Dark Energy – The Most Elusive Force in the Universe

To understand what is one of the most puzzling and fascinating forces in modern astrophysics, we first must understand just what exactly the universe is made of.

Universal energy breakdown

Universal energy breakdown

Einstein gave us the famous equation e=mc2 , which essentially means the energy of a system (e) equals the mass of the system (m) multiplied by the square of the speed of light (c). Therefore, matter with mass can be mathematically converted into pure energy (and vice versa) while maintaining the law of Conservation of Energy.

When thinking about matter this way, we can then directly compare the amount of matter to the amount of energy in the universe. What was discovered was astounding. Approximately five percent of the universe is physical matter we can see. Every single atom in the universe, including every star, planet, and human, makes up only four percent of the total energy within the universe.

Another 27% of the total universe energy can be attributed to dark matter. Dark matter is matter that we can detect by means of gravity, but cannot witness it directly. It has similar properties to regular matter, except it does not interact directly with the electromagnetic spectrum – thus we cannot see it.

The remaining 68% of the universe is made up of dark energy.

Albert Einstein and Edwin Hubble

A History Lesson in Dark Energy

In 1917, Albert Einstein modified some of his General Relativity calculations to account for something he referred to as the “Cosmological Constant”. This was a mysterious and universal force he deemed was necessary to keep the universe from collapsing on itself by the force of its own gravity. Einstein was under the impression the universe was static, and therefore needed some explanation for why the observable matter was not forcing the universe to contract.

In 1929 Astronomer Edwin Hubble discovered all distant galaxies are moving away from us at a relatively uniform rate relative to their distance, which shattered the idea of a static universe. The cosmological constant was removed from Einstein’s equations, as it was no longer needed to explain why the universe was not collapsing. Einstein was quoted as referring to the Cosmological Constant as his “biggest blunder.”

Einstein would be vindicated almost 70 years later, when modern technology discovered distant galaxies were not only receding from us, but actually accelerating as they got further away. No calculations to that point could account for such a discovery, so Einstein’s cosmological constant was revisited.

So what is Dark Energy?

Illustration of the expanding universe

In a short answer, we don’t know. Like dark matter, it does not interact with regular matter or the electromagnetic spectrum, so we have no way of detecting it directly. All we know is the universe is expanding at an accelerated rate, which should not happen if it was made up of only matter and dark matter. One could think of dark energy as a “anti-gravity” force that pushes everything apart. In a sense, space itself is stretching due to the force of dark energy.

There are a few proposed explanations for the existence of dark energy, but none have been confirmed. One option is the idea that space itself has this associated expansion energy locked within it, even in a complete vacuum. This is the modern interpretation of Einstein’s Cosmological Constant. As this energy pushes outward to expand the space, more energy is created because it is proportional to the space itself.

Another alternative is found in Quantum Field Theory. Vacuum energy is the concept of “virtual particles” that temporarily exist in entirely empty space. These virtual particles are made up of perfectly opposite pairs that briefly flash into existence then disappear when they collide. The energy resulting in this annihilation could explain dark energy’s origins.

A third explanation is the concept of “quintessence”. This theory states dark energy could actually be a fifth type of fundamental force in addition to gravity, electromagnetic, strong nuclear, and weak nuclear. It is different than other explanations for dark energy in that it states the strength of the force has changed over time. Particularly about 10 billion years ago, it increased in strength to begin forcing the universe into its current accelerated expansion.

Implications of Dark Energy and an Expanding Universe

Regardless of the exact nature of dark energy, we are fairly certain the universe will keep accelerating in its expansion. This has some interesting consequences. As the space between distant galaxies and Earth grows, the galaxies will eventually recede at a rate faster than that of the speed of light. Thus, light emitted from those galaxies will never reach us – effectively removing them from our observable universe.

Additionally if the dark energy remains constant, there is a point at which it will reach divergent expansion, where the other universal forces are overpowered. In this scenario, all visible matter will be torn apart down to the very atoms, in what is known as the “Big Rip”

2 Responses to “Dark Energy – The Most Elusive Force in the Universe”

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