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Newton's law of gravity passes its biggest test

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Re: Newton's law of gravity passes its biggest test

#131

Post by dnautics »

Tuna-Fish wrote: post #90
dnautics wrote: post #60

Earlier quoted context omitted.

MOND explains 1. 2 is "who can say" because nobody has reconciled MOND with Relativity (not that it's impossible, it's just hard and annoying math, could be a lack of effort thing, could also be a real theoretical constraint that invalidates MOND). 3 is subject to questions like "is the CMB really what we think it is" -- if it's early thermalized dust, then that ALSO resolves hubble tension, e.g. MOND explains severa…

2 needs a more substantive rebuttal. LCDM correctly predicts where the dark matter is located after a galaxy collision, such as in the bullet cluster. There is no reasonable interpretation of MOND that has the center of mass of the galaxy shifted away from where it's visible matter lies, precisely how LCDM says it should be. There is a reason why LCDM used to be a lot more disputed before the work of Clowe, Gonzales…

> LCDM correctly predicts where the dark matter is located after a galaxy collision, such as in the bullet cluster. There is no reasonable interpretation of MOND that has the center of mass of the galaxy shifted away from where it's visible matter lies, precisely how LCDM says it should be.

It does not really make that "prediction", its a post hoc assignment of dark matter density based on weak lensing for which you can make a plausible "this is how it started" explanation.

you can counter with lcdm cant explain tons of stuff that MOND can, from tully fisher relation through barred spiral galaxies (n >> thousands) etc.

Re: Newton's law of gravity passes its biggest test

#132

Post by antognini »

throwaway27448 wrote: post #73
pessimist wrote: post #53

Earlier quoted context omitted.

There are multiple independent observations pointing toward dark matter: 1. Galaxy rotation curves. 2. Galaxy cluster mass measurements from gravitational lenses and infrared. 3. Cosmic Microwave Background models (mass measurements from inhomogeneities that correspond to acoustic waves, for eg). MOND only explains 1. Dark matter accounts for all 3. Only catch is that it hasnt been directly observed.

> Only catch is that it hasnt been directly observed. Ok, so... why do people take it seriously as a concept? Occam's razor would point towards some general misunderstanding on which we have no evidence to reasonably speculate a cause.

We already know that some particles interact extremely weakly with others. Neutrinos were postulated as a "dark" particle in order to preserve conservation of energy and momentum, but it took more than a decade before they were observed directly. There's no reason there couldn't be another particle with an even weaker interaction.

Re: Newton's law of gravity passes its biggest test

#133

Post by Tadpole9181 »

throwaway27448 wrote: post #73
pessimist wrote: post #53

Earlier quoted context omitted.

There are multiple independent observations pointing toward dark matter: 1. Galaxy rotation curves. 2. Galaxy cluster mass measurements from gravitational lenses and infrared. 3. Cosmic Microwave Background models (mass measurements from inhomogeneities that correspond to acoustic waves, for eg). MOND only explains 1. Dark matter accounts for all 3. Only catch is that it hasnt been directly observed.

> Only catch is that it hasnt been directly observed. Ok, so... why do people take it seriously as a concept? Occam's razor would point towards some general misunderstanding on which we have no evidence to reasonably speculate a cause.

Because the discrepancy exists and shows consistency. This gap needs to be called something, you can't just pretend it's not real. But the underlying model seems fine and all alternatives are broken.

So we came up with an idea that fills the gap in the current model and allows us to continue predictive science until we find out more.

People get so absurdly touchy about Dark Matter just because it's named and "weird". It's just a placeholder value.

Re: Newton's law of gravity passes its biggest test

#134

Post by drdeca »

dnautics wrote: post #62
adgjlsfhk1 wrote: post #21

Earlier quoted context omitted.

MOND only really does well on galactic rotation curves because it has free parameters that are tuned to "predict" the correct answer for galactic rotation curves.

I think you mean LCDM only does well on galactic rotation curves because it has free parameters per galaxy. MOND only has one free parameter, maybe two if you use the MOND+Relativity model that doesn't work.

I don’t think these are free parameters in the same sense.

Like, if one theory says that a hunk of metal actually is made of many microscopic grains of various sizes and orientations, where the sizes and orientations of these grains has an effect on the behavior of the metal, you don’t count the “the sizes and orientations of these grains” as free parameters, do you?

Re: Newton's law of gravity passes its biggest test

#135

Post by [deleted] »

throwaway27448 wrote: post #73
pessimist wrote: post #53

Earlier quoted context omitted.

There are multiple independent observations pointing toward dark matter: 1. Galaxy rotation curves. 2. Galaxy cluster mass measurements from gravitational lenses and infrared. 3. Cosmic Microwave Background models (mass measurements from inhomogeneities that correspond to acoustic waves, for eg). MOND only explains 1. Dark matter accounts for all 3. Only catch is that it hasnt been directly observed.

> Only catch is that it hasnt been directly observed. Ok, so... why do people take it seriously as a concept? Occam's razor would point towards some general misunderstanding on which we have no evidence to reasonably speculate a cause.

[deleted]

Re: Newton's law of gravity passes its biggest test

#136

Post by fsckboy »

throwaway27448 wrote: post #73
pessimist wrote: post #53

Earlier quoted context omitted.

There are multiple independent observations pointing toward dark matter: 1. Galaxy rotation curves. 2. Galaxy cluster mass measurements from gravitational lenses and infrared. 3. Cosmic Microwave Background models (mass measurements from inhomogeneities that correspond to acoustic waves, for eg). MOND only explains 1. Dark matter accounts for all 3. Only catch is that it hasnt been directly observed.

> Only catch is that it hasnt been directly observed. Ok, so... why do people take it seriously as a concept? Occam's razor would point towards some general misunderstanding on which we have no evidence to reasonably speculate a cause.

>Occam's razor would point toward...

Occam's razer is not a thing with explanatory or legal or even scientific force. if Occam's razor was really a thing, quantum theory and general relativity would be ruled out as complicated and neither 100 percent explanatory.

Re: Newton's law of gravity passes its biggest test

#137

Post by bsder »

towledev wrote: post #128
bsder wrote: post #125

Earlier quoted context omitted.

> Occam's razor would point towards some general misunderstanding on which we have no evidence to reasonably speculate a cause. Dark matter is the Occam's Razor theory. It explains almost all of the observations while assuming the least. Why do you assume we have no evidence just because we don't have direct observations? Black holes were a similar phenomenon that we had no direct evidence for a fairly long time even…

The razor is commonly misunderstood. William of Ockham objected to his fellow theologians inventing things out of whole cloth (like dark matter question mark). That’s the point, not that a simpler explanation is more likely to be true. The common understanding would have us believe that creationism, being simpler, outshines evolution, or that there is no such thing as a color revolution because the simplest explanati…

Yours is a common misunderstanding, as well.

Occam's Razor only kicks in when the hypotheses have equal predictive and explanatory power.

The MOND hypothesis does NOT have equal explanatory power with the dark matter hypothesis. As such, Occam's Razor is not relevant.

Re: Newton's law of gravity passes its biggest test

#138

Post by adgjlsfhk1 »

drdeca wrote: post #134
dnautics wrote: post #62

Earlier quoted context omitted.

I think you mean LCDM only does well on galactic rotation curves because it has free parameters per galaxy. MOND only has one free parameter, maybe two if you use the MOND+Relativity model that doesn't work.

I don’t think these are free parameters in the same sense. Like, if one theory says that a hunk of metal actually is made of many microscopic grains of various sizes and orientations, where the sizes and orientations of these grains has an effect on the behavior of the metal, you don’t count the “the sizes and orientations of these grains” as free parameters, do you?

You would if you didn't have any ability to observe those sizes and orientations.

Re: Newton's law of gravity passes its biggest test

#139

Post by not2b »

rappatic wrote: post #41

When I see dark matter in the news I'm always reminded of the story of Vulcan. In the 1800s, detailed observations of the planet Mercury showed that its orbit was slightly different than Newtonian mechanics predicted-- a difference of about 43 arcseconds per century. The study was rigorous enough to rule out any observation errors. Le Verrier, the astronomer who made these observations, wondered how to explain the di…

The strongest evidence that something like MOND isn't the answer is that in some galaxy collisions, the visible matter and the dark matter appear to separate: the collision disrupts the visible matter and the dark matter appears to pass right through, uninterrupted, and we see galaxy remnants that look like they don't have dark matter. If MOND or some other modification of gravity were the answer we'd never see this kind of sorting.

See, for example, https://www.caltech.edu/about/news/dark-matter-flies-ahead-o...

Re: Newton's law of gravity passes its biggest test

#140

Post by Izkata »

throwaway27448 wrote: post #73
pessimist wrote: post #53

Earlier quoted context omitted.

There are multiple independent observations pointing toward dark matter: 1. Galaxy rotation curves. 2. Galaxy cluster mass measurements from gravitational lenses and infrared. 3. Cosmic Microwave Background models (mass measurements from inhomogeneities that correspond to acoustic waves, for eg). MOND only explains 1. Dark matter accounts for all 3. Only catch is that it hasnt been directly observed.

> Only catch is that it hasnt been directly observed. Ok, so... why do people take it seriously as a concept? Occam's razor would point towards some general misunderstanding on which we have no evidence to reasonably speculate a cause.

I blame sci-fi.

As a kid in 90s who was into this stuff, it seemed like anyone who knew about dark matter knew it was just theorized and never observed. It was included as a caveat in a lot of things I read to ensure the readers understood this.

Then in sci-fi it started showing up as a material the characters would interact with, and a lot more people were introduced to the term.

Then as a teen in the 2000s the caveat was usually gone and it started being treated as something we had proof of. People I knew started thinking it was something we'd actually found and was now fact instead of theory.

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