Science Demo - Expanding Universe
Description
Vocal Characteristics
Language
EnglishVoice Age
Middle Aged (35-54)Accents
British (England - South East - Oxford, Sussex) British (General) British (Received Pronunciation - RP, BBC)Transcript
Note: Transcripts are generated using speech recognition software and may contain errors.
the discovery that the universe is expanding was one of the great intellectual revolutions of the 20th century. With hindsight, it is easy to wonder why no one had thought of it before. Newton and others should have realised that a static universe would soon start to contract under the influence of gravity. But suppose instead that the universe is expanding. If it was expanding fairly slowly, the force of gravity would cause it to eventually stop expanding and then to start contracting. However, if it was expanding Atmore than a certain critical rate, gravity would never be strong enough to stop it, and the universe would continue to expand forever. This is a bit like what happens when one fires a rocket upwards from the surface of the Earth. If it has a fairly low speed, gravity will eventually stop the rocket and it will start falling back. On the other hand, if the rocket has more than a certain critical speed about seven miles per second, gravity will not be strong enough to pull it back, so it will keep going away from the Earth forever. This behaviour of the universe could have been predicted from Newton's theory of gravity at any time in the 19th the 18th or even the late 17th century. Yet so strong was the belief in a static universe that had persisted into the early 20th century. Even Einstein, when he formulated the general theory of relativity in 1915 was so sure that the universe had to be static, that he modified his theory to make this possible. Introducing a so called cosmological constant into his equations, Einstein introduced a new anti gravity force, which, unlike other forces, did not come from any particular source but was built into the very fabric of space time. He claimed that space time had an inbuilt tendency to expand, and this could be made to balance exactly the attraction off all the matter in the universe so that a static universe would result. Only one man, it seems, was willing to take the general relativity at face value. And while Einstein and other physicists were looking for ways of avoiding general relativity is prediction of a non static universe, the Russian physicist and mathematician Alexander Friedman instead set about explaining it