Formation Of Galaxies And Largescale Structure

The s o-called hot Big Bang model (which basically includes all of the aforementioned ideas except for the inflation and quantum fluctuations of the very, very early universe) also provides a framework in which to understand the formation of galaxies (and other S arge-scale structures observed today) from more elementary kinds of matter. At about 10,000 years after the Big Bang, the temperature had fallen enough so that the energy density of the universe began to be dominated by massive particles, rather than the light and other radiation that previously dominated the universe's matter-energy distribution. This time is called matterradiation equality, and it is really after this time that general relativity can be said to govern large-scale physics.

Interestingly, observations suggest that cosmic structures from galaxies ranging in size to the universe itself are held together by invisible matter whose presence is only inferred indirectly through its gravitational effects (the so-called dark matter). It is not known whether there is truly a new breed of matter that our experiments have failed to detect or whether our theoretical understanding of the mechanism underlying gravity is missing some crucial piece that would unify the theory with measurements.

It would be remiss not to mention that the current time, as this book is being written, is a very exciting time for particle physics and cosmology, in which precision measurements of the cosmic microwave background are providing us with much new information about the early universe! The references will direct you to more information about how to follow the research of current experts in this exciting field.

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