As Man probes ever deeper into the mysteries of the Universe, his search seems to yield more questions than answers. Some of the most mysterious phenomena discovered in space are dark matter and dark energy.
Approximately 80 per cent of the mass in known Universe is made up of "dark matter," a strange and intangible substance that yet scientists have not been able to identify or observe directly. Dark matter is not visible to the naked eye, and does not emit light or energy.
So how do we know it even exists?
Well, its invisible status ensures that remains a huge enigma to science, but a growing body of evidence appears to confirm that, whatever it is, it does exist. The concept of dark matter was first discovered in 1933 by the Swiss astronomer Fritz Zwicky, who was attempting to determine the mass of a cluster of galaxies by measuring their speed and the light they emitted. The matter in galaxies holds them together in rotating clusters by generating a gravitational force. Zwicky's results suggested that the galaxies contained far more matter than he could perceive, though no light appeared to emanating from the unseen matter, a fact that led to it being termed as "dark matter."
Similar experiments in the 1950s confirmed that galaxies appeared to contain far more mass than was visible, and since then scientists have been able to produce a map of dark matter in the universe. This has been achieved by monitoring how light is distorted by galaxy clusters, a method first developed by Einstein who illustrated that massive objects can bend light, therefore allowing them to be used as lenses.
It is possible, however, that the accepted laws of gravity used by scientists to measure the motion of celestial bodies may need to be revised. If there is a flaw in the current theory of gravity then the case for dark matter could potentially evaporate. A hypothesis was made in the 1980s by physicist Mordehai Milgrom of the Weizmann Institute of Science in Rehovot, Israel, who suggested that a simple modification to Newtonian physics could explain away the gravitational discrepancies without requiring the presence of dark matter.
The theory was unable to describe all celestial objects, however, and to encompass all gravitational interactions a modification to Einstein's theory of general relativity would also be required.
Later reviews of the theory declared that, in order for these modified versions to work, some form of unseen matter must still be in place, which brought the whole concept back once more to dark matter. Pedro Ferreira, a University of Oxford cosmologist and one of the review paper's co-authors, commented:
"If you try and build a consistent, relativistic theory that gives you modified Newtonian dynamics, you have no choice but to introduce extra stuff," he said. "I don't think it will be described by particles, in the way that dark matter is described—it may be described in a more wavelike form or a more fieldlike form."
So if we are fairly happy that dark matter does exist, what is it?
Scientists know that identified universal matter, known as baryonic matter, is made up of protons, neutrons and electrons, but the general consensus amongst astro-physicists is that dark matter is most likely consists of non-baryonic matter. The most likely contender for this type of matter is WIMPS (weakly interacting massive particles). Despite their size - up to a hundred times the mass of a proton - WIMPS are not easy to detect as their interact very feebly with normal matter. Other potential candidates for dark matter are neutralinos, a slower, heavier form of neutrino; the more petite neutral axion and uncharched photinos.
Whatever its composition, in order to hold all of the elements of the universe together, dark matter must make up approximately 80 percent of its matter, so it is a slightly disturbing fact that we do not know what constitutes such a large part of our universe. Yet dark matter is a minority shareholder in the universe; though it is a relative giant compared to normal matter, which makes up a minute 5 per cent of the total universal mass, dark matter makes up just 27 per cent of its composition. The dominant force in the universe is the even more enigmatic "dark energy," which comprises an astonishing 68.3 per cent of all energy in the cosmos.
So what is this dark force that sounds more like an idea from science fiction?
Scientists are equally as baffled by this strange energy as they are by dark matter; it was identified in the 1990s when it was discovered that, instead of slowing down as it should be after billions of years, the expansion of the universe was actually speeding up! The propulsion of the original "Big Bang" that formed the universe initially caused the universe to expand outwards. Scientists had previously thought that the energy to drive this expansion would one day begin to decrease, causing the growth of the universe to slow down, but the opposite appears to be true. This means that something must have sufficient force to overcome gravity and continue the outward spread, but it is not apparent what this energy is.
The unknown force came to be known as "dark energy" and its properties are still unknown, though it is believed to have behaved in a consistent manner since the birth of the universe.
One hypothesis to explain the energy is "quintessence," an irregular, changing energy field considered by some physicists to be a fifth fundamental force. The leading theory to explain its presence, however, is that dark energy is essentially more "space" coming into being. Albert Einstein was the first to understand that space is not just an empty nothingness, and that it was perfectly feasible for more space to come into existence.
Einstein's theory of general relativity includes a cosmological constant, to explain the idea favored by scientists that the universe was stationary. When it was discovered that, far from being constant, the universe was actually expanding, Einstein considered that he had made a huge bungle but in fact his mistake could help to explain what dark energy is. By predicting that space can create its own energy, the constant theory suggests that more energy would then need to be added to the universe, explaining its rate of expansion.
Though the mathematics appear to clarify the process by which it is emerging, it does not explain what dark energy is or why it materialises. One thing is certain, it is one of the most important substances in the universe. There are concerns that, if it continues to increase as it has done, dark energy could eventually destroy the universe, ripping the fabric of space apart in a cataclysmic cosmic tear that could reduce everything to atoms. Consequently, identifying it and assessing its potential is of paramount importance.
"Many cosmologists regard determining the nature of dark energy and dark matter as the most important scientific question of the decade," wrote Alan Heavens from Scotland's University of Edinburgh in an issue of Nature.
He is undoubtedly correct, and we are all waiting for the mysteries to be revealed.The unexplained is what drives Man to explore further out into the great unknown, but explaining these two perplexing cosmic phenomena could force us to expand our minds as well as our universe. There could be far more fantastic explanations for each:is dark energy a force generated by our own expanding consciousness? Is dark matter all around us, as a vividly alive world that we can sense, but cannot see?
What do you think they are? Share your valued thoughts and opinions with us here, at the Edge of the World.