Unlike normal matter, dark matter does not interact with the electromagnetic force. This means it does not absorb, reflect or emit light, making it extremely hard to spot. In fact, researchers have been able to infer the existence of dark matter only from the gravitational effect it seems to have on visible matter. Dark matter seems to outweigh visible matter roughly six to one, making up about 27% of the universe. The matter we know and that makes up all stars and galaxies only accounts for 5% of the content of the universe.

Dark energy makes up approximately 68% of the universe and appears to be associated with the vacuum in space. It is distributed evenly throughout the universe, not only in space but also in time – in other words, its effect is not diluted as the universe expands. The even distribution means that dark energy does not have any local gravitational effects, but rather a global effect on the universe as a whole. This leads to a repulsive force, which tends to accelerate the expansion of the universe. The rate of expansion and its acceleration can be measured by observations based on the Hubble law. These measurements, together with other scientific data, have confirmed the existence of dark energy and provide an estimate of just how much of this mysterious substance exists.

Significance

• While dark matter attracts and holds galaxies together, dark energy repels and causes the expansion of our universe.
• experiments like XENON1T, which are designed to detect dark matter, could also be used to detect dark energy.
• Dark matter originates from our efforts to explain the observed mismatch between the gravitational mass and the luminous mass of galaxies and clusters of galaxies. The gravitational mass of an object is determined by measuring the velocity and radius of the orbits of its satellites, just as we can measure the mass of the sun using the velocity and radial distance of its planets.
• The dark matter problem can also be viewed as a question of the nature of clustering matter. Dark matter must be the basic building block of the largest structures in the universe: galaxies and clusters. Without dark matter, the universe would be a very different place, according to current theories.
• And dark matter is not just for explaining the behavior of distant bodies in the cosmos, but is abundant within our galaxy as well. It is estimated that our solar system is passing through a fine sea of dark matter particles with a density as high as roughly 105 per cubic meter. We may hope to detect the flux of dark matter passing though the Earth, and even to detect the seasons of dark matter, corresponding to the times of year when the Earth is moving with, or against, the flow of dark matter orbiting the center of the Milky Way.

• Dark energy, on the other hand, originates from our efforts to understand the observed accelerated expansion of the universe. In a nutshell, current theory cannot explain the acceleration.
• It is responsible for the cosmic speeding, and international teams of astronomers are working to refine measurements of that acceleration.
• At stake is judgment on Einstein’s greatest blunder (the cosmological constant), possible insight into the fundamental theory of nature (quantum gravity and the quantum state of the universe), and the fate of the universe (a Big Chill or a Big Rip)

Other experiments

• The LUX-Zeplin experiment is a next-generation dark matter experiment in the United States.
• PandaX-xT in China.

Reference:

https://indianexpress.com/article/explained/what-is-dark-energy-have-scientists-detected-it-finally-7534930/

How to structure:

• Start with the definition of dark matter and dark energy
• Explain why it is necessary to research on it
• Mention the recent advancements/works/missions related to it. If there are any Indian contributions, add them
• Conclude