Though we often teach about the principle of conservation of energy during our Physics tuition classes, the truth is that we are still unable to verify all forms of energy in our universe. A few decades ago, it was thought that the universe would slowly stop expanding due to gravity. However, it was more recently discovered that the expansion of the universe has been accelerating, baffling astrophysicists. Since then, theories began to emerge in attempt to explain this phenomenon. The most popular theory included the existence of dark energy and dark matter – which theoretically constitutes 95.1% of the total content in the observable universe, in terms of mass and energy. Although no one has ever observed dark matter, theorists are certain of its existence, along with dark energy.
Due to its effects on the universe’s expansion, it was determined that dark energy makes up the majority of the observable universe. It is currently accepted that there are two forms of dark energy: scalar fields (e.g. quintessence), and the cosmological constant.
Scalar fields define points in space by assigning a magnitude to each point, regardless of the point of origins of the observers. Quintessence, a scalar field proposed to explain dark energy in terms of this model, is different from the cosmological constant and is seen as a potential fifth fundamental force. Its properties includes a dynamic nature (changes over time), and the property of being either attractive or repulsive.
The cosmological constant is another form of dark energy, indicating the value of energy density in the vacuum of space. Albert Einstein proposed this concept in 1917 explaining how this plays a role in achieving a static universe. However, he discarded this idea when Edwin Hubble discovered the outward movement of nearby galaxies, implying that the universe is still expanding. Nevertheless, theorists still use this concept to explain certain cosmological anomalies, and consider it the simplest form of dark energy.
Dark matter cannot be observed through the use of telescopes, but its existence was discovered primarily through its effects on “normal” (visible) matter, and on the general structure of the universe. Its gravitational effects are partly responsible for concepts such as gravitational lensing and the temperature distribution of heated gas within galaxies. Therefore, the effects of dark matter on the universe is essential to maintain its structure and to promote its high rate of expansion.
One of the most interesting properties of dark matter, besides its current effects on normal matter, and its un-observable nature, is that the majority of dark matter throughout the observable universe is not made up of baryons – thus emitting no electromagnetic radiation and cannot form, or consist of, atoms.