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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..."
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?
Ahem; that's "Matter of Color", thank you very much.
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physics at that scale simply isn't the same as we know it "down here"?
All the descriptions I remember assume dark matter is weakly interacting including with itself and often modeled as a form of incompressible gas so I don't understand surprise in either TFA or article. Who were the people thinking otherwise and why?
Perhaps the gravity equations break down at large distances or low accelerations. If that is the case, putting spheroid clouds of invisible matter everywhere could get the equations to work, but in the end it will need to be equivalent to the new math.
I don't think the hidden/dark matter hypothesis is ruled out at all, it has gotten pretty far. It really does sound just like epicycles though.
If there is a vacuum in space, would their need to be a corresponding antivacuum?
The answer to what they're missing: Electric charge and currents.
The electric universe folks explain that galactic rotation rates do not require dark matter to make sense. The electric current through the galaxy adds forces on the charged stars and gasses that adds up to explain the observed motions. This article sheds more light on the problems with the dark matter theories. It's time to more strongly consider the possibility that dark matter isn't the answer.
--Jaborandy
Just partially kidding...
Paul B.
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
Apparently it had an abortion in the end.
Theorist with publications in dark matter here. This aspect of dark matter is not something new or a "mystery" but something that has been assumed for quite a long time. The alternative to this, "self interacting dark matter" is not entirely ruled out by observatins and explains some issues like the core-cusp problem but it's generally disfavored.
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.
yeah. that could work.
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.
Either you misread it or they changed it without noting the edit. I hope it's the former. the RSS feed also has "than", which lends a small bit of extra credence to that.
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"
You are right about that, even including all the trillions of stars the *average* density of the Milky Way is only 40 nucleons per cc (our best vacuum pumps do three hundred thousand molecules per cc!) That's a hella lot of mostly empty space
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.
I've fallen off your lawn, and I can't get up.
Matter and energy are convertible one into the other. Is what scientists call dark matter/dark energy the same as "zero point energy"? Zero point energy is what is left in a container that has been emptied of all matter and then cooled to absolute zero. This energy has been measured and verified to exist. It pervades all space, including the spaces between the particles of atoms. Zero point energy is what limits how much a signal can be amplified and is the reason why liquid helium cannot be made solid without great pressure. There are many other known effects.
A sufficiently advanced simulation is indistinguishable from reality.
Dark matter doesn't actually exist
My pomposity meter went off when you implied the paper was longer than 3 pages. Oh, there is a fourth page, but all it has on it is 6 references. Anyway, I couldn't continue reading your comment because of this. Please correct your egregiously misleading remark and repost your comment so that I can continue reading it.
That Dark Matter is a real thing and not just a "theory"? Do we have any proof yet? I know there is a lot of intel coming in on it, but it is hard to keep up with and/or follow.
If you could reason with religious people, there would be no religious people
I think it doesn't interact with itself because it DOESN'T EXIST. It's a math error based on the arrogance that we can estimate all the mass in the entire universe.
Dark Matter seems to me to be a placeholder item for differences between the calculated trajectories and real.
It do adjust for the effects observed but it does not explain what it really is.
If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
I parsed the summary like this:
1. The gravity of dark matter affects luminous matter (we knew this.)
2. The gravity of dark matter doesn't affect other dark matter (...wtf?)
That would have been... interesting.
But I made the mistake of clicking the article and it looks like they're just talking about kinetic interactions (no observed slowdown due to "friction" between separately moving clouds.) I guess it's news, but given that we're already pretty sure it doesn't interact with baryonic matter (except through gravity) I'm not really shocked that it doesn't interact with itself either.
The energy density in the universe from light is much less than the energy density from baryonic matter, which is in itself much less than the total matter energy density of the universe (which is why we infer the existence of non-baryonic, or "dark", matter).
I was wondering if dark matter could be matter in a 4 (or more)-dimensional space, so instead of coordinates x,y,z it is w,x,y,z. Ordinary matter is at w=0, while dark matter has some distance to ordinary matter in this 4th dimension. Adding a 4th dimension to gravity formulas is straightforward. We would feel the gravity of such matter on distances comparable to the w value of this matter.
If the dark matter's w value would become similar to ours it would suddenly appear in our 3-dimensional space. Since we never observed it the w value might be fixed. For example this could be galaxies in parallel universes. They would feel each others gravity and drag each other along with ech other, but otherwise they are invisible to each other.
At the risk of feeding a troll.. what the hell are you talking about?
Set theory indicates that the integers are infinite so therefore discovering new things in the universe that aren't covered by our known science is somehow nullified by edge cases in propositional logic?
You're not even discussing the same disciplines never mind making any sort of meaningful connection between your statements.
This leads to models of these theories essentially asserting that there are countable numbers which are greater than the number of particles in the observable universe.
So what? There are also countable numbers which are greater than the number of coffee mugs currently on my desk. What of it? I'm assuming you just don't understand what "countable" means in a mathematical sense.
There must be a practical physical limit on counting
Why? I mean if you started at one today and counted until you died, there would be a "practical physical limit" on how high you get based on your speed and lifespan. But what does that have to do with anything? I could perform the same "experiment" and reach a different number. Again, I'm assuming you don't know what "countable" actually means.
The problem with the foundations of mathematics as they are is that they are incompatible with physical plausibility
I.. don't even know where to start. What does "physical plausibility" even mean? The universe can do whatever the hell it wants. Its up to us to make our math fit the universe, not the other way around. If the math doesn't work we try to invent different math that does work. The universe continues not giving a shit and does whatever it wants as always.
Just for reference, not that I necessarily trust you'll understand it, but "countable" in a mathematical sense means "can be mapped to the set of natural numbers (aka positive integers.)" It says nothing about an upper limit to the size of the set and the mapping doesn't have to be in any way obvious. The full set of integers for example can be mapped as {0:1},{1:2},{-1:3},{2:4},{-2:5},... where the first value is one of the integer and the second is its mapping on to the natural numbers. Turns out the rational numbers (fractions) can be mapped with a bit of cleverness as well. The real numbers however cannot be, and therefore are uncountable.
But in no way does "countable" mean "do I have enough fingers/beans/particles in the universe." Those values are countable to be sure, but there are many countable sets that are far larger than those values, including infinitely countable sets such as the natural numbers themselves. You can start at one and keep incrementing by one at any speed you want and go until long past the heat death of the universe and still never find a point where you can say "I've done it! There is no next number!" But even with all of that, you still were just counting from one the same way you were taught in elementary school.
Of course there's no way to actually write a number that has more zeroes than there are particles in the universe but we've come up with notations to describe such numbers nonetheless. Consider the fact that you can't fully write out the decimal expansion of 1/3 either even if you used all of the particles in the universe for 3's and so we have to use the notation 1/3 to be accurate.
We just accept that because 1/3 is a number that has meaning at the human scale while 10^^^^75 is so far beyond our comprehension that its hard to imagine what it describes. But not being able to imagine it doesn't mean its not legitimate. It just means you aren't good enough at imagining things.
I expect physicist to have thousands of hypotheses about dark matter.
Until you can design an experiment to distinguish between those that are bollocks and those that are true, you're not going to make any progress. That's the hard part - designing and performing such experiments. This is why beautiful and simple demonstrations like the double-slit experiments are considered the most artistic and wonderful pieces of science.
The problem with dark matter is that we have so little information about the phenomenon that all hypotheses fit and few can be eliminated.
"It could mean our theories of gravitation are wrong" versus "there's something exerting gravity that we can't see any other way yet with our current instruments".
I know which head I'd put the fucking insulting "propeller beanie" on. Questioning is one thing, ridicule another.
Looks like you don't just despise climate scientists but all of them. What broken corner of society is turning out people spreading the drivel like this idiot's posting history? We need to prop it up with more jobs, better education funding or something to avoid drowning under a wave of destructive idiots.
What if, like in OpenGL when you set the near and far clipping planes too far apart, you begin to lose precision on calculations at distances farthest away from the camera. The same thing happens at a certain point when you examine something near the camera too closely; you observe the limit of the floats describing the modelview matrix. This assumes of course that the universe is a simulation and that, being a part of the simulation, we "can't see the forest for all the trees". It might explain the discrepancy between the behavior of matter and energy at quantum scales versus galactic scales and why "normal" (as in Newtonian) physics seems to work perfectly at human scales.
Second, what if there are multiple dimensions affecting space/time/matter/energy/etc. and we and our observations are generally constrained to but a few. If dimensions were like pages in a book, sometimes the words on the next page faintly bleed into the one you're reading if the paper's thin. Perhaps these unexplained phenomena are the result of one or more other dimensions faintly bleeding over into the one we can reliably observe. Dark matter and dark energy could be the shadows of something larger that by our nature we're blind to. To further the craziness, singularities could be gateways that when in sufficient number make the effects observable at galactic scales.
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The lack of evidence for dark matter is becoming kind of embarrassing to the theory. Anything that should provide direct evidence doesn't - dark matter is seemingly only necessary to explain large-scale gravitational behavior, but is not otherwise in evidence.
For me, as a layman, dark matter was never persuasive: "there's this stuff that only has an effect way out there where we need it, but has no local effect where it would screw up our nice models". Sure there is. There are other theories that seem to be at least as reasonable. For example, what if the speed of light is not a constant across all time and space? This could dramatically change the behavior of the universe on large scales. I'm no cosmologist, but I understand that there are other theories as well.
Enjoy life! This is not a dress rehearsal.
They are both "Dark" because they do not exist. This article is a perfect case example of how Dark Matter would have to be distributed in a manor that generally ignores gravity itself. If it ignores the influence of gravity then how is it that its properties are defined by its influence on other objects through gravitational attraction? Do they really think that it can pull on things but ignore its own pull towards that non-dark matter?