cosmic microwave background

History

In 1948, Ralph Alpher and Robert Herman predicted the existence of such radiation based on the Big Bang theory. In 1965, Arno Penzias and Robert Wilson accidentally discovered it using a large antenna, for which they later received the Nobel Prize.

How it works

After the Big Bang, the Universe was a plasma of particles and light. When it cooled down about 380,000 years later, electrons were able to combine with nuclei (the era of recombination), and light began to travel freely. Since then, it has "cooled" as space expanded and now reaches us as microwaves. Its almost perfect uniformity with tiny ripples shows where galaxies later formed.

History

In 1948, Ralph Alpher and Robert Herman predicted the existence of such radiation based on the Big Bang theory. In 1965, Arno Penzias and Robert Wilson accidentally discovered it using a large antenna, for which they later received the Nobel Prize.

How it works

After the Big Bang, the Universe was a plasma of particles and light. When it cooled down about 380,000 years later, electrons were able to combine with nuclei (the era of recombination), and light began to travel freely. Since then, it has "cooled" as space expanded and now reaches us as microwaves. Its almost perfect uniformity with tiny ripples shows where galaxies later formed.

History

The theoretical prediction was made in the works of George Gamow, Ralph Alpher, and Robert Herman in 1948. They estimated the temperature of the remnant radiation at several kelvins. The experimental discovery occurred in 1965 by Arno Penzias and Robert Wilson, who detected excess noise in an antenna, which turned out to be radiation with a temperature of about 3 K. Subsequent satellite missions (COBE, WMAP, Planck) measured the CMB spectrum and anisotropies with extreme precision, turning cosmology into an exact science.

How it works

The CMB arises at the epoch of recombination (about 380,000 years after the Big Bang), when the Universe became transparent to photons. Its spectrum is described by the Planck law for a black body. Temperature anisotropies reflect initial quantum density fluctuations amplified by inflation. Acoustic oscillations in the photon-baryon plasma produce characteristic peaks in the angular power spectrum, from which cosmological parameters (baryon and dark matter densities, the Hubble constant, and others) are determined. These processes are described by the Friedmann equations and the physics of non-equilibrium thermodynamics.

Open problems & fun facts

Anomalies in large-scale fluctuations: "axis of evil," alignment of the quadrupole and octupole.; Tension in measurements of the Hubble constant (discrepancy between Planck data and local measurements).; The nature of dark matter and dark energy, which affect the anisotropy spectrum.; The need for direct confirmation of inflation through the search for B-mode polarization.

💡 The cosmic microwave background is almost the same in all directions (differences are millionths of a degree). But these tiny temperature fluctuations are the seeds from which all stars and galaxies grew.