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 BIG BANG

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مُساهمةموضوع: BIG BANG   الخميس 24 يناير 2008, 18:03


BIG BANG



Only one in three Americans accept the so-called Big Bang as the origin of the universe. British cosmologist Fred Hoyle thought the idea so ridiculous that he dubbed it, mockingly, as the "Big Bang" and the name stuck. Hoyle had his own theory of the universe, the quite different "steady state" theory, which although an attractive idea was subsequently disproved.
The Big Bang idea originated from Edwin Bubble's discovery in 1929 that the universe is expanding. So that in the past it must have been smaller, until ultimately it must have been a point. Improbable as it may seem the concept of an explosion from that point to the present size is based on many lines of evidence, that are strengthened by each new observation.
So everything in our universe was once concentrated in a tiny region called a singularity of unimaginable density. Then, 13,700 million years ago, it began expanding faster than the speed of light from smaller than a proton to the size of a tennis ball. This period is called inflation.
This seems to contradict Einstein's special theory of relativity, which says that no body can travel faster than the speed of light, but in this case space itself is expanding and Einstein's restriction does not apply.
Slowly the cosmos cooled and atoms formed with electrons about 380,000 years after the Big Bang. This allowed light to travel through space. After a few million years clouds of gas condensed and fragmented to form stars which collected into galaxies.
There are five reasons to accept the idea that the universe originated in the Big Bang, without a reasonable doubt.
One: Why is the night sky so dark? This is known as Olber's Paradox. If the universe is infinitely old and large the sky should be as bright as the surface of a star, since although stars' brightness decreases as the square of the distance, the number of stars increase as the cube of the distance. So every line of sight should end on a star's surface. This is not so. Therefore the universe must be of limited age and extent.
Two: In the mid 1920s Edwin Hubble, using the 2.5m telescope on Mount Wilson, near Los Angeles, showed that the then called Andromeda Nebula was far outside the Milky Way, which thus did not constitute the entire universe as had been thought previously.
He went on to show that other nebulas are still more distant and moving away from us at speeds that increased in proportion to their distance from us. Thus, the universe is expanding.
Three: In 1965 two scientists at the Bell Telephone Laboratories in the United States, unexpectedly, picked up a radio noise with a peak wavelength of one millimetre, coming uniformly from all parts of the sky. After seeking advice from physicists at Princeton University, it was realised that the radiation fitted the profile of radiation that had been predicted to permeate space as a left over from the original Big Bang.
By the time it reached Earth in 1965 it had cooled to 3 degrees Kelvin (-270ºC). The discoverers, Arno Penzias and Robert Wilson, were awarded the Nobel Prize for physics in 1978.
In the early 1990s NASA's Cosmic Background Explorer (COBE) measured the temperature of the background radiation as 2.73 degrees Kelvin. In 2001 NASA's Wilkinson Microwave Anisotropy Probe (WMAP) mapped variations in the temperature of the background radiation to 1 part in 100,000.
Four: Extrapolating the rate of universal expansion backward for 13,700 million years astronomers can estimate the conditions under which the lightest atomic nuclei cooked. The fusion was fast, only lasting a few minutes, but it resulted in 25% of the primal hydrogen being converted into helium. Some deuterium (heavy hydrogen) and a small amount of lithium (element number three) were also formed.
The proportion of all three is in agreement with calculation based on the Big Bang theory. The figure for helium is especially important as its proportion in stars determines their behaviour.
Five: The Bubble Space Telescope has taken photos showing the universe far away in space, and therefore far back in time, showing mini-galaxies with balzingly hot stars, previously a mystery, but now known to be young newly formed galaxies.
The elements are formed in stars and then dispersed into space, largely from supernovas (exploding stars). The oldest stars contain small amounts of elements heavier than helium. The proportion of heavy elements has already increased with time showing that the universe is evolving in time, as the Big Bang predicts.



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مُساهمةموضوع: رد: BIG BANG   السبت 09 فبراير 2008, 12:53

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مُساهمةموضوع: رد: BIG BANG   السبت 09 فبراير 2008, 12:55

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مُساهمةموضوع: رد: BIG BANG   الجمعة 22 فبراير 2008, 11:29

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مُساهمةموضوع: رد: BIG BANG   السبت 10 مايو 2008, 05:14

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مُساهمةموضوع: رد: BIG BANG   السبت 10 مايو 2008, 05:17

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