What is cosmic radiation and the scattering experiment?

GCSE. Please make the answer idiot proof! I think it's something like background radiation, is that right?What is cosmic radiation and the scattering experiment?
'In cosmology, the cosmic microwave background radiation CMB (also CMBR, CBR, MBR, and relic radiation) is a form of electromagnetic radiation filling the universe. With a traditional optical telescope, the space between stars and galaxies (the background) is pitch black. But with a radio telescope, there is 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, hence the name cosmic microwave background radiation. The CMB's discovery in 1964 by astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned them the 1978 Nobel Prize.



The CMBR is well explained by the Big Bang theory 鈥?when the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its red-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, stable atoms could form. These atoms could no longer absorb the thermal radiation, and the universe became transparent instead of being an opaque fog. The photons that were around at that time have been propagating ever since, though growing fainter and less energetic, since the exact same photons fill a larger and larger universe. This is the source for the term relic radiation, another name for the CMBR.



Precise measurements of cosmic background radiation are critical to cosmology, since any proposed model of the universe must explain this radiation. The CMBR has a thermal black body spectrum at a temperature of 2.725 K, thus the spectrum peaks in the microwave range frequency of 160.2 GHz, corresponding to a 1.9 mm wavelength. The glow is almost but not quite uniform in all directions, and shows a very specific pattern equal to that expected if the inherent randomness of a red-hot gas is blown up to the size of the universe. In particular, the spatial power spectrum (how much difference is observed versus how far apart the regions are on the sky) contains small anisotropies, or irregularities, which vary with the size of the region examined. They have been measured in detail, and match to within experimental error what would be expected if small thermal fluctuations had expanded to the size of the observable space we can detect today.



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 theory of the universe to be the best explanation for the CMBR. ...'



'.... Measurements of the CMB have made the inflationary Big Bang theory the standard model of the earliest eras of the universe.This theory predicts that the initial conditions for the universe are originally random in nature, and follow a roughly Gaussian distribution. The power spectrum of these fluctuations has been calculated, and agrees startlingly well with the observations, although certain observables, for example the overall amplitude of the fluctuations, are more or less free parameters of the cosmic inflation model. ...'



'... The CMB gives a snapshot of the Universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thus making the universe transparent to radiation. When it originated some 400,000 years after the Big Bang 鈥?this time period is generally known as the "time of last scattering" or the period of recombination or decoupling 鈥?the temperature of the Universe was about 3,000 K. This corresponds to an energy of about 0.25 eV, which is much less than the 13.6 eV ionization energy of hydrogen. Since then, the temperature of the radiation has dropped by a factor of roughly 1100 due to the expansion of the Universe. As the universe expands, the CMB photons are redshifted, making the radiation's temperature inversely proportional to the Universe's scale length. ...'



'... The anisotropy of the cosmic microwave background is divided into two sorts: primary anisotropy 鈥?which is due to effects which occur at the last scattering surface and before 鈥?and secondary anisotropy 鈥?which is due to effects, such as interactions with hot gas or gravitational potentials, between the last scattering surface and the observer. ...'



'... Subsequent to the discovery of the CMB, hundreds of cosmic microwave background experiments have been conducted to measure and characterize the signatures of the radiation. The most famous experiment is probably the NASA Cosmic Background Explorer (COBE) satellite that orbited in 1989鈥?996 and which detected and quantified the large scale anisotropies at the limit of its detection capabilities. Inspired by the initial COBE results of an extremely isotropic and homogeneous background, a series of ground- and balloon-based experiments quantified CMB anisotropies on smaller angular scales over the next decade. ... In June 2001, NASA launched a second CMB space mission, WMAP, to make much more precise measurements of the large scale anisotropies over the full sky. The first results from this mission, disclosed in 2003, were detailed measurements of the angular power spectrum to below degree scales, tightly constraining various cosmological parameters. The results are broadly consistent with those expected from cosmic inflation as well as various other competing theories, and are available in detail at NASA's data center for Cosmic Microwave Background (CMB) (see links below). Although WMAP provided very accurate measurements of the large angular-scale fluctuations in the CMB (structures about as large in the sky as the moon), it did not have the angular resolution to measure the smaller scale fluctuations which had been observed using previous ground-based interferometers. ...(Wikipedia)'.