The Expanding Universe | Physics for GCSE/IGCSE - Year 11 PDF Download

Galaxies & Redshift

• Objects emitting waves typically have wavefronts spreading out symmetrically.
• Movement of the wave source can lead to wave compression or stretching.

Understanding the Doppler Effect

• When an object is in motion, it alters the wavelength (λ) and frequency of waves:
  • In front of the moving source, the wavelength decreases, and the frequency increases.
  • Behind the moving source, the wavelength increases, and the frequency decreases.
• This phenomenon is referred to as the Doppler effect.

Impact on Wavelength

• The wavelength in front of the source decreases, leading to an increase in frequency.
• The wavelength behind the source increases, causing a decrease in frequency.

Impact on Light

• The Doppler effect is also applicable to light:
  • When an object moves away from an observer, the wavelength of light increases.
  • This phenomenon is known as redshift, as the light shifts towards the red end of the spectrum.

Redshift and Blueshift in Astronomy

• If an object moves away from an observer, the wavelength of light increases. This phenomenon is known as redshift, indicating that the light shifts towards the red end of the spectrum.

Understanding Redshift

• Redshift refers to the increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies.

Observing Redshift

• The Milky Way is just one of billions of galaxies in the Universe. Light emitted from distant galaxies appears redshifted when compared to light emitted on Earth.

Comparing Light from Close Objects and Distant Galaxies

• The illustration below depicts how light appears from a nearby object like the Sun and a far-off galaxy.

• The diagram also reveals that light reaching us from remote galaxies experiences redshift.
• Redshift indicates a shift of spectral lines towards the red end, suggesting galaxies' recession.
• This redshift implies the universe's expansion, aligning with the Big Bang theory.

The Expanding Universe

• Observation from Light Spectrums of Distant Galaxies:
  • As galaxies get farther, redshift increases, indicating faster movement away from us.
  • This relationship implies that distance correlates with the speed of galactic motion.
• Hubble's Law and Redshift:
  • Greater distances to galaxies result in greater redshifts, illustrating accelerated galactic recession.
  • The phenomenon suggests an expanding universe where galaxies move away from each other over time.