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Dark Matter Is Even More of a Mystery Than Expected
schwit1 writes: Using the Hubble and Chandra space telescopes astronomers have discovered that dark matter is not only invisible to direct observation, it is invisible to itself! Quoting: "As two galactic clusters collide, the stars, gas and dark matter interact in different ways. The clouds of gas suffer drag, slow down and often stop, whereas the stars zip past one another, unless they collide — which is rare. On studying what happens to dark matter during these collisions, the researchers realized that, like stars, the colliding clouds of dark matter have little effect on one another. Thought to be spread evenly throughout each cluster, it seems logical to assume that the clouds of dark matter would have a strong interaction — much like the colliding clouds of gas as the colliding dark matter particles should come into very close proximity. But rather than creating drag, the dark matter clouds slide through one another seamlessly." The data here is on the very edge of reality, built on too many assumptions. We know that something undetected as yet is influencing the motions of galaxies, but what exactly it is remains completely unknown. These results only make the mystery more mysterious.
Isn't this what one would expect if dark matter is WIMPs?
"99 dead duelists of Dios on the wall. 99 dead duelists of Dios! Take one's ring, pass it around..."
Ahem; that's "Matter of Color", thank you very much.
Left MS Windows for Linux Mint and never looked back!
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If there is a vacuum in space, would their need to be a corresponding antivacuum?
No. Because of Heisenberg's uncertainty principle, there can never be a complete vacuum. Even if there was, you couldn't measure it without destroying it.
isn't there a good chance that the dark matter theory is incorrect, and was created to account for an error in certain physics equations? Mb dark matter is so invisible because it doesn't actually exist?
It really bothers me to see quotes like this one: "There is more dark matter in the Universe than visible matter, but it is extremely elusive."
That's so matter of fact, and leaves no room for the possibility that the theory of dark matter is wrong. I feel that the certainty level around our understanding of this topic is low enough that it isn't fair to competing theories to say things like that as if they are observed fact. In fact, we've never detected dark matter. We infer its existence from a number of things that don't add up gravitationally without it, indicating we're missing something. Dark matter that interacts gravitationally allows us to model a universe that adds up, if only this invisible stuff were distributed just so.
This article shows yet another data point indicating that dark matter may not exist, because of how it continues to not react with stuff, just as it would if it weren't there at all. I don't mean to say that it's 100% wrong, but I think it's unfair to say with 100% certainty that it's true either. Shouldn't we as scientists be more careful with our words, and say that dark matter is BELIEVED to make up more of the universe than does visible matter, based on our current leading theories? I think being careful with what we know and how well we know it is important to maintaining trust with the public and with each-other.
--Jaborandy
We're trying to explain inflation and the motions of stars orbiting galaxies not matching our naive model.... couldn't a non-linear gravity model explain all this without the dark energy/matter hocus pocus?
Sure, but that would involve even greater hocus pocus than the current theory and fails at explaining other observations. So far, trying to come up with any hypothetical explanation involving MOND has been so complex that nobody has been able to come up with one that explains even the rotation of galaxies. If you or any other person could come up with a good law of nonlinear gravity that works, even if it completely fails at any of the other observations, there's a paper in a prestigious journal and some physics cred for you.
Thank you for the link, AC.
I saw two errors so egregious in the first three pages that I can dismiss that paper immediately. First the authors claimed that stellar gasses need to be sufficiently ionized that magnetic field lines could be frozen in them. This represents a fundamental misunderstanding of electromagnetism. These people could not possibly give fair treatment to an electromagnetic theory with such a basic misunderstanding. Second, they claim that obviously stars are not affected by the magnetic fields, and therefore they can falsify the opposing claim by demonstrating that gasses and stars move together. The plasma universe theories require a corresponding adjustment to our understanding of the stars themselves as strong electrically charged objects themselves, but more importantly the modeling of the flow of current is the key to understanding the electromagnetic forces acting on the gasses and stars.
Those folks took down a straw man.
--Jaborandy
Here some someone with a propeller beanie on his head will tell me that dark matter must exist because "math"... which is fine only "math" is not actually evidence of something being there absent emperical evaluation because even if the numbers add up a certain way so do orbital epicycles.... and they were bullshit.
A pitfall of the "math" argument is that if you have some very clever people come up with some very clever theories they can confuse Tolken-like world building with "reality".
The justification for dark matter is unexplained gravity. And the gravity is something we know exists because we are seeing the speed at which galaxies spin around and there shouldn't be enough mass to explain that speed. And that extra mass because we can't find it is called "dark matter"...
Well, that's great... only that doesn't mean dark matter exists. It could mean our theories of gravitation are wrong or any number of other things.
same thing with "Dark energy"... which in so far as I've figured out only exists because galaxies are accelerating away from each other and we have no idea what could cause every galaxy to propel itself at speeds like that except some other unexplained energy and that's what is dark energy.
In both cases it just sounds like they don't have enough observational data to really have a valid cosmological model. And I would much rather them make that admission then talk to me about "dark" whatever.
I've decided to stop wasting my time responding to AC trolls/sockpuppets... so if you want a response from me... login.
If there is a vacuum in space, would their need to be a corresponding antivacuum?
There is an antivacuum in the universe . . . more specifically, in my apartment.
At least that is what my cleaning girl claims . . . when she tries to vacuum here . . .
An antivacuum is usually called 'gas'.
I should use this sig to advertise my book ISBN-13 : 978-1501515132.
What I find more interesting is why stars rarely collide?
Too much empty space.
Thought to be spread evenly throughout each cluster, it seems logical to assume that the clouds of dark matter would have a strong interaction
It would actually be completely illogical to assume that precisely BECAUSE Dark Matter is spread evenly through each cluster. If it had a strong self interaction then, just like matter, it would bump into itself and coalesce into clumps just like that other strongly, self interacting stuff we call matter. The fact that Dark Matter has a completely different mass distribution than ordinary matter is clear evidence that it does not have a large self interaction cross-section...and we have had direct evidence of this since the Bullet Cluster was discovered.
It's always nice to have more confirmation but since another recent story on the same site was talking about the "new" possibility of invisible Higgs decays to Dark Matter particles (something we looked for 15+ years ago at the Tevatron as well as the previous Run 1 of the LHC) I have to wonder if the writers of the site have suffered extreme time dilation for the past decade or two.
It is because space is BIG. Look at our galaxy, our closest neighbor is what 4.6 lightyears away. Even if you double the amount of stars in the same space, they will interact gravitationally sure, but colliding is like dumping 1000 toothpicks in random places in the oceans and having them collide.
Silence is a state of mime.
This.
Consider that for two stars to hit each other, they essentially have to pass within one stellar diameter of each other (absent gravity, but they're moving at over escape speed relative to each other, so gravity won't enlarge that distance a whole hell of a lot).
So, one stellar diameter is ~1.4 Gm for Sol. Nearest star is 40,000,000 Gm away. If that nearest star were headed toward us (it's not), it's course would have to be within 0.01 seconds of arc of our Sun in order to actually hit it.
And stars farther away have an even smaller course window to be in to smack us....
"I do not agree with what you say, but I will defend to the death your right to say it"
Dateline: Millions of light years (even faster parsecs than the Kessel run)
Lede: Scientists in the Dark; Does it Matter?
Today scientists announced that they can't see anything happening with stuff they can't see, but think is there, because otherwise the math is no good. After receiving directions to his laboratory on the phone, I went to see an authority on dark matter. During the interview, Dr. Seemore Lichspittle told this Any Paper, Any Time reporter that the thing about dark matter that one has to understand is that "it goes to eleven." When confronted with the observation that the sensing instruments only had scales from 0-10, he responded "Yes, yes, that's exactly it. The numbers... the numbers only work out in the dark. When the instruments are off. Matter of fact, it's all dark, really." At that point the interview was cut short as two lab assistants in white coats hustled Dr. Lichspittle into his own custom white lab jacket. Late for an important meeting, no doubt. As he left, nodding, he called back "it's really quite dark." Food for thought! Leaving Arkham, I was struck by the picturesque beauty of the stonework, and very appreciative of the tight security. We can rest easy, knowing that national treasures like Dr. Lichspittle work in such a safe enviroment.
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We know about Dark Energy because objects are moving away from us faster than light. Since it is impossible for something to move through space faster than c, then more space must be getting created. If space is being created, and objects are receding away from us at a known rate, then we can calculate the amount of energy required.
A change to gravity does not work because we have already measured the gravity at these ranges to be within 99.9% of the expected values. Advancements in optics and sensors has allowed us to measure minute changes in red shifts and detect curved paths that light takes. Mix all of this together and you can measure gravity quite accurately. It's working as expected. Even worse, we're able to see the gravity but unable to see the matter causing it.
There have been several theories built on that assumption, most prominently one called MOND (MOdified Newtonian Dynamics), but more recently one that builds on relativity rather than Newtonian gravity/dynamics.
But none of these theories (hypotheses?) have gained much acceptance from the physics community, as far as I know.