OCR Physics B Research Project - The Expanding Universe

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A2 Physics Research Project (OCR B)                Raoul Harris

The Expanding Universe

Originally most people believed that the universe was constant as this seemed both more sensible and more comforting. Most Greeks set the planets, sun and other stars in a series of fixed spheres. Newton’s religious beliefs lead him to create a static and eternal model 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, despite obvious problems with this idea.

Even once most scientists agreed that the universe is expanding or that it has done so in the past, there was much speculation about why it is expanding and what will happen to it in the future. Hypotheses such as the Big Bang and Steady State models of the universe have persuaded physicists over the past century. Some remain in favour while many others have been dismissed on the basis of observational evidence.

The static universe

This was historically the most popular view as it seems to fit best with everyday experience of the universe. Until Newton developed his Theory of Gravitation, there seemed to be no particular reason to dismiss this idea. It became ingrained in the minds of many people to the extent that scientists who could see that it was not consistent with currently accepted Theories rejected the idea of a changing universe.

Once the idea of a universal attraction between masses was introduced, people used two different ideas to justify a belief in a static universe. The first was that God held everything apart. The second was by introducing a force which opposed gravity on a large scale.

When Einstein formulated his Theory of General Relativity, he introduced a force called the “cosmological constant” to fit in with his views of a stationary universe.

Speculation regarding a non-eternal and expanding universe

Olber’s 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 large amount of light should reach us. From this, it can be concluded that the universe is not infinite in size and age.

After the Russian mathematician, Alexander Friedmann, learned of Einstein's Theory of General Relativity, he saw that it implied a changing universe. He saw the cosmological constant as unnecessary.

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In 1922 he published an article in a publication called Zeitschrift für Physik. In this he put forward three possible realities based upon his calculations. He worked from the starting point of an expanding universe; this allows everything plenty of time to happen, while a universe created in a static state might be expected to contract in a small amount of time.

The scenarios differed in their average density of the universe. A high average density relative to speed of expansion would lead gravity to pull all matter back to one point, an idea now commonly referred to ...

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