Dhristi JEE 2022-24

Dark Energy Definition

The unknown force that causes the rate of expansion of our universe to increase rather than slow over time is known as dark energy. This is the polar opposite of what one might expect from a cosmos that started with a Big Bang. In the twentieth century, astronomers discovered that the cosmos is expanding. They speculated that the expansion may go on indefinitely, or that it could reverse and trigger a Big Crunch if the universe had enough mass and thus enough self-gravity. That concept has evolved in early twenty-first-century cosmology. Today, the cosmos appears to be growing faster than it did billions of years ago. What could be causing the expansion rate to accelerate? Astronomers are now talking about a repelling force as a possible explanation.


What is Dark Energy and Dark Matter?

The vast majority of our cosmos is concealed from view. Most astronomers believe that dark matter and dark energy make up the majority of the cosmos, despite the fact that we can't see or touch it. But what is this invisible, impenetrable substance that surrounds us? What is dark energy and dark matter? What is the difference between dark matter and dark energy? 

Dark matter slows the expansion of the cosmos, but dark energy accelerates it. Dark matter acts as an attracting force, like cosmic cement, holding our world together. Because dark matter interacts with gravity but it does not absorb, reflect, or emit light, this is the case. Dark energy is a repulsive force — a kind of anti-gravity — that propels the universe's rapid expansion.

Dark energy is by far the more powerful of the two, accounting for around 68 percent of the total mass and energy in the universe. Dark matter accounts for 27% of the total. The rest – a meagre 5% — is all the ordinary matter we see and interact with on a daily basis.


Dark Matter

Fritz Zwicky, a Swiss-born astronomer, investigated photographs of the Coma Cluster's about 1,000 galaxies in the 1930s and noticed something odd about their activity. The galaxies were moving so quickly that they appeared to be colliding. He theorised that they were held together by "black matter."

A similar phenomenon was identified when astronomers Vera Rubin and Kent Ford studied the rotation speeds of individual galaxies decades later. The stars in the galaxy's periphery should rotate at a slower rate than those in the core. Planets in our solar family orbit in this manner. Instead, they discovered that stars on the edges of a galaxy orbit equally as rapidly — if not faster — than those closer in. Rubin and Ford have discovered more proof that the universe is held together by an invisible type of substance.

Many other lines of evidence now point to the existence of dark matter, according to astronomers. Indeed, the presence of dark matter is so widely acknowledged that it is included in the so-called standard model of cosmology, which is the basis for how scientists comprehend the universe's formation and evolution. We won't be able to explain how we got here without it.

However, cosmologists are under pressure to discover solid proof that dark matter exists and that their model of the universe is true because of their elevated stature. Physicists all across the world have been using increasingly high-tech tools to try to find dark matter for decades. They haven't uncovered any evidence of it so yet.


Dark Energy

For over a century, astronomers have known that our universe is expanding. Most galaxies are migrating away from each other, according to telescopic studies, implying that they were closer together in the past. As a result, it provided enough evidence for Big Bang Theory. Astronomers anticipated, however, that the gravitational attraction of all the universe's stars and galaxies would slow the universe's growth. It could even collapse back in on itself in a Big Crunch at some point.

However, that theory was debunked in the late 1990s when two teams of astronomers discovered something strange. Researchers looking at supernovae in the farthest galaxies determined that they were travelling away from us quicker than neighbouring galaxies. The cosmos wasn't simply expanding; it was expanding faster.

However, rather than refuting it, further observations have only strengthened the case for dark energy. Even some of the most outspoken detractors of dark matter believe in the existence of dark energy.

That isn't to say that scientists have figured out what dark energy is. Not at all. However, according to theory of general relativity, they can describe its role in the cosmos. Even though Einstein was unaware of dark energy, his calculations showed that new space could exist. He also inserted the cosmological constant as a fudge factor in relativity, which he added — and later regretted — to keep the cosmos from imploding inward.

This concept permits space to have its own energy. Scientists, on the other hand, have yet to see this force in action on Earth. Some theoretical physicists believe that there is a vast unknown realm of particles and forces waiting to be uncovered. Whatever dark energy and dark matter are made of, they appear to be tugging at the fabric of our universe, holding it together while also pushing it apart.


Conclusion

Cosmos is one of the vast and interesting field of science. Big Bang Theory is the accepted theory for birth of universe as it explain about how the universe was created initially. After that some invisible forces are making it bigger and bigger as these forces are the major cause of expansion of universe. One of these forces is dark energy. Dark energy is responsible for expansion of universe. It is responsible for red shift in galaxy spectrums. Which actually means that galaxies are moving away from each other. The second force is Dark matter. It functions reverse of the dark energy. As it is responsible to hold the visible matter of universe. According to the Big Bang theory the universe created after Big Bang and after that it is expanding continuously. Speed of expansion was very fast in the initial days of big bang but it is decreasing after that. One more theory is there which explain the end of universe. This theory is reverse of Big Bang theory. This is known as Big Crunch Theory or Space Crunch Theory. Space crunch meaning here is with end of universe due to a big crunch. This crunch will be the end of universe and it will concentrate the whole universe to a tiny point. Now the role of Dark Energy and Dark Matter is clear for us. When Dark Energy is dominant over dark matter universe is expanding. When the Dark Matter will dominant the dark energy the space crunch will begin. Our today’s understanding of cosmos is limited and we are searching for new evidence and mysteries unfolded till now.


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FAQs (Frequently Asked Questions)

1. What are facts and discoveries of dark energy?

Dark Energy is the topic which is unclear to cosmologist. As the existence of Dark energy is only established by expansion of universe. The main evidence of dark energy is the redshift in galaxy spectrum. Which prove the invisible energy Most cosmologists thought the cosmos didn't have enough mass to create a Big Crunch until the late 1990s. Data from the 2dF Galaxy Redshift Survey and the Sloan Digital Sky Survey, in particular, seemed to show that the universe will continue to expand indefinitely, albeit at a slower rate as the universe's own mass and gravity tried to pull it back. 


2. What is responsible for the the expansion and crunch of universe?

Dark Energy is responsible for expansion of the universe. Dark matter will be responsible for crunch of universe. As the universe expands, expansion is slowing down. At one point of time the expansion will stop and crunch will begin. Initially it will have less speed but with time it will increase and space crunch will take place.

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