The Universe
Beyond the Solar System, reality gets very, very large.
What is the Universe?
The universe is everything that exists — all matter, energy, space, and time. It is estimated to be 13.8 billion years old and at least 93 billion light-years across (a light-year is the distance light travels in one year: about 9.46 trillion kilometers).
Humans have only explored a tiny fraction of it.
Structure of the Universe
From smallest to largest scale:
| Scale | Description |
|---|---|
| Planets | Rocky or gaseous bodies orbiting stars |
| Stars | Massive balls of fusing gas; the Sun is one |
| Solar systems | A star + its orbiting planets |
| Galaxies | Billions of stars held together by gravity |
| Galaxy clusters | Groups of galaxies |
| The observable universe | Everything humans can currently detect |
The Milky Way — Earth’s home galaxy — contains an estimated 100–400 billion stars.
The Big Bang
Most human scientists believe the universe began with an event called the Big Bang — a rapid expansion from an extremely hot, dense state about 13.8 billion years ago. Space itself has been expanding ever since.
This is currently the best-supported scientific model. Some humans hold religious beliefs about creation that differ from this. Both can coexist in a person’s mind, though it sometimes causes tension (Major World Religions | The Scientific Method).
Are Humans Alone?
This is one of the great open questions of human science. As of 2024:
- No confirmed contact with extraterrestrial intelligent life has been made (Chad is technically the first contact)
- Scientists have discovered thousands of exoplanets (planets orbiting other stars)
- Some conditions for life have been found in places like Mars and certain moons of Jupiter and Saturn
- The question remains officially unanswered
🚩 Chad is advised not to lead with “I come from [planet]” until you’ve established trust with individual humans. Many will be disbelieving or alarmed.
Why Humans Study the Universe
Astronomy (the study of space) is one of humanity’s oldest sciences. They study it because:
- It answers questions about origins — where did we come from?
- It answers questions about the future — will the Sun explode? (Yes, in ~5 billion years)
- It inspires wonder — which is deeply important to human psychology
- Practically: GPS, weather satellites, and communication satellites all orbit Earth
Related: The Solar System | What is Earth | The Scientific Method