Dark Energy and Dark Matter

Scientists are continuously discovering more about our universe and what composes it. One of the main enigmas of the universe is dark energy and dark matter. Dark energy is responsible for the expansion of our universe, and makes up around 68% of it. Dark matter, on the other hand, is a mysterious invisible substance that makes up roughly 27% of the universe. The other 5% of the universe is made up of “normal matter”. Dark matter and dark energy are two of the biggest enigmas that scientist are still trying to understand about our universe

In 1929, American astronomer Edwin Hubble studied exploding stars, known as supernovae, to determine that the universe is expanding. Since then, scientists have sought to determine just how fast the universe is expanding. In the 1990s, two independent teams of astrophysicists began studying a distant supernova to calculate its deceleration. To their surprise, they found that the expansion of the universe wasn't slowing down, it was speeding up. The scientist figured that there must be something that counteracts gravity, which the scientists then called "dark energy."

Scientists calculate the mass of large objects in space by studying their motion. The concept of dark matter was first brought up when astronomers in the 1970s were examining spiral galaxies and expected to see the matter in the center moving faster than on the outer edges. Instead, they found the stars in both locations traveled at the same velocity, indicating the galaxies contained more mass than could be seen at the moment. This was also supported by the studies of gas within elliptical galaxies, which indicated that the universe needed more mass than can be found in invisible objects.

Dark energy is a property of space; this is known due to Albert Einstein's discovery that empty space is not nothing. As the universe continues to expand, the force of dark energy also expands. The properties of this energy are consistent with cosmological constants, which is the energy density of space, or vacuum energy that arises in Einstein′s field equations of general relativity. He explains that this constant counteracts gravity, which keeps the universe from falling apart. As the expansion of the universe is accelerating, saying dark energy is a cosmological constant could neatly explain how space-time is being stretched apart. However, this still fails to explain why the force exists in the first place.

Einstein's theory about cosmological constants suggests that “empty space” can possess its own energy. This energy is a property of space itself; it does not dilute as space expands. As space continues to grow, more of this same energy would continue appearing which would cause the universe to expand exponentially faster. There is still no explanation as to why the cosmological constant is there, or why it can predict the observed acceleration of our universe.

Albert Einstein showed that massive objects in the universe bend and distort light which allows them to be used as lenses. By studying how light is distorted by galaxy clusters, astronomers have been able to create a map of dark matter in the universe.

Most scientists think that dark matter is composed of non-baryonic matter. The lead candidate for non-baryonic matter has ten to a hundred times the mass of a proton. However, their weak interactions with "normal" matter make them difficult to detect. Neutralinos, which are massive hypothetical particles that are heavier and slower than neutrinos, are the foremost candidate, though they have yet to be spotted.

Because dark matter is still a very unknown force, scientists have developed several experiments to gather more information about this enigma. The Alpha Magnetic Spectrometer (AMS), a sensitive particle detector on the International Space Station, has been operating since its installation in 2011. So far, AMS has tracked more than 100 billion cosmic ray hits in its detectors. They have found an excess of positrons, which could lead to the creation of dark matter. There is also the European Space Agency's Planck spacecraft that has been building a map of the universe since it was launched in 2009. It observes how the mass of the universe interacts, and the spacecraft investigates both dark matter and dark energy.

Although scientists have some idea of what dark matter and energy might be, there is still a lot of uncertainty surrounding these forces. The effort to solve all of these questions has mobilized a generation of astronomers to think revolutionarily. Our universe continues to grow, and so does our technology. The growth of technology is what brings us closer to figuring out all of these doubts and allows us to better understand the universe we live in.