If you’re sufficiently curious about the universe we live in and have dabbled in searches online to further understand our universe, it’s certain that you might have come across the terms “Dark Matter” and “Dark Energy”. The two elements have puzzled physicists and astronomers for the past few decades, ever since its emergence thirty odd years ago.
The existence of dark matter and dark energy was theorised as a possible explanation for all the unaccounted for matter and space in the universe and we are yet to fully understand or detect and observe them using technology.
From our observations of the universe through highly powerful telescopes since the 1990’s we have found that what we can see of all matter that comprises the universe from Earth represents just 15% of that of the entire universe. The rest of the universe i.e. 85% is made up of something we cannot see with our eyes or even detect with with highly powered devices.
The universe appears to be made of a mysterious, invisible substance called ‘Dark Matter’ which accounts for 25% of the mass of the universe and a force that appears to repel gravity known as ‘Dark Energy’ that accounts to the remaining 60% of the universe.
We can’t see it with our eyes, we can’t detect it with radio waves or microwaves or any other kind of light and it passes straight through matter without interacting with it. But we know it is there because of its influence on what we can see.
An analogy that can be used to explain dark matter and dark energy present in space is if we draw out a map of the Earth at night, we can see the regions that use the most energy in the form of patches of light across the map of the Earth, but we can’t see the mountains and rivers and people who inhabit the Earth, but we know that they’re there.
It’s the same case with dark matter and dark energy. We can’t see it or observe it, but we know it’s there.
The properties of dark matter are strange because it doesn’t interact with regular or baryonic matter and it’s completely invisible to light and other forms of electromagnetic radiation, making it impossible to detect with instruments currently available to us. But scientists are confident it exists because of the gravitational effects it appears to have on galaxies and galaxy clusters.
Dark matter is fundamental to the formation of our universe because without it stars, planets and galaxies can’t be formed. You need at least a million times the mass of the Sun in one dense region of the universe, before you can start forming stars. Without dark matter interacting with gravity, you never get enough mass in a pocket of space to form stars, planets and galaxies.
If we make a model of the universe starting from the big bang, we see that the entire universe started out pretty smooth, but there are some regions where there was a little bit more material or mass. Gravity comes in and brings more and more mass into those particular spots that started out with a little bit extra. Over time, you get enough mass in one place that the hydrogen gas, which was initially well mixed with the dark matter, starts to separate from it, cool down, form stars, and you get a small galaxy. Over time, over billions and billions of years, those small galaxies crash into each other and merge and grow to become larger galaxies, just like our own galaxy, the Milky Way.
If you draw out two computer models of the universe forming from the time of the big bang over 13.8 billion years, one with dark matter present and one without dark matter, we observe that if you don’t have dark matter, those certain areas with some mass collecting, never get large enough to form stars, planets and galaxies.
In the model with dark matter present, in that universe, it’s really easy to form galaxies. In the other universe, without dark matter, the parts of the universe that start out like small clumps, just stay really small. Not much happens. In that universe, you wouldn’t get our galaxy or any other galaxy. You wouldn’t get the Milky Way, you wouldn’t get the Sun, you wouldn’t get us. We just wouldn’t exist in that universe.
I touched upon dark matter and dark energy in an old post five years ago about Einstein’s general relativity and our universe: Musings About The Universe – From Einstein’s General Relativity to Current Observations of Uniformity, Expansion and Dark Energy
But what do we know about dark matter now, five years on?
The answer is that we don’t know anything more about dark matter yet.
“We have a lot of educated guesses, and a lot of ideas for how to find out more about dark matter. Physicists hypothesise that dark matter is a particle, similar in many ways to the subatomic particles that we know of, like protons and neutrons and electrons. Whatever it is, it behaves very similarly with respect to gravity. But it doesn’t emit or absorb light, and it goes right through normal matter, as if it wasn’t even there. We’d like to know what particle it is. For example, how heavy is it? Or, does anything at all happen if it interacts with normal matter? Physicists have lots of great ideas for what it could be, they’re very creative. But it’s really hard, because those ideas span a huge range of theories. It could be as small as the smallest subatomic particles, or it could be as large as the mass of 100 Suns.”
“Physicists and astronomers have a lot of ways to look for dark matter. One of the things we’re doing is building sensitive detectors in deep underground mines, waiting for the possibility that a dark matter particle, which goes through us and the Earth, would hit a denser material and leave behind some trace of its passage. We’re looking for dark matter in the sky, for the possibility that dark matter particles would crash into each other and create high-energy light that we could see with special gamma-ray telescopes. We’re even trying to make dark matter here on Earth, by smashing particles together and looking for what happens, using the Large Hadron Collider in Switzerland.”
“In the next several years, we’re going to make much more precise maps of the sky. And those will help refine our movies of the whole universe and the entire galaxy. Physicists are also making new, more sensitive experiments to try to catch some sign of dark matter in their laboratories.”,
“Dark matter is still a huge mystery. But it’s a really exciting time to be working on it. We have really clear evidence it exists. From the scale of the smallest galaxies to the scale of the whole universe. Will we actually find it and figure out what it is? I have no idea. But it’s going to be a lot of fun to find out,” says astrophysicist Risa Wechsler in her TED Talk exploring why dark matter may be the key to understanding how the universe formed and about our ongoing pursuit of finding out more about this mysterious element of our universe.
It’s certainly an exhilarating time that we’re living in and the hope is that in the coming decades, as technology advances further, we might be that much closer to finding out more about dark matter, the mysteries about it that currently elude us and the possibilities that it may unhinge.
Words For Reveries 
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