Galaxy rotation curves show that the orbital velocities of stars in galaxies do not decrease as expected based on the visible mass of the galaxy, suggesting the presence of additional mass, i.e., dark matter.

The Big Bang model is the prevailing cosmological model for the universe from the earliest known periods through its present expansion and cooling. It is based on the observation that the universe is expanding and that the cosmic microwave background radiation is consistent with the thermal radiation of a hot, dense early state.

Weakly interacting massive particles (WIMPs) are hypothetical particles that are massive but interact very weakly with ordinary matter. They are a popular candidate for dark matter because they can explain the observed properties of dark matter, such as its abundance and distribution.

Supernovae observations, particularly those of Type Ia supernovae, have shown that the expansion of the universe is accelerating, which is attributed to the presence of dark energy.

The cosmological constant problem refers to the large discrepancy between the observed value of dark energy density and the value predicted by quantum field theory, which is many orders of magnitude smaller.

String theory is a theoretical framework that attempts to unify general relativity and quantum mechanics by postulating that the fundamental constituents of the universe are not point-like particles but tiny, vibrating strings.

The cyclic cosmological model proposes that the universe undergoes a series of cycles of expansion and contraction, with each cycle ending in a Big Crunch followed by a Big Bang.

Quintessence is a hypothetical scalar field that is thought to be responsible for the dark energy. It is characterized by a negative pressure that drives the acceleration of the universe's expansion.

The flat universe model suggests that the universe is spatially flat and infinite in extent, meaning that parallel lines remain parallel and the angles of a triangle add up to 180 degrees.

WIMP (Weakly Interacting Massive Particle) is a hypothetical particle that is thought to be responsible for the dark matter. It is characterized by a weak interaction with ordinary matter and a large mass.

The spherical universe model suggests that the universe is finite in extent and has a spherical shape, meaning that it has a center and a boundary.

Quintessence is a hypothetical scalar field that is thought to be responsible for the dark energy. It is characterized by a negative pressure that drives the acceleration of the universe's expansion.

The closed universe model suggests that the universe is spatially curved and finite in extent, meaning that parallel lines eventually meet and the angles of a triangle add up to more than 180 degrees.

Axion is a hypothetical particle that is thought to be responsible for the dark matter. It is characterized by a very small mass and a very weak interaction with ordinary matter.

The flat universe model suggests that the universe is spatially flat and infinite in extent, meaning that parallel lines remain parallel and the angles of a triangle add up to 180 degrees.