評(píng)論
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版本1：宇宙的兩個(gè)理論，一個(gè)說(shuō)物質(zhì)會(huì)變化但總量不變，一個(gè)是會(huì)膨脹，最后說(shuō)一個(gè)遙遠(yuǎn)的恒星的發(fā)現(xiàn)說(shuō)明后一個(gè)理論更正確；
版本2：講的是universe expanding 的兩種理論，一個(gè)是density在變小。另一種是density不變。因?yàn)椴粩鄋ew creation補(bǔ)充變大的空間，然后發(fā)現(xiàn)了一種q.它表明前一種理論更可信。
解析：
big-bang model
widely held theory of the evolution of the universe. Its essential feature is the emergence of the universe from a state of extremely high temperature and density-the so-called big bang that occurred at least 10,000,000,000 years ago. Although this type of universe was proposed by Alexander Friedmann and Abbé Georges Lema?tre in the 1920s, the modern version was developed by George Gamow and colleagues in the 1940s.
The big-bang model is based on two assumptions. The first is that Albert Einstein's general theory of relativity correctly describes the gravitational interaction of all matter. The second assumption, called the cosmological principle, states that an observer's view of the universe depends neither on the direction in which he looks nor on his location. This principle applies only to the large-scale properties of the universe, but it does imply that the universe has no edge, so that the big-bang origin occurred not at a particular point in space but rather throughout space at the same time. These two assumptions make it possible to calculate the history of the cosmos after a certain epoch called the Planck time. Scientists have yet to determine what prevailed before Planck time.
According to the big-bang model, the universe expanded rapidly from a highly compressed primordial state, which resulted in a significant decrease in density and temperature. Soon afterward, the dominance of matter over antimatter (as observed today) may have been established by processes that also predict proton decay. During this stage many types of elementary particles may have been present. After a few seconds, the universe cooled enough to allow the formation of certain nuclei. The theory predicts that definite amounts of hydrogen, helium, and lithium were produced. Their abundances agree with what is observed today. About 1,000,000 years later the universe was sufficiently cool for atoms to form. The radiation that also filled the universe was then free to travel through space. This remnant of the early universe is the microwave background radiation (three degree background radiation) discovered in 1965 by Arno A. Penzias and Robert W. Wilson.
In addition to accounting for the presence of ordinary matter and radiation, the model predicts that the present universe should also be filled with neutrinos, fundamental particles with no mass or electric charge. The possibility exists that other relics from the early universe may eventually be discovered.
expanding universe
dynamic state of the extragalactic realm, the discovery of which has transformed 20th-century cosmology. The development of general relativity and its application to cosmology by Albert Einstein, Wilhelm de Sitter, and other theoreticians, along with the detection of extragalactic redshift (a shift to the longer wavelengths of light from galaxies beyond the Milky Way) by VestoSlipher, led to the realization in the 1920s that all galaxies are receding. Edwin Hubble correlated these observations in mathematical form to provide evidence that the universe is expanding. The discovery of the 2.7 K background radiation in 1965 by Arno A. Penzias and Robert W. Wilson is regarded as convincing evidence that the universe originated approximately 15 billion years ago in a very dense and hot state referred to as the big bang (seebig-bang model).
Observations so far have not succeeded in determining whether the universe is open (of infinite extent in space) or closed (of finite extent) and whether the universe in the future will continue to expand indefinitely or will eventually collapse back into an extremely dense, congested state. See also cosmology.
