Dark matter is a widely known word for all science enthusiasts. It is a label used for “missing” matter in the universe whose presence becomes evident only through observation of massive galaxies and quasars. Though suggestions of its existence were made over 8 decades ago, nobody has been able to describe its properties or its structure. WIMP (Weakly interacting massive particles) was the popular model for the dark matter but, most experiments to detect WIMP dark matter led to nowhere.
Now scientists are rethinking their strategy to hunt dark matter and are trying to look for them using their gravitational interaction with ordinary matter. As we know dark matter makes up 27% of matter in the universe whereas ordinary matter makes up only 5%. And since dark matter doesn’t interact with ordinary matter electromagnetically or in other forces usually, the only logical way forward would be to detect them by their gravitational interaction with ordinary matter.
“Our proposal relies purely on the gravitational coupling, the only coupling we know for sure that exists between dark matter and ordinary luminous matter,” said study co-author Daniel Carney, a theoretical physicist jointly affiliated with NIST, the Joint Quantum Institute (JQI) and the Joint Center for Quantum Information and Computer Science (QuICS) at the University of Maryland in College Park, and the Fermi National Accelerator Laboratory.
The experiment proposed will be able to detect dark matter particles over a range of mass from a minimum of 1/5000th of a milligram to several milligram. Interestingly, this range is also the range in which Planck mass falls.
The experiment proposes two plans. Both involve millimetre-sized sensors, cooled to temperatures just above absolute zero, to minimize noise due to heat or cosmic rays. One plan uses tiny pendulums as detectors, which get deflected slightly whenever dark matter passes by. And the other plan uses tiny spheres levitated by magnets or laser, which are made to free fall as the experiment begins. If dark matter particles pass near these freely falling spheres their path is deflected.
This experiment is aiming to find only the mass of dark matter particles, if at all dark matter is made of particles. If it turns up to give no result, we can eliminate a lot of models for dark matter. To make this experiment practically possible, scientists calculated that an array of almost a billion detectors must be embedded on a cubic meter volume. If true dark matter passes through this, it will cause every detector to jiggle in a pattern, observing which one can find the path of dark matter. Also since such small sensitive detectors must be produced, a technology from a smartphone or automotive industries should be borrowed. The experimental setup can also be used for other purposes, such as detecting weak seismic waves, or passage of subatomic particles like neutrinos, photons etc.
Reference:
- Daniel Carney, Sohitri Ghosh, Gordan Krnjaic, Jacob M. Taylor. Proposal for gravitational direct detection of dark matter. Physical Review D, 2020; 102 (7) DOI: 10.1103/PhysRevD.102.072003
- National Institute of Standards and Technology (NIST)
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