BRAINCAKEThe Fate of the Universe
The universe is expanding, but gravity between all the matter in it acts to slow that expansion down. Its ultimate fate depends on the average density ρ of the universe compared with a critical density ρc, which is only about 10−26 kg m−3 (a few hydrogen atoms per cubic metre).
• ρ > ρc (closed universe): gravity is strong enough to stop the expansion. The universe will eventually contract, ending in a 'Big Crunch'.
• ρ < ρc (open universe): gravity is too weak to stop the expansion, so the universe expands forever.
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Key terms in this lesson
- dark energy
- A hypothesised form of energy thought to cause the observed acceleration of the expansion of the universe.
More in Space
- White Dwarfs, Neutron Stars and Black Holes
- Trigonometric Parallax
- Standard Candles
- The Doppler Effect and Red Shift
- Hubble's Law
- The Age of the Universe
- The Expanding Universe
- Dark Matter
All 18 lessons in Space · All Edexcel A-level Physics topics