Cosmic microwave background

Cosmic microwave background radiation, the afterglow of the Big Bang filling the entire observable universe.

About this subject

The cosmic microwave background (CMB) is electromagnetic radiation that fills the entire universe. Discovered accidentally in 1965 by Arno Penzias and Robert Wilson, it represents the oldest light we can observe, emitted about 380,000 years after the Big Bang. Before that, the universe was an opaque plasma; with expansion and cooling, protons and electrons combined into neutral atoms, allowing photons to travel freely. This radiation originally had a temperature of about 3000 K, but due to cosmic expansion it has been redshifted to a current average temperature of 2.725 K, in the microwave range.

The CMB is nearly uniform but exhibits tiny anisotropies (temperature variations on the order of 1 part in 100,000). These fluctuations are the seeds of cosmic structures like galaxies and clusters. The Planck satellite (2009-2013) mapped these variations with high precision, confirming the standard cosmological model (ΛCDM) and providing parameters such as the age of the universe (13.8 billion years) and the composition of dark matter and dark energy. The CMB is one of the strongest pieces of evidence for the Big Bang, along with Hubble's expansion and the abundance of light elements.

Interesting facts: The CMB temperature is almost the same in all directions, but a small dipole exists due to Earth's motion relative to the cosmic background. Microwave detectors use cryogenic technology to isolate the weak signal from instrumental noise. The study of the CMB also allows testing theories of cosmic inflation, a rapid exponential expansion in the first moments of the universe.

Frequently Asked Questions

What is the cosmic microwave background radiation?

It is the afterglow of the Big Bang, filling the entire universe. Discovered in 1965, it corresponds to the heat emitted when the universe became transparent about 380,000 years after the start.

What is the current temperature of the CMB?

The average temperature is 2.725 Kelvin, just 2.7 degrees above absolute zero. It is nearly uniform, with fluctuations on the order of 0.0002 K.

Why is the CMB important for cosmology?

It provides information about the early universe, such as age, composition, and geometry. The anisotropies reveal the seeds of galaxies and support the model of cold dark matter and dark energy.