Other topics:
Emergence
Strings
Gravity and Cosmology
Condensed Matter Physics
Nanoscience
Quantum Mechanics
Elementary Particles
Quantum Fluids
GRAVITY and COSMOLOGY
In 1916 Einstein completed his general theory of relativity, which gave a unified theory of spacetime and gravitation. It was then gradually realised that for the first time, we had a theory which could claim to talk about the entire universe. Some of the consequences of this theory were so revolutionary that even Einstein had trouble with them. These included the prediction in 1916 of an expanding universe and a 'Big Bang' at the beginning of it, and the prediction in 1938 of regions of collapsed spacetime- later called 'black holes'. However as the decades have gone by, these predictions have been dramatically confirmed by astronomers. In 1928 Hubble found the universe was expanding, and in 1964 the microwave background radiation from the Big Bang was found. In 1967 neutron stars were discovered, and we now have evidence for many black holes in our galaxy, as well as 'supermassive' black holes in the centres of many galaxies. Many high-energy processes occurring in stars can not be explained without using general relativity.
It is now
possible, using different kinds of space telescope, to
look back to events that occurred only a short time
after the Big Bang. However we cannot look back all the
way, and at the heart of the big bang lies a mystery-
it can only be properly understood if we include
quantum mechanics alongside
Einstein's theory of gravity. This 'unified field
theory' has not yet been found (the best current effort
is string theory). Modern
cosmology is also confronted with a new mystery- the
discovery that almost all of the matter and energy in
the universe is in a mysterious 'dark' form, whose
nature is for the moment completely unexplained.
Einstein's theory has excited the popular imagination
(and science fiction) like no other, partly because of
Einstein's remarkable life and personality. Many of the
popular ideas about the theory (eg., time travel) are
rather wild extrapolations from it- but the actual
consequences of general relativity have proved far
stranger than most science fiction.
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