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Dark Matter Grows Hair Around Stars and Planets (forbes.com)
StartsWithABang writes: Dark matter may make up 27% of the Universe's energy density, compared to just 5% of normal (atomic) matter, but in our Solar System, it's notoriously sparse. In particular, there's just a nanogram's worth per cubic kilometer, which makes the fact that we've never directly detected it seem inevitable. But recent work has demonstrated that Earth and all the planets leave a "wake" of dark matter where the density is enhanced by a billion times or more. Time to go put those dark matter detectors where they belong: in the path of these dark matter hairs.
Ockham's razor: The facts suggest that gravitational force without visible source is being exerted.
Since the only known source of gravity we know is matter, we assume that gravitational source comes from some invisible matter, but we don't currently have any solid proofs for this specific assertion (although neither do we have any to the contrary, nor alternate viable theories).
It may yet appear that it does not. It may be some form of existence different than matter or energy; some wrinkles of spacetime or some sourceless gravity clusters. Since we don't know anything like that, "dark matter" is a convenient shorthand to describe that effect.
It's a bit like both with Rutheford's atom model and with Planck's quantization of spectrum.
The first - assuming that atom structure is a kind of "dough" with electrons being "raisins" fit the knowledge of that time explaining the "solid" nature of solids. It was blatantly wrong, proven by later experiments that found tiny nuclei in huge empty space. It was still a convenient shorthand for a time, to describe several observed phenomena and fit some observations - and for lack of better alternatives, it was accepted until disproven.
The latter sounded so incredible at first, that it was used strictly as a *hack* to obtain results that fit the experimental data, with belief that the underlying mechanism is vastly different, but undiscovered as of yet - so the "hack" was again a shorthand used to explain given phenomena, out of convenience, because again, we didn't know any better way to explain the behavior of photon emissions, or the stability of atom - even though practically nobody believed it to be true, just a conveniently close approximation. And then, surprise-surprise, more and more experiments confirmed - that "hack" was actually how the reality worked, that was not a mistake but a very unlikely - though ultimately true - description of the nature of atom.
Whether Dark Matter is another Rutheford's Atom, or another Planck's Quantum distribution, is to be determined and it will either be confirmed or invalidated. Currently, as a shorthand explaining the observed phenomena, it's doing pretty well.
Remember, when the facts don't match your theory
Correct. The facts don't match the theory. Galaxies could not hang together the way they do if all they consist of is the things we've already observed in the laboratory unless we change the law of gravity [to something enormously more complex - c.f. epicycles] or postulate the existence of something that interacts gravitationally but doesn't interact with light.
too bad for the facts
I don't get this. Nobody is ignoring the facts. That's why we need to change things. Dark matter is the heliocentric solution. No dark matter is the epicyclic solution.
The [difference between facts and] theory is easily explained
Don't know about easily. There's been a lot of "dark matter" theories that have fallen due to one or more inconsistencies with known physics.
by an abundant (making up 96% of the universe),
Necessary otherwise we have to change the theory of gravity
invisible,
If by invisible you mean doesn't interact with EM radiation then yes, this is required by the facts.
undetectable
It's not undetectable. If it were undetectable then we wouldn't need it. It's very detectable - its gravity is what makes galaxies hang together. Its gravity is what allows gravitational lensing to happen where there isn't any (visible) matter to make it happen.
magic
Definitely not magic. It has to agree with all the laws of physics. Conservation of momemtum, conservation of energy, speed of light etc.
"dark matter"
it's called dark matter because it doesn't interact with the EM spectrum. It neither emits EM radiation nor absorbs it.
that is everywhere and affects everything.
Actually, I think this is one of the great unknowns. Whether it's large numbers of light particles or smaller numbers of massive particles. Its primary interaction with the known universe is through gravity which yes, does affect everything, everywhere, at the speed of light.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
Dark matter isn't a case of "fact vs. theory", but "fact vs. fact". We have multiple methods of determining the mass of galaxies and galaxy clusters. One method - counting all the light-emitting stuff - gives a certain number, and all other methods (rotation curves, gas kinematics, gravitational lensing, large-scale structure analysis, and more) give a much higher number. Two possible conclusions: 1) Our understanding of gravity is wrong, or 2) There is a new component of the universe that does not interact with light. Option 1) fails a lot of tests: if you try to make solutions for gravity for certain systems, it doesn't work for others. Option 2) has a solution called "dark matter", a new weakly-interacting massive particle that explains almost all the observations (it's not 100% perfect, but it does much better than the changing-gravity option).
At the same time that all this was happening in cosmology, our particle physics friends were developing extensions to the Standard Model. In many theories they predicted new kinds of particle: ones that just happened to have a lot of the right kind of properties that the cosmologists needed for dark matter. Voila.
Dark matter is the simplest, most parsimonious, most elegant known solution that fits the observational data.
Source: I'm an astrophysicist and I do a podcast, and one of my first episodes was on exactly this.
You have that backwards. They're modifying theory to match the facts. They've tried to ignore darkmatter for nearly 100 years, but they can't get rid of it. The more information we get, the more real it becomes. It has reached a point in science where the numbers are slapping us in the face, saying, "STOP IGNORING ME!"
>> why is it that such arrogant fucktards always end up on /,
I for one welcome our SlashComma overlords.