Years ago, a nearly inconceivable stretch of time has hidden the evolution of stars, galaxies, and even life itself. To put this into perspective, imagine compressing the entire life of the universe into a single year: each month representing just over a billion years, and each day nearly 38 million years.

In this model, the Big Bang, the event that gave rise to space, time, and matter, occurs exactly at midnight and one second on January 1. In the first moments after this primordial explosion, the universe was an ocean of elementary particles immersed in unimaginably high temperatures. Only about 380,000 years later—equivalent to the first seconds of January 1—did the universe cool enough for atoms to form, releasing light that we now call the cosmic microwave background radiation (CMB), an observable relic still telling the story of the universe’s origins.

By mid-January on the cosmic calendar, the first stars ignite. Around two months later, in mid-March, our galactic home, the Milky Way, is born. A long, silent path unfolds over the millennia until our Solar System emerges in September, formed from the collapse of a cloud of gas and interstellar dust.

Planet Earth forms about 4.5 billion years ago, near the end of the “cosmic September,” but life remains a rare and primitive phenomenon until the close of the month, when the first unicellular life—simple yet extraordinarily resilient organisms—appear as autumn begins.

In mid-December, the first complex life forms, such as plants and animals, emerge. Dinosaurs roam the Earth on December 24, reigning for “just” five days (approximately 200 million years) before going extinct 65 million years ago. Finally, in the last minute before midnight on December 31, the first humans arrive.

This timeline offers a humbling perspective on the extreme brevity of our history compared to the vastness of cosmic time.

Measuring Cosmic Time

The age of the universe, precisely calculated through modern cosmology, comes from observations of the cosmic microwave background radiation, discovered in 1964 by Arno Penzias and Robert Wilson. This fossil radiation is one of the strongest pieces of evidence for the Big Bang model. Fluctuations in this primordial light allow us to estimate not only the universe’s age but also its composition. Its three components are:

  • Ordinary Matter (about 5%): This is the matter that makes up stars, planets, galaxies, and everything we can observe and measure using traditional instruments. It consists of particles like protons, neutrons, and electrons.
  • Dark Matter (about 27%): A form of matter that does not emit light or radiation, making it invisible. Its existence is inferred from its gravitational effects on visible objects such as stars and galaxies. While its composition remains unknown, it is believed to play a crucial role in the formation and stability of galaxies.
  • Dark Energy (about 68%): A mysterious form of energy that permeates all of space and causes the universe’s expansion to accelerate. Though its nature remains a mystery, it is thought to account for most of the universe’s total energy.

In summary, only a small fraction of the universe is composed of “normal” matter that we can directly observe; most of it consists of enigmatic entities that remain poorly understood.

Every point of light in the sky illuminated by cosmic radiation tells a story 13.8 billion years in the making—the time it took for this light to reach us. With increasingly powerful telescopes, such as the James Webb Space Telescope, scientists hope to peer even further back in time, closer to the first moments after the Big Bang, to deepen our understanding of this event.