Cosmological redshift

Definition

Cosmological redshift refers to the phenomenon where light from distant galaxies is stretched to longer wavelengths as the universe expands. This stretching causes the light to shift towards the red end of the spectrum, indicating that those galaxies are moving away from us. It is a key observation that supports the expanding universe model and is intrinsically connected to Hubble's law, which describes the relationship between a galaxy's distance and its recessional velocity.

5 Must Know Facts For Your Next Test

1. Cosmological redshift is distinct from Doppler redshift; it results from the expansion of space itself rather than the motion of objects through space.
2. The amount of redshift can be quantified using the formula: $$z = \frac{\lambda_{observed} - \lambda_{emitted}}{\lambda_{emitted}}$$, where $$\lambda$$ represents the wavelengths of light.
3. Hubble's discovery of redshift in distant galaxies led to the formulation of Hubble's Law, which quantitatively links redshift to distance.
4. The greater the distance of a galaxy, the more pronounced its redshift, allowing astronomers to measure how fast it is moving away from Earth.
5. Cosmological redshift supports the Big Bang theory by showing that the universe has been expanding since its inception approximately 13.8 billion years ago.

Review Questions

• How does cosmological redshift provide evidence for the expanding universe?
  • Cosmological redshift demonstrates that light from distant galaxies shifts towards longer wavelengths as they move away, indicating that these galaxies are receding due to the expansion of space. The more distant a galaxy is, the greater its redshift, which correlates with Hubble's Law. This relationship shows that as space expands, it stretches light waves, providing crucial evidence supporting the model of an expanding universe.
• Compare and contrast cosmological redshift with Doppler redshift in terms of their causes and implications for our understanding of the universe.
  • Cosmological redshift results from the expansion of space itself, causing light to stretch as galaxies move away from each other. In contrast, Doppler redshift occurs due to relative motion between an observer and a source of light. While both phenomena cause light to shift towards longer wavelengths, cosmological redshift implies a dynamic universe that is constantly expanding, whereas Doppler redshift relates to specific motions within a fixed space. Understanding both helps clarify our grasp of cosmic movements and distances.
• Evaluate the significance of cosmological redshift in relation to observational evidence for the Big Bang theory and cosmic evolution.
  • Cosmological redshift is crucial in establishing evidence for the Big Bang theory by demonstrating that distant galaxies are receding from us, indicating an expanding universe. This aligns with predictions made by cosmological models about the early universe's rapid expansion. Additionally, analyzing redshifts allows scientists to trace cosmic evolution over billions of years, revealing insights into galaxy formation and distribution throughout history. This reinforces our understanding of how the universe has changed since its inception.

Related terms

Doppler Effect: The change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave.

Hubble's Law: The observation that the farther away a galaxy is, the faster it appears to be receding from us, implying a relationship between distance and velocity due to cosmic expansion.

Cosmic Microwave Background: The remnant radiation from the Big Bang, which fills the universe and provides evidence of its early state and expansion.