What is dark energy? Dark energy in simple terms

Dark energy is a term that refers to an unknown form of energy that is believed to be responsible for the accelerating expansion of the universe. Discovered in the late 1990s, dark energy is now known to make up nearly 70% of the universe’s mass-energy density, dwarfing the contribution of matter and radiation combined.

The concept of dark energy emerged from observations of distant Type Ia supernovae made by two independent teams of researchers, the Supernova Cosmology Project and the High-z Supernova Search Team. These distant, exploding stars were found to be farther away and fainter than they would be in a universe that is not expanding at an accelerating rate.

The explanation for this accelerating expansion lies in the mathematical equations of Albert Einstein’s theory of general relativity, which describe how gravity affects the structure of the universe. The equations predict that the expansion of the universe is influenced by the distribution of matter and energy within it. If the density of this matter and energy is high enough, gravity will eventually slow the expansion and cause the universe to collapse in on itself. If the density is too low, the universe will expand forever. But neither of these scenarios matches observations of the universe.

To solve this mystery, astronomers proposed the existence of dark energy, an unexplained energy that is distributed uniformly throughout space and is driving the universe to expand at an accelerating rate. Some theories suggest dark energy may be a property of space itself, like a property of the vacuum. This type of energy is called vacuum energy, and it has the property that it exerts a negative pressure on the universe, pushing it apart.

While there is no direct evidence for dark energy, there are other observations that support its existence. For example, measurements of the cosmic microwave background radiation, which is a relic from the Big Bang, suggest that the universe is flat or nearly so. This implies that the universe must contain a certain amount of dark energy to balance the gravitational pull of all the matter and radiation in the universe.

Despite years of research, scientists still do not know what dark energy is made of or how it functions, but it is believed to be a fundamental part of the universe. The search for dark energy continues to be one of the most important topics in cosmology, with new experiments and telescopes aimed at detecting its signature and unraveling its mysteries.