Here’s what you’ll learn when you read this story:
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We have not been able to detect dark matter yet, even though there are many aspects of the universe that suggest the existence of invisible matter.
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In one new theory, it is possible that dark matter exists in a mirror universe where there are only dark versions of forces that hold the universe together.
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Another new theory suggests that dark matter may have been created at the edge of the universe right after the Big Bang, then radiated into space as the universe expanded.
Hypothetically, dark matter is supposed to exist, even though it has managed to elude every single detection attempt so far. It neither absorbs nor reflects light. Still, something has to be generating enough gravity to hold together immense galaxies that rotate so fast, they would otherwise end up annihilating themselves. We keep searching for it—but we might be searching in the wrong universe.
There might be more exotic explanations for invisible matter that is supposedly right in front of us. Physicist Stefano Profumo of the University of California, Santa Cruz, suggests it could have come from one of two origins. It might be lurking in a dark mirror universe contained within the visible universe. The merging of dark matter black holes in that realm may cause gravitational waves which can be detected. If this is starting to sound like one of the multiple mirrorverses in Stephen King’s The Dark Tower, think of it as a shadow version of the same rogue chasing the same man in black through space and time.
“The nature of dark matter remains one of the most pressing mysteries in modern cosmology and particle physics,” Profumo said in a study recently published in Physical Review D. “While numerous candidates have been proposed, from weakly interacting massive particles to axions, the search for the fundamental nature of the dark matter and of the ‘dark sector’ it resides in continues.”
Alternately, dark matter particles might have formed at the edge of the observable universe, or the cosmic horizon, as it expanded at breakneck speed right after the Big Bang. Profumo thinks these particles might still be radiated into space similarly to how Hawking radiation describes particles evaporating from right outside the event horizon of a black hole. The cosmic horizon is something like the universe’s equivalent to a black hole’s event horizon.
Though Profumo admits both of his theories are highly speculative, they are not impossible. He was inspired by quantum chromodynamics (QCD), which explains how the strong force of gravity binds together the quarks and gluons which make up protons and neutrons. The dark mirror universe he envisions has its own versions of particles and forces that operate just like those in the universe we exist in. Dark quarks (which create protons) and gluons (which glue quarks together into protons) should be able to bind and create baryons such as protons and neutrons, which are the dark reflection of the baryons we can detect.
Black holes (or at least objects that behave much like them) could have formed from dark baryons in the nascent universe. While there have been theories about primordial black holes forming as dark matter, researchers have seen them as the product of density fluctuations rather than emerging from a mirror universe. If clouds of dark baryons became dense and massive enough, they would have collapsed into themselves and formed nano-black hole. Enough of these black holes can contain all the dark matter in existence. With such a behemoth amount of gravity, they would also have a profound effect on the shape of the universe.
Another possibility that Profumo explores is dark matter particles radiating from the cosmic horizon. The universe is already thought to have fast-forwarded through a period of inflation after its birth, and he argues that in the beginning, because it expanded faster than the speed of light, dark matter particles were released from its edges. While inflation has slowed down dramatically since then, the universe and the very fabric of spacetime are still expanding, which can be seen by the increasing distance between objects that are not gravitationally bound. That means dark matter should keep radiating for as long as expansion continues.
“The underlying mechanism leading to the production of the cosmological dark matter (DM) is at present an open question and a matter of ongoing, intense scrutiny,” Profumo said in a second study also published in Physical Review D.
If a mirror universe controlled by the dark side of physics really does exist, is there a portal into it? Maybe the answer to that question will see the light someday.
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