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Could Modified Gravity Kill Planet Nine?
- nerbert 3y agoFascinating. So this MOND theory works in this case. If I understand correctly, scientists still prefer the dark matter theory because it applies in more cases at galactic scale, and this is just one occurrence of the MOND theory working fine?
- bena 3y agoI think dark matter is more appealing to them because the first person to discover a dark matter object is going to get something named after them.
- Ar-Curunir 3y agoFirst, most modern research in physics (especially experimental physics) have a ton of coauthors; we’re well past the stage of things being named for a single person. Second, what makes you think there isn’t great fame in disproving dark matter?
- mr_mitm 3y agoThat doesn't make any sense at all unless they simultaneously believe that DM is actually the right answer.
- bena 3y agoI’m sorry, I can see where I was ambiguous. I meant I can see why dark matter is appealing to more researchers in general and why MOND is in the minority. If dark matter is right, we can find it. If MOND is right, we’ve just been doing incomplete math this whole time. One of those is way more exciting.
- kadoban 3y agoThe last person who figured out we were doing incomplete math is the single most famous scientist in the history of the world. Being the next one isn't more exciting than getting some particle named after yourself?
- cdelsolar 3y agoYeah I interpreted that person’s post as saying “we’ve been doing incomplete math this whole time” is way more exciting, which I completely agree with.
- cryptonector 3y agoThe real issue is that you need a lot of money to test DM for real, but not so much to test MOND.
- mr_mitm 3y agoThey prefer it because it fits the data best. The biggest piece of evidence for DM is the BAO patterns in the CMB. Forget all the other numerous mountains of evidence, that is the biggest one. MOND has no good explanation for this without introducing something that's effectively DM.
- beautifulfreak 3y agoPerhaps you meant... DM = Dark Matter, BAO = Baryon Acoustic Oscillations, CMB = Cosmic Background Radiation, MOND = Modified Newtonian Dynamics
- moffkalast 3y agoTo put some sources to that unsubstantiated "data", it's about the Bullet Cluster specifically. https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to_dark_matter https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to...
- throwawaymaths 3y agoDM can't explain renzo's rule, or the tully-fisher relationship, or why the milky way has a keplerian return (efe from the magellanic clouds), or why elliptical and lenticular galaxies don't seem to have dark matter. All these are explainable by MOND. MOND also predicted early galaxies, and a group seeking to disprove MOND by disproving EFE changed their mind because they found evidence of EFE. > it fits the data best. It's easy to fit the data when you can conjure a parameter to explain anything. What if I told you that GR is wrong and there's a ball of dark matter orbiting the sun that distorts Mercury's orbit. You wouldn't be able to prove me wrong.
- mr_mitm 3y agoI wouldn't have to prove you wrong. If your stance is that Mercury's perihelion shift is explained by DM, then I'll counter that GR explains that, gravitational lensing, gravitational waves, black holes, the CMB, the helium abundance, and then some. By Occam's razor, GR would be the preferable theory. The claim that DM requires conjuring up parameters is completely baseless. There are one or two parameters (besides a handful other parameters from LambdaCDM) that determine the statistics of the DM distribution, and observations match well with simulations based on those parameters. There are small deviations called the dwarf galaxy problem and no one is inventing parameters to explain those, so what are you talking about?
- rocqua 3y agoWe have found galaxies with differing amounts of dark matter (as measurer by rotational speed) and have confirmed these measurements with gravitational lensing being more or less effective.
- pfdietz 3y agoIf MOND were a single theory such ideas would be more interesting.
- adastra22 3y agoYou could say the same about dark matter.
- nubinetwork 3y agoPluto is a planet ( /s but not really)
- aquova 3y agoFine, but then so is Eris
- moffkalast 3y agoCeres to beltalowda!
- LoganDark 3y agoWasn't this a Rick and Morty episode?
- FrustratedMonky 3y agoPluto should have had some grand-father clause. Keep it a planet for historical sake, but with an asterisk. So we wouldn't keep arguing about the new objects that are same size or bigger, yes, Pluto isn't a planet. But lets just go ahead and acknowledge that we are going to call Pluto a planet in 'name-only' for the memories.
- pwdisswordfishc 3y agoThat’s what the "dwarf planet" term is.
- iraqmtpizza 3y agothey prefer the term "planets with dwarfism"
- vundercind 3y agoColloquial language doesn't have to follow scientific language. No facts about the physical universe changed with the name change. We can just keep calling Pluto the ninth planet, which lets the hypothesized distant planet be "Planet X" which is way the hell cooler than "planet 9". There's no need for any permission to do this.
- antonioevans 3y agoDr Becky explaining the MOND theory and why it's invalid --> https://www.youtube.com/watch?v=HlNSvrYygRc https://www.youtube.com/watch?v=HlNSvrYygRc
- lolinder 3y agoFor those of us who don't already know her, can you explain who Dr Becky is and why we should trust her perspective? I can't watch it just yet, but judging from the thumbnail this feels like just another educational YouTube video, and while I watch more than my fair share of that genre I don't tend to implicitly trust it on complicated scientific topics.
- boesboes 3y agoShe has a PhD in astrophysics and is a specialist on blackholes. In her video's such as this one she goes into what the paper claims and then looks at the evidence for and against, based on other research and theory. She knows her stuff and approaches things rationally.
- Jleagle 3y agoWikipedia: `Rebecca Smethurst, also known as Dr. Becky, is a British astrophysicist, author, and YouTuber who is a junior research fellow at the University of Oxford. She was the recipient of the 2020 Caroline Herschel Prize Lectureship, awarded by the Royal Astronomical Society, as well as the 2020 Mary Somerville Medal and Prize, awarded by the Institute of Physics. In 2022, she won the Royal Astronomical Society's Winton Award "for research by a post-doctoral fellow in Astronomy whose career has shown the most promising development".`
- sapiogram 3y agoShe has a PhD in astrophysics, with her academic work centered around the co-evolution of supermassive black holes and their host galaxies. As far as I can tell, she's still an active researcher, even though she clearly spends a lot of her time on her Youtube channel.
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- GordonS 3y agoIf I understand correctly, MOND is suggesting that gravity behaves differently at sufficiently large scale (galactic), similar to how we observe different physics at a quantum level?
- lisper 3y agoThe analogy is a teensy bit strained but you are substantively correct.
- samus 3y agoMOND and DM try to explain the same phenomena, and the debate can probably be settled on way or the other by looking at enough interesting galaxies, or by finding dark matter or definitely ruling out that it exists. GR and Quantum Mechanics are not even really talking about the same thing and use incompatible mathematical frameworks. Another problem is also that there are actually not so many phenomena that we would need Quantum Gravity for. Particle physicists are yearning to find experimental evidence that would force us to retire the Standard Model to the history books. And their event horizon makes it kinda hard to study what is going on inside black holes.
- catlifeonmars 3y agoAs a layperson, it’s hard to tell from the debate of evidence I read elsewhere in the comments: what are the falsifiable predictions of e.g. DM and MOND?
- jfengel 3y agoI wouldn't have put it that way, since the quantum/classical transition is an emergent phenomenon without additional parameters, while MOND proposes a new term being a added to the physics. Still, at a broad level there are similarities, yes. In QM scale practically has a life of its own -- made explicit in the Copenhagen interpretation.
- adastra22 3y agoWhat? Quantum physics definitely adds new terms…
- lolinder 3y agoWhether or not they're right in their answer, it's interesting to me that this debate is a modern repeat of the discussion about the oddities of Mercury's orbit that some attempted to explain with a hypothetical planet Vulcan [0]. One of the early evidences for Einstein's general relativity was that it accounted for those oddities with only the planetary bodies that had already been observed. [0] https://en.m.wikipedia.org/wiki/Vulcan_(hypothetical_planet) https://en.m.wikipedia.org/wiki/Vulcan_(hypothetical_planet)
- vikingerik 3y agoAnd since readers may find this interesting: The various writeups all say that relativity explained the precession of Mercury's orbit, but they never say exactly what factor was accounted for by relativity. The answer: Mercury is heavier when it is at perihelion in its elliptical orbit, because it's moving faster. The increased relativistic mass makes for increased momentum at perihelion, which carries the planet a little farther than expected before it starts to swing back up out of the gravity well, so the perihelion precesses more. And the effect exists and is known for the other planets now; the mass increase is proportional to velocity-squared and the velocity difference depends on the eccentricity of the orbit, so it's an order of magnitude smaller for Earth, but still measurable and now known. It's also known for other objects: one example is stars in elliptical orbits around the galaxy's central black hole, which undergo extra precession in the same way.
- sigmoid10 3y agoThis might sound true if you have a superficial understanding of relativity (and I would not be surprised to see people repeating this stuff on the internet), but it's completely false. The correction to Mercury's orbit precession from General Relativity has nothing to do with Mercury itself (its mass, speed or otherwise). It is purely based on the sun's gravitational field. If you want to interpret it as a potential field in the classical Newtonian sense, it basically picks up an additional 1/r^3 term. That's what disturbs the orbit and it's also the reason why this effect is negligible for other planets apart from Mercury, because it drops off much faster than the normal 1/r potential. Any object very close to a large mass like the sun would feel this distortion, irrespective of how fast it travels.
- lupire 3y agoI don't know MOND at all, but is it still highly plausible that decades of modern astronomy haven't found better more direct evidence for Planet Nine existing?
- Tuna-Fish 3y agoThe evidence from clustered orbits points towards planet nine likely being right in the middle of the busiest part of the night sky, nestled between millions of stars of the milky way. The assumption is that we already have pictures of it, it's just that when you photograph that part of the sky you are not likely to notice one very faint point of light in the middle of the ten million brighter points of light on the same plate.
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- Qem 3y agoDetecting planets or other cold objects is hard, when they are far from the sun. Illumination from the sun falls with inverse square law (~1/r^2). When the reflected light does the return trip, it also falls with (~1/r^2). The effect compounds on both legs of the trip, and overall the brightness of a planet falls proportional to ~1/r^4, quickly getting lost amidst all the noise in the night sky as distance increases.
- gray_-_wolf 3y agoCould you build an uber radar for detecting the planet, possibly working together with the radiotelescopes we already have? Given the article, it should be ~150 light hours from sun, which round trip time wise sounds doable.
- pfdietz 3y agoRadar faces the same inverse fourth power effect.
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- eigenspace 3y agoBlows my mind that MOND still gets attention.
- russdill 3y agoThere's still plenty of room to study MOND. There's a lot of people outside the scientific community that seem to misjudge the general scientific consensus on it. But doing publishing research on things like MOND is still important.
- dudeinjapan 3y ago[flagged]
- sspiff 3y agoI've always thought that a good model or theory predicts observations (like a new particle, or an unseen planet) and is confirmed to be accurate by those observations. A new model that is designed to fit existing observations that don't match our expectations based on the old model, without it correctly predicting new unexpected observations, seems like a rather weak proposition to me.
- Wowfunhappy 3y agoThis new model was designed to fit existing observations without the presence of dark matter, and turns out to also predict the orbits of planets without planet nine.
- Arech 3y agoMOND was there years before Batygin (co-author of planet Nine hypothesis) was born.
- Izkata 3y ago> co-author of planet Nine hypothesis Are you referring to what he published in 2016? Because it's much older than that, we used to call it Planet X.
- lamontcg 3y ago"Planet Nine" is a term of art that refers specifically to the 2016 theory. "Planet X" refers specifically to a theory proposed by Percival Lowell in 1906 about the orbit of Uranus which was disproven in 1993 by Voyager 2 flyby data. They are both more specific theories than just "a trans-Neptunian planet we haven't discovered" which is overly broad.
- dragonwriter 3y agoSomewhat related are "Nemesis", the 1984 hypothesis of a distant companion red or brown dwarf to the Sun, and "Tyche", the 1999 hypothesis of a gas giant in the Oort Cloud. On "Planet X" specifically, the effect it was offered to explain was determined to have been measurement error after recalculation of Neptune's mass and consequently effect on Uranus's orbit in 1993 based on Voyager 2 data.
- denton-scratch 3y agoI thought MOND only kicked-in in regions of a galaxy where acceleration was much lower than in the Sun's region. These guys appear to be reasoning that because the Oort Cloud is far from the Sun (i.e. relatively low acceleration) then MOND might apply. But isn't part of the reasoning for MOND that its effects can't be tested anywhere near Earth, because this whole galactic neighbourhood experiences much too much acceleration? The article was very thin on explaining how MOND could explain anomalous orbits of Oort Cloud objects, or what kinds of anomaly they are trying to address.
- mannykannot 3y agoThe relevant distance here is not that to the sun, but that to the galactic center, which is within the range over which MOND is proposed to be noticeable. The argument is that, according to MOND, the galactic center would perturb orbits in the Kuiper belt, creating the alignment which has heretofore been taken as evidence for Planet Nine.
- vld_chk 3y agoWhenever I read about Planet Nine search, I have a very naive (as a non-physicist) childish question: if we detect anomaly in our Solar System just less than a decade ago and can’t find anything visual which explains it, assuming there is giant planet/piece of ice floating somewhere at the edge of Solar System, how we are sure that there are not a lot of such objects and real space is not as “empty” as we think it is? Simply, what is the probability that let’s say space between us and Alpha Centaurs is not filled with objects like this? Invisible and leaving a tiny gravitational trace at the edge of our ability to detect it?
- ano-ther 3y agoVery good question. As a non-astronomer, my guess is that we don’t observe a lot of transient black outs for example of the milky way. Which would happen if there’s a lot of these around. That gives you an upper bound of how many objects like that exist.
- perihelions 3y agoMicrolensing events! (to be slightly more precise) https://en.wikipedia.org/wiki/Rogue_planet#Microlensing https://en.wikipedia.org/wiki/Rogue_planet#Microlensing - "They found 474 incidents of microlensing, ten of which were brief enough to be planets of around Jupiter's size with no associated star in the immediate vicinity. The researchers estimated from their observations that there are nearly two Jupiter-mass rogue planets for every star in the Milky Way.[26][27][28] One study suggested a much larger number, up to 100,000 times more rogue planets than stars in the Milky Way, though this study encompassed hypothetical objects much smaller than Jupiter.[29]"
- lamontcg 3y agoAnd "MACHOs": https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Massive_compact_halo_object In the 1990s I went to a talk which suggested that "WIMPs" (Weakly Interacting Massive Particles aka supersymmetric particles that would give rise to dark matter) was an acronym for "Well It Might be Physics" while MACHOs was "Maybe Astrophysics Can Help Out". The upper bound on MACHOs has looong since eliminated them as the explanation for all of dark matter though...
- cratermoon 3y agoMilgrom's theory has a problem. There's no theoretical basis for it. It arises from observations, but nobody can say why or how it fits in cosmology.
- tgv 3y agoTBF: doesn't the same apply to dark matter? It originated because something didn't fit, and it was an easy explanation, without further evidence.
- patrakov 3y agoAnd that's good: anything that has a theoretical basis is definitely not new physics. And we are talking about new physics here. The same could be said about special relativity or quantum mechanics in the past.
- mannykannot 3y agoA seemingly obvious question is whether dark matter could provide an equivalent result. I'm not really sure, but the paper's authors seem to be saying 'no' in this passage: Equations (B2), (B5), and (B7) are the main results of this section. They provide an expression for the phantom mass that sources anomalous effects in the inner solar system. As discussed above, these effects are absent in Newtonian gravity and hence absent in any dark matter model. Perhaps someone more knowledgeable could comment on this?
- pmayrgundter 3y agoCould Barnard's Star Kill Planet Nine? https://www.listennotes.com/podcasts/the-demystifysci/great-year-unveiled-suns-xUQScLVvk-w/?t=2067 https://www.listennotes.com/podcasts/the-demystifysci/great-...
- bradley13 3y agoDark matter is the modern ether. There is zero evidence that it exists. What we have are distant phenomena that we can't explain. If not MOND, then something like it.
- ngcc_hk 3y agoNeed some context like evidence. The article mentioned but I think you need more elaboration. Only recall the guy killing Pluto said as a consolation he gave us another planet.