BRAINCAKEThe Big Bang Theory
The Big Bang theory states that the universe began about 13.8 billion years ago from an extremely small, extremely hot and dense state, and has been expanding and cooling ever since.
The Big Bang was not an explosion of matter into existing empty space. Space and time themselves began with it, and it is space itself that has been expanding since. So there is no centre of the universe where the Big Bang happened: it happened everywhere.
The theory follows from Hubble's law. If galaxies are moving apart now, they must have been closer together in the past. Running the expansion backwards, all the matter and energy in the universe must once have been concentrated in a tiny, very hot region.
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Key terms in this lesson
- hubble's law
- The recession speed of a galaxy is directly proportional to its distance from us.
More in Astrophysics and Cosmology
- Stellar Parallax
- The Cosmological Principle
- The Doppler Effect and Red Shift
- Hubble's Law
- Cosmic Microwave Background Radiation
- The Age of the Universe
- Evolution of the Universe
- Dark Matter
All 24 lessons in Astrophysics and Cosmology · All OCR A-level Physics topics