There was a thread about this not that long ago. On the face of it yes - even a single galaxy that obeys the default Newtonian dynamics would disprove MOND. The proponents of MOND, however, believe that secondary MOND effects from neighbouring galaxies may explain this.lamdar said:I’ve been reading about LCDM and MOND recently. And there have been reports of galaxies with little dark matter. I know the lack of dark matter in NGC1052-DF2 was shown not true afterwards. But if such a galaxy without dark matter is actually discovered, would this be sufficient to disprove MOND?
Is it maybe in the "Similar Threads" list at the bottom of this page?PeroK said:There was a thread about this not that long ago.
Not if the parachute didn't open!Ibix said:There's also the point V50 makes about the quality of evidence. One measurement being enough to falsify a theory is an idealisation. It has to be one measurement by skilled observers with high confidence that possible measurement errors have been controlled and possible confounding factors eliminated. Otherwise we'd falsify Newtonian gravity every time someone did a parachute jump.
Terminal velocity for a human isn't very high (Wikipedia says 55-90m/s depending on whether you spread out or curl up), so even without a working chute you don't fall according to a naive application of Newtonian gravity. And we're way off topic here!PeroK said:Not if the parachute didn't open!
Dark matter has not been discovered, it is predicted, there is a difference.lamdar said:I’ve been reading about LCDM and MOND recently. And there have been reports of galaxies with little dark matter. I know the lack of dark matter in NGC1052-DF2 was shown not true afterwards. But if such a galaxy without dark matter is actually discovered, would this be sufficient to disprove MOND?
MOND, or Modified Newtonian Dynamics, is a hypothesis that proposes modifications to Newton's laws of motion to account for the observed properties of galaxies without invoking dark matter. It suggests that at very low accelerations, the force of gravity deviates from Newton's inverse-square law.
MOND explains galaxy rotation curves by proposing that at low accelerations, typical in the outer regions of galaxies, the effective gravitational force is stronger than predicted by Newtonian gravity. This increased force can account for the observed flat rotation curves of galaxies without requiring additional unseen mass, such as dark matter.
The discovery of a galaxy without dark matter would challenge MOND, as MOND predicts that its modified gravitational laws should apply universally. If a galaxy exhibits normal Newtonian dynamics without needing dark matter, it could suggest that MOND's modifications are not universally applicable, thereby weakening its validity as a comprehensive theory.
Yes, there have been claims of galaxies with little to no dark matter, such as the galaxy NGC 1052-DF2. However, these claims are still under scrutiny and debate within the scientific community. Confirming such galaxies' existence and properties is crucial for evaluating the implications for both dark matter and MOND.
A single galaxy without dark matter would not necessarily disprove MOND, but it would pose a significant challenge. MOND would need to explain why its modified laws do not apply to that particular galaxy. If multiple such galaxies were found, it would more strongly suggest that MOND is not a complete theory of gravity and that other factors or models might be required to explain galactic dynamics.