And what is the MOND theory, which this analysis seems to support?
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They’re not saying that gravity breaks down, they’re saying that our current model of gravity does not give the results that are observed in this case. This is similar to how a long time ago it was observed that Mercury’s orbit didn’t match what was predicted by Newton’s model of gravity and planetary orbits, which was an indication of general relativity.
Now this new paper doesn’t necessarily mean anything, because it is just one paper. Another paper could come along and say something completely different, or more papers could come along that back it up. We do not know, these things take time.
Assuming it is correct, it is an indication that our model of gravity (general relativity) is incomplete/incorrect. A small number of experts over the past several decades have worked on alternatives, and these are often referred to under the umbrella term of MOND, which means MOdified Newtonian Dynamics. It is called this because it starts off by taking Newton’s law of gravity and modifying the equation to something else.
The reason some people have been interested in MOND is because they believed it did away with the need for dark matter, however observations over the years have shown that this is not the case, and that even with MOND dark matter must still exist. This hasn’t stopped some people from still being interested in the possibility that MOND is still correct, even if it doesn’t do away with dark matter, and it would potentially reduce the amount of dark matter that must exist.
>And what is the MOND theory, which this analysis seems to support?
There are tons of observations and measurements we make of distant galaxies that don’t match what should be going on based on their light alone.
The simplest explanation is that there is more mass than just stars and gas, aka ‘dark’ matter. We can posit that this dark matter exists with a given density, and that *single* number accounts for *dozens* of observational discrepencies.
There are other explanations that don’t involve dark matter. Modified Newtonian dynamics (MOND) involve using Newton’s mechanics and altering them to develop a model that explains the observations. The problem with MOND explanations, is that typically involve many arbitrary quantities and numbers to fit the model to the data, which is poor science (and, arguably, not science at all).
The dark matter explanation can explain *dozens* of observations with just a single number (the density of dark matter), whereas MOND explanations involve lots of unknown quantities that can be freely selected to fit the model to the data.
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