- Galaxies spin much faster than expected based on Newton’s laws applied to visible matter. To keep them from flying apart, scientists proposed the existence of dark matter, an invisible substance providing extra gravity.
- The Standard Model of particle physics doesn’t include dark matter particles, leading to the Milgromian dynamics (MOND) theory. MOND suggests gravity changes its behaviour in low-acceleration environments, like at the edges of galaxies.
- MOND successfully predicts galaxy rotation curves without needing dark matter by tweaking gravity at low accelerations, not at specific distances.
- Cassini Mission Insights: The Cassini spacecraft (2004-2017) helped test MOND by precisely measuring Saturn’s orbit. Contrary to MOND’s predictions, Cassini found no deviations from Newtonian gravity, suggesting Newton’s laws still apply to Saturn.
- Adjustments to galaxy mass calculations or the influence of surrounding galaxies don’t reconcile MOND with Cassini’s data. The likelihood of MOND matching these results is extremely low.
- Binary Stars Test: MOND predicted that wide binary stars should orbit each other faster than Newton’s laws allow. However, recent detailed studies have ruled out this prediction, further challenging MOND.
- Outer Solar System Objects: MOND also fails to explain distant comets’ energy distribution and orbital inclinations, which align better with Newtonian gravity.
- Galaxy Clusters: MOND struggles to explain the motions within galaxy clusters, where Newtonian gravity and dark matter provide a better fit.
- Although the dark matter model isn’t flawless, MOND cannot replace it. Dark matter remains the most accepted explanation, though its exact nature remains unknown.
- Gravity might behave differently on large scales, but MOND, as it stands, isn’t a viable alternative.
- The dark matter theory continues to dominate our understanding of the universe.
Dark Matter
- Dark matter, unlike normal matter, does not interact with electromagnetic force, meaning it neither absorbs, reflects, nor emits light, making it extremely difficult to detect.
- Its existence is inferred from its gravitational effects on visible matter.
- Dark matter outweighs visible matter roughly six to one, constituting about 27% of the universe, while known matter makes up only 5%.
- One theory suggests dark matter could consist of “supersymmetric particles,” partners to those in the Standard Model.
- Dark matter candidates often appear in theories beyond the Standard Model, like supersymmetry and extra dimensions.
- Some theories even propose a “Hidden Valley,” a parallel world of dark matter.
Dig Deeper: Read about Dark energy and compare it with Dark matter.
