable Universe
The universe is mainly empty, with billions of galaxies floating within it. For each galaxy, there are billions of stars, planets, and nebulae (clouds of gas and dust). Chemically, the universe is made up of approximately 75% hydrogen, 20% helium, and 5% of all other chemical elements. This represents approximately 10% of the total matter in the universe.
Dark Matter
For several decades, it has been found that the gas and dust in the universe are subject to gravitational attraction far greater than that caused by the detected substance. This suggests that the remaining 90% of the substance has a composition and properties that we do not know, and that it does not emit radiation; therefore, it is called dark matter.
Galaxies
Large groups of stars, gas, and dust. They differ in their forms (spiral, elliptical, and irregular), size, and the number of stars they contain.
Galaxy Clusters
Groups of galaxies. In these groups, elliptical galaxies are arranged in the center, while irregular and spiral galaxies are arranged around them. The Milky Way (the galaxy belonging to the solar system) is part of the cluster called the Local Group. It consists of three spiral galaxies (Milky Way, Andromeda, and M33) and about thirty smaller galaxies.
Nebula
Large clouds of gas and dust, with diverse forms. Several types are distinguished:
- Emission Nebula: Emit electromagnetic radiation. Thought to be connected with the formation of new stars.
- Reflection Nebula: Illuminated by nearby stars. They do not emit their own energy.
- Planetary Nebula: Originated by some low-mass stars at the end of their life cycle.
Supernova
Result of large explosions that occur at the end of the life cycle of massive stars.