The 20th century was the time in which hundreds of astronomers were discovering new things, which were strange and fascinating at the same time, about our vast universe. One of the major discoveries was made by Vera Rubin in 1970 when she was observing spiral galaxies. She figured out that the gravitational pull calculated from Einstein’s general theory of relativity by considering the visible matter alone in the galaxy is not enough to prevent everything from flying away. So the mysterious, invisible, matter we couldn’t detect was referred to as dark matter.
However, in 2009, an astronomer named Erik Verlinde proposed a new theory of gravity, emergent gravity, which might change physics entirely and could even make dark matter irrelevant. So, now the big question before the scientific community is: does dark matter, really matter?Introduction/Background: Sir. Isaac Newton had made exceptional discoveries throughout the course of his lifetime. The most famous is him discovering gravity when an apple fell on his head.
Well, that is what the legend says, but instead, Newton was actually trying to solve the mystery of why things fall down for years, but it was only when the apple fell on his head he thought that gravity is a force that attracts every atom to one another.About 2 centuries later Albert Einstein published his theory of relativity. His theory stated that gravity is actually a curvature in space and time. This curvature is created with the presence of planets, stars, and asteroids.
Also, the more massive objects seem to attract other smaller objects into their curve. What made the people believe in Einstein was because of a Total Solar Eclipse on May 29, 1919. It has been 4 years after Einstein had written his theory of relativity, but he needed astronomers to prove his theory correct. After many tries, Sir Frank Watson Dyson (the great astronomer of Britain) stepped up to help Einstein. All Dyson had to do was to plot the stars according to Einstein’s theory, and if the theory were correct, then us humans can see that stars are located behind the Sun because light bends near massive objects.
And that very day was the moment Einstein must have felt on top of the world !!! It wasn’t only Einstein though who was making discoveries because Vera Rubin in the 1970s was observing how galaxies rotate and she found out that the gas clouds on the outer edges of galaxies were moving faster than she had expected to because our very own Solar System, the planets further away from the Sun move slower than the ones closer to the Sun. Because everyone believed in Einstein’s theory of relativity, Rubin thought that there must be some matter out there which we cannot detect.
Later this was the mysterious matter was known as dark matter. Main Body: So what is a dark matter you ask. Well, dark matter is basically invisible/undetectable matter. This doesn’t just mean that we can’t see it with our eyes, but it also means that it doesn’t emit heat, radio waves, or any other form of electromagnetic radiation. These all contributed to make the dark matter a big mystery that everyone wanted to solve. Also nowadays scientists have started to predict what can be dark matter?
They first thought of some suspects such as gas clouds, low-mass stars, white dwarfs, neutron stars, and black holes, but in the end after running various experiments they knew that dark matter was something completely different. So what did they end up with you ask? They were thinking of neutrinos to be dark matter but they don’t have one key characteristic. That characteristic is that neutrinos are hot dark matter instead of cold dark matter. What is the difference between the two types of dark matter you ask?
Well, hot dark matter is dark matter which has smaller particles which enables them to move faster, such as neutrinos. Cold dark matter on the other hand is the exact opposite because it consists of bigger and slower particles. How does this have to do anything to do with dark matter? Well, all we needed is to find a particle with the properties of a neutrino but instead, it is a bigger particle. Scientists then made up a hypothetical particle WIMP. WIMP stands for Weakly Interacting Massive Particle.
Scientists had to make a hypothetical particle because they had run out of all of the possible things which could make up dark matter. So now WIMPs are the most reliable dark matter candidate but the big question is that do they exist? One thing which makes detecting WIMPs easier for scientists is the fact that they will have to overcome similar challenges to the ones they faced while trying to detect neutrinos. This turned out to be right because the main problem in detecting WIMPs is that they have a really small chance of colliding with an atom and we somehow need to detect that collision. These detectors work like this: when a WIMP hits an atom, the atom goes and knocks a couple of more atoms. These hard hits cause a slight temperature change, flashes of light, and electrons moving away from atoms.
The goal of the detector is to detect one of these things to prove that WIMPs actually are out there. There are few experiments around the globe trying to detect WIMPs. One is called DAMA (dark matter) and it is taking place in a tunnel through the Gran Sasso Mountain nearby Rome. There is also one in an old iron mine in Minnesota and it is called CDMS (Cryogenic Dark Matter Search). We haven’t found WIMPs yet but if we do then we will solve one of the greatest mysteries of all time. However, if we don’t then it might be a dark end to our dark matter.
Emergent Gravity: Emergent gravity is a theory proposed by Erik Verlinde in 2009 which states that gravity is an entropic force that is derived from the interaction of some particles instead of curvature in space-time as Einstein predicted. This theory also supports that dark matter does not exist and that gravity is stronger at longer distances because of the nonconstant relationship between the force of gravity at larger distances. Erik Verlinde also says that in a universe with dark energy you don’t need dark matter because gravity doesn’t follow general relativity. This race on starting a new theory on gravity has been there for the past few decades. This started with Theodore Jacobson who tied gravity with thermodynamics.
Then came Thanu Padmanabhan who started the talk about quantum gravity. Only recently did Erik Verlinde propose his new theory on gravity. Also just recently his theory went under the first test: gravitational lensing. Gravitational lensing is when gravity bends the light coming from incoming galaxies and stars. When they tested Verlinde’s theory they actually figured out that his results were more accurate at confirming the universe’s gravity distribution than Einstein’s theory of relativity!! So could this be our new way of understanding the universe?
So gravity has went on a pretty exciting adventure. Starting of with Isaac Newton saying that gravity is a force that attracts every atom to one another, to Einstein who said that gravity is a curvature in space-time. And now Erik Verlinde opens a whole new chapter for us by describing gravity as an emergent phenomenon and saying that dark matter does not exist!! So in the end you can choose to believe in any theory you want, but what I believe is that it doesn’t matter if dark matter exist or not, but the only thing which matters is that us humans always have the spirit to explore the unknown.
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