Cosmology

Cosmology is the branch of science that aims to understand the universe on its largest scales. It explores how the cosmos originated, how it has evolved over billions of years and what its ultimate fate might be. By combining observations with theories from physics and astrophysics, cosmology seeks to answer some of the deepest questions humans have ever asked about existence, space and time.

Cosmology and astronomy: what is the difference

Cosmology and astronomy are closely connected, but they do not have the same focus:

• Astronomy
  Astronomy studies stars, planets, galaxies, black holes and all observable objects in space. It focuses on how these objects form, evolve and interact, and on the physical processes that shape them.
• Cosmology
  Cosmology looks at the universe as a whole. It investigates its origin, structure and expansion, exploring topics such as the Big Bang, the formation of galaxies, dark matter and dark energy.

In simple terms, astronomy zooms in on individual objects in the universe, while cosmology zooms out to study the entire cosmic picture.

A brief journey through the history of cosmology

Since ancient times, humans have looked at the sky and wondered where everything came from. Early civilizations mixed observation with myth, trying to make sense of the cosmos. Over the centuries, scientific ideas replaced legends, opening the way to modern cosmology.

In ancient Greece, philosophers such as Plato and Aristotle imagined a perfect, eternal universe with Earth at its center. Many religions developed their own cosmological stories, each with a different explanation of creation. During the Middle Ages, the dominant view saw the universe as a divine, Earth-centered structure, based on the model of Ptolemy.

The real turning point arrived in the 16th century with the Copernican Revolution. Nicolaus Copernicus proposed that Earth moves around the Sun, opening the way to a radically different understanding of the universe. The invention of the telescope and the work of Galileo and Newton transformed this new vision into a scientific foundation.

In the 19th century, the German astronomer Heinrich Wilhelm Olbers raised a famous question known as Olbers' Paradox: if the universe is filled with stars, why is the night sky dark instead of bright in every direction? The answer, found much later, helped establish that the universe has a finite age and has not always been filled with shining stars.

Modern cosmology took shape in the early 20th century with Albert Einstein's theory of general relativity. Einstein showed that gravity is not just a force, but the effect of curved spacetime. His equations made it possible to build new models of the universe and to predict phenomena such as black holes and cosmic expansion.

Soon after, Edwin Hubble provided the key observation: galaxies are moving away from each other. This demonstrated that the universe is expanding and gave rise to the Big Bang model, which describes the universe as emerging from an extremely hot and dense beginning over 13 billion years ago.

Today, thanks to advanced instruments such as radio telescopes, the Hubble Space Telescope and the James Webb Space Telescope, we can observe galaxies that formed when the universe was still young. Images like the Hubble Deep Field reveal a cosmos brimming with galaxies, while measurements of the cosmic microwave background allow us to look back to the first moments after the Big Bang.

The big questions that cosmology still must answer

Despite huge progress, many mysteries remain open. Researchers are trying to understand what the universe is made of and how it will evolve in the distant future.

• Dark matter
  Dark matter makes up about 27 percent of the total content of the universe, yet it is invisible and its nature is unknown. Scientists do not yet know whether it is made of new types of particles or whether it requires a rethink of current physics.
• Dark energy
  Dark energy accounts for around 68 percent of the universe and appears to drive its accelerating expansion. What it is and how it works are still open questions.
• The origin of the universe and cosmic inflation
  According to the inflation model, the universe expanded extremely rapidly in a fraction of a second after the Big Bang. Observations confirm that the expansion is accelerating, but we still do not know how the story will end. The universe might expand forever, collapse or reach a stable state.
• The horizon problem
  Some distant regions of the universe look too similar to each other to be explained by standard models. This is known as the horizon problem and it suggests that something is missing from our current understanding.
• Unifying general relativity and quantum mechanics
  The largest and smallest scales of the universe are described by two different theories: general relativity and quantum mechanics. Unifying them into a single framework is one of the greatest challenges in modern physics.

Cosmology remains one of the most dynamic fields of science. With every new observation, we learn more about where we come from and where we are heading, even though some of the biggest questions are still waiting for answers.