Exploring Space, Time, Matter and the Cosmos
The Universe is everything that exists, including space, time, matter, energy, galaxies, stars, planets, black holes, radiation, and the laws of physics that govern them. It is the largest known physical system and extends over enormous distances measured in billions of light-years.
Modern cosmology estimates that the observable Universe is approximately 93 billion light-years across and contains hundreds of billions of galaxies, each containing millions to trillions of stars.
The leading scientific explanation for the origin of the Universe is the Big Bang Theory . According to this theory, the Universe began approximately 13.8 billion years ago from an extremely hot, dense state and has been expanding ever since.
| Time | Event |
|---|---|
| 13.8 billion years ago | Big Bang |
| 380,000 years | Formation of the Cosmic Microwave Background |
| 100–500 million years | First stars formed |
| 1 billion years | Formation of early galaxies |
| 4.6 billion years ago | Formation of the Solar System |
| Present day | Universe continues expanding |
Galaxies are not randomly distributed throughout space. Instead, they form large-scale structures including:
Together these structures create what astronomers call the Cosmic Web, one of the largest known patterns in nature.
| Component | Approximate Percentage |
|---|---|
| Dark Energy | 68% |
| Dark Matter | 27% |
| Ordinary Matter | 5% |
Ordinary matter includes atoms that form stars, planets, gas clouds, living organisms, and everything visible to the human eye. Most of the Universe consists of dark matter and dark energy, which remain among the greatest mysteries in modern physics.
Galaxies are vast collections of stars, gas, dust, and dark matter held together by gravity. Types of galaxies include:
Our own galaxy, the Milky Way, contains roughly 100–400 billion stars.
Stars are enormous spheres of hot plasma powered by nuclear fusion. They convert hydrogen into helium, releasing tremendous amounts of energy as light and heat.
Massive stars may eventually become supernovae, neutron stars, or black holes.
Planets orbit stars. The Solar System contains:
Black holes are regions where gravity is so intense that not even light can escape. They form from collapsing massive stars or exist as supermassive black holes at the centres of galaxies.
Astronomers continue to study the long-term evolution of the cosmos. Possible scenarios include: