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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

#81

Post by MattPalmer1086 »

gwynforthewyn wrote: post #50
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…

Of course it can be that this is the case. There are predictions from the dark matter hypothesis, though, that have been testable. For example, there're some of the asymmetries in the cosmic microwave background that are explained presently by the dark matter hypothesis. Something that's worth bearing in mind is that "dark matter" doesn't actually mean "totally new never before seen thing" it means "we don't know wha…

As far as I know, dark matter hasn't made any testable predictions which were subsequently proved correct. It's an infinitely tunable hypothesis that can be retro fitted to new observations, since it has many tweakable parameters.

Could you point me to a prediction made by dark matter theory which was subsequently confirmed by observation, rather than a dark matter theory which explains it post facto?

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

#82

Post by yongjik »

ricksunny wrote: post #67

If it had failed, would we be hearing about it in Science before the researchers continued testing it until it passed? (i.e. is this a blindspot in our collective epistemology?)

If it had failed it would've been a top science news. Every scientist dreams about the day when they're mentioned as "(...)'s experiment puts Newton's law of gravity in jeopardy."

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

#83

Post by wvenable »

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.

> Ok, so... why do people take it seriously as a concept?

Historically, science has predicted lots of true things about the universe that could not be observed at the time.

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

#84

Post by cactacea »

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 stuff like the Bullet Cluster exists. Dark matter is in fact the simplest answer.

https://en.wikipedia.org/wiki/Bullet_Cluster

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

#85

Post by Tuna-Fish »

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 have indirectly observed it a bunch, and our understanding of physics allow the existence of material that flatly cannot be directly observed.

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

#86

Post by chmod775 »

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.

It doesn't even matter whether it actually exists, because it works for modeling the universe and making accurate predictions about it.

That means for now it's useful.

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

#87

Post by sigbottle »

wvenable wrote: post #83
throwaway27448 wrote: post #73

Earlier quoted context omitted.

> 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.

> Ok, so... why do people take it seriously as a concept? Historically, science has predicted lots of true things about the universe that could not be observed at the time.

I don't know what or why our science education is like this, but it seems like everybody's understanding of science bottomed out at a straw man version of popper & positivism.

And to be clear, falsification and being empirical & skeptical about theoretical claims is great. What I see all too often on the Internet is just pattern matching to the words "observable" and "falsification" without a second thought, without actually looking into how science develops, and any and all narratives are historically rewritten to fit only those two categories.

Which is why it's even more impressive to be a real scientist, to actually be able to navigate the muddy waters properly where it's not just some simple adjective checklists to run through. (As a non scientist)

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

#88

Post by yxhuvud »

jahnu wrote: post #66
PaulHoule wrote: post #4

Earlier quoted context omitted.

MOND does amazingly well at galactic rotation curves, less well at anything else. If you think it started with Vera Rubin in 1966 MOND seems natural, but if you know that it started with Fritz Zwicky in 1933 than dark matter is easier to believe.

There are galaxies that appear to be free of dark matter and rotate accordingly. How does MOND account for that? My understanding is that these observations are a fatal blow to any serious MOND models.

MOND obviously don't have to account for the lack of dark matter, as all galaxies lack it under MOND.

You have to actually do the calculations and compare what MOND output to the observed behaviour of the galaxies in question.

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

#89

Post by gostsamo »

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…

You might be interested in that. We have observations of galaxies where dark matter likely is not present.

https://news.ycombinator.com/item?id=47641057

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

#90

Post by Tuna-Fish »

dnautics wrote: post #60
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.

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 and others on the bullet cluster, and is now generally treated as settled science by practitioners. We might still be surprised by something, the universe is more wondrous and complex than we can possibly understand, but Occam's razor massively supports LCDM now. If you want to propose any alternative, you need to start by showing how it explains bullet cluster as well or better than LCDM. (And the bullet cluster specifically is not the only place where this is visible, there are others like MACS J0025.4-1222.)

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