Does Dark Energy Really Exist?

The Ancient Cosmology
From the very beginning of human history, the cosmos, the universe with sophisticated rules of science and logic, allured many people to be interested in various phenomena and routines, which eventually led them to think about the start of the universe. A famous astrophysicist, Stephen Hawking stated: “Most people would feel ridiculous if our image of the universe was an infinite tower of turtles. But what is the basis for thinking that we know better than that? What do we know about the universe, and how do we know it? Where does the universe come from, and where is it going? Did the universe have a starting point? If so, what happened before that? What is the nature of time?” Luckily, the scientists were able to find out a glimpse of the cosmos–although there are lots of obstacles toward getting to the truth.

The Debate
The first main debate on cosmology starts from Einstein’s static universe. Einstein, one of the eminent physicists of the 20th century, thought the universe must be static and non-moving. In 1917, he assumed that a cosmological constant, 𝛬 exists in his field equation in order to maintain his solution to make it seems like the space is neither expanding nor crunching. Imprudently, Einstein concluded that his calculation was correct, and argued that the space is static–which he later regrets saying the “biggest blunder” in his career. According to his interpretation, gravity would gradually crumple the universe since there is no adverse force encountering it. His confidence about the solution broke down after Alexander Friedman and Georges Lemaître proved that the field equation can be solved without Einstein’s cosmic constant. One of the critical pieces of evidence that shows the space is expanding was the discovery of Hubble’s law in 1929. Edwin Hubble’s observation toward outer galaxies revealed the redshift on spectrums, suggesting that they are going far away from our galaxy, the milky way. In 1931, Einstein finally accepted the expanding universe model in the Prussian Academy of Sciences.

One of the famous debates on cosmology would be the Big Bang theory by George Gamow and Steady State theory stated by Fred Hoyle. Gamow concluded that there was a hot singularity at the start of the universe–it had infinite density and the tiny volume converging to zero, and the universe started to expand due to the explosion of the singularity. In contrast, Hoyle argued that space keeps expanding, creating matter to fill the empty spaces of the universe. He even sarcastically named Gamow’s theory as ‘Big Bang’, describing the explosion of the singularity. However, with the discovery of cosmic microwave background radiation (CMB) in 1964, their debate was finished–the estimated degree and the existence of CMB of Gamow was almost correct.

Limitations
Although Gamow’s Big Bang theory constructed a big frame in cosmology, there still existed ironies within. The ‘magnetic monopole problem’ suggests that according to the Big Bang theory, there should be monopoles in the universe, not only dipoles. However, the observations only show dipoles, not seeing any glimpse of monopoles. The second problem is the ‘flatness problem.’ As Hawking explained, there wasn’t any abundant time for light to reach the other side of the universe from the opposite site of the universe right after the explosion. According to the relative theory, any other information cannot reach the other side if the light can’t. Therefore, the different areas of the early universe cannot have the same temperature except if there was an unknown reason. However, the observed space is completely flat.

Inflation Model vs. Young-Wook Lee
The physicist Andrei Linde’s inflation theory was the breakthrough of the unsolved problems of Big Bang theory. Linde’s inflation model suggests that enormous amount of expanding rate (the radius of space was increased 1030 times bigger in one second) forced the non-uniform state of the universe to be flat, just like the balloon. One of the key points of the inflation theory is that the expansion rate is accelerating, not decelerating as the scientists until then had thought. This unknown force, the repulsive force encountering gravity, is called ‘dark energy.’

This compelling argument was refuted by Young-Wook Lee at Yonsei University very recently, stating that “Dark energy might not exist.” Lee and his team conducted researches on 30 type Ia supernovae and figured out that “Supernovas in younger galaxies are fainter than in older galaxies, which would upsend the assumption that supernova luminosity doesn’t evolve over cosmic time.” This can affect the existence of dark energy to collapse, and make a new paradigm in cosmology. Lee’s idea was then questioned by Adan Riess, but Lee and his team reused the source which Riess got for the opposition to strengthen their state. The debate between these two opinions has not finished, but it is an absolute fact that this would derive modern science and cosmology to a better status regardless of the winner.