Origins of the Universe
The Big Bang Theory
One theory that explains the origin of the universe is the Big Bang Theory.
- The Big Bang Theory was first suggested in the 1920s.
- It says that the universe began as a tiny, extremely hot and dense point of concentrated energy, around 13.8 billion years ago.
- The universe then expanded rapidly, and it is still expanding today.
- As it expanded, particle formed from energy and started to clump together due to gravity, eventually forming stars and galaxies.
The Steady State Theory (Historical Alternative)
An alternative idea, called the Steady State Theory, was suggested in 1948.
- This theory also says the universe is expanding.
- However, it argues that the universe has always existed and has no beginning.
- To explain why it doesn’t become less dense as it expands, the theory says that new matter is constantly created to fill the gaps.
Evidence Supporting the Big Bang Theory
1. Red-Shift
- Both the Big Bang Theory and the Steady State Theory explain red-shift as evidence that the universe is expanding.
- However, this evidence alone cannot prove which theory is correct.
2. Cosmic Microwave Background Radiation (CMB)
In 1964, two scientists accidentally discovered microwave radiation coming from every direction in the sky.
- At first, they thought it was a problem with their equipment.
- But it turned out to be real – this radiation is called Cosmic Microwave Background Radiation (CMB).
- According to the Big Bang Theory, huge amounts of high-energy radiation (like gamma rays) were released in the early universe.
- As the universe expanded, this radiation’s wavelength stretched, and it cooled down.
- Today, we detect it as microwave radiation.
CMB radiation is strong evidence for the Big Bang Theory, and the Steady State Theory cannot explain it.
Why Most Scientists Accept the Big Bang Theory
- Red-shift supports both the Big Bang and Steady State theories.
- But CMB radiation supports only the Big Bang Theory.
- Because of this, and other modern observations, the Big Bang Theory is accepted by most astronomers as the best explanation of how the universe began and how it is changing.
Scientific Theories Can Change
Science is based on evidence. When new evidence is discovered, scientists:
- May need to change an existing theory, or
- Come up with a new theory that fits the new observations.
Dark Matter and Dark Energy
There are still many things we don’t understand about the universe.
- Observations of supernovae from 1998 onwards show that the expansion of the universe is accelerating — galaxies are moving away faster and faster.
- Scientists believe most of the universe is made of things we cannot directly observe:
- Dark matter: An unknown substance that seems to hold galaxies together but does not emit light or radiation.
- Dark energy: A mysterious force that might be responsible for the accelerating expansion of the universe.
No one knows exactly what dark matter or dark energy are, but scientists are testing new ideas to try to understand them better.