Which type of energy is associated with the acceleration of the universe's expansion?

The type of energy associated with the acceleration of the universe's expansion is dark energy. This mysterious form of energy is believed to make up about 68% of the total energy content of the universe. Dark energy exerts a negative pressure, which counteracts the effects of gravity, leading to the observed accelerated expansion of the cosmos.

This phenomenon was first recognized in the late 1990s when astronomers observed distant supernovae and found that they were dimmer than expected, indicating they were further away than they should be if the universe were only expanding due to gravity. Hence, this indicated that an unseen force—dark energy—was driving the acceleration. The exact nature of dark energy remains one of the biggest mysteries in cosmology, but its effects are clear in the large-scale structure and behavior of the universe.

The other forms of energy listed have specific characteristics and roles that do not relate to this expansive acceleration. Kinetic energy relates to the motion of objects; nuclear energy involves processes within atomic nuclei; and potential energy refers to energy stored in an object due to its position in a force field. None of these energies explain the overall dynamics of cosmic expansion as dark energy does.