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A pair of researchers from the University of Nevada, Reno, in an attempt to detect and better define dark matter, have pulled off a pretty amazing science experiment. The team used 16 years worth of GPS data to turn the whole planet into a massive detector that might detect clumps of dark matter that could extend beyond the solar system.
Dark matter makes up roughly 85% of all matter in the universe, which is a real bummer for us humans — as we simply have no idea what it is, what it looks like, nothing. Astrophysics has provided multiple evidence that it actually exists, but so far, it’s always been beyond our grasp. As generally tends to happen when faced with great unknowns, we do however have quite a lot of hypotheses pertaining to its nature.
"So, the two gathered data from the 32 satellites that make up the 31,000-mile-wide GPS constellation and ground-based GPS stations, retrieving figures recorded every 30 seconds for the last 16 years. Data was retrieved from sources around the world, and in particular from NASA’s Jet Propulsion Laboratory. They then used a model to sift through this data, looking for irregularities in atomic clock signals.
[...] Aaaaaaand they didn’t find anything. It’s a bit disappointing, sure, but it’s not really surprising given how elusive dark matter has proven itself to be up to now. It has to be said, however, that while the team didn’t find any definitive proof to support their theory, it could be that the effect is simply more subtle than anything we can pick up, or that the Earth crosses lumps of dark matter very rarely."
https://www.zmescience.com/science/earth-dark-matter-sensor-gps/
(Score: 4, Interesting) by Gaaark on Sunday November 05 2017, @01:07AM (15 children)
Explain this, then, a simple question:
1. Dark matter is affected by gravity.
2. Dark matter is needed at the outer edges of a galaxy in order to keep it from flying apart, but NOT needed at the central part of the galaxy at all, where it's existence would throw off the results given by general relativity even further.
3. The greater gravity at the center of the galaxy would draw the dark matter from the outer edges into the center of the galaxy.
Question: would this not make the galaxy spin faster, thus making the outer edges want to fly apart even more?
Dark matter is simply a kludge to make the data fit General Relativity.
Just putting up links does NOT make it true: I would love to have a real conversation instead of [link...see it's true].
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 0) by Anonymous Coward on Sunday November 05 2017, @01:13AM
I agree. The dark matter concept makes it seem like they are shaving hamsters until someone figures out what assumption is wrong. The only evidence for it is that their models predict the wrong thing. Then you get the ridiculously pompous claims that "GR is the best tested theory in the world".
(Score: 2) by takyon on Sunday November 05 2017, @01:18AM (3 children)
Sounds like a false premise:
https://www.space.com/25359-dark-matter-milky-way-galaxy-fermi-discovery.html [space.com]
https://en.wikipedia.org/wiki/Dark_matter_halo [wikipedia.org]
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by FatPhil on Sunday November 05 2017, @01:48AM
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 5, Interesting) by Gaaark on Sunday November 05 2017, @02:44AM
Playing the linky game:
1. https://arxiv.org/abs/astro-ph/0601581 [arxiv.org]
"To make dark matter fit general relativity to the oberved galaxy rotations you have to assume that it stays spread out in a halo around the galaxy, and therefore does not have structure on small scales. Scarpa et al. looked at globular clusters which are small areas within the Milky Way, where the stars are arranged slightly more densely than in surrounding areas. They found that the globular clusters behaved like little galaxies: whenever their internal accelerations dropped below a critical acceleration, a0, their dynamics became non-Newtonian. Their crucial point was that you can't use dark matter to explain the anomalous dynamics of tiny globular clusters since to fit it to galaxies you've already specified it must spread out: you can't have it both ways." http://physicsfromtheedge.blogspot.ca/2013/04/data-points-way-globular-clusters.html [blogspot.ca]
2. https://arxiv.org/abs/astro-ph/0204521 [arxiv.org]
"Dark matter usually only needs to be added to the edges of galaxies since in their centres they behave normally. Sanders and McGaugh (2002) pointed out that the radius at which galaxies start to spin too fast for their own good, and to need dark matter, is not a set distance, but it always occurs where the rotational acceleration drops below 1.2*10^-10 m/s^2: a very low acceleration called 'a0': a regime not previous encountered by our experiments. This is difficult to explain by dark matter - you'd have to invent a kind of matter that suddenly appears when accelerations are below this value."
https://arxiv.org/abs/astro-ph/0601581 [arxiv.org]
"Since dark matter is needed only at the galactic edge, its supporters need to have some new physics that keeps it smooth and diffuse. Brilliantly poking a hole in that, Scarpa et al. (2006) looked at globular clusters which are small dense congregations of stars within the galaxy, a bit like clumps of mistletoe in an oak tree. They found that whenever the 'internal' acceleration of these clusters drops below 1.2*10^-10 m/s^2 (a0 again) they spin far too fast to be stable, just like the full-sized galaxies, but in these globular clusters this anomaly cannot be explained by dark matter, since to work for galaxies dark matter must be smooth on these smaller scales."
3. https://phys.org/news/2015-03-galaxy-clusters-collidedark-mystery.html [phys.org]
"Harvey et al. have looked at the light from familiar objects like galaxies as seen from behind galaxy clusters, and looked at the distortion in the images due to gravitational lensing. They know what a typical galaxy looks like: a disc, so if it looks like a U-bend instead when it's behind the galaxy cluster, then they can infer the bending of the light that must be occurring and assume this bending is due to dark (invisible) matter in the cluster. They looked at 72 galaxy cluster collisions, and have modeled the collisions using several kinds of dark matter, and have shown that the only kind of dark matter that fits the observations, is a kind that doesn't interact with itself. I'd like to point out here that this makes the dark matter hypothesis self-contradictory since the dark matter particles have to be given a lot of kinetic energy (momentum) so that inertial/centrifugal forces keep them spread out in their usual orbital halo, but if you now imagine that two clouds of dark matter hit each other there should be a 'push' as the particles collide. This study proves there isn't any such push, so the simplest solution is that there is no dark matter. "
--- Karl Popper made a statements that should by engraved above the entrance to every proud physics department:
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by maxwell demon on Sunday November 05 2017, @07:19AM
Your spoiler apparently is made of dark matter.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2, Troll) by FatPhil on Sunday November 05 2017, @01:46AM (9 children)
Apparently dark matter:
a) is only affected by gravity, yet doesn't form any of the shapes you expect from gravity. It requires *haloes*, for pity's sake.
b) doesn't interact with electromagnetic fields (thus "dark"), but bends *light* with its gravity.
Scientists doing some good khutszpah...
Nima needs to eat his hat (he promised, he never delivered)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 3, Insightful) by maxwell demon on Sunday November 05 2017, @07:16AM (8 children)
A halo is spherical. You really want to tell me that spherical is not one of the shapes you expect from gravity?
Do you know why planets and stars are spherical?
Yes, that's basic General Relativity. Gravity is spacetime curvature, and the light just goes along a straight line (a geodesic) in the curved spacetime.
Also, I would actually have been surprised if the experiment had found lumps of dark matter. Due to their lack of interaction, it effectively forms an ideal gas. Imagine a box of air. You wouldn't expect to find lumps of air in that either; you'd expect the air to be equally distributed (except that it is a bit denser closer to the center of gravity).
That doesn't mean it was wrong to do that experiment, but the surprise would have been if they had found something.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by FatPhil on Sunday November 05 2017, @10:55AM (7 children)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 3, Informative) by maxwell demon on Sunday November 05 2017, @01:21PM (6 children)
Wikipedia disagrees. [wikipedia.org] Emphasis by me:
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by HiThere on Sunday November 05 2017, @05:36PM (3 children)
Wikipedia is a lousy source for this kind of argument. Pick an astronomy site.
That said, I believe that a galactic halo is a thick, roughly spherical shell. Not a sphere, the inside has been generally eaten away by a black hole. OTOH, I don't have a link for this, and maybe the central black hole is normally counted as a part of the halo, but I wouldn't take Wikipedia's word that this was true. Also, it's not really spherical, even as a shell, because it's rotating (to varying degrees) which squashes it into an approximate ellipsoid of rotation. (Even that isn't quite right, but in the first place it's not a simple solid with a name, and in the second place when you start getting detailed, different galaxies are different, sometimes considerably.)
However, as an argument about dark matter, I have no opinion. I find I really dislike the theory, but it is the only one I know of that fits most of the evidence without LOTS of custom adjustment. Come up with something better. (MOND doesn't appear to be that "something better" as it is reported to need lots of custom adjustment.)
This is sort of why I don't like string theory. It can predict nearly anything when you tune all the adjustable factors that can't be determined from theory. If string theory is correct, then I have to side with either the parallel or sequential multiverse (i.e., either every choice that can be made is made at the same time, or the universe oscillates through cycles of expansion and compression, with lots of arbitrary "constants" give random values with each big bang.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 3, Interesting) by Gaaark on Sunday November 05 2017, @06:02PM (2 children)
An interesting read here:
http://physicsfromtheedge.blogspot.ca/ [blogspot.ca]
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by HiThere on Sunday November 05 2017, @07:33PM (1 child)
I am very tempted by the arguments presented, particularly since I don't believe in continuity, though I tend to think the scale on which the universe should be discontinuous should be around 10^-33cm. I have trouble, however, with distances seeming to be independent of orientation.
OTOH, I don't feel myself competent to really accept or deny any cosmological argument. I know there's lots of evidence I don't know. What I feel competent to do is *try* to understand what is generally agreed. I don't always agree with it, but I acknowledge that my disagreeing isn't a valid sign that it isn't correct.
So while I'm tempted by the arguments, it seems the scale at which is being proposed for discontinuity isn't what I expect, and in any case I don't feel qualified to judge. Also I didn't see any peer reviewed papers on Renzo's rule. If I had I couldn't have evaluated them, but their absence is, in and of itself, a point against it (to someone who can't independently evaluate it against the evidence).
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 3, Interesting) by Gaaark on Sunday November 05 2017, @08:10PM
I'm kinda the same: I'm willing to look at alternatives.
I believe there has to be something wrong with his theories where time travel is possible; the whole travel back in time and kill your grandfather so you could never be born so you could never go back in time and kill your grandfather, so you WERE born so you COULD go back in time so....
You read about physicists saying "something" would stop you from killing him: the gun would magically jam, or the knife would magically 'jam': shite like that.
I'd rather believe Einstein, or an interpretation, is wrong in some way. That is why I like the people looking at alternatives, the likes such as Julian Barbour:
https://en.m.wikipedia.org/wiki/Julian_Barbour [wikipedia.org]
He is working from a Machian point of view where time and space are separate (which is what Einstein originally believed, but found the math would be an agonizing beyotch and went with time and space being inseparable instead).
Time travel goes away when you separate time and space (or, like Mr. Barbour, believe time exists only as a product of movement in space (the sun moves, creating the illusion of time, etc etc).
I don't like kludges, and to me, dark matter is a kludge to make General Relativity work. I'd rather say "something is not right with GR: let's find out what is wrong.
Analogy: your car is leaking oil.
Dark matter theory: it's leaking oil because magic.
Better theory: something is wrong....hmmm...oh! Your plug is loose! Let's tighten it!
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by cubancigar11 on Sunday November 05 2017, @05:37PM
Maxwell solving difficult physics problems, even as a demon! Thank the lord for rejecting his application to heaven.
(Score: 2) by FatPhil on Monday November 06 2017, @10:49AM
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves