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Ch 26 Cosmology Pt 2

Vocabulary

TermDefinition
Critical Density corresponds to the dividing line between a universe that collapses and one that expands forever
Critical Universe equal to the critical density, where expansion will continue forever but approach zero
Actual Density universe's mass (luminous & dark) divided by its volume (space)
High-Density Universe (closed universe) self-gravity slows the expansion until it halts and collapses
Closed Universe above the critical density, with enough mass to stop expanding & eventually collapse
Riemannian Geometry positively curved space (such as the surface of a sphere)
Flat Universe when straight lines will extend forever and parallel lines will never cross each other
Euclidian Geometry flat space, where the sum of the angles making up a triangle equals 180 degrees
Low-Density Universe (open universe) self-gravity is insufficient to stop expansion, continuing forever
Open Universe below the critical density, with not enough mass to stop expansion of the universe
Lobachevsky Geometry negatively curved space (like that of a saddle's surface)
Luminous Matter normal matter that interacts with other matter and radiation
Decelerating Universe velocity at which a galaxy recedes from the observer is decreasing with time
Accelerating Universe velocity at which a galaxy recedes from the observer is increasing with time
Dark Energy distinct from any type of normal matter or radiation, even dark matter
Quintessence form of dark energy proposed to explain the accelerating expansion of the universe
Created by: john_bailey720
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