Cosmic microwave background radiation

Definition

Cosmic microwave background radiation (CMB) is the afterglow of the Big Bang, filling the universe with a faint, uniform glow of microwave radiation. It serves as a critical piece of evidence for the Big Bang theory, as it represents the remnants of the hot, dense state of the universe when it first expanded and cooled. CMB provides insights into the early universe's conditions, supporting concepts like Hubble's Law and the expanding universe.

5 Must Know Facts For Your Next Test

1. CMB was first detected in 1965 by Arno Penzias and Robert Wilson, who observed the uniform microwave radiation coming from all directions in space.
2. The temperature of the CMB is approximately 2.7 Kelvin, which corresponds to a nearly perfect black body spectrum, indicating its origins from an early hot phase of the universe.
3. The anisotropies (tiny fluctuations) in CMB reveal important information about the density variations in the early universe, leading to galaxy formation.
4. CMB serves as a critical test for cosmological models, providing evidence for inflationary theories that explain the uniformity and isotropy of the universe.
5. By studying CMB, scientists have been able to determine key parameters of our universe, such as its age (about 13.8 billion years) and the relative amounts of dark matter and dark energy.

Review Questions

• How does cosmic microwave background radiation support Hubble's Law and our understanding of an expanding universe?
  • Cosmic microwave background radiation supports Hubble's Law by providing a snapshot of the universe's early conditions shortly after the Big Bang. The uniformity of CMB across the sky shows that all parts of the universe were once hot and dense, correlating with Hubble's observation that galaxies are moving away from us. This expanding nature implies that if we trace back their motion, they originated from a singular point, reinforcing both concepts.
• What role do anisotropies in cosmic microwave background radiation play in understanding galaxy formation?
  • Anisotropies in cosmic microwave background radiation are slight temperature fluctuations that indicate regions of varying density in the early universe. These density variations acted as seeds for gravitational attraction, leading to the clumping of matter and ultimately forming galaxies. By analyzing these anisotropies, scientists gain insight into the large-scale structure of the universe and how it evolved over billions of years.
• Evaluate how the discovery and study of cosmic microwave background radiation has transformed modern cosmology and our understanding of the universe.
  • The discovery of cosmic microwave background radiation revolutionized modern cosmology by providing concrete evidence for the Big Bang theory and establishing a framework for understanding cosmic evolution. It has allowed astronomers to refine models of universal expansion, gauge the age and composition of the universe, and explore concepts like dark matter and dark energy. Furthermore, ongoing studies of CMB continue to challenge and enhance our understanding of fundamental questions regarding cosmic inflation and the fate of the universe.

Related terms

Big Bang Theory: The leading explanation of how the universe began, proposing that it started from an extremely hot and dense point and has been expanding ever since.

Redshift: The phenomenon where light from an object moving away from an observer shifts to longer wavelengths, used to measure the speed at which galaxies are receding.

Hubble's Law:

A fundamental observation that states galaxies are moving away from us at speeds proportional to their distance, implying that the universe is expanding.