Delving into the Dark Universe

The pull of gravity could not halt or slow down the expansion of Universe since the Big Bang explosion. Rather it is expanding at an accelerating rate. Something dark is at work which is hidden from the plane sight. This dark entity is in the form of matter as well as energy.  It is invisible because it does not emit or reflect the light which only passes around.

We are aware about the texture of normal baryonic matter and also about antimatter but dark matter has none of their properties except mass and it interacts through gravity only. It acts as an adhesive that holds the galaxies together and appears as halo in and around them.  Dark matter prevents the fast-rotating galaxies from ripping apart. However, there is also a mysterious force or energy in space which pushes the galaxies far, much like the dots on a rubber band when it is stretched. It is called dark energy. It is more abstract, strange and frustratingly elusive than dark matter. It is an inherent property of space. The empty space is not ‘nothing’ but it carries more energy than everything else in the Universe combined. What Einstein had called cosmic energy comes out to be dark energy in a slightly altered form.  The all-time extra empty space needed to accommodate the ever-expanding Universe is generated by a mechanism not known to us even by an iota.

By now, even a casual student of science knows that 95% of the bulk created at the time of Big Bang, whether material or radiation, forms the dark component of Universe not known to us in its essence and we constitute an insignificant fraction of 5% of what was there in the beginning together with all galaxies, black holes, white dwarfs, planets, satellites and whatever could so far be detected with all our measuring instruments. Some well-known space telescopes used to probe our largely dark Universe are Hubble’s telescope, James Webb telescope, Euclid telescope, Atacama telescope and Fermi-gamma ray telescope. These map the dark matter by studying some indirect effects like galaxy rotation rates and fluctuations in cosmic background radiation. Dark matter distorts the light coming from distant stars and greater its concentration at a place, greater is the bending of light. This phenomenon is known as gravitational lensing and is also helpful in locating the black holes at the center of galaxies. These are strongly gravitational, sucking in everything and anything approaching them. According to a latest study reported early this year, black holes could be the sources of dark energy.

The conclusion was drawn while studying how black holes grow over time by a team of 17 researchers from nine different countries led by the University of Hawaii in the U.S.A. The work has been published in two leading physics journals. However, the theory needs a lot more to withstand all debate and discussion about it before it goes well across the astrophysicist community. India has also joined the hunt for dark matter by opening an underground laboratory at the Jaduguda mining complex in west of Kolkata in 2017. This subterranean lab has been set up at just a cost of 20 lakh rupees and is well equipped with cutting-edge instruments to look for signatures of exotic particles. The lab filters out cosmic radiations that can interfere with experimental procedure. The Indian researchers have tried to relate dark matter with neutrino mass and one such paper from a trio of researchers from IIT Guwahati has got published in a leading international physics journal. It is important to build theories and do simulations to provide the necessary framework for experimental processes. To further ascertain the credibility of results and outputs these have to reproduced elsewhere. This can be done by cross-checking our results with other sensitive experiments going around the world to detect the dark matter.  In addition to such sensitive experiments or observatories like LUX, LZ and SuperCDMS, which are trying hard to detect the dark matter, there are also efforts going on to create dark matter by smashing into the territory of atom to collide two high energy protons. This is essentially happening at the Large Hadron Collider (LHC), the world’s biggest science experiment. It takes the necessary motivation from string theory which proposes ten instead of the three dimensions (x, y and z). The theory assumes that gravity might be a strong force but it appears weak because it has to escape through a large number of extra dimensions. Then it should so happen that if we collide two fast moving subatomic particles, the resulting particle should be densest. Let us stay curious, let us stay tuned.

Dr. Qudsia Gani, Assistant Professor, Dept. of Physics, Govt. College for Women, Srinagar