Edexcel iGCSE Physics -8.13–8.14P The Big Bang Theory and Its Evidence- Study Notes- New Syllabus
Edexcel iGCSE Physics -8.13–8.14P The Big Bang Theory and Its Evidence- Study Notes- New syllabus
Edexcel iGCSE Physics -8.13–8.14P The Big Bang Theory and Its Evidence- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.
Key Concepts:
update
Past Evolution of the Universe and the Big Bang Theory
The Big Bang theory is the currently accepted explanation for the origin and evolution of the universe. It describes how the universe began from a very hot, dense state and has been expanding ever since.
Key Statement
Statement: The universe began in a hot, dense state and has been expanding and cooling over time.
Key idea: Evidence from observations supports this model.
Past Evolution of the Universe
- The universe began extremely hot and dense.
- It expanded rapidly.
- As it expanded, it cooled.
- Matter formed from energy.
- Stars and galaxies formed later.
Important: The Big Bang was not an explosion into space — it was an expansion of space itself.
Main Evidence Supporting the Big Bang Theory
1. Red Shift of Galaxies (Expanding Universe)
- Light from distant galaxies is shifted toward the red end of the spectrum.
- This red shift shows galaxies are moving away from Earth.
- More distant galaxies show greater red shift.
Conclusion: The universe is expanding.
2. Cosmic Microwave Background Radiation (CMB)
- Weak microwave radiation is detected in all directions.
- It is left over from the early hot universe.
- It has cooled as the universe expanded.
Conclusion: This radiation supports the idea of a hot early universe.
3. Abundance of Light Elements
- The universe contains large amounts of hydrogen and helium.
- The proportions match predictions from the Big Bang model.
- These elements formed shortly after the Big Bang.
Conclusion: Observed element ratios agree with theoretical predictions.
Summary of the Evidence
| Evidence | Observation | Supports Big Bang because… |
|---|---|---|
| Red shift | Galaxies moving away | Universe is expanding |
| CMB radiation | Microwave radiation everywhere | Remnant heat from early universe |
| Light element abundance | Hydrogen and helium dominate | Matches Big Bang predictions |
Why the Big Bang Theory Is Accepted
- Multiple independent observations support it.
- Predictions match experimental data.
- No alternative theory explains all evidence as well.
Example
Explain how red shift provides evidence for the Big Bang theory.
▶️ Answer / Explanation
- Light from distant galaxies is red shifted.
- This shows galaxies are moving away.
- More distant galaxies move away faster.
- This indicates the universe is expanding.
- An expanding universe supports the Big Bang theory.
Example
Explain why the existence of cosmic microwave background radiation supports the Big Bang theory.
▶️ Answer / Explanation
- The early universe was extremely hot.
- Radiation was emitted in all directions.
- As the universe expanded, this radiation cooled.
- It is now detected as microwave radiation.
- This matches predictions of the Big Bang theory.
Evidence Supporting the Big Bang Theory
The Big Bang theory is supported by strong observational evidence. Two key pieces of evidence are the red-shift of galaxies and the cosmic microwave background (CMB) radiation.
Key Statement
Statement: Evidence for the Big Bang theory includes the red-shift of distant galaxies and the existence of cosmic microwave background radiation.
Key idea: Both observations show that the universe is expanding and was once much hotter.
1. Red-Shift of Galaxies
What is observed:
- Light from distant galaxies is shifted towards the red end of the spectrum.
- This shift increases with distance.
Explanation:
- Red shift occurs when a light source moves away from the observer.
- The wavelength of light increases.
- This means galaxies are moving away from Earth.
Conclusion:
- The universe is expanding.
- If we trace this expansion backwards, the universe was once much smaller and denser.
Link to the Big Bang Theory
- An expanding universe supports the idea of a beginning.
- This beginning is described by the Big Bang theory.
Key idea: Red shift provides evidence that the universe is still expanding today.
2. Cosmic Microwave Background (CMB) Radiation
What is observed:
- Weak microwave radiation is detected in all directions.
- The radiation has nearly the same temperature everywhere.
Explanation:
- The early universe was extremely hot.
- It emitted high-energy radiation.
- As the universe expanded, this radiation cooled.
- It is now detected as microwave radiation.
Conclusion:
- The CMB is leftover radiation from the early universe.
- This supports a hot origin of the universe.
Why the CMB Is Strong Evidence
- It is detected everywhere in space.
- It matches predictions of the Big Bang model.
- No other theory explains it as well.
Comparison of the Evidence
| Evidence | What is observed | What it shows |
|---|---|---|
| Red shift | Galaxies moving away | Universe is expanding |
| CMB radiation | Microwaves in all directions | Universe was hot and dense |
Why These Together Support the Big Bang
- Red shift shows expansion.
- CMB shows a hot early universe.
- Both are predicted by the Big Bang theory.
Example
Explain how the red-shift of galaxies provides evidence for the Big Bang theory.
▶️ Answer / Explanation
- Light from distant galaxies is red shifted.
- This means the galaxies are moving away.
- More distant galaxies move away faster.
- This shows the universe is expanding.
- An expanding universe supports the Big Bang theory.
Example
Explain why the detection of cosmic microwave background radiation supports the Big Bang theory rather than a steady-state universe.
▶️ Answer / Explanation
- The CMB shows the universe was once very hot.
- As the universe expanded, this radiation cooled.
- The radiation is detected in all directions.
- This matches predictions of the Big Bang theory.
- A steady-state universe does not explain this radiation.