Big Bang vs Steady State
Two rival theories once explained the universe. Discover why red-shift alone could not choose between them, and how one faint whisper of radiation from all directions settled the argument.
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How did the universe begin? 🌌
For much of the 20th century, scientists argued between two big ideas. The **Big Bang** theory says the universe began from a tiny, hot, dense point and has been **expanding** ever since. The **Steady State** theory said the universe has **always existed**, staying much the same over time. This module compares the two, and looks at the **evidence** that finally decided between them.
Key terms 🔑
Four ideas run through the whole debate:
What does the Big Bang theory say? 💥
According to the Big Bang theory, how did the universe begin?
- It began from a tiny, hot, dense point and has been expanding ever since
- It has always existed and never changes at all
- It stays the same size, with matter created to fill the gaps
- It started very large and has been shrinking
Match each term to its meaning 🔗
- Big Bang theory
- Steady State theory
- Red-shift
- CMB radiation
- The universe began from a hot dense point and is expanding
- The universe has always existed and stays much the same
- Light from distant galaxies stretched to red, showing they recede
- Faint microwave radiation left over from the hot early universe
Two rival theories ⚖️
Both theories agree the universe is expanding, but they disagree about its beginning.
Evidence for the Big Bang ✅
Select the TWO pieces of evidence that support the Big Bang theory.
- Red-shift, showing that distant galaxies are moving away
- Cosmic microwave background radiation from all directions
- Objects falling when you drop them on Earth
- The daily rise and fall of the sea tides
What settled the debate? 📡
Here is the key grade-9 point: **both** theories can explain **red-shift** and an expanding universe, so red-shift alone did **not** decide between them. The deciding evidence was the **CMB radiation**. The Big Bang predicts it as the leftover heat of the early universe, but the Steady State theory **cannot** explain it. Its discovery made the **Big Bang the accepted model**.
Complete the picture 🧱
The _____ theory says the universe began from a hot, dense point and has been expanding. The rival _____ theory said the universe has always existed. Light from distant galaxies shows _____, evidence of an expanding universe. Both theories can explain that, so the evidence that settled the debate was the _____ radiation. Because only one theory can explain it, the accepted model is now supported by more _____.
Spot the correct statements 🖍️
An interactive activity.
How the debate was settled 🪜
An interactive activity.
Why was the CMB decisive? 🎯
Why did the discovery of CMB radiation settle the debate in favour of the Big Bang?
- Both theories explain red-shift, but only the Big Bang predicts the CMB
- The CMB signal is much louder than red-shift
- The Steady State theory predicted the CMB first
- The CMB has nothing to do with either theory
You are the scientist 🔀
An interactive activity.
Explain the accepted model ✍️
An interactive activity.