Cosmos: Origin and Evolution

• Cosmos is the universe as a whole, seen as a well-ordered and harmonious system.
• It includes all space, time, matter, energy, and the physical laws governing them.
• Cosmology is the scientific study of the origin, evolution, and eventual fate of the cosmos.

Origin and Evolution

• The prevailing cosmological model is the Big Bang theory.
• The Big Bang theory posits that the cosmos originated from an extremely hot, dense state about 13.8 billion years ago.
• The cosmos has been expanding and cooling since the Big Bang.
• In the first few minutes after the Big Bang, light elements like hydrogen and helium were formed through Big Bang nucleosynthesis.
• Over time, gravity caused slight density variations in the early cosmos to grow, leading to the formation of galaxies and larger structures.
• The first stars and galaxies formed several hundred million years years after the Big Bang.
• Supernovae explosions of massive stars scattered heavier elements into space, which later became incorporated into new stars and planets.

Components of the Cosmos

• The cosmos consists of:
  • Ordinary matter (baryonic matter): This includes stars, galaxies, gas, dust, and everything we can see and interact with.
  • Dark matter: An invisible form of matter that interacts gravitationally but does not emit or absorb light. It makes up about 27% of the cosmos's total mass-energy density.
  • Dark energy: A mysterious force that is causing the accelerated expansion of the cosmos. It makes up about 68% of the cosmos's total mass-energy density.
• Galaxies are large collections of stars, gas, dust, and dark matter, bound together by gravity.
• Galaxies come in different shapes and sizes, including spiral, elliptical, and irregular galaxies.
• Our solar system is located in the Milky Way galaxy, a spiral galaxy.
• Stars are massive, luminous balls of plasma that generate energy through nuclear fusion in their cores.
• Planets are celestial bodies that orbit stars.
• There are different types of planets:
  • Rocky planets: like Earth and Mars composed primarily of rock and metal.
  • Gas giants: like Jupiter and Saturn composed primarily of hydrogen and helium.
  • Ice giants: like Uranus and Neptune composed primarily of heavier elements like oxygen, carbon, nitrogen, and sulfur.
• The space between celestial objects is filled with the interstellar medium, which consists of gas and dust.

Large-Scale Structure

• On the largest scales, the cosmos exhibits a network of interconnected structures.
• Galaxies are organized into groups and clusters.
• Clusters of galaxies are further organized into superclusters.
• Superclusters form filaments, which are long, thread-like structures that surround large voids.
• This network of filaments and voids is known as the cosmic web.

Cosmic Microwave Background (CMB)

• The CMB is the afterglow of the Big Bang.
• It is a faint, uniform radiation that permeates the entire cosmos.
• The CMB provides valuable information about the early cosmos, including its age, composition, and geometry.
• Small temperature fluctuations in the CMB correspond to density variations in the early cosmos that seeded the formation of galaxies and other structures.

Expansion of the Cosmos

• The cosmos is expanding, meaning that the distance between galaxies is increasing over time.
• The expansion of the cosmos was first discovered by Edwin Hubble in the 1920s.
• The rate of expansion is described by the Hubble constant.
• The expansion of the cosmos is accelerating, driven by dark energy.

Fate of the Cosmos

• The ultimate fate of the cosmos is uncertain and depends on the nature of dark energy.
• Possible scenarios include:
  • Big Rip: The cosmos continues to expand at an accelerating rate, eventually tearing apart all matter.
  • Big Crunch: The expansion of the cosmos slows down and eventually reverses, causing the cosmos to collapse in on itself.
  • Big Freeze: The cosmos continues to expand indefinitely, becoming colder and darker over time.
  • Heat Death: The cosmos reaches a state of maximum entropy, where no further work can be done.

Mysteries and Open Questions

• The nature of dark matter and dark energy are major unsolved mysteries in cosmology.
• The origin of the matter-antimatter asymmetry in the cosmos is not fully understood.
• The very early cosmos and the nature of the Big Bang singularity remain subjects of active research.
• There are many other open questions about the cosmos, such as the existence of other cosmoss and the possibility of life beyond Earth.