A flat (zero curvature) universe is a cosmological model in which the geometry of space is Euclidean, meaning it has no overall curvature. This implies that parallel lines never meet, and the angles of a triangle add up to 180 degrees.
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A flat universe indicates that the total density of matter and energy is exactly equal to the critical density.
The concept of a flat universe arises from solutions to Einstein's field equations in General Relativity.
Cosmic Microwave Background (CMB) measurements support the hypothesis that our universe is very close to being flat.
In a flat universe, the expansion rate will slow down over time but will never completely halt.
Observations suggest dark matter and dark energy contribute significantly to making the universe flat.
Review Questions
What does it mean for the geometry of space if the universe is described as flat?
How does a flat universe relate to the critical density?
What role do dark matter and dark energy play in maintaining a flat universe?
Related terms
Critical Density: The precise density at which the universe is perfectly balanced between collapsing back on itself and expanding forever.
Cosmic Microwave Background (CMB): Radiation leftover from an early stage in the development of the universe, providing evidence for its shape and composition.
Dark Matter: A form of matter thought to account for approximately 27% of the mass and energy in the observable universe. It does not emit light or energy, making it invisible.