In the mid-1960s, Arno Penzias and Robert Wilson detected leftover, cooled down radiation from early in the Universe's history by carefully scanning the sky with a device called the Holmdel Horn Antenna. Their discovery was important evidence in support of the Big Bang theory and won them the Nobel prize.
Image: A map of the CMB created by the COBE satellite (credit: NASA, DMR, COBE Project)
Traces of the early Universe are found.
Prof Brian Cox listens to light from the Big Bang.
Prof Brian Cox is able to witness the oldest light in the Universe, by listening to its stretched wavelengths through a radio. This first light from the Big Bang has been stretched and transformed into radio waves and microwaves and is known as the Cosmic Microwave Background, or CMB.
Scientists map the early Universe.
The astronomers Arno Penzias and Robert Wilson discovered the cosmic microwave background (CMB) radiation by chance in the mid-1960s while using the Holmdel Horn Antenna in New Jersey to map the sky. The CMB was later mapped with satellites, including the WMAP probe.
The Cosmic Background Explorer maps the early Universe.
Nobel prize winner Professor George Smoot explains how the Cosmic Background Explorer (COBE) launched in 1989 and mapped the cosmic microwave background radiation - leftover, cooled down radiation from early in the Universe's history. The most widely accepted age for the Universe is now 13.7 billion years, not 15 billion years as stated in this clip.
Dr Chris Lintott reports on the spacecraft's launch.
The Sky at Night's Dr Chris Lintott reports on the launch of the Herschel and Planck satellites from the European Space Agency's spaceport in Kourou, French Guiana.
Cosmologists try to explain the Universe's uniformity.
Cosmologists have written a series of mathematical equations sometimes referred to as the Standard Model of Cosmology that attempts to describe the Universe as it is today. Working the equations backwards in time has allowed scientists to predict how the Universe started - the Big Bang. However, they've encountered problems along the way. One issue is that the Universe's temperatures are uniform - something at odds with the expected vast temperature variations. This conundrum led particle physicist Alan Guth to develop the inflation theory.
The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the "Big Bang" of cosmology. In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation." The CMB is a cosmic background radiation that is fundamental to observational cosmology because it is the oldest light in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The CMB's serendipitous discovery in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned the discoverers the 1978 Nobel Prize.
The CMB is well explained as radiation left over from an early stage in the development of the universe, and its discovery is considered a landmark test of the Big Bang model of the universe. When the universe was young, before the formation of stars and planets, it was denser, much hotter, and filled with a uniform glow from a white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, protons and electrons combined to form neutral atoms. These atoms could no longer absorb the thermal radiation, and so the universe became transparent instead of being an opaque fog. Cosmologists refer to the time period when neutral atoms first formed as the recombination epoch, and the event shortly afterwards when photons started to travel freely through space rather than constantly being scattered by electrons and protons in plasma is referred to as photon decoupling. The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time (and wavelength is inversely proportional to energy according to Planck's relation). This is the source of the alternative term relic radiation. The surface of last scattering refers to the set of points in space at the right distance from us so that we are now receiving photons originally emitted from those points at the time of photon decoupling.
Precise measurements of the CMB are critical to cosmology, since any proposed model of the universe must explain this radiation. The CMB has a thermal black body spectrum at a temperature of 2.72548±0.00057 K. The spectral radiance dEν/dν peaks at 160.2 GHz, in the microwave range of frequencies. (Alternatively if spectral radiance is defined as dEλ/dλ then the peak wavelength is 1.063 mm.)
The glow is very nearly uniform in all directions, but the tiny residual variations show a very specific pattern, the same as that expected of a fairly uniformly distributed hot gas that has expanded to the current size of the universe. In particular, the spectral radiance at different angles of observation in the sky contains small anisotropies, or irregularities, which vary with the size of the region examined. They have been measured in detail, and match what would be expected if small thermal variations, generated by quantum fluctuations of matter in a very tiny space, had expanded to the size of the observable universe we see today. This is a very active field of study, with scientists seeking both better data (for example, the Planck spacecraft) and better interpretations of the initial conditions of expansion. Although many different processes might produce the general form of a black body spectrum, no model other than the Big Bang has yet explained the fluctuations. As a result, most cosmologists consider the Big Bang model of the universe to be the best explanation for the CMB.
The high degree of uniformity throughout the observable universe and its faint but measured anisotropy lend strong support for the Big Bang model in general and the ΛCDM model in particular. Moreover, the WMAP and BICEP experiments have observed coherence of these fluctuations on angular scales that are larger than the apparent cosmological horizon at recombination. Either such coherence is acausally fine-tuned, or cosmic inflation occurred.