There's a strange pattern in our Solar System – if you look at the orbits of the first seven planets, each one gets increasingly distant from the Sun in a predictable and quantifiable regularity.
This coincidence was noticed in the 18th century and further explored by astronomers Johann Titius and Johann Bode. It was named the Titius-Bode Law, or regularity, and it was later used to predict the position of Uranus and dwarf planet, Ceres.
It's also not perfect - Titius-Bode Law failed to predict the orbit of Neptune in 1846. Since then, many researchers have dismissed it as nothing more than an odd coincidence.
But a group of physicists now say there might be something more to it. Their work shows that something called 'pilot wave gravity' could explain the pattern. In fact, it could replace the concept of gravity altogether.
Okay, so it's not so much a replacement as it is an update on the gravity we know and love, based on an often overlooked interpretation of quantum mechanics, called pilot wave theory.
Currently, the majority of physicists subscribe to the Copenhagen interpretation of quantum mechanics, which states that particles do not have defined locations until they are observed.
Pilot wave theory, on the other hand, suggests that particles do have precise positions at all times, but in order for this to be the case, the world must also be strange in other ways – which is why many physicists have dismissed the idea.
But in recent years, the pilot wave theory has been increasing in popularity.
Now, researchers from the Centre for Philosophy of Sciences of the University of Lisbon in Portugal have taken the idea and expanded it into the macro world, by applying it to the arrangement of planets.
Currently it's accepted that our Solar System is held together by gravity – predominantly, the way our massive Sun curves space-time.
But pilot wave gravity assumes that each celestial body also generates a huge wave field that plays a role in the placement of planets.
"We call this field a gravitational theta field, a very extended subquantum perturbation propagating through space," one of the researchers Paulo Castro told ScienceAlert in an exclusive interview.
"Then, we use a piloting principle, stating that each celestial body will tend to move to the regions where its gravitational theta wave has higher intensity. In this way the wave will pilot its massive body having a kind of gravitational pull over it. Hence the name pilot wave gravity."
That's a little complex, but a simple way to think about it is to imagine waves undulating out of the Sun and also out of each planet. The researchers suggest that where and how those waves interlap determines where a planet's orbit lies, in addition to the regular pull of gravity.
And according to the team's calculations, this model could finally explain the strange Titius-Bode pattern seen in the Solar System.
Not only that: if we consider pilot wave gravity to be correct, it could finally help unite the two biggest ideas in physics – general relativity and quantum mechanics.
"There are two main conclusions to be drawn from the paper," said Castro.
"The first is that some physical features of the Solar System are best explained if one applies an undulatory model, instead of classical Newton physics or even general relativity. This seems to be the case of the Titius-Bode regularity."
"The second conclusion is that it now seems reasonable to think that a theory unifying the quantum and the macroscopic realms may be at reach."
The most appealing part is that pilot wave gravity doesn't require either general relativity or quantum mechanics to be thrown out entirely. Just tweaked slightly in order to work together.
Importantly, quantum mechanics would need to embrace the existence of real subquantum waves – as predicted in pilot wave theory – not just consider probability waves.
"General relativity, on the other hand, must accept that gravitational phenomena can only be fully described if one also applies a wave model. In other words, there will be some aspects best described using general relativity and others best described using pilot wave gravity," said Castro.
"It is a huge shift in our way of thinking."
Before we get too carried away, let's be clear that this work is all very theoretical for now. We currently have no easy way to test whether this is actually happening in our Universe.
One clue will be to see if Titius-Bode regularity holds up in other distant solar systems, says Castro – but it's also worth keeping in mind that other scientists think Titius-Bode law is nothing more than a flawed coincidence.
But seeing as we still don't have a feasible way to fully explain our Universe with one handy theory of everything, it doesn't hurt to be open to new ideas.
And the fact that this new theory already explains an enduring puzzle about how our Solar System is laid out is a good start.
The research has been published in the journal New Horizons in Mathematical Physics.