The Cosmological Constant – A Brief Explanation
Having tried to justify the form of Einstein’s ‘bare’ field equations in the last video (GR - 19), this video (GR - 20) attempts to give some justification for the ‘Cosmological Constant’ when those equations are applied to the cosmos as a whole.
It discusses the ideas of a static, expanding or contracting universe - and the usual analogy with ‘escape velocity’ in considering diagrams to illustrate such things. It then goes into some assumptions used for applying Einstein’s Equations to the cosmos - ‘homogeneity’, ‘isotropy’, the ‘perfect fluid’ and the ‘Friedmann–Lemaître–Robertson–Walker Metric’. This is, inevitably, a very superficial discussion, but the Friedmann Equations are then given and discussed - along with the reasons for Einstein’s inclusion of a Cosmological Constant in the early 20th century, his later ‘removal’ of that constant, and then the need for it once again at the end of the 20th century.
This video is the final one in a series of videos on General Relativity (GR-01 to GR-20), which has been created to help someone who knows a little bit about “Newtonian Gravity” and “Special Relativity” to appreciate both the need for “General Relativity”, and for the way in which the ‘modelling’ of General Relativity helps to satisfy that need – in the physics sense.
The production of these videos has been very much a ‘one man band’ from start to finish (‘blank paper’ to ‘final videos’), and so there are bound to be a number of errors which have slipped through. It has not been possible, for example, to have them “proof-watched” by a second person. In that sense, I would be glad of any comments for corrections ……. though it may be some time before I get around to making any changes.
By ‘corrections and changes’ I clearly do not mean changes of approach. The approach is fixed – though some mistakes in formulae may have been missed in my reviewing of the final videos, or indeed some ‘approximate explanations’ may have been made which were not given sufficient ‘qualification’. Such changes (in formulae, equations and ‘qualifying statements’) could be made at some later date if they were felt to be necessary.
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