Difference Between Dark Energy and Dark Matter

Dark Energy vs Dark Matter
 

Dark energy and dark matter are two fundamental concepts discussed under astronomy and cosmology. These two concepts hold significance when explaining the expansion of the universe and many other phenomena. This article explains the basics of dark energy and dark matter, and their differences.

What is Dark Matter?

In cosmology and astronomy, dark matter means any form of matter that is not detectable through optical or radio telescopes. What telescopes see is the emitted, reflected, or scattered light or other forms of electromagnetic waves. Dark matter is any form of matter that does not emit, scatter or reflect light and other electromagnetic wave. For now, it is only through the gravitational effects that the presence of dark matter can be predicted. There are several gravitational methods to detect and estimate the amount of dark matter in a system. One method is to use the gravitational lensing of the background radiation from the dark matter, to estimate the amount of dark matter present. For galaxies, galaxy clusters, and galactic rotations, attractions and collisions can be used to determine the amount of dark matter present. According to the observations on large structures of the observable universe based on Friedmann equations and the FLRW metric, it has been estimated that dark matter accounts for about 23 percent of the total mass–energy density of the observable universe, whereas ordinary matter only contributes approximately 4.6 percent for the mass–energy density of the observable universe. The amount of dark matter in the universe plays a vital role in deciding the expansion rate and thereby the future of the universe.

What is Dark Energy?

Dark energy is a concept involved in expansion of the universe. In cosmology, astrophysics and astronomy dark energy is defined as a hypothetical form of energy that contributes to the expansion of the universe. Dark energy is not detectable through ordinary methods. The properties of dark energy are not fully known. A cosmological constant was proposed as one form of dark energy. Cosmological constant was proposed such that the universe can be expanding, static or shrinking depending on the value of the cosmological constant. Cosmological constant suggests a constant dark energy distribution over the space. The other form of dark energy proposed is the dark energy spread out in the space as a scalar field. In this case, the energy density of the universe may not be distributed constantly. Dark energy is estimated to contribute 72 percent to the mass–energy density of the observable universe. A highly precise measurement for the expansion of the universe is required to calculate the exact amount of dark energy in the observable universe.