Dark energy is a mysterious form of energy that makes up about 68% of the universe’s total energy density. It is thought to be responsible for the observed accelerated expansion of the universe. Unlike ordinary matter or dark matter, dark energy does not interact with electromagnetic forces and is not directly observable; its presence is inferred from its gravitational effects on the large-scale structure of the universe.

1. 1. Discovery and Evidence

• • • Discovery: The concept of dark energy emerged from observations in the late 1990s. Two independent teams studying distant supernovae found that the expansion of the universe is accelerating, rather than slowing down as previously expected.
    • Evidence: The primary evidence for dark energy comes from these supernova observations, as well as measurements of the cosmic microwave background (CMB) and large-scale structure of the universe.

 

1. 2. Characteristics

• • • Effect on Expansion: Dark energy exerts a repulsive force that counteracts the gravitational pull of matter and causes the expansion of the universe to accelerate.
    • Homogeneous and Isotropic: Dark energy appears to be uniformly distributed throughout space and does not cluster in specific regions.

 

1. 3. Theories and Models

• • • Cosmological Constant (Λ): Originally introduced by Albert Einstein as a modification to his theory of general relativity, the cosmological constant represents a constant energy density filling space homogeneously. This is one possible explanation for dark energy.
    • Quintessence: A theoretical form of dark energy that changes over time and space, unlike the cosmological constant. It involves a dynamic field that evolves and interacts with matter.
    • Extra Dimensions: Some theories propose that dark energy could be explained by the existence of extra spatial dimensions beyond the familiar three. These additional dimensions might influence the expansion of the universe.

 

1. 4. Impact on Cosmology

• • • Cosmic Acceleration: Dark energy is a key factor in the current understanding of the universe’s expansion rate and fate. It influences the rate at which the universe is growing and impacts predictions about its fate.
    • Structure Formation: Dark energy affects the formation and distribution of large-scale structures in the universe by altering the dynamics of cosmic expansion.

 

1. 5. Current Research and Observations

• • • Surveys and Missions: Observational projects such as the Dark Energy Survey (DES), the European Space Agency’s Euclid mission, and the Nancy Grace Roman Space Telescope aim to study dark energy by examining the expansion of the universe, the distribution of galaxies, and the behaviour of supernovae.
    • Challenges: Dark energy remains one of the most significant unknowns in cosmology. Understanding its nature requires precise measurements and new theoretical insights.