KILLING Pluto was only the beginning. The dwarf planet Eris, named for the Greek goddess of strife, could also bring down the most popular explanations for dark matter and dark energy.
Many galaxies appear to have stronger gravity - and thus more mass - than can be explained by their visible matter alone. Overly massive galaxies are most often attributed to dark matter, an invisible substance that interacts with matter through gravity. To date, though, no one has directly detected dark matter particles.
But a well-established notion in physics could hold another explanation for their size. This says that empty space is really a frothy, turbulent sea full of virtual particles - matter and antimatter that spring in and out of existence so fast that we can't see them.
Though they are tiny, quantum objects, Dragan Hajdukovic, a physicist at CERN near Geneva, Switzerland, thinks these bubbling particles may have opposing gravitational charges, similar to electrical charges. In the presence of a gravitational field, the particles would generate a secondary field, which, in the case of galaxies, could explain the mass discrepancy.
Hajdukovic's theory could also explain dark energy, the baffling force thought to be driving the universe apart at an accelerated pace. If virtual particles have gravitational charges, then space-time itself is imbued with a small charge that could be causing objects in the universe to speed away from each other.
To test whether quantum-scale gravity is at work, Hajdukovic plans to borrow a trick from Einstein (see diagram). Due to gravitational effects in the solar system, such as the tug of other planets, Mercury's oval-shaped path around the sun slowly turns, or precesses. In the 1800s astronomers noticed that this happens at a different rate than predicted by Newtonian physics. Einstein showed that the sun's mass creates a curvature in space-time that affects Mercury enough to explain the difference, lending credence to his theory of general relativity.
Hajdukovic's quantum gravity might create a similar discrepancy with more distant orbiting bodies, he says - which is where Eris and its moon Dysnomia come in.
Best known for depriving Pluto of planethood by showing that there are many similar bodies in orbit beyond Neptune, Eris's great distance from the sun means the effects of general relativity become negligible. Newtonian physics should dominate, putting Dysnomia's precession rate around Eris at 13 arc seconds per century. But if quantum gravity exists, the rate should be -190 arc seconds per century, Hajdukovic calculates (Astrophysics and Space Science, doi.org/j6r).
He thinks the required measurements could be made from Earth using existing observatories. "Einstein was lucky that there is a planet so close to the sun as Mercury," he says. "My theory might be lucky that there are trans-Neptunian objects allowing astronomical tests."
Gary Page of Longwood University in Farmville, Virginia, is sceptical that Earth-based tests would be sensitive enough to pick up the effect. Still, he praises Hajdukovic for going beyond the party line. "It's always good when people are willing to go a little bit out on a limb."
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