←back to thread

355 points jchanimal | 2 comments | | HN request time: 0.398s | source
Show context
uoaei ◴[] No.42158729[source]
I follow the lead author, Stacy McGaugh, via his blog where he posts discussions and musings about the latest research into the dark matter vs MOND debate: https://tritonstation.com/new-blog-page/

His arguments are very convincing and relatively clear. I am not an astrophysicist but I have two degrees in physics and have always found the dark matter theory to be lacking -- in absence of any evidence of causation whatsoever, dark matter can only be described trivially as "where we would put matter if we could to make our theory of gravity make sense," which is totally backwards from a basic scientific perspective.

Predictions based on modern MOND postulates are shown to be more and more accurate as our observational instruments continue to improve in sensitivity.

replies(4): >>42158855 #>>42158981 #>>42159032 #>>42159078 #
griffzhowl ◴[] No.42158981[source]
> 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.

replies(2): >>42159094 #>>42159171 #
njtransit ◴[] No.42159171[source]
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.
replies(4): >>42159345 #>>42159399 #>>42159470 #>>42160476 #
renewiltord ◴[] No.42159345[source]
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?
replies(1): >>42159584 #
MattPalmer1086 ◴[] No.42159584[source]
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.
replies(1): >>42161587 #
1. uoaei ◴[] No.42161587[source]
"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!
replies(1): >>42161992 #
2. mannykannot ◴[] No.42161992[source]
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.