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from the as-long-as-it-predicts-apples-dropping dept.
https://physics.aps.org/articles/v14/143
"Researchers pursuing an unconventional view of cosmology that dispenses with dark matter have developed a model that can match observations of the cosmic microwave background (CMB), the leftover glow of the big bang [1]. This dark-matter-free model is an extension of the so-called MOND (modified Newtonian dynamics) theory, which assumes that the gravitational force on galaxy scales is different from the standard Newtonian force. Previous MOND-based models could not reproduce the CMB. The researchers say that their model can be further tested with observations of galaxy clusters and gravitational waves."
The MOND theory was devised more than 30 years ago as a way to explain galactic rotation data without invoking the existence of the mysterious dark matter [2]. MOND proponents offered an alternative mystery in which the gravitational force changes for accelerations smaller than a threshold of 10−10m/s2. The idea did not spring from any underlying theory, but surprisingly, the same acceleration threshold works for nearly all galaxies—small and large, young and old.
The main reason that dark matter has been favored over MOND is that dark matter is consistent with a much larger range of astrophysical observations. For example, dark matter can explain galaxies' bending of light from distant sources (gravitational lensing), whereas MOND in its initial form could not. Researchers have devised so-called relativistic MOND models that can fit the lensing observations [3], but until now, none of these revised versions of the theory were able to reproduce CMB data. "If the theory can't do that, then it's not worth considering further," says Constantinos Skordis from the Czech Academy of Sciences in Prague.
The APS Physics article is a review of this paper:
C. Skordis and T. Złośnik, “New relativistic theory for modified Newtonian dynamics” Phys. Rev. Lett. 127, 161302 (2021).
(Score: 0) by Anonymous Coward on Tuesday October 19 2021, @04:06PM (5 children)
If I understand you correctly, you are proposing the unseen Baryonic matter out there?
Read somewhere that even accounting for unseen or free roaming black holes and dark bodies like MACHOs, still can not account for the discrepancies with observations.
Here is as close as we have gotten so far:
https://www.universetoday.com/137446/astronomers-find-missing-normal-matter-universe-still-looking-dark-matter-though1/ [universetoday.com]
(Score: 4, Interesting) by HiThere on Tuesday October 19 2021, @04:43PM (1 child)
It's my understanding that this doesn't rule out "primordial black holes", on those that formed after the re-ionization. (Well, actually they need to form slightly earlier, as the current baryonic matter is needed to explain the proportion of various elements...but it's also true that I've seen those estimates claimed as a lot more imprecise than earlier claims...so...maybe?
Anyway, my personal favorite variation of that theory is that dark matter is primordial black holes that are smaller than a proton, and have too small a capture cross-section to emit Hawking radiation. (That requires swallowing half of a pair of virtual particles.) But I'm no astrophysicist of any variety, including armchair, so don't take this too seriously. And a MOND variant would be interesting, as perhaps it would allow FTL. (Maybe it wouldn't, too, but nobody's really looked, and anyway they're still flexing the theory to make it fit the data.)
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 1, Funny) by Anonymous Coward on Tuesday October 19 2021, @04:52PM
Nice additional info, thanks!
If I could mod this up I would...but then again, the moderation system on here is a difficult as looking for dark matter.
(Score: 2) by Immerman on Tuesday October 19 2021, @07:07PM
The problem is that you *can't* account for unseen matter - if there's no evidence, we have no idea how much is there, and thus whether there's a mass discrepancy. Instead you have to try to rule it out by painstakingly searching for the evidence you know must be there if X is the cause, for all possible X's.
Black holes as dark matter in contrast must have formed very early in the universe's history, I think before first light spawned the CMBR. Most possible sizes have been ruled out by careful searches for gravitational lensing, but extremely small (atomic scale) has not been ruled out (lensing would be so minor as to be undetectable to current tools). Neither has a narrow window in the range of several(IIRC) solar masses.
Your article is about something unrelated - the fact that theory posits a large amount of normal matter that we didn't see direct evidence of, but now do. Exactly where the consensus expected to find it.
(Score: 3, Funny) by Mykl on Tuesday October 19 2021, @10:11PM (1 child)
Has anyone considered Phlogiston [wikipedia.org]?
(Score: 3, Funny) by kazzie on Wednesday October 20 2021, @04:41AM
Yeah, but that idea went up in flames.