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The Structure and Composition of the Universe

The universe is the space and time that contains all the matter that ever existed.

The Three Characteristics of the Universe

1.) The universe is composed of baryonic matter, dark matter, and dark energy

  • The baryonic matter (ordinary matter) is composed of baryons such as protons and neutrons. It includes the planets, stars, and other celestial bodies such as comets, meteors, and asteroids.

  • Dark matter is composed of particles that do not absorb, reflect, or emit light. A common example is the black hole.

  • Dark energy is the mysterious force that is responsible for the expansion of the Universe.

2.) Hydrogen and Helium are the most abundant elements in the Universe

  • Hydrogen and Helium make up almost 99% of its chemical composition. Most stars are made up of hydrogen. These elements led to the formation of all the elements humans know today.

3.) The universe contains different astronomical bodies and is expanding

  • A star is any astronomical body made up of plasma that can produce heat and light.

  • Galaxy refers to a group of stars

  • There are about 100 billion stars in a single galaxy.

  • You will have to travel the entire length of the solar system 10 million times to reach the next closest galaxy.

  • The size of the universe that humans can observe is 93 billion light years in diameter

Theories about the Origin of the Universe

1.) Big Bang Theory

  • This theory was first proposed by Georges Lemaitre in 1927.

  • He stated that the universe started as a singularity that contained all the energy, space, and time. Around 14 billion years ago, the singularity started to expand and the energy contained in it was released.

  • As more atoms form, they combine with one another through the process called nucleosynthesis.

  • 1st evidence that supported the Big Bang Theory → redshift

  • The redshift was explained by Edwin Hubble in 1929, and it refers to the increase in the wavelength of light caused by distant galaxies

  • 2nd evidence that supported the Big Bang theory → the discovery of CMB ( Cosmic Microwave Background radiation)

  • The CMB radiation → was discovered by Robert Wilson and Arno Penzias in 1965

  • The CMB radiation → is a remnant of the heat found during the early years of the Universe

2.) Steady-state theory

  • This theory was proposed by Sir Hermann Bondi, Thomas Gold, and Sir Fred Hoyle.

  • It states that the Universe has no beginning and no end

  • It claims that as the universe expands, new matter is created in the form of galaxies and stars

What is the age of the universe? → 4.6 billion years

Theories about the Origin of the Solar System

1.) The nebular