What exactly is "spin"?

No the scientifc evidence shows it, the right hand rule and the relative motion, not the mathematics. And people have been measuring gravitational anomalies for decades. That’s why it’s the dark matter hypothesis. Nobody can find any dark matter, remember? And see the FLRW metric and note where it says The FLRW metric starts with the assumption of homogeneity and isotropy of space. Now what did Einstein say? Neither homogeneous nor isotropic. Simple.

Except that

a) The FLRW model is not used to measure the amount of dark matter from galaxy rotation curves. You should know this, as probably a dozen people on the internet have pointed this out to you. And this is something that anyone who says anything about dark matter physics should know. So apparently you haven’t done any research and you are dishonest about the evidence for your theory. Address the galaxy rotation curves.
b) Einstein’s personal, preferred model was a special case of the FLRW model. Are you saying that Einstein was wrong about his own theory?

Dark matter isn’t being measured. Rotation curves are being measured. By your logic somebody could advance tiny dancing angels as a causative hypothesis, and assert that tiny dancing angels are being measured. They’re not.

No, Einstein wasn’t wrong. He said space was “neither homogeneous nor isotropic”. But “The Friedmann–Lemaître–Robertson–Walker (FLRW) metric is an exact solution of Einstein’s field equations of general relativity” and it "starts with the assumption of homogeneity and isotropy of space". Something got dropped somewhere along the line. Inhomogeneous space has been replaced by homogeneous space, and the result is the dark matter hypothesis, along with people promoting one hypothesis above alternatives in an attempt to establish it as a consensus.

If someone showed how to measure a parameter of tiny dancing angels with these rotation curves, then, yes, tiny dancing angels would be measured. This is how physics works. Whether or not we would believe in tiny dancing angels is another matter. However, even tiny dancing angels is a better answer than you have given so far because your answer not only doesn’t provide an explanation with the possibility of measurement, you are actively contradicting the use of general relativity in the actual scientific papers. You are pursuing your personal fantasy and demanding not only that others believe it, but that they disregard every scientific paper in favour of your fantasy.

As per usual, you did not answer the relevant question. Do you think that Einstein was wrong to prefer a homogeneous model of the universe?

He means that measuring the distance between balls in a cube of balls isn’t measuring the balls, but instead measuring the distance between them.
If, now, you could not see or sense the balls, but could only sense where passing through them was not possible and where it was; using this as a measure of “between” area of the balls…shrug more or less like sonar in a sub…then you would have no direct ability to declare what the objects where the sensors do not pass through are exactly…you would not be able to say they are balls or dancer statues.
For all anyone knows, they could be dancer statues in balls…or boxes with obtuse spin that results in a rather rounded feedback to the sensors.
shrug

The point is that the gaps are measured…not the objects.
By reduction, we assume the measure of the objects.

But it’s called dark for a reason, and that reason is that we simply don’t truly know what that stuff is.
For all we know, there could be 500 different classifications of matter within what we call “dark” matter today.

Did you mean these question for me?

I do not know what it means for a particle to be “disbanded”. There are many interactions that can take place where particles are destroyed and other particles are created. Sometimes this involves photons. Every explanation of how this happens involves specific predictions and mathematical descriptions about how these events happen.

I do not know how general relativity would do away with dark matter, this is an imagining of Farsight, not a supposition of physics. Every measurement of dark matter that I know of involves either scales where general relativity is not supposed to have a significantly different measurement from Newtonian physics or uses general relativity directly. According to astronomers, it is general relativity that suggests that dark matter exists.

Yes, there were intended for you… thanks for trying to answer. But… this is all extremely vague, not really anything of substance. Farsight may be lying, but so far I have to just take his critics at their words. They might be totally in the dark. Which is how it appears to me, because all I get is references to links and comments like ‘there are many ways things happen. But I won’t get into the mathematical details.’ Vaguer than vague.

Anyway, I was under the impression that it is the rotation of galaxies suggest a much greater mass that what is measured, that suggests dark matter. I always found this a bit of a stretch. I am open to the suggestion there is a more elegant solution.

I hope you note that Farsight is also vague on mathematical details. He is someone that, in his own words, refuses to develop mathematical details.

The reason that my answers may be a bit vague is because Farsight is literally so wrong that he is not really talking about physics. When you ask a question about what alternatives to his theories could be, one can only point to the work that actual physicists do because Farsight refuses to actually produce specific predictions of his theory. If one criticizes Farsight on a particular point, he dodges the questions by discussing something else or by claiming that he means something else. He can’t be pinned down because there is really no content to his theory.

I ask him about the rotation curves of galaxies because that is one specific prediction that he has made (perhaps the only one). He is saying that if one calculated the rotation curves of galaxies using general relativity, then there would be no need for the hypothesis of dark matter. Now he has never actually shown how to do this (and there are many papers that actually do this calculation and show that we still need to hypothesize dark matter). That Farsight refuses to support the one prediction he has ever made is a bad sign for his ability to produce a real physical theory.

The rotation curves of most galaxies suggests that the visible part of galaxies are surrounded by a much larger distribution of mass. So too does the way that light bends around galaxies. So too do the orbits of galaxies around each other. So too does the bending of light around groups of galaxies.

Looking at the way that galaxies form into clusters in general suggests that there is some sort of dark matter. So too does the behaviour of particles in the early universe.

These are all research projects with a lot of physicists and astronomers making careful observations and calculations. Almost all of these scientists use general relativity. Despite this, Farsight claims that if we used general relativity correctly, we would not have a need for dark matter. So Farsight is saying that all of these scientists are wrong, though he will not show anyone exactly how these scientists are wrong. Even on a message board with dozens of professional astronomers and astrophysicists, Farsight could not produce the relevant calculations.

Farsight does seem good at offering confident statements. Unfortunately, science is often not as confident as we would wish it to be. Additionally, Farsight never delivers on the evidence that his confidence suggests.

PhysBang = correct.

Farsights point is that Einsteins statement that space is not homogenous does away with the necessity of dark matter.

The argument for dark matter is curiously similar to the argument for God. There’s a phenomenon we can’t account for, so we posit an invisible entity to account for it. That entity is subsequently proven by measuring the phenomenon again, and concluding it is consistent with itself. I don’t see any proof anywhere except that we’re lacking knowledge about the relation between gravity and mass on a large scale. Given that on a very small scale, certain laws do no longer apply, shouldn’t the possibility for a similar discontinuity on the other end of the scale at least be considered?

Yes, but what does that mean?

Einstein believed that space on the large-scale average was homogeneous. We know that because he endorsed a cosmological model in which this was the case both before and after he made the claim that Farsight quotes. So what did Einstein mean when he said that space is not homogeneous? Well, he meant pretty much what he said afterwards, which is that in order to explain gravity, we have to look to the distribution of matter in spacetime and use this to determine the geometry of spacetime. (And this is what every relativistic cosmological model does and what every astronomer who measures dark matter using relativistic means does also.)

But what does Farsight mean when he says that inhomogeneous space will do away with the need for dark matter? Nobody knows. I suspect not even Farsight knows. If we could see an actual calculation of how to calculate a galaxy rotation curve “the Farsight way” then we would have an idea of what he means. But unlike every scientific paper on dark matter, Farsight refuses to actually demonstrate the relationship between measurements of gravitational phenomena and dark matter.

Physics is more than the ability to state things confidently. Physics involves the ability to make claims about physical systems that we can either use in application or that we can support with observations that include measurements. Farsight has never made such a claim.

There is a difference between the argument for dark matter and the argument for god: measurement evidence and the properties of dark matter. While god can have any properties, dark matter cannot. And we can measure the properties of dark matter in many, many ways. And people do consider the possibility that a change in the way gravity works might change the need for dark matter. So far, these other projects have failed.

Note that Farsight claims that he is not trying to change gravitational theory. He seems to be saying that if people calculated correctly, then there would be no need for dark matter or an alternative to standard gravitational theory. Yet he refuses to demonstrate how to calculate correctly.

I will let Farsight counter these challenges if he feels the need to - dark matter isn’t really the focus of this thread anyway - I think I’ll just order his book and form my judgment based on that.

Didn’t Einstein have had a position on Dark matter himself, by the way? And did he not propose this cosmological constant which now somehow comes back as dark energy, responsible for the expansion of the universe? I know it’s not the same, but the theory of dark matter existed when he was still alive, didn’t it?

If you are interested in physics, I would recommend that you start with more basic books on the subject.

The problem that there might be a matter that cannot be seen was considered since at least the 1930s, but there was no evidence for a need for dark matter until after Einstein’s death.

Don’t worry about me, PhysBang. Go chase Farsight, he must be somewhere spreading his false propaganda.

Or maybe you could point me to literature about this?

PB - I’m pretty annoyed here - you act as if you’ve actually said or explained something, where in fact you’ve only accused Farsight of lying, and made some statements about unnamed models and sources when I asked you to show that he is. Look at what you said.

Source?

Specification? Source?

Source?

Aha

It’s very obvious what he means.

Of course we can’t, because if space is not homogenous, we don’t have any math to work with.

That makes no sense at all, the relation between gravitational phenomena and dark matter is only the hypothesis that there is a relation.

Very confidently stated!

Very confidently stated! Never mind that you say nothing at all!

Jakob: I find it very sad that some people dismiss and deny what Einstein actually said. They won’t enter into a sincere discussion, they won’t furnish evidence to back up their assertions, they do not hesitate to attempt to discredit, and they have a sneering arrogance that treats the public with utter contempt. There’s an elitist aspect to all this, it’s been hampering scientific progress, and it’s got to stop.

Relativity, by Albert Einstein

One could see also, for example, scienceworld.wolfram.com/physics … Model.html
Or wikipedia: en.wikipedia.org/wiki/Static_universe

See above.

See everything ever written by Einstein after 1915, in which he actually explained the use of spacetime with very detailed mathematical physics.

Really? Could you use Farsight’s idea to calculate the rotation curve of a galaxy? Even Farsight can’t do this.

There are an infinite number of solutions to the Einstein Field equations that have an inhomogeneous distribution of matter and energy. Most applications of general relativity use an inhomogeneous distribution of matter and energy. These solutions use mathematics and they are what actually convinces physicists that general relativity is correct. Einstein did not succeed because he was good at prose.

Yes, but that hypothesis is backed up by specific predictions and by measurements. Farsight has nothing of the sort.

I am not the one telling you that everything in every physics textbook is wrong. Farsight is setting himself up as the saviour of physics. If you want to find out if he is correct, you should read some relevant physics texts. You will soon discover how wrong Farsight is and how I have been saying merely the obvious.

Better still, read what Einstein said. See viewtopic.php?f=4&t=171501 and follow the links. PhysBang dismisses Einstein.