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?
Not necessarily. MOND proposes modifications to Newton's laws to explain the galaxy rotation curves without invoking dark matter. If a galaxy without dark matter were found, it would be a challenge for MOND, especially if MOND cannot account for the dynamics of such a galaxy. However, it might not completely disprove MOND as the theory could still potentially be applicable or accurate in other contexts or require further modification.
MOND, or Modified Newtonian Dynamics, is a theoretical framework proposed by Mordehai Milgrom in the 1980s. It was developed as an alternative to the dark matter hypothesis to explain why the observed rotational speeds of galaxies are faster than what would be expected based on the visible matter alone. MOND modifies Newton's laws of motion at very low accelerations, typical of the scales of galaxies, to account for the discrepancy without needing additional, unseen mass.
The existence of a galaxy without dark matter would be significant because the dark matter hypothesis is primarily used to explain why galaxies do not fly apart despite their high rotational speeds, suggesting a large amount of unseen mass. A galaxy operating without this unseen mass could indicate that our understanding of gravity or galaxy formation might need revising, or it could suggest variations in dark matter distribution that are not currently accounted for in the standard model of cosmology.
Yes, there have been a few galaxies observed that appear to lack dark matter, such as NGC 1052-DF2 and NGC 1052-DF4. These galaxies are unusual because they do not fit the typical profiles expected under either the dark matter hypothesis or MOND. Their discovery has sparked significant debate and further investigation as they could provide crucial insights into the nature of gravity and the validity of theoretical models including both dark matter and modifications to Newtonian dynamics.
To significantly challenge or potentially disprove MOND, a broad and consistent set of observational data that contradicts the predictions made by MOND would be required. This could include data from galaxy rotation curves, gravitational lensing, and cosmic background radiation measurements that consistently align better with Newtonian dynamics with dark matter or another theory, rather than with MOND. Additionally, a theoretical breakthrough that provides a more compelling and universally applicable explanation of gravitational phenomena could also challenge MOND.