A New Theory on Dark Matter and Dark Energy
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Exactly one century ago, on an evening in 1918, renowned physicist Albert Einstein wrote down an idea in the pages of his notebook. That idea could be the key to solving one of the grandest and most elusive mysteries in all of physics: that of dark matter and dark energy. Together they make up over 95% of the universe, working invisibly to envelop galaxies and at once continuing to expand our universe at an accelerating rate, driving us away from nearby star systems and into a future with great divides.
The idea Einstein wrote about was an adjustment to general relativity where empty space would become negative mass moving under the influence of gravity. These negative masses would populate interstellar space. But this idea emerged as a way to explain the cosmological constant — or what Einstein referred to as his life’s greatest mistake. At the time when the cosmological constant was created, it was a widely accepted belief that the universe was static. That is, it was neither expanding nor contracting. But if this was true then something had to be countering gravity to prevent the universe from collapsing in on itself. Thus the cosmological constant with antigravity properties was born.
Today we understand the universe is not static and that it continues to expand, and so the cosmological constant has taken on a new meaning. It represents dark energy within the Lambda CDM, our current and most accepted model of the universe. The newest theory on dark matter and dark energy does not contradict the standard model and instead builds off of the note Einstein made to himself all those years ago.
The theory, created by astrophysicist Jamie Farnes from Oxford University, unifies dark matter and dark energy into a single pervasive substance known as a dark fluid. The dark fluid is made of negative masses that posses negative gravity. With positive, normal matter and positive gravity, objects attract each other. But objects with negative mass would repel matter so that pushing negative mass away from you actually resulted in it moving closer and not farther away. But this also means that two negative mass particles would repel one another, a phenomenon which contradicts general relativity. This characteristic of repulsion isn’t backed by any mathematical equations and is simply an addition Farnes made based on his own intuition. It is, however, crucial to his hypothesis.
This dark fluid would help explain the formation of dark matter halos around galaxies. As they are, galaxies spin so rapidly that stars towards the outer regions should shred and disperse into the universe. This is because there is less gravitational influence the farther out one moves from the center of the galaxy, leaving stars on the outskirts to rotate faster and disperse. But dark matter allows galaxies to form as it creates an invisible “halo” around the structure. Our own solar system moves through this dark matter at 143 miles (230 km) per second, perceiving it more as an undetectable, fast-moving wind.
But physicists are skeptical of Farnes’s theory for many reasons, one of them being the universe’s density as it expands. If dark energy were made of negative mass, its density would decrease as the universe expanded whereas research shows the universe’s density remains the same as it grows. To answer this problem, Farnes draws on another established idea known as “matter creation”. This says that matter is created all the time throughout the universe, constantly populating it with more and more negative masses. These newly created negative masses would replace the ones that disappear, keeping the density fixed. But this in turn leads to another problem. According to quantum mechanics, everything would become unstable if negative mass could be created in the vacuum of space. As far as we can tell, this isn’t the case.
While there’s nothing scientifically stopping negative mass from existing in the universe, it’s also never been observed outside of a laboratory. Scientists aren’t sure what natural mechanism would allow negative mass to exist, but research going on at CERN and future technology like the Square Kilometre Array (a project to build the world’s largest radio telescope) could help give Farnes’s concept a more solid foundation. For now it’s based on some older ideas and preliminary research using computer simulations and mathematics.
Up until now, the most prominent theory on dark matter suggests that it’s an exotic particle which doesn’t interact with light but still exerts gravity on objects around it. Experiments at the Large Hadron Collider continue to look for rare particles — one of which might be responsible for dark matter. Other scientists believe gravity on larger scales differs greatly from the gravity we’re accustomed to on a smaller scale and to solve dark matter we need to look at gravity from a different perspective. As for ideas about dark energy, well, that’s an even bigger mystery we struggle to define.
While Farnes’s theory suggests we’re boats of positive matter slipping over a dark fluid sea, it’s also attractive because of the symmetry it provides. Two of the greatest mysteries have been condensed into one and the universe exhibits a balanced positivity and negativity. That vast ocean of dark energy and dark matter that has eluded us for so long can be explained by a small, elegant minus sign.
The models Farnes has created so far are promising; they account for the universe’s ongoing expansion and several properties of galactic rotation. Fellow astrophysicists warn that it’s important to keep an open mind when it comes to new theories. They can be strange and can seem to challenge our established scientific notions, but many of our greatest insights into the universe began exactly in that way — with a sense of disbelief.
