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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

#151

Post by zamalek »

pessimist wrote: post #53
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…

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.

Associating dark matter with epicycles is unfair, but it's still a risk (CDM, WDM, SIDM, and probably more by next year). In that light, of course it has more observations (by virtue of creating branches to explain incompatible observations) - but counterpoint is that it has made some predictions.

My stance is that anyone pointing at it in either light probably isn't taking everything into account. It's an incredibly immature theory space - are we going to get 20 more branches of it (making it modern epicycles), or are we going to see one of the current branches pay off?

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

#152

Post by SiempreViernes »

layer8 wrote: post #112
SiempreViernes wrote: post #111

Earlier quoted context omitted.

I don't think "leading" is correct, more like "ill regarded but still standing". It has fallen far from its glory days, and is more an old reliable tool than a leading physical theory.

It’s correct because there is no competing theory for quantum gravity that most physicists would consider being more likely to be on the right track. This is different from MOND, which is a distant second contender compared to dark matter.

Ok, I'll present my evidence an you can present yours.

In the latest Marcel Grossman meeting (2024) there was no string theory parallel session but there was an explicit Loop Quantum Gravity session: https://indico.icranet.org/event/8/program

So string theory is now pretty officially an "also ran", definitely not a leading theory.

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

#153

Post by MattPalmer1086 »

MattPalmer1086 wrote: post #81
gwynforthewyn wrote: post #50

Earlier quoted context omitted.

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?

Not sure why the downvotes just for asking a question.

Dark matter (well, LCDM) has predicted many things which were proven false, e.g. that big galaxies assembled through merging with smaller ones over long periods of time. JWST shows us this is not in fact the case. There are now lots of papers showing how LCDM can explain that, but these are post facto explanations.

Happy to be proven wrong if someone can point me to a prediction subsequently confirmed by observation.

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

#154

Post by towledev »

bsder wrote: post #137
towledev wrote: post #128

Earlier quoted context omitted.

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.

Maybe you can point me to the "equal predictive and explanatory power" bit in William's writings.

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

#155

Post by ricksunny »

ykonstant wrote: post #148
ricksunny wrote: post #104

Earlier quoted context omitted.

Would it? Or would it be treated as an errant experiment by either the journal or the experimentalists themselves, foregoing publishing until they had a result that was better aligned with established norms? Rightly or wrongly, I expect that stakeholders would tend to invoke Sagan’s ECREE over the course of the publication process.

Yes. Yes, it would. This is so tiring.

It is not my intention to induce fatigue in anyone, though I am impressed that a reply comment in a forum is capable of doing so.

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

#156

Post by alirezaxdehghan »

ricksunny wrote: post #155
ykonstant wrote: post #148

Earlier quoted context omitted.

Yes. Yes, it would. This is so tiring.

It is not my intention to induce fatigue in anyone, though I am impressed that a reply comment in a forum is capable of doing so.

now I'm tired too

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

#157

Post by ricksunny »

alirezaxdehghan wrote: post #156
ricksunny wrote: post #155

Earlier quoted context omitted.

It is not my intention to induce fatigue in anyone, though I am impressed that a reply comment in a forum is capable of doing so.

now I'm tired too

I hope you manage to get some rest after the tiring tribulations people pose on forums.

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

#158

Post by dnautics »

pixl97 wrote: post #101
dnautics wrote: post #63

Earlier quoted context omitted.

I mean sure nature has no obligation to not have a unfalsifable particle, but you wind up in weird places, like, there exists a distribution of dark matter that explains the poltergeist that knocked over your coffee cup last week.

I mean I don't believe a particle that only reacts with gravity is unfalseifiable , it's that gravity just demands the use of unimaginable energies that we've not accomplished at this time. You act like we've managed to probe the depths of physics with certainty when in reality you find any means to reject that which offends your sensibilities.

> You act like we've managed to probe the depths of physics with certainty when in reality you find any means to reject that which offends your sensibilities.

At the root of science is "sensibilities", like occam's razor, even "what counts as experimental reproduction", etc.

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

#159

Post by gus_massa »

MattPalmer1086 wrote: post #153
MattPalmer1086 wrote: post #81

Earlier quoted context omitted.

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?

Not sure why the downvotes just for asking a question. Dark matter (well, LCDM) has predicted many things which were proven false, e.g. that big galaxies assembled through merging with smaller ones over long periods of time. JWST shows us this is not in fact the case. There are now lots of papers showing how LCDM can explain that, but these are post facto explanations. Happy to be proven wrong if someone can point me…

Is this the "hot" vs "cold" dark mater discussion? (Not my area. I just read that in Wikipedia.)

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

#160

Post by MattPalmer1086 »

gus_massa wrote: post #159
MattPalmer1086 wrote: post #153

Earlier quoted context omitted.

Not sure why the downvotes just for asking a question. Dark matter (well, LCDM) has predicted many things which were proven false, e.g. that big galaxies assembled through merging with smaller ones over long periods of time. JWST shows us this is not in fact the case. There are now lots of papers showing how LCDM can explain that, but these are post facto explanations. Happy to be proven wrong if someone can point me…

Is this the "hot" vs "cold" dark mater discussion? (Not my area. I just read that in Wikipedia.)

Not really, Cold Dark Matter is part of LCDM, the main cosmological model. Whether hot or cold, I'd like to see a solid prediction made for it confirmed subsequently by observation.
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