What is Dark Energy
Spoiler we don't have an answer just yet, just a plethora of valid theories, but I can help you understand the origin of the question.
The year was 1929, Caltech scientist Edwin Hubble announces a critical discovery that but a fundamental base of astrophysics today. he discovered that the universe is expanding.
Edwin Hubble measured the distance between stars using their brightness or luminosity. then he compared the redshift (increase in electromagnetic wavelength) recorded from these stars. He found a functional relationship i.e, the further star the higher the redshift but the magnitude was increasing. He had just proven that the Universe was expanding. Today research with more advanced technology on the same topic has yielded an identical conclusion.
Whilst Edwin Celebrates, Elsewhere einstein is kicking himself. When he first developed the General Theory of Relativity and his popular definition of gravity, he faces the same problem Newton did: their equations suggested that the universe should be either expanding or collapsing. However, einstein assumed that the universe was static so he developed a cosmological constant that cancelled out the effect of gravity on large scales. In simpler terms — His equations results did not fit his theory so he added a fixed value that he created so that the equations favoured his theory. In the words of einstein himself, it was his “Greatest blunder”
According to current theories of gravity (general relativity), the expansion of the universe is set to eventually slow down. This is because every object has its own gravity. There will be a point where the gravity of these objects is larger than the outward force from the big bang that was believed to be propelling the expansion. And once it stopped it would have supposed contacted again and our universe would have recollapsed into itself. However, this theory was burned to the ground when in 1998 the Hubble Space Telescope recorded observations of a really distant supernova that suggested that, a long time ago, the universe’s rate of expansion was much slower.
The universe: Hahahah. Suprise idiots.
Astrophysicists everywhere: uytrhejirfguyhrjkfgivuhfrjfkgvjhf — WHAT!!??
So very clearly something stronger than gravity is causing an acceleration of the universe’s rate of expansion. But We can't see, detect or prove it. What is it? — DARK ENERGY. A theoretical force that pushes the universe outward. As the universe expands matter gets more spread out. this weakens gravity and therefore its pulling force on the universe's expansion decreases. A theoretical force, dark matter, is what scientists believe push the universe outward. this explains the acceleration in expansion. But We don't know what it really is, we can't see it, we can't detect it, we cant prove it.
This Is just one of the many paradoxes of our universe, and it is the stuff of nightmares- no doubt one of the many questions that astrophysicists around the world lose sleepover.
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