Cosmology

Question 1

Describe the past evolution of the universe and the main arguments in favour of the Big Bang theory.

Answer 1

• The universe began as a hot, dense singularity.
• It rapidly expanded and cooled, allowing the formation of subatomic particles and simple atoms.
• Over time, gravity pulled matter together to form galaxies, stars, and planets.
• The expansion of the universe is still ongoing, as observed through red shift.
• The Big Bang Theory is supported by red shift and cosmic microwave background radiation (CMBR).

Question 2

What is the evidence that supports the Big Bang Theory?

Answer 2

• Red shift: Light from distant galaxies is stretched to longer wavelengths, showing they are moving away.
• Cosmic Microwave Background Radiation (CMBR): Leftover radiation from the early universe, detected as weak microwaves across the sky.
• Composition of elements: The abundance of hydrogen and helium matches Big Bang predictions.
• Large-scale structure: The distribution of galaxies supports the expansion model.

Question 3

Describe how a moving wave source affects observed frequency and wavelength (Doppler Effect).

Answer 3

• When a wave source moves toward an observer, waves are compressed, leading to higher frequency and shorter wavelength (blue shift).
• When a wave source moves away, waves are stretched, leading to lower frequency and longer wavelength (red shift).
• This applies to sound waves (e.g., ambulance sirens) and light waves from galaxies.
• The red shift of galaxies indicates that the universe is expanding.

Question 4

What is the equation for red shift?

Answer 4

• The equation is: Δλ / λ₀ = v / c
  Where:
  
  • Δλ = change in wavelength
  • λ₀ = original wavelength from source
  • v = velocity of the galaxy (speed at which it is moving away)
  • c = speed of light (3.0 × 10⁸ m/s)
• This equation helps calculate how fast a galaxy is moving away based on its red shift.

Question 5

Describe the red shift in light received from galaxies at different distances from Earth.

Answer 5

• Light from distant galaxies is more red-shifted than light from closer galaxies.
• This means that distant galaxies are moving away faster than nearer ones.
• The observation that all galaxies are moving apart supports the theory of universal expansion.

Question 6

Why does the red shift of galaxies provide evidence for the expansion of the universe?

Answer 6

• Red shift shows that galaxies are moving away from us.
• More distant galaxies have greater red shifts, meaning they are moving away faster.
• This suggests that the universe was once much smaller and is expanding outward.
• Matches predictions of the Big Bang Theory, providing strong evidence for its validity.

Question 7

Explain red shift using a simple analogy.

Answer 7

• Imagine you hear an ambulance siren:
  
  • Moving toward you → Higher pitch (compressed waves).
  • Moving away → Lower pitch (stretched waves).
• The same thing happens with light:
  
  • A galaxy moving away → Light waves stretch, making them appear redder.
  • The further a galaxy is, the more its light is stretched (greater red shift).
• This provides evidence that the universe is expanding.