Kosmologie - Energy of The Cosmos

Energy of The Cosmos

Light chemical elements, primarily hydrogen and helium, were created in the Big Bang process (see Nucleosynthesis). The small atomic nuclei combined into larger atomic nuclei to form heavier elements such as iron and nickel, which are more stable (see Nuclear fusion). This caused a later energy release. Such reactions of nuclear particles inside stars continue to contribute to sudden energy releases, such as in nova stars. Gravitational collapse of matter into black holes is also thought to power the most energetic processes, generally seen at the centers of galaxies (see Quasar and Active galaxy).

Cosmologists cannot explain all cosmic phenomena exactly, such as those related to the accelerating expansion of the Universe, using conventional forms of energy. Instead, cosmologists propose a new form of energy called dark energy that permeates all space. One hypothesis is that dark energy is the energy of virtual particles, which are believed to exist in a vacuum due to the uncertainty principle.

There is no clear way to define the total energy in the Universe using the most widely accepted theory of gravity, general relativity. Therefore, it remains controversial whether the total energy is conserved in an expanding universe. For instance, each photon that travels through intergalactic space loses energy due to the redshift effect. This energy is not obviously transferred to any other system, so seems to be permanently lost. On the other hand, some cosmologists insist that energy is conserved in some sense; this follows the law of conservation of energy.

Thermodynamics of the Universe is a field of study that explores which form of energy dominates the cosmos - relativistic particles which are referred to as radiation, or non-relativistic particles referred to as matter. Relativistic particles are particles whose rest mass is zero or negligible compared to their kinetic energy, and so move at the speed of light or very close to it; non-relativistic particles have much higher rest mass than their energy and so move much slower than the speed of light.

As the Universe expands, both matter and radiation in it become diluted. However, the Universe also cools down, meaning that the average energy per particle gets smaller. Therefore radiation becomes weaker, and dilutes faster than matter. Thus with the expansion of the Universe, radiation becomes less dominant than matter. The very early Universe is said to have been 'radiation dominated' and radiation controlled the deceleration of expansion. Later, as the average energy per photon becomes roughly 10 eV and lower, matter dictates the rate of deceleration and the Universe is said to be 'matter dominated'. The intermediate case is not treated well analytically. As the expansion of the universe continues, matter dilutes even further and the cosmological constant becomes dominant, leading to an acceleration in the universe's expansion.