Redshift

Definition

Redshift is the phenomenon where light from an object moving away from an observer is shifted to longer wavelengths, making it appear redder than it actually is. This effect is significant in the context of the expanding universe, as it provides key evidence for the Big Bang theory and helps scientists understand the dynamics of galaxies and cosmic structures.

5 Must Know Facts For Your Next Test

1. Redshift can be quantified using the formula: $$ z = \frac{\Delta \lambda}{\lambda_0} $$, where $$ z $$ is the redshift, $$ \Delta \lambda $$ is the change in wavelength, and $$ \lambda_0 $$ is the original wavelength.
2. There are three types of redshift: Doppler redshift, gravitational redshift, and cosmological redshift, each caused by different phenomena.
3. The measurement of redshift is critical for determining the rate at which the universe is expanding, as observed in distant galaxies.
4. High redshift values indicate that an object is moving away at high speeds, often implying it is from an earlier stage in cosmic history.
5. Redshift observations support the Big Bang theory by showing that galaxies are generally moving away from us, implying that they were once closer together in a hot, dense state.

Review Questions

• How does redshift provide evidence for the expanding universe?
  • Redshift shows that light from distant galaxies is shifted toward longer wavelengths, indicating these galaxies are moving away from us. This observation suggests that the universe is expanding, as described by Hubble's Law, which states that more distant galaxies recede faster. The pattern of redshifts observed across many galaxies supports the idea that everything was once concentrated in a small area, aligning with the Big Bang theory.
• Discuss the significance of Hubble's Law in relation to redshift and what it reveals about cosmic distances.
  • Hubble's Law establishes a direct correlation between a galaxy's distance and its recessional velocity as measured by redshift. This relationship implies that the farther away a galaxy is, the faster it is moving away from us. The law not only reinforces the concept of an expanding universe but also allows astronomers to estimate cosmic distances based on measured redshifts, facilitating our understanding of large-scale cosmic structure.
• Evaluate how different types of redshift—Doppler, gravitational, and cosmological—contribute to our understanding of the universe's behavior.
  • Different types of redshift illustrate various physical phenomena affecting light and matter in the universe. Doppler redshift explains changes due to relative motion, helping us understand galaxy velocities. Gravitational redshift reveals insights into massive objects' influence on light within gravitational fields, indicating how space-time behaves near them. Cosmological redshift supports the idea of an expanding universe by showing how light stretches over vast distances, uniting these concepts to offer a comprehensive view of cosmic dynamics and structure.

Related terms

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

Cosmological Redshift: The redshift that occurs due to the expansion of the universe, where distant galaxies move away from us, causing their light to stretch and shift toward longer wavelengths.

Hubble's Law:

A law stating that the recessional velocity of a galaxy increases with its distance from us, providing a relationship between distance and redshift.