The universe is the totality of everything that exists. It includes all of space and time, all matter and energy, from the smallest particles to the largest structures like galaxies and beyond. When we look up at the night sky, we are seeing just a tiny fraction of this vast cosmic expanse that contains billions of galaxies, each with billions of stars.
To truly understand what the universe is, we must grasp its incredible scale. Starting from atoms, which are unimaginably small, we scale up through humans, planets, solar systems, and galaxies. The observable universe spans ninety-three billion light-years across and contains over two trillion galaxies. Each galaxy contains billions of stars, making the total number of stars in the universe greater than all the grains of sand on all the beaches on Earth.
The universe is composed of three main components, and surprisingly, the matter we can see and touch makes up only a tiny fraction. Ordinary matter, including all stars, planets, gas, and dust, accounts for just five percent of the universe. Dark matter, which we cannot see but can detect through its gravitational effects, makes up twenty-seven percent. The largest component is dark energy at sixty-eight percent, which is responsible for the accelerating expansion of the universe.
The universe is not static but constantly expanding and evolving. It began with the Big Bang thirteen point eight billion years ago, starting from an infinitely dense point. The first stars formed about four hundred million years later, followed by the formation of galaxies. Today, we observe that the universe continues to expand at an accelerating rate due to dark energy. Scientists predict that in the far future, the universe may experience heat death as it continues to expand and cool.
To summarize what we have learned about the universe: It is the totality of everything that exists, spanning an incredible ninety-three billion light-years across. The universe consists of ordinary matter, mysterious dark matter, and dark energy. It began with the Big Bang thirteen point eight billion years ago and continues to expand and evolve today, making it one of the most fascinating subjects of scientific study.