Science is the study of matter and energy. Matter, as even a middle-school student would define, is anything that occupies a space and has a mass. Energy is anything that doesn’t have a mass and doesn’t occupy a space. But did you know that only 5% of the entire universe can be measured by the instruments currently available? If all the matter and energy which can be measured amounts to only 5%, where is the remaining 95%, and what is it composed of? These are burning questions which step beyond the realm of classical physics.
A stunning disclosure of the late twentieth Century was that the universe was expanding at a quickening rate. This is in stark contrast to the existing theory that the rate must be slowing down as the universe expanded. To make matters worse, there was no explanation for this acceleration at the time of discovery. Modern science proposes that a mysterious form of energy which has not been properly observed yet, is the cause of this acceleration but fails to properly explain what this energy is. However, studies point out that this mysterious form of energy makes up at least 68% of the entire universe. The term “Dark Energy” was given to this mysterious component of the universe.
A major argument is that Dark Energy could be a property of space-time. This arises from an amazing consequence of Einstein’s theory on general relativity that empty space isn’t empty. Empty space can have its own energy, inherent to the very nature of space-time. This energy appears as the Cosmological Constant in the Einstein Field Equations. The purpose of this constant is to explain that as more space comes into existence, it would appear with this vacuum energy. The vacuum energy could be the missing dark energy of the universe, causing space-time itself to expand. However, no one knows where the thing this cosmological constant describes comes from or if it is even correct. The only supporting evidence is that there is a mysterious acceleration of the universe that might possibly be tied to this phenomenon.
Another plausible explanation is that Dark Energy could be a quantum effect. According to this theory, “empty space” is loaded with impermanent particles that materialize and vanish ceaselessly. But when physicists attempted to ascertain how much energy this would give empty space; the answer came out 10120 times too big.
The third possibility is that Dark Energy could be a completely new field, different from matter and energy. This new field could be theorized as something that fills all of space but having the opposite effect of normal matter and energy. Some scientists have even named this “quintessence” after the fifth element of Greek philosophers. However, there is no scientific evidence or reasoning of where or why such a field would exist.
The least likely theory regarding Dark Energy is that Einstein’s theory on general relativity is wrong. This is highly unlikely as this theory has withstood intense scrutiny through a vast number of experiments over the years. However, a modified version of the theory could be the solution to the problem, if it manages to correctly describe the motion of bodies in the solar system.
Dark energy, despite being an overwhelming part of the physical universe, lacks a powerful hypothetical clarification for its existence or magnitude. The accelerated expansion of the universe, along with dark matter, is the observed phenomenon that most specifically exhibits that our theories of fundamental particles and gravity are either incorrect or incomplete. Therefore, the nature of dark energy ranks high among the most compelling of all outstanding problems in physical science.
References:
Dark Energy, Dark Matter | Science Mission Directorate. (2017). Retrieved from NASA Science Beta Website: https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/
Sam. (2017, July 23). Dark Energy, What could it be? Retrieved from Skeptic Society Magazine: https://skepticsociety.co.uk/dark-energy-what-it-could-be/
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