James Webb Space Telescope finds evidence for alternate theory of gravity

> which is totally backwards from a basic scientific perspective

This is not right, because if we have a situation where our theories and observations don't cohere, it's not given whether the theory requires modification or we're missing something in our observations (or both). A classical illustration is the orbit of Uranus being observed in the nineteenth century to be contrary to the predictions of Newtonian theory. Calculations were made assuming the truth of the Newtonian theory and that we were missing something in our observations - the position of Neptune was predicted and it was subsequently discovered.

On the other hand, the orbit of Mercury diverged from the prediction of Newton's theory. Again, a previously unobserved planet closer to the sun was postulated as being responsible, but in this case it really did require a modification to the theory of gravity: general relativity, which accurately predicted the 43 arcseconds per century of perihelion precession by which Mercury's orbit diverges from Newtonian predicitions.

GR has obviously made many other predictions, such as the gravitational bending of light, black holes, and gravitational waves, which have been vindicated.

So there's obviously a problem of the theory and observations not cohering, but whether the solution is a modification of the theory or a new form of matter is not clear in advance, and the latter is not unreasonable and certainly it's not unscientific to make as a hypothesis, to see where it leads.

The difficulty is in coming up with a theoretical framework that retains all the successful predictions of GR while also accounting for the galactic rotation curves.

Well put, thanks for sharing! Never saw it phrased in such a clear narrative. As a novice, it seems like there's one big difference between those anecdotes and the current situation, though: sample size. Sure, if we were observing Andromeda spinning too slowly I'd be open to our instruments not capturing some massive objects/clouds, but we're actively observing, what, ~1E5-6 galaxies? In the case of a missing planet there were accidents of history/solar system makeup that led to our otherwise solid frameworks missing a key piece of information. But that clearly couldn't happen millions of times; whatever explains the inconsistencies we're seeing has to be a fundamental misunderstanding.

Once we've arrived at this point, we can compare the two theoretical re-workings on their own terms: one is that we're glossing over some important detail of how gravitational relations in spacetime work, and the other is that we're failing to observe some new class of matter. I mean, right? There's no way this conundrum will be solved by "whoops turns out there was more plain ol' dust than we thought" at this point, right?

In those terms, I feel parsimony clearly favors one possibility over the other. Every hypothesis is worth exploring (I mean, QM and GR are dumb as hell, yet nonetheless turned out to be correct), but when funding is on the line it's also not out of line to favor one explanation explicitly. That's already happening anyway, just in the other direction.

But also I'm just some kid who's awed and grateful to be living in times of such profound mystery and discovery. Could be totally off base -- I barely passed physics I!

> ...turned out to be correct

What we have learned so far is that our theories and models are only correct up to our ability to precisely observe and measure.

In that sense, Newtonian physics is still very much correct under a very wide set of circumstances, and as such amazingly useful.

GR improves on that (adds precision) on what would be extreme cases for NP, but it is likely as correct as Newtonian laws are: up to a point.

All this to say that "correct" is not the right term to use: many of the theories are simultaneously "correct" with sufficient constraints and a particular error range. What matters more is if they are useful in predicting behaviour, and that's where I like using "correct" instead (as above).

One difference between dark matter and Neptune is that the existence of Neptune is falsifiable. The formulation of dark matter inherently is not. Falsifiable hypotheses is the cornerstone of science.

Surely the idea of it being a new kind of matter that interacts gravitationally but not electromagnetically yields some testable result? Does it actually yield nothing testable with today’s experimental methods?

Is the existence of a planet so easily falsifiable? It hasn't been so long since the Planet Nine hypothesis started going around, and while we've observationally ruled out a big chunk of the original parameter space, there's still lots of room for a big dark dwarf planet to be floating around out there. It doesn't seem so different from how we've gradually been ruling out the parameter space for dark-matter observations.

I mean, dark matter may be discoverable, we just don't know how if it exists. There was time between the irregularities that were noticed in the orbit and the discovery of a new planet.

There is a lot of indirect evidence for dark matter. All the direct tests for dark matter particles we have performed have found nothing so far - but since we have no idea what it might be, there's a lot of possibilities to test.

I'm not sure it's inherently unfalsifiable. There are some specific proposals for dark matter that could be ruled out by experiments, such as right-handed neutrinos: https://en.wikipedia.org/wiki/Sterile_neutrino#Sterile_neutr...

Maybe if you're being very broad in definitions then some class of proposals describable as "dark matter" might be unfalsifiable, but to be taken seriously as a scientific proposal I think it should be specific, concrete, and indeed testable, and there are a few of these within the "dark matter" class.

Again, we're in the perhaps unsatisfying position of having observations which don't cohere with our current theoretical understanding. What's the solution? It's not easy...

Thanks. I'm also no expert - I'm just learning general relativity - but that's also my rough understanding: either there needs to be a modification of the theory, or there's a new form of matter. It might seem more parsimonious to modify the theory, but then how do you do that in a way that retains all the successful predictions of GR while explaining the recalcitrant observations? That's the hard part.

It seems at the moment that the minimal and most elegant adjustment to the worldview required is to postulate the new form of matter. But I think it's safe to say it's a genuine problem in our knowledge: we don't know how to solve it

Have you ever encountered the phrase "grasping at straws"? The pursuit of explaining dark matter has gone through many waves of "we just need to invent detectors for this particle that has never been observed" and is littered with the wreckage.

Planets that reflect light are easy to detect.

"Evidence" in heavy scare quotes, considering, again, the tautological nature of the claims around the existence of dark matter. "Something must be here that we are missing" is, frankly, a bullshit hypothesis that need not be entertained unless researchers can actually prove there is some worthiness to the claim. Anything stronger than "maybe our theory is wrong" would suffice!

It is tendentious to point out only the difficulties in finding affirmative evidence for dark matter when MOND is doing no better in that regard. If, by that standard, dark matter is bullshit, then, mutatis mutandis, so is every other hypothesis that has been presented so far - but the observations that prompted them in the first place are not going away. It is inconsistent to call just one of them bullshit, and pointless to call them all that.

By that extremely simplistic logic, so is literally any other theory of gravity. This is not an argument, this is a flailing and empty justification.

Most of the history of physics involves making detectors for things that weren't previously observed... Consider: either most researchers in the field are stupid, for still pursuing an idea which you've apparently ruled out by simple reasoning, or your simple reasoning is fallacious

Almost: most of the history of physics is based on detectors being sensitive to things people didn't even know existed. Fits and starts based on happy accidents. The teleology of scientific progress is a myth. The most famous example is of course the Galilean moons.

Proposing detectors for particles that no one is even sure can exist is like setting up traps for Bigfoot...