Dark energy is a hypothetical form of energy that is thought to make up approximately 70% of the total energy in the universe. It is believed to be responsible for the observed accelerated expansion of the universe.
Dark energy was first proposed in the late 1990s when astronomers observed that the expansion of the universe was accelerating. This discovery was made by measuring the brightness of distant supernovae and comparing it to their redshift.
There are several theories about dark energy, but the most widely accepted one is the cosmological constant, which suggests that dark energy is a constant energy density that exists throughout space. Other theories include quintessence, which suggests that dark energy is a dynamic field, and modified gravity, which proposes that the laws of gravity are different on a large scale.
Dark energy is believed to be the driving force behind the accelerated expansion of the universe. It counteracts the gravitational pull of matter, causing the expansion to accelerate instead of slowing down. This ultimately affects the structure of the universe and the formation of galaxies and galaxy clusters.
Currently, dark energy cannot be directly observed or measured. However, its effects can be observed through its impact on the expansion of the universe. Scientists are also studying the cosmic microwave background radiation, which may provide more insights into the nature of dark energy.