Time and time again, the predictions made by scientific luminaries like Einstein and Newton have been confirmed through experimentation. One place where the greats seem to fall a bit short is gravity — what we see doesn’t quite match the models. Most scientists currently believe the iron grip of gravity is augmented by dark matter, an invisible material that makes up about 85 percent of the universe. A new study makes the case for an alternative model, one in which dark matter doesn’t exist, and gravity works a little differently than we thought.
Interest in dark matter can be traced back to the 1930s when Swiss astrophysicist Fritz Zwicky was unable to explain the faster-than-expected rotation of galaxy clusters. Based on what we understand of the underpinnings of gravity, the force should be proportional to mass. Since dark matter only interacts with normal matter via gravity, it plugs the hole in the model quite ably. But what if there is no dark matter out there?
The leading alternative to dark matter is known as Modified Newtonian Dynamics (MOND), and it’s getting a boost from the new study. At its most basic level, MOND claims we are missing an important aspect of gravity. Instead of gravity depending only on the mass of an object, it might also depend on the gravitational pull of other massive objects in the universe. This interaction, known as the External Field Effect (EFE), means that gravity at low accelerations is stronger than Newton or Einstein predicted.
The study went looking for evidence for modified gravity in 153 galaxies by calculating the field effects under MOND. Some galaxies should have greater apparent gravity as a result of EFE based on the mass of other nearby objects. The team reports that the galaxies predicted to have strong external fields slowed more frequently than those with weaker external fields, which is what you’d expect if MOND is right. The researchers claim no other theory has anticipated this behavior.
This result doesn’t spell the end for dark matter — most scientists are expressing understandable skepticism at the result. It will be tested in more detail by other scientists, and eventually, someone will figure it out; they’ll prove or disprove it. That’s how science works. In the meantime, those who believe dark matter is the best explanation for the observable universe will keep looking for the unseen mechanism.