OCR physics B research project Essay

Origin tout ensembley most pot believed that the domain was unalterable as this seemed both more sensible and more comforting. Most Greeks set out the planets, solarize and other adepts in a series of fixed spheres. Newtons religious beliefs lead him to create a passive and eternal manikin of the universe where there is an infinite number of stars and each of them are the same and equally distant equally distant, thus causing their attractions to cancel out, disrespect obvious problems with this imagination.Even once most scientists agreed that the universe is scattering or that it has done so in the prehistoric, there was more than speculation nigh why it is expanding and what will happen to it in the future. Hypotheses such as the adult slapdash and pixilated secernate poses of the universe devour stockd physicists everywhere the past century. several(prenominal) remain in favour fleck many others impart been dismissed on the basis of observational eviden ce. The static universe This was historically the most everyday view as it seems to drop dead best with everyday experience of the universe.Until Newton developed his Theory of Gravitation, there seemed to be no particular reason to dismiss this vagary. It became ingrained in the minds of many people to the extent that scientists who could see that it was non consistent with currently accepted Theories spurned the idea of a changing universe. Once the idea of a universal proposition attraction between masses was introduced, people employ two varied ideas to comelyify a belief in a static universe. The initiative was that God held everything apart. The blurb was by introducing a force which opposed gravitative attraction on a super scale.When Einstein formulated his Theory of global Relativity, he introduced a force called the cosmo analytic invariable to fit in with his views of a stationary universe. Speculation regarding a non-eternal and expanding universe Olbers paradox, first described in 1823, suggests that the idea of an infinite universe does not fit with observational evidence. If there is an infinite number of stars, an infinitely astronomical inwardness of weak should reach us. From this, it can be concluded that the universe is not infinite in size of it and age.After the Russian mathematician, Alexander Friedmann, intimate of Einsteins Theory of General Relativity, he saw that it implied a changing universe. He saw the cosmological constant as unnecessary. In 1922 he published an obligate in a publication called Zeitschrift fur Physik. In this he put preliminary three possible realities establish upon his calculations. He worked from the beginning point of an expanding universe this allows everything plenty of time to happen, while a universe created in a static state qualification be expected to contract in a small descend of time. The scenarios differed in their average density of the universe.A high average density relative to secureness of expanding upon would lead gravity to pull all matter back to one point, an idea now commonly referred to as a considerable Crunch. A low density would leave the gravitational attraction too weak to stop the expansion completely. The universe would expand forever and become cold and desolate. In the remaining option, the density would be plentiful to slow the expansion to a rate low enough to give a universe that remains edgyly the same size for a long limit. Einstein rejected Friedmanns work, initially claiming that the calculations were incorrect.He neverthelesstually admitted that the work was mathematically sound, but he maintained that it did not represent reality. If the assumption that the universe is expanding is removed, collapse is the only possible outcome. plea for this assumption was required and it soon arrived as a result of meticulous observation and measurement of the stars by Edwin Hubble. But first, another important idea was anno unced. In 1927, a Belgian cosmologist named Georges Lemaitre reasoned that if the universe is expanding, it moldiness have previously been smaller.He extrapolated back from this to theorize that the whole universe must have once been small and compact. He called this state the primeval part and it was the origin of the Big Bang Theory. This is not the only possible logical conclusion of the creation of an expanding universe, but it seems the most obvious and childlike one, and consequently the first choice using Ockhams Razor, the idea that a simple solution is usually preferable to one that seems needlessly complicated. Lemaitres work, just like Friedmanns, was rejected by the majority of the scientific community, including Einstein, upon whose possibility their ideas were based.To persuade people, data was needed. Observations suggesting an expanding universe The easiest way to get a rough idea of the outdistance to a star is to compare its brightness to that of a star of cog nize distance. The amount of take down observed is inversely relative to the solid of the distance to the star. If two stars are equally bright, this can be used to work out the ratio of their distances. Stars vary greatly in brightness, so this method can only give a very rough figure. Its accuracy was improved by focusing on a separate of stars that are believed to be of approximately the same level of brightness.This group came in the form of Cepheid variables. The brightness of these fluctuates over time and the speed at which this happens can be measured. Data from Cepheids in the Small Magellanic Cloud (so the distances should all be reasonably similar) suggested that the amount of enlighten emitted could be linked to the period of oscillation. It therefore seemed reasonable to assume that the ratio of the squares of the distances of two Cepheid variables was inversely proportional to the observed brightness. (http//map. gsfc. nasa. gov/universe/uni_expansion. hypertext m arkup language) Edwin Hubble used this to work out the distances to a large number of stars.All he now needed to see whether the universe was expanding, contracting or staying roughly the same in size was the ceding back velocities of the stars. If the recessional velocities were mainly positive and proportional to distance from the Earth, it suggested an expanding universe. Mainly disconfirming and getting more negative as you get further from us would indicate contraction. Mainly positive or negative with no correlational statistics between speed and distance might suggest expansion in the first case and contraction in the second, but it would not be as simple as the other cases.A roughly even mixture of positive and negative recessional velocities would indicate a static universe. Recessional velocities cannot be measured right away. The change in distance over a short period is too small relative to the starting distance for the imprecise measurement system previously descri bed to detect. Hubble quite used the Doppler Effect to find out the speed of retreat. The spectrum of observed light varies depending upon the elements present within a star. Each element gives a grotesque pattern of spectral lines.The amount these lines are red wobbleed can be used to measure the recessional velocity. Higher speeds result in a greater red shift. Observed relative frequency = f+fv/c f is transmitted frequency, v is velocity of approach of the object and c is the speed of the waves (the speed of light). (http//library. thinkquest. org/27948/doppler. html) Hubble made measurements of the distance to and the red shift of a bulky number of stars and concluded that stars have a recessional velocity directly proportional to their distance from us, as would be expected in an expanding universe.He came up with Hubbles Law, which states v=H0d v is recessional velocity, H0 a constant (Hubbles constant) and d is distance. (Advancing Physics A2, p. 74) image00. png Hubble drew the above graph to introduce his results. The distance estimates have since been revised upwards. (http//www. phys. unsw. edu. au/astro/wwwlabs/hdfSize/hdfSize_intro. html) Early estimates of Hubbles constant placed it at around 50-100kms-1Mpc-1, while newer estimates have narrowed it have to around 70-80kms-1Mpc-1. Hubbles constant can be used for nigh(prenominal) things, including estimating the age of the universe.I shall use it to work out the approximate distance away a star would have to be for the observed frequency to be half the emitted frequency. observed frequency One Mpc is roughly 3. 26106 light years, so the star would be about 6. 5 one thousand thousand light years distant. Fred Zwicky suggested in 1929 that light may lose vigor as it travels, which would explain the proportional relationship between red shift and distance.This idea was called the Tired Light hypothesis. This idea has not been very popular as it has trouble explaining some observations whil e expansion seems a much simpler solution. (http//www. astro. ucla. edu/wright/tiredlit. htm) Theories to explain expansion Although many hypotheses were posited, two took prominence, the Big Bang and Steady enounce theories. The Big Bang theory gradually developed from Lemaitres idea of the primeval atom, while Fred Hoyle, Thomas Gold and Hermann Bondi created the Steady recite theory. The Big Bang is the idea that the whole universe was created by the expansion of a very small and heavy region.The Steady State theory states that the universe is infinite in age, but new matter is forever being created and space is expanding. Both theories gained great popularity, but there were some problems with the Steady State idea (http//www. alief. isd. tenet. edu/Hastings/student/2/steadystatestands. html). Some stellar objects, such as quasars, were only found at large distances, suggesting that the universe has changed in appearance over time, contrary to the Steady State principle that the universe should have been similar throughout time, despite its expansion.It excessively had trouble explaining the relative abundance of different elements, which is something the Big Bang model was able to do after a variety of calculations, including those published in the Alpher-Bethe-Gamow paper (http//physicsworld. com/cws/article/news/30915). Olbers paradox may once again be seen as a problem, though the suggestion was put forward that the light would be red shifted, so the sky would not endlessly be bright as the red shift would move the light to a non-visible region. Despite this, the Steady State theory remained popular.One set of observations, however, changed this. The existence of Cosmic Background Radiation was predicted by the Big Bang model and it was detected in 1964 (http//archive. ncsa. uiuc. edu/Cyberia/Cosmos/Footprints. html). Some proponents of the Steady State theory attempted to explain this as the result of scattered light from distant stars, but they could not explain the black body spectrum produced. succeeding(a) these results, the Big Bang theory became dominant and it currently remains so.Bibliography report sources All the sections up to, but not including, Observations suggesting and expanding universe are sourced from Big Bang by Simon Singh. Published by Fourth Estate in 2005. Advancing Physics A2, IoP, 2001 These sources should both be safe as the second was published by the IoP, while the first is a well known popular science book, so any errors would have probably been highlighted by now.Internet sources http//www. phys. unsw. edu. au/astro/wwwlabs/hdfSize/hdfSize_intro. html http//www. astro. ucla. edu/wright/tiredlit. htm http//www. alief. isd. tenet.edu/Hastings/student/2/steadystatestands. html http//archive. ncsa. uiuc. edu/Cyberia/Cosmos/Footprints. html http//adsabs. harvard. edu/abs/2005ApJ 635L.. 37R These sources are all from university websites, so should be reliable. http//physicsworld. com/cws/article /news/30915.Physics World is a magazine published by the IoP, so should also be reliable. http//library. thinkquest. org/27948/doppler. html According to the website, Thinkquest is written by students under a qualified teacher. Although it is not necessarily as reliable as the other sources, I feel that this is suffici.