Galaxies spin faster than they should. Space is spreading when it should not. And it's all starting to look like we'll always be in the dark when it comes to the big issues in physics.
The solution of a physicist is in a hypothetical "fluid" with negative mass. No, this material has never been seen before. But the quest for exotic particles and energies is getting harder every day, so it pays to keep our options open.
Jamie Farnes of the University of Oxford suggests that we go back to Einstein's theory of general relativity – the one that describes gravity in terms of space-time geometry – and tweak it a little to allow matter with negative mass to arise.
This emergence of a strange "pushing" particle could solve two of the most frustrating mysteries of physics – why do galaxies hold together as they spin? And why does the Universe seem to be growing so fast today compared to the past?
Now the best explanation for each observation is that things that are very difficult to see are being pushed or pulled.
Dark matter is what happens to be responsible for "pulling" together stars and galaxies, plus all that we can see. It is more than likely that some kind of massive particle does not interact well with visible matter, making it virtually invisible.
Dark energy, on the other hand, is a theoretical phenomenon responsible for neutralizing gravitational forces, causing large-scale structures to move away and causing the Universe to appear to be expanding at an ever-increasing rate.
Now, these are the best answers we have. Although there are many suggestions as to what is behind each of them, we are still a little closer to a smoking gun. This despite the fact that the two combine to form about 95% of all energy and matter in the cosmos.
"It's embarrassing," says Farnes in his article on The conversation. "But astrophysicists are the first to admit that."
Farnes wonders if this obscure percentage of 95% comes down to the same thing. He proposed a dark "fluid" permeating everything, which appears in the empty space and weakly pushes the surrounding matter.
This gentle push would not only drive away the galaxies, creating additional space for a darker fluid to become reality, but would also push their stars away from the galaxy as it spins.
As for the potential theories, it seems somewhat parsimonious. Nothing like a two solution for a single price.
Even better, Farnes negative mass models could be tested using data on the distribution of collected galaxies using the Square Kilometer Array.
"The result looks pretty good," says Farnes.
"Dark energy and dark matter can be unified into a single substance, both effects being simply explicable as matter of positive mass surfing in a sea of negative masses."
Linda, of course. But even Farnes agrees that the idea is a little out there with regard to supporting physics.
First, although there are phenomena exhibiting negative mass characteristics, they are not the same thing as negative mass particles that appear spontaneously.
Second, while quantum mechanics predicts particles to appear and disappear in a vacuum, this does not contribute to the perpetual generation of a dark soup of negative masses.
Yet, before we anticipate, Albert Einstein himself proposed a similar correction factor in outlining general relativity. So there is room in mathematics to explain this concept.
"In terms of Newtonian theory," he wrote in 1918, "modifying the theory is necessary for empty space to assume the role of gravitating negative masses that are distributed throughout interstellar space."
Remember, he also dismissed the negative mass of empty space as his biggest mistake.
Still, what seems to be moving away from space and holding the galaxies together, we do not have an answer.
We could use some more suggestions in case all other ideas fail. In that case, Farnes's extravagant model of a universe that leaks dark fluid can only see its day in the sun, after all.
"If it were real, I would suggest that the missing 95% of the cosmos had an aesthetic solution," he says.
"We forgot to include a simple minus sign."
This research was published in Astronomy and Astrophysics.