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Could Modified Gravity Kill Planet Nine?

nautil.us

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Re: Could Modified Gravity Kill Planet Nine?

#31

Post by Wowfunhappy »

sspiff wrote: post #29

I'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.

This 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.

Re: Could Modified Gravity Kill Planet Nine?

#32

Post by mr_mitm »

throwawaymaths wrote: post #30
mr_mitm wrote: post #11

Earlier quoted context omitted.

They 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.

DM 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 bes…

I 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?

Re: Could Modified Gravity Kill Planet Nine?

#33

Post by Qem »

lupire wrote: post #24

I 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?

Detecting 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.

Re: Could Modified Gravity Kill Planet Nine?

#34

Post by [deleted] »

Tuna-Fish wrote: post #28
lupire wrote: post #24

I 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?

The 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…

[deleted]

Re: Could Modified Gravity Kill Planet Nine?

#35

Post by weego »

sapiogram wrote: post #19
lolinder wrote: post #16

Earlier quoted context omitted.

For 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.

She 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.

AFAIK spreading interest in the field through social media was/is part of her post doc job goals

Re: Could Modified Gravity Kill Planet Nine?

#36

Post by GuB-42 »

lolinder wrote: post #16
antonioevans wrote: post #7

Dr Becky explaining the MOND theory and why it's invalid --> https://www.youtube.com/watch?v=HlNSvrYygRc

For 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.

From her bio, she is a legit astrophysicist, who publishes in peer-reviewed journals.

But more important than that, if you want more, you can read the paper her entire video is based on [1]

Also be aware that Sabine Hossenfelder, also a popular science YouTuber and published physicist released a video supportive of that paper, even though she was somewhat in favor of MOND before [2]. She even co-authored a paper about it [3] which she presented in a video [4]

[1] https://doi.org/10.1093/mnras/stad3393

[2] https://www.youtube.com/watch?v=i4lu9AxRtqA

[3] https://arxiv.org/abs/2401.10202

[3] https://www.youtube.com/watch?v=J7MVl1cSmYE

Re: Could Modified Gravity Kill Planet Nine?

#37

Post by Arech »

sspiff wrote: post #29

I'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.

MOND was there years before Batygin (co-author of planet Nine hypothesis) was born.

Re: Could Modified Gravity Kill Planet Nine?

#38

Post by Arech »

lupire wrote: post #24

I 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?

With our current, but especially decades ago capabilities, it's (was) similar to Russell's teapot problem.

Re: Could Modified Gravity Kill Planet Nine?

#39

Post by api »

lupire wrote: post #24

I 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?

It would be incredibly dark. The sun would just be a bright star out there.

There’s also some interesting speculation that planet nine could be a primordial black hole, in which case it could only be located by its indirect effects. It likely wouldn’t radiate much at all, making it basically invisible.

Re: Could Modified Gravity Kill Planet Nine?

#40

Post by gray_-_wolf »

Qem wrote: post #33
lupire wrote: post #24

I 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?

Detecting 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.

Could 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.
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