Cosmic Microwave Background (CMB) radiation is a faint glow of radiation that fills the universe, and it is a key piece of evidence for the Big Bang theory of the universe’s origin. Essentially, it is the afterglow of the Big Bang, the radiation that was released when the universe was about 380,000 years old.
Here’s a more detailed breakdown:
- Origins: In the very early universe, everything was incredibly hot and dense, with particles, photons, and other forms of matter constantly interacting. As the universe expanded and cooled, it reached a point where electrons and protons could combine to form neutral hydrogen atoms. This process is called recombination, and it allowed photons to travel freely through space without being scattered by charged particles. These photons became the cosmic microwave background.
- Characteristics: The CMB radiation is in the microwave range of the electromagnetic spectrum, which is why it’s called “microwave” radiation. It is almost uniform in all directions but does have tiny fluctuations that provide crucial information about the structure and development of the universe.
- Temperature: The CMB has a very uniform temperature of about 2.7 Kelvin (which is just above absolute zero), but tiny variations in temperature across the sky (on the order of one part in 100,000) correspond to the early density fluctuations that eventually gave rise to galaxies and other structures in the universe.
- Significance: Studying the CMB allows cosmologists to learn about the early universe’s conditions, the rate of expansion, the composition of matter, and many other important aspects of cosmology. It provides a “snapshot” of the universe just 380,000 years after the Big Bang and serves as one of the most direct pieces of evidence for the Big Bang theory.
The CMB was first detected in 1965 by Arno Penzias and Robert Wilson, and its discovery earned them the Nobel Prize in Physics. It has since been studied in great detail, with spacecraft such as the Cosmic Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP) making important measurements. The most recent probe, the Planck satellite, has given us the most detailed maps of the CMB.