Dark matter and dark energy: Welcome back to “Science For Everyone”, ABP Live’s weekly science column. Last week, we discussed the Manhattan Project and the science behind the atomic bomb. This week, we discuss what dark matter and dark energy are, and what a CERN scientist says about these unseen phenomena. It will come as a surprise to many that the observable universe comprises only five per cent of the cosmos, but dark matter and dark energy encompass the majority of the universe.
An astounding phenomenon occurs within galaxies. It is flabbergasting that galaxies do not tear themselves apart despite rotating at high speeds. The gravity generated by the observable matter of galaxies is not enough to hold them together, which means that they should have been shredded into pieces long ago if this were the only source of gravity.
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Similarly, galactic clusters are not ripped apart because gravity, apart from that created by observable matter, keeps them together. Planets in the solar system also do not fall off their orbits. This led scientists to believe that matter, apart from observable matter, is holding these cosmic objects together. The unfamiliar, uncanny and undetermined matter, which is giving galaxies extra mass, and is generating the extra gravity required to stay intact is known as "dark matter". The main reason why scientists call this dark matter is that it is not visible.
ABP Live spoke to Dr Archana Sharma, a senior scientist at the CERN laboratory in Geneva, Switzerland, and asked her about what dark matter and dark energy are.
Explaining that scientists put too many constraints on the Standard Model of Particle Physics in order for it to work, Dr Sharma said: "There is a quest for dark matter and energy. We do not know if we will see particles of dark matter. Of course, gravity is not included in the Standard Model of Particle Physics. This is because, on the energy scale, the graviton has to be discovered. So, we need to have an all-encompassing theory."
Dr Sharma also said that the movement of galaxies is affected due to dark matter, and if it was not there, the cosmic objects would be moving in some other manner.
“Now, if you look at the movement of galaxies, you see that the speed at which they are moving is accelerating. And the expansion of the universe is also accelerating. If I put a magnet under the table, and if I don't tell you that you have some magnetic materials on top, and I just move the magnet below and you don't know about the magnet, by the movement of the magnetic things on the table, you will be able to guess the position, and also the force of the magnet. This is electromagnetic force. But with the galaxy movements, there is of course, the gravitational pull. The movement is such that it is telling us that there is something very massive out there which we are unable to explain completely. If it wasn't there, we would be moving in some other way. So, it is telling us that there is something out there which is dark matter. It is 'dark' simply because we do not understand it. It is not real matter, because if it was matter, we would have observed signatures just like we found the rest of the matter out there. But there is something which is very heavy and denser than anything that we know, and the whole movement is affected because of that 'dark' matter,” Dr Sharma explained.
Normal matter interacts with electromagnetic force, but dark matter does not. Due to this, dark matter does not absorb, reflect or emit light, and is extremely difficult to locate. It is due to the gravitational effect an unknown matter has on visible matter that scientists are able to decipher the existence of dark matter. The ratio of dark matter to visible matter is six to one, according to CERN. This implies that dark matter constitutes 27 per cent of the universe.
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It is hypothesised that dark matter contains supersymmetric particles, whose partners have already been included in the Standard Model of Particle Physics. Scientists may obtain more signs of dark matter with the help of experiments conducted at the Large Hadron Collider (LHC).
Dark matter particles are often theorised to be light enough to be produced at the LHC, and are likely to escape through the detectors unnoticed.
Therefore, if dark matter particles are produced in the LHC and escape through the detectors, the amount of energy and momentum "missing" after a collision would help scientists under the existence of these strange particles.
There are several theories which incorporate physics phenomena beyond the Standard Model in order to explain dark matter. These theories talk about phenomena such as supersymmetry and extra dimensions.
According to a particular theory, there exists an alternate universe called "Hidden Valley", which is made up of dark matter, and has very little in common with the matter we know of in our universe. It is believed that researchers will be able to better understand the composition of the universe, and what keeps galaxies from being ripped apart if any of the theories are proved to be true.
Apart from dark matter, another bizarre phenomena that cannot be explained is dark energy.
Dr Sharma explained that everything apart from matter and dark matter is accounted for by dark energy. “The universe is made up of matter, dark matter, and dark energy. Everything apart from matter and dark matter is accounted for by dark energy.”
Since normal matter and dark matter comprise about 32 per cent of the universe, and the rest of the cosmos is accounted for by dark energy, it means that dark energy makes up about 68 per cent of the universe.
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According to CERN, dark energy is believed to be associated with the vacuum in space, and is distributed evenly throughout the universe. A confounding fact is that scientists say dark energy is not only distributed evenly throughout space, but also in time. Therefore, the expansion of the universe does not dilute the effect of dark energy.
Since dark energy is evenly distributed, it has a global effect on the cosmos as a whole, rather than local gravitational effects.
The universe is believed to expand due to dark energy. This is because the compounded effect dark energy has on the universe results in a repulsive force, which in turn accelerates the expansion of the universe.
Hubble's Law has helped scientists make certain observations which allow them to measure the rate of expansion and acceleration of the universe. According to Penn State University, Hubble's Law states that a galaxy's velocity is directly proportional to its distance from Earth, is believed to be a direct consequence of the ongoing expansion of the universe, and tells us about the state of the universe. The galaxies are moving away from Earth at velocities proportional to their distance from the Blue Planet.
The observations obtained using Hubble's Law, and other scientific data have not only confirmed the existence of dark energy, but have also given an estimate of how much of dark energy exists in the universe.