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Red-shift and the Big Bang
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Light from distant galaxies is stretched. Measuring this shows the universe is expanding, which supports the Big Bang theory.
Red-shift
If a source of waves moves away from an observer, the observed wavelength increases and frequency decreases (the Doppler effect).
Light from distant galaxies is shifted towards the red end of the spectrum: red-shift.
Δλ ÷ λ_0 = v ÷ c
Δλ = change in wavelength, λ_0 = reference wavelength, v = velocity of the galaxy, c = speed of light (3.0 × 108 m/s).
Light from distant galaxies is shifted towards the red end of the spectrum: red-shift.
Δλ ÷ λ_0 = v ÷ c
Δλ = change in wavelength, λ_0 = reference wavelength, v = velocity of the galaxy, c = speed of light (3.0 × 108 m/s).
An expanding universe
More distant galaxies have a greater red-shift, so they are moving away faster.
This shows the universe is expanding. If we run time backwards, everything was once together in one place.
This shows the universe is expanding. If we run time backwards, everything was once together in one place.
The Big Bang
The Big Bang theory: the universe began from a very small, extremely hot and dense region and has been expanding and cooling ever since.
Evidence: (1) red-shift of galaxies, increasing with distance; (2) the cosmic microwave background (CMB) radiation, which comes from all directions and is the cooled remains of radiation from the early, hot universe.
Evidence: (1) red-shift of galaxies, increasing with distance; (2) the cosmic microwave background (CMB) radiation, which comes from all directions and is the cooled remains of radiation from the early, hot universe.
A spectral line with reference wavelength 500 nm is observed at 505 nm in light from a galaxy. Find the galaxy's speed.
- Δλ = 505 − 500 = 5 nm
- v = c × Δλ ÷ λ_0 = 3.0 × 108 × 5 ÷ 500
- = 3.0 × 108 × 0.01
Answer: 3.0 × 106 m/s, moving away
Red-shift is the increase in wavelength of light from galaxies moving away: Δλ/λ0 = v/c. More distant galaxies show more red-shift, so the universe is expanding. Red-shift and the cosmic microwave background are evidence for the Big Bang.
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