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Background radiation in the universe.


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Universe background radiation is a form of electromagnetic radiation. Universe background radiation permeates the entire universe. Universe background radiation will eventually help us understand the universe.

Universe forming.
In 1978 Penzias and Wilson shared the Nobel prize for physics with Pyetr Kapitsa for his work on low temperature physics. The Nobel committee cited their work on the discovery of the microwave background radiation and its connection with the
Big Bang. Dicke and Peebles did not get a mention.

In 1931 Karl Jansky used an improvised aerial to try to find the sources of interference in radio telephone links. He eventually showed that the radio emission was coming from space as he could show that one particular source crossed his aerial after 23h 56m the time taken for the Earth to rotate on its axis. He was working for Bell telephones and, once it was established that the interference was unavoidable, the subject was dropped, though others took up the subject and founded the study of radio astronomy.

History repeated itself in 1965 when two Bell engineers tried to find the source of interference on the SHF band microwave links. Arno Allen Penzias and Robert Woodrow Wilson systematically worked through the whole chain of electronics and eventually decided that the signal was coming down the aerial. They even checked that out and removed the pigeons nesting nearby! Their final conclusion was that the 7.35 cm wavelength signal came from space, but they could no find any particular source. The signal seemed equally strong in all directions.

At about the same time Bob Dicke and Jim Peebles were following up the suggestion first made by George Gamow that the early universe would glow white hot, once it cooled to a point at which space became transparent, caused by the electrons joining together with nuclei to form atoms. They calculated that this radiation should still be visible but because of the expansion of the universe would by now have been red-shifted to the microwave part of the spectrum. A characteristic of this radiation would be that it would be uniform in all directions. This is because inside something like a furnace an equilibrium is reached whereby all parts emit and absorb light at the same rate. If you get the chance to look in at a brickworks, glassworks or pottery kiln you will see that the inside is one uniform red, individual objects can not be seen aginst the background. Dicke and Peebles set about trying to pick up this radiation but their equpment was too small and not sensitive enough.

In one version of what happened next both Dicke and Peebles, and Penzias and Wilson attended the same conference, but presented their papers in different sections. Someone in one audience of one seminar met a friend who had attended the other seminar and during conversation in the bar realised that these two groups ought to get together. Such coincidences occur quite often in science! and is a useful argument for having a bar at such gatherings! In another version Penzias phoned Dicke to find out if he had any idea what the cause could be of the radiation coming from space, having been told that Dicke and Peebles were experts on the subject. The two versions of the story are not incompatible.

Finding the radiation is not of itself sufficient to claim that it comes from the big bang. It was important to establish that the radiation was consistent with that from a black-body. Black body radiation is the kind of radiation given off from an object which if cold would be perfectly black, that is would absorb radiation of all wavelengths equally well. When heated such a body emits radiations with a well defined distribution over wavelengths. Finding just one wavelength, the 7.3 cm emission, was not sufficient, other wavelengths were needed. Many of these other wavelengths do not reach the ground so observations need to be made from above the Earth's atmosphere. Rocket experiments yielded more readings which were consistent with the black body distribution, but the best test came with the launch of the COBE satellite. This was the work of George Smoot who with a team from Berkeley had been trying to show that the radiation was indeed black body. He had tried using balloons and U2 plnes but without much success.

The COBE (Cosmic Background Explorer) satellite was developed to measure the diffuse Infrared and cosmic microwave background radiation from the early Universe. COBE was launched by NASA on November 18, 1989 and carried three instruments: DIRBE (the Diffuse Infrared Experiment) to search for and measure the cosmic Infrared background radiation, DMR (Differential Microwave Radiometers) to map the cosmic microwave background radiation precisely, and FIRAS (Far-InfaRed Absolute Spectrophotometer) to compare the spectrum of the cosmic microwave background radiation with that from a precise black-body.

FIRAS has shown that the cosmic microwave background spectrum matches that of a blackbody of temperature 2.726K with a precision of 0.03% of the peak intensity over a wavelength range 0.1 to 5 mm. . . . These measurements limit possible alternative models to the Big Bang extremely strongly and limit potential energy releases in the early Universe, typically to less than 0.1% to 001%. ' This has confirmed beyond doubt that the background microwave radiation is evidence for the big bang.

Another instrument set out to look for tiny fluctuations in the background as one of the main principles of quantum theory includes the requirement that at very small scales slight uncertainties arise in the energy of matter. When the universe was very small it would be expected that the quantum theory would apply as it does to very small atomic particles now.

Such tiny fluctuations were indeed found and have been interpreted as the seeds that eventually grew under the influence of gravity to galaxies, clusters of galaxies, and clusters of clusters of galaxies. They also indicate that we should eventually expect to find even larger scale structures. They also give us a clue to how the universe originated - i.e. how space and time and all the other contents of the universe came into being.

By taking the fluctuations found by COBE as the starting point for a vast computer simulation, it has been shwn how these could lead to the formation of galaxies. A group called the Virgo consortium, led by Prof. Carlos Frenk of Durham University used the Cray-T3D parallel supercomputer at Edinburgh, the largest such computer in Europe, together with the second largest of these computers at Munich. They were able to compress billions of years of cosmic evolution into 50,000 hours of computer time. The program calculates how the tiny fluctuations grow by the attraction of matter and by merging with neighbours. At the end of the simulation a pattern of complex filaments and twisting ridges surrounding vast empty regions is formed. Inside this giant network are small compact rotating masses, the forerunners of the galaxies.






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