A new study proposes that the vacuum of outer space may be a non-Newtonian fluid, resurrecting a decades-old astrophysics mystery concerning two NASA space probes. The new approach not only provides an exact solution to the space probes’ anomaly but also proposes a whole new way of thinking about outer space, the universe, and Einstein’s theory of general relativity.
In this new theory, an equation is proposed that assumes outer space is a shear-thickening (dilatant) fluid, a type of non-Newtonian fluid that defies Newton’s law of viscosity. An example of this is oobleck, the strange slurry made of cornstarch and water that becomes more viscous when compressed. Objects traveling through this fluid, such as NASA probes, would be slowed down by the viscosity.
Oobleck is a strange substance made from cornstarch and water that has both properties of a liquid and a solid. Learn more about it here.
Pioneer 10 and 11
In the 1970s, two NASA space probes, Pioneer 10 and 11, were launched into space destined for Jupiter and Saturn. As NASA followed their trajectory, they saw that at one point the probes were thousands of kilometers closer to Earth than expected—somehow they had slowed down by 0.874 nm/s2 (nanometers per second squared).
The scientific community started searching for answers as to why the space probes mysteriously decelerated, and in 2012, a paper was published that suggested the anomaly was due to the thermal photons of the probes recoiling from heat dissipating unevenly from the probes. An analogy would be firing a shotgun straight ahead and feeling the recoil force on your shoulder.
According to the paper, the probes’ recoil should have caused a 0.74 ± 0.25 nm/s2 deceleration that was dubbed close enough to the actual value. An editorial was published in Nature Physics entitled …and farewell to the Pioneer anomaly, effectively closing the issue.
“After such a tombstone on the Pioneer anomaly it has been difficult for me to publish new results; there was no desire to reopen the issue,” said Dr. Marco Fedi, an Italian researcher who published the new study in the Canadian Journal of Physics. “But science never stops and my results were surprising.”
In his paper, Fedi obtained the exact deceleration value of 0.874 nm/s2 measured by NASA. According to his theory, the NASA probes decelerated because outer space was acting as a viscous fluid, slowing the probes down.
Testing the theory: stability of planetary orbits
If Fedi’s theory is correct, it implies that everything in outer space is moving through a dilatant fluid and slowing down, even our planets. If the planets in our solar system slowed down too much, however, they would fall out of orbit and effectively crash into the sun. To test if his theory is compatible with orbital stability, Fedi calculated how long it would take Earth to fall out of orbit assuming it is moving through a dilatant fluid and the answer is trillions of years, thanks to its much larger mass in comparison with the Pioneer spacecraft.
Testing the theory: Mercury’s precession of perihelion
Until Einstein proposed his theory of general relativity, researchers had no explanation for why Mercury’s elliptical orbit around the sun slowly shifted its direction over time more than expected from classical physics laws and in a notably more pronounced way than other planets.
The mystery, called Mercury’s precession of perihelion, was solved when Einstein proposed that the mass of the sun creates a gravitational field around it and that Mercury’s orbit is affected because it is the closest planet to the sun.
Fedi, to test the validity of his theory, derived Einstein’s formula for the precession of perihelion using his equations for space as a dilatant fluid. This led him to the precise result for Mercury’s precession, the same as the traditional equations for general relativity do. This suggests that his results are perfectly compatible with Einstein’s theory and that they could add to it by explaining the quantum foundations of general relativity.
The dark spectrum and the Higgs field
Since fluids must be composed of particles, the new theory also opens questions as to what this shear-thickening fluid could be made of. Fedi discussed dark matter and dark energy, which account for 95% of the universe but have yet to be experimentally proven to exist. Interactions with probes and planets could be some of the first direct evidence. As cornstarch granules in water cause the non-Newtonian behaviour of oobleck, diffused dark matter particles in a sea of dark energy could be the reason for a dilatant vacuum.
Fedi also discussed the Higgs field, a ubiquitous viscous field made up of Higgs bosons, as a possible reason for the existence of a dilatant vacuum. Both could be the reason that outer space acts as a viscous fluid, and now, more specific research needs to be done to determine how.
If outer space truly acts as a shear-thickening fluid, it would add new elements to Einstein’s theory of general relativity and fundamentally alter the way the universe is conceptualized.
“After a century from general relativity and from its purely mathematical formulation of space-time, I am convinced that we are a step closer to a change, whose secrets are probably in the vacuum. Ex nihilo omnia [from nothing comes everything],” concluded Fedi.
Read the full study: Physical vacuum as a dilatant fluid yields exact solutions to Pioneer anomaly and Mercury’s perihelion precession in the Canadian Journal of Physics.
