Dark Matter Filament Finally Found 190
An anonymous reader writes "Everyone is talking about the recent Higgs boson announcement by the scientists at CERN, but another significant scientific discovery was revealed this week as well. In a study published online in the journal Nature on Wednesday, scientists show that they have successfully found the first dark matter filament."
Here's a better article... (Score:5, Informative)
http://www.space.com/16412-dark-matter-filament-galaxy-clusters.html [space.com]
Re:Here's a better article... (Score:5, Informative)
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Not so strange. Space.com is one of many more or less hermetically sealed news sites.
Not to mention the context ads that I got served with this article:
What Happens When You Die [RobertLanzaBiocentrism.com]
New theory says death isn't the end
How to be a true disciple [www.brunstad.org]
Think that you can partake of God's own nature - mercy, love, goodness.
UFOs in the Bible [www.rael.org]
Crop Circles, UFOs, Religions Get Answers! Free eBook Download.
I mean...what? Seriously? These are context ads for a scientific article?
Re:Here's a better article... (Score:4, Interesting)
Looking at "six sigma" is stupid. If you are talking about the management fad, it assumes the data follows a normal distribution. Generally, frequentist statistics is misleading. It's not wrong, but it is very commonly used improperly. For example, if you hear that a null hypothesis that the mean of a distribution is less than zero, H0:mu H0 is true, and that the data follow the assumed distribution, 99% of the sample means you get would be less than 0.
This article actually uses Bayesian statistics (samples the posterior PDF using MCMC), rather than frequentist.
Futurama fans already know... (Score:5, Funny)
Re:Futurama fans already know... (Score:5, Insightful)
Yeah this post didn't deserve a downmod. It was an applicable use of pop-culture humor.
Re:Futurama fans already know... (Score:5, Funny)
Did you mean "poop"-culture?
Re:Futurama fans already know... (Score:5, Funny)
Did you mean "poop"-culture?
What a shitty post.
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It should also be very heavy, and warm.
so .. (Score:2)
Re:so .. (Score:4, Funny)
so .. what colour are they ?
African American.
Re:so .. (Score:5, Funny)
"African American."
Umm... I'm not so sure such "dark" humor is quite appropriate.
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Re:so .. (Score:4)
Transparent.
Up next (Score:3)
The dark lightbulb. The darkbulb?
Re:Up next (Score:5, Funny)
Dark suckers. [msu.edu]
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Heh, that was fairly good. Never heard that one before.
You can tell from the background and hand crafted HTML that the page was written in the 90s, when there are a much higher signal to noise ratio on the Internet.
well that article sucks (Score:5, Informative)
Re:well that article sucks - but read this (Score:5, Informative)
There are 2 galaxies kinda far apart but they're really overlapped from Earth's point of view. Like one is almost entirely behind the other. So the back galaxy's light passes along where the filament would be estimated to be between the galaxies. So the light travels through the dark matter's gravitational field for a really long time, running practically parallel to the filament. Even after that much light gravity tugging, it's barely perceptable by our current telescopes. So someone had some pics of this set of galaxies from 2001 but never did anything with them because they didn't realize the opportunity. This new team noticed it, compared it to background light to detect additional possible lensing, and discovered unmistakeable slight lensing. So something is obviously there and it has to be a particular shape, density, and reflect no light.
Re:well that article sucks (Score:5, Informative)
Yeah because 'real' scientists would have hopped in their VW wagon and drove out to the galaxy to test and take measurements and be 100% sure....
The thing is bazillions of kilometers away, all they have to work with is mathemtical models to provide/disprove theories.
Re:well that article sucks (Score:4, Funny)
Volkwagon? VOLKSWAGON?! REAL scientists use police telephone boxes to travel intergalactic distances! Everyone knows that! Only wizards and mad scientists fly by car.
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Only wizards and mad scientists fly by car.
Except for repo men [imdb.com] who fly Chevy Malibus.
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Now, that anomaly can happen for any reason but it's just easier to assume that it's some kind of matter that we cannot see yet. What I'm thinking is that now that we know the Higgs boson exists we could try and see if it interacts with da
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Neurons? Sentient galaxies?
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So that would makes the filaments synapses, and signal propagation is going to take about 2 million years between neurons (based on our neighborhood, maybe less or more elsewhere in the structure and assuming a speed limit of c).
In 14 billion years the sentient universe won't have got far past "Now, what will I have for breakfast?"
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If you accept the premise that the universe is fractal and self-similar on different levels, and the premise that at least some human beings are sentient, then the logic is inescapable: She is sentient.
Of course it is easier to get your religion out of a book written by some dead guys back in the days before science, arithmetic that used zero as a placeholder, or most of today's technology. When you bind a God between the pages of an ancient story book, then you do not have to worry about how to interact
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Put down the bong.
Re:well that article sucks (Score:4, Insightful)
"Well, on the "prove/disprove" front, all this has done is fail to disprove the existence of dark matter. There's a difference between that and actually proving its existence."
Science doesn't prove things exist or don't exist. The only thing science does is collect objective observations and come up with math that predicts what future observations will be given a set of conditions. Someone also makes up an interesting story to goes along with the math but aside from being consistent with the math the story (hypothesis/theory) doesn't really matter that much. Unlike the story, future observations can't break the math (although they can supercede it). Just ask Mr. Newton.
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Very well put.
Science is nothing more than making models of what may or may not be, and determining which of those models is closer to reality than the others. It has nothing at all to do with reality itself: that is way too complex for the human mind to comprehend. But if we can come up with simple models that are close enough to what is Really Out There, then we can devise some neat things like cell phones and maybe sustainable fusion generators that make our lives more fun. And that making of neat thing
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Re:well that article sucks (Score:5, Informative)
It would have helped if the summary had pointed at the actual Nature article [nature.com] or the ArXiv preprint [arxiv.org].
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"So in other words, they didn't find anything other than a mathematical equation suggesting dark matter exists. Congratuations are in order indeed."
Yes, I get a kick out of how that article, as well as the one on space.com linked to above, are both written under the assumption that we know "dark matter" exists... but we know no such thing. It is still a matter of much controversy (no pun intended).
We have various theories to account for the observations. Among them the most popular of the string theories, which support the existence of dark matter. But on the other hand, there have been a number of recent findings that call "string theory" itself in
Re:well that article sucks (Score:4, Interesting)
Yes, I get a kick out of how that article, as well as the one on space.com linked to above, are both written under the assumption that we know "dark matter" exists... but we know no such thing. It is still a matter of much controversy (no pun intended).
We have various theories to account for the observations. Among them the most popular of the string theories, which support the existence of dark matter. But on the other hand, there have been a number of recent findings that call "string theory" itself into strong question. Perhaps even rendering it invalid.
Much hinges upon whether the true God particle, the gravitron, really exists. If it does, it would shake up the standard model. If it doesn't, it would shake up the standard model.
Safest right now is to sometimes believe in it, and treat its existence as as unfalsifiable as God, while having a drink at the multi-dimension (including string theory) bar.
In short, we are a tad short on understanding how mass and gravity really interact, and the implications. Which dark matter hinges on - both whether and what.
Magnets, how do they work? (Score:5, Insightful)
At the bottom of every rabbit hole is an explicit assumption. You just have to accept these fundemental assumptions as fact until someone comes along and peels another layer off the onion, assuming there is another layer? You can identify these explicit assumptions fairly easily because they cannot be described by anything more fundemental than themselves therefore all current descriptions of these fundemental properties of the universe are self referencing (or as Feynman put it "cheating"). Dark matter, gravity, spacetime, etc, are examples of these fundemental properties (slashdot challenge: try to come up with a description of a fundemental force or property of the universe that is not self referencing).
Modern physics accepts that we have no idea how these fundemental properties "work", like the universe itself they "just are". This is the "faith" part of science that confuses the hell out of religious and atheistic people alike, science (Natural philososphy) requires the "faith that the real world exists", it answers the proverbial "tree falling in the forest" question with a self-confident - yes! However all is not lost since we do know a hell of a lot about how these fundemental "miricales' behave, so faith in science is not blind faith, it is a faith that's deeply rooted in the utility of the results. ie: we have labeled our best description of this previously unobserved behaviour of the universe as "dark matter" in a way that is consistent with our current understanding of how the universe behaves.
Dark matter is therefore simply the label for the description of what we observe. If it suggest new observations via predictions then great, if it gets them right even better, but even though you have leant a lot more about how it behaves, you still don't actually know what dark matter is [youtube.com] ( I particularly like clip for his sly one finger salute to book burning priests at ~2:42).
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science (Natural philososphy) requires the "faith that the real world exists"
Working as if something is true because it has been useful to do so is not the same as having faith. The fact that you can repeat the same experiment as many times as you want, and get the same result is evidence that the real world exists. That's much more support than anything people typically take on faith.
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I wont arguee over the definition of 'faith', except to say that yours is certainly different from Feyman's, but:
No, it's not. There is no evidence that the real world exists, and lots of evidence that any such evidence is impossible to get.
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I wont arguee over the definition of 'faith', except to say that yours is certainly different from Feyman's, but:
Feynman's definition is certainly different than that used by religious folk.
There is no evidence that the real world exists
Except for the fact that every time you do an experiment you get the same result. How can that not be evidence for the existence of the real world? Not that it's proof, you can't prove the non-existence of magic.
and lots of evidence that any such evidence is impossible to
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This is the "faith" part of science that confuses the hell out of religious and atheistic people alike, science (Natural philososphy) requires the "faith that the real world exists", it answers the proverbial "tree falling in the forest" question with a self-confident - yes!
The problem with this claim is you're using the same word--"faith"--to describe two completely unrelated things. A belief that the world that exists exists is not faith in the relevant sense. It's either a tautology, or contingent on evidence and therefore subject to change like any other scientific (Bayesian) proposition.
To a Bayesian--which is to say, a scientist--"faith" describes a particular type of epistemic error: ascribing to a proposition a plausiblity that is strictly 1 or 0. Such a propositio
Re:well that article sucks (Score:4, Informative)
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However, there has been much work being done on both "sides" of the matter, and I really don't feel I have time to get into a detailed discussion of the matter right now. But there have recently been findings that seriously call string theory into question, and in turn, that somewhat weakens the arguments for dark matter.
I'm not saying that anything is conclusive in either direction. But I sense the pendulum swinging...
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"String theory isn't testable using current technology, but it's largely unrelated to dark matter."
Apologies, I did not read this quite right the first time, or I would have answered it.
Yes, indeed, string theory is one of the pillars upon which dark matter theory is formed. It may be possible for it to exist without "strings", but in most current models they are inextricably intertwined. I.e., string theory does not depend upon dark matter theory, but dark matter theory (most models, anyway) very much DO depend upon string theory.
So anything that is evidence against string theory, is also an argum
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I will look to see if I have a reference. It might take me a day or so. I am very busy with work and personal issues right now.
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>Congratuations are in order indeed.
So the only difference with 80 year old computations that this time it's more localized?
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Because anyone with the slightest interest knows gravitational microlensing studies are done by measuring the elliptical shapes of galaxies, and presuming a uniform distribution of actual orientations. And anyone who doesn't know it will get annoyed and leave before you finish explaining it.
And round about the podium was darkness, for the points of light had rearrainged themselves at a bar and exerted no gravitational attraction in the lecture hall.
How do they know it's dark matter? (Score:2)
Okay, so even assuming the light-bending is real, what's their evidence that it's dark matter and not simply non-luminous normal matter? I can see something like the bullet cluster strongly supports dark matter versus alternative theories (e.g. using general relativity rather than Newtonian gravitational theory apparently explains the odd galactic rotational characteristics ) since the vast bulk of matter appears to have passed through without interacting. Then again , should the dark matter have "collide
Re:How do they know it's dark matter? (Score:5, Interesting)
Non-luminous normal matter absorbs light (and so becomes luminous normal matter evenutally, at least at some frequency).
BTW, the confirmation for dark matter vs other theories for galaxy rotation came from the WMAP [wikipedia.org] data. IIRC, about 80% of the early matter of the universe was shown to be somehting that interacted gravitationally, but did not interact with light (or electrons). The actual % of dark matter measured matched the amount predicted by the dark matter hypothesis for galaxy rotation rates, which is a pretty convincing confirmation IMO.
Re:How do they know it's dark matter? (Score:5, Insightful)
Actually, it generally goes the other way - when a non-star initially forms it will be hot, and has to radiate all that energy away, becoming less bright until it eventually becomes effectively non-luminous. Starlight simply isn't dense enough to significantly heat anything substantially - it will be radiated away as fast as it gets absorbed, and that's *way* below what we can currently detect. Our telescopes may eventually become sensitive to detect such MACHOs directly, but they're not there yet. And micro-lensing studies seem to limit them to comprising roughly the same amount of matter as luminous objects unless they're predominantly >100 solar masses (which would likely tend to be radiant) or less than Moon-sized, in which case there would need to be so many of them that they would likely be passing through the solar system on a fairly regular basis, which we haven't seen.
If we're talking about stuff in intergalactic filaments though - well, they make interstellar space look positively dense, anything non-luminous would be so close to absolute zero, and so far away, that it would be effectively invisible unless directly in front of something. And it would have to be in a pretty frakking dense cloud to significantly blot out a galaxy Remember that as a wave light will bend around any object in it's path, not much, but slightly (this effect is completely separate from gravitational lensing) and over intergalactic distances that's enough that the "cumulative effects" of a million individual objects each blocking one millionth of the "disc" of a distant galaxy will be far less than you would expect.
As for galactic rotation and WMAP - there is correlation there, I'll give you that, and when two independent measures give you similar results you should probably sit up and take notice. However, when something like the general-relativity explanation for galactic rotation speeds comes along and says - "Hey, you know that really weird behavior we couldn't explain that made us come up with a really bizarre theory to explain? Well we finally have the computational power to run the analysis using the currently accepted theory of gravity instead of the much simpler but known-flawed centuries old model, and everything works out pretty close to what we actually see." Well, that should make you take notice as well. In fact that should make you sit back and take a long hard look at all your "cosmological gravity weirdness", because most of that happens on a scale where galactic distances look positively local, so you'd expect the discrepancy between instantaneous Newtonian gravity and GR gravity to be even larger.
Astronomy is a somewhat shaky field - all theories are fundamentally untestable - all you can do is look out at the universe and try to find phenomena that seem to support or counter theory, but in doing so you're making numerous assumptions about what exactly you're looking at to begin with, and assuming it behaves in a manner consistent with other widely accepted but still fundamentally untestable theories. Now that technique is surprisingly effective, but it is vulnerable to flaws in analysis, especially when much analysis is based on something that is known to be inaccurate (Newtonian gravity) because the alternative is too computationally expensive to use.
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"Well we finally have the computational power to run the analysis using the currently accepted theory of gravity instead of the much simpler but known-flawed centuries old model, and everything works out pretty close to what we actually see."
Sounds like you are referring to MOND, or something like it?
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No, just a straightforward use of the GR equations of gravity rather than the known-flawed Newtonian ones. The Newtonian ones don't even describe the motion of Mercury accurately, and the velocities involved in galactic rotation are considerably higher (~225km/s versus Mercury's 48km/s).
I believe this was the article: http://arxiv.org/abs/astro-ph/0507619/ [arxiv.org]
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Oh, and MOND is referring to slight changes in the Newtonian equations of gravity (it's right there in the name), and since we now know Newtonian gravity is at best a convenient first-order approximation that has already been supplanted by General Relativity, which is both widely accepted and far more accurate, it seems to me that MOND is very much a matter of putting lipstick on a pig. You don't try to explain bizarre phenomena at extreme scales in terms of a theory that everyone already agrees is bunk.
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"He indicated elsewhere in the post that he was referring to General Relativity, not MOND. (It would be a bit odd to refer to MOND as "the currently accepted theory of gravity", I think - I believe MOND is still considered a hypothesis rather than a theory, even by the people fronting it.)"
MOND relates to making very tiny adjustments to a few constants like gravity, and nothing more. Since GP was referring to slight changes which make up the "modern" understanding of gravity and perhaps other constants, but was not spedific about it, MOND was not an unreasonable guess.
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Astronomy is a somewhat shaky field - all theories are fundamentally untestable - all you can do is look out at the universe and try to find phenomena that seem to support or counter theory, but in doing so you're making numerous assumptions about what exactly you're looking at to begin with, and assuming it behaves in a manner consistent with other widely accepted but still fundamentally untestable theories. Now that technique is surprisingly effective, but it is vulnerable to flaws in analysis, especially when much analysis is based on something that is known to be inaccurate (Newtonian gravity) because the alternative is too computationally expensive to use.
Makes me feel better about studying Economics
Easy, the sampled it (Score:5, Funny)
And it turned out that it was made of what we long suspected the mising mass of the universe wa composed of: AOL discs.
These people are just not up on the classics. (Score:5, Funny)
Dark Matter was proven decades ago as this following article demonstrates.
Bell Labs Proves Existence of Dark Suckers
For years it has been believed that electric bulbs emitted light. However, recent information from Bell Labs has proven otherwise. Electric bulbs don't emit light, they suck dark. Thus they now call these bulbs dark suckers. The dark sucker theory, according to a Bell Labs spokesperson, proves the existence of dark, that dark has mass heavier than that of light, and that dark is faster than light.
The basis of the dark sucker theory is that electric bulbs suck dark. Take for example, the dark suckers in the room where you are. There is less dark
right next to them than there is elsewhere. The larger the dark sucker, the greater its capacity to suck dark. Dark suckers in a parking lot have a
much greater capacity than the ones in this room. As with all things, dark suckers don't last forever. Once they are full of dark, they can no longer suck. This is proven by the black spot on a full dark sucker. A candle is a primitive dark sucker. A new candle has a white wick. You will notice that after the first use, the wick turns black, representing all the dark which
has been sucked into it. If you hold a pencil next to the wick of an operating candle, the tip will turn black because it got in the path of the dark flowing into the candle.
Unfortunately, these primitive dark suckers have a very limited range. There are also portable dark suckers. The bulbs in these can't handle all
of the dark by themselves, and must be aided by a dark storage unit. When the dark storage unit is full, it must be either emptied or replaced before
the portable dark sucker can operate again.
Dark has mass. When dark goes into a dark sucker, friction from this mass generates heat. Thus it is not wise to touch an operating dark sucker.
Candles present a special problem, as the dark must travel in the solid wick instead of through glass. This generates a great amount of heat. Thus it can be very dangerous to touch an operating candle. Dark is also heavier than light. If you swim deeper and deeper, you notice it gets slowly darker
and darker. When you reach a depth of approximately fifty feet, you are in total darkness. This is because the heavier dark sinks to the bottom of the lake and the lighter light floats to the top. The immense power of dark can be utilized to mans advantage. We can collect the dark that has settled to the bottom of lakes and push it through turbines, which generate electricity and help push it to the ocean where it may be safely stored.
Prior to turbines, it was much more difficult to get dark from the rivers and lakes to the ocean. The Indians recognized this problem, and tried to
solve it. When on a river in a canoe travelling in the same direction as the flow of the dark, they paddled slowly, so as not to stop the flow of dark, but when they traveled against the flow of dark, they paddled quickly so as to help push the dark along its way.
Finally, we must prove that dark is faster than light. If you were to stand in an illuminated room in front of a closed, dark closet, then slowly open the closet door, you would see the light slowly enter the closet, but since the dark is so fast, you would not be able to see the dark leave the closet.
In conclusion, Bell Labs stated that dark suckers make all our lives much easier. So the next time you look at an electric bulb remember that it is indeed a dark sucker.
Re:These people are just not up on the classics. (Score:5, Funny)
I don't know if I believe you about the dark suckers, but I know how to prove that Dark Matter exists - just redirect one of the mars probes to go visit this dark matter filament and bring back a sample. The Curiosity Rover already has a drill, which would aid in extracting the matter. It should be a simple matter of stellar mathematics (provided that we're willing to wait a bit longer) to set it on a course to the filament. On the way there the rover can be reprogrammed to autonomously land and extract the matter. Since it will be a bit further from Earth than it was designed for, it might be out of radio contact so it will have to be self sufficient.
Easy-peasy, in a "few" years we could be examining samples from this dark filament here on earth.
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Uhm?
This filament is between two neighboring GALAXIES.
Compare:
fastest manmade objects in existence: voyager space probes.
But the lightbulbs-as-dark-suckers theory is still correct, right?
P.S. You're off by a few orders of magnitude - these galaxies are 2.7 billion light years away, if Voyager 1's 10 miles / second speed is comparable (currently the fastest speed from the sun as any manmade object though I suspect we could do better if we were only interested in launching the probe into interstellar space), it would take around 5 x 10^13 years for the probe to reach the galaxy.
I don't know about you, but I've already set my DV
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"I don't know about you, but I've already set my DVR to record that moment just in case I'm not home when it happens."
Be sure to go into the "advanced" menu and override the default exponent.
Bigger than the Higgs (Score:5, Interesting)
I'd call this bigger than the Higgs.
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Another type of matter that differs in that it doesn't absorb or emit light, but is detected by the effects of its mass, is bigger than the particle that implements mass itself? A type of matter is bigger than the the instance of a fundamental parameter of existence? No it's not.
Doesn't follow... (Score:3)
The top quark has a mass of about 173GeV, which comfortably beats the 125 of the particle dete
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"I'd call this bigger than the Higgs."
I'm not really sure about the scales here, but just off the top of my head, you could probably call this bigger than the Higgs by around 30 orders of magnitude.
This is truly exciting. (Score:2)
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"It boggles my mind that people couldn't believe in 'invisible' mass."
It should not boggle your mind, at all. Because it's not a matter of "belief" at all. It is a matter of evidence. And conclusive evidence is not there.
There are MANY very smart people who "believe" in that invisible mass. But they, themselves, know that belief is not the measure by which their work will be judged.
This is actually far more important (Score:3)
Re:This is actually far more important (Score:5, Informative)
Un-doing 7 well-deserved mod points to post this, so pay attention. Higgs was not a given. A particle in the same range without the ability to generate the Higgs field was also a possibility. The team explicitly stated that further confirmation is needed before they can say they found Higgs, or a Higgs-sized particle that does not do the things Higgs Boson is supposed to do.
It is still up in the air as to whether we have a Higgs Boson, or a Higgs-less theory of mass. Obviously everyone is leaning towards Higgs because it matches predictions. But what if it is Higgs sized without having the correct properties? Then you're wrong, and also an idiot for assuming it is a given.
If we indeed found it, then you're a lucky guess at best.
I agree this is more important, but only because we have been zeroing in on a Higgs-sized particle for quite some time. Dark matter has been purely theoretical until now (and still this is only the first sighting, subject to review and revision as with all experimental results). More important because it's newer.
In truth, we won't know for a hundred years which is more important. If dark matter has been theorized since 1930's and we just confirmed it, it is no more important than such ideas as gravitational lensing which have been around for decades before being confirmed. We have known it for a long time, in other words. To me, more important would be strong evidence that a 90 year old hypothesis was completely incorrect and in need of revision.
Neither one of these, to me, beats a fat man finally seeing his toes after 30 years. He had a feeling they were there, and had been told as much, but to finally see them is a whole different ball game.
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"Higgs was not a given. A particle in the same range without the ability to generate the Higgs field was also a possibility."
Thank you! You have just confirmed what I stated in the Higgs thread, for which I was modded "troll" more than once.
They Rolf Heuer said they are 5-sigma confident that they found a particle, which so far seems consistent with predictions about the Higgs. That is not the same thing as crying to the heavens that the Higgs has been found.
Re:This is actually far more important (Score:4, Interesting)
Un-doing 7 well-deserved mod points to post this, so pay attention. Higgs was not a given. A particle in the same range without the ability to generate the Higgs field was also a possibility.
Correct me if I'm wrong, but I think a pairing between a Z and W boson was also considered a candidate.
And also if assuming the Higgs' boson, the question was whether it was in the 120-130 GeV or in the ~182 GeV range - the energy difference could have significant impacts on the standard model, especially in higher order Higgs (when it interacts with itself), but also in how rare the sub-particle would be, and in predicting where to find the last couple of missing particles (not counting the elusive Gravitron).
All in all, the LHC discovery, although predicted, is a great discovery that will give physicists data they sorely needed.
Dark matter? Not so much. We know there are unobservable gravitational effects, but we can't currently say what they are even if we can point to a place where they are. Nailing the Higgs' boson may, in the future, help with this, but not yet.
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"Dark matter? Not so much. We know there are unobservable gravitational effects, but we can't currently say what they are even if we can point to a place where they are. Nailing the Higgs' boson may, in the future, help with this, but not yet."
Haha! I seem to have suddenly stumbled upon a couple of people on Slashdot who actually THINK!
I was beginning to think they were a real rarity.
Our Universe Makes My Brain Hurt (Score:5, Funny)
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Another case of the professor's inability to understand his subject lowering an inventive student's grade.
Eheh (Score:2)
So, you go tell the student that, the guy is unstable in the extreem! Wiped out an entire planet just because people wouldn't listen to him. Imagine what he do with a professor that gives him a C. Would be a sight to see. Preferably from another universe.
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Good for them (Score:4, Funny)
Now maybe they can help me find my keys.
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You don't own a ferret, by any chance?
Dark Energy? (Score:3)
Some explanations of dark matter say that most of the gravitational effects are from dark energy, not condensed into matter. But if dark matter differs from other matter in that it doesn't absorb or emit light, how does dark energy differ from other energy? Energy doesn't absorb or emit light, so how is dark energy different? Unless they mean that it doesn't get absorbed or emitted as light, the way other energy does (ie. photon beams). Without that property it seems rather unlike other energy, enough that it's not really energy.
And if it is dark energy, then where is all the cold, dark info? The next more subtle form of existants.
From what elements is dark matter composed of? (Score:2)
Normally, all known chemical elements reflect light in one degree or another...so, what is this dark matter made of? what is its chemical composition?
Re:From what elements is dark matter composed of? (Score:5, Informative)
Dark matter is expected to be non-barionic, that means, amongst other things, that it is not formed by atoms (so, no elements as we know them).
Dark Matter Filament (Score:4, Funny)
Is it something like that thing in Star Trek Generations ?
Comment removed (Score:5, Informative)
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They are also under the influence of all the masses around them for their entire existence, like everything else. That's why all the Universe's matter is not clumped together in an infinitely massive, infinitesimally small point, but is spread through the Universe in wisps, clumps and intertwined folds. They're also subject to electrostatic repulsion, and the effects of the other fundamental forces, among the rest of matter, space, energy and other forms of what exists not yet categorized.
Re:Occam's Razor - Dark matter is nothing special (Score:5, Informative)
"For example, wouldn't a nebula-sized cloud of free electrons still collapse under their gravitational influence?"
Hell, no. Gravity is orders of magnitude weaker than electrical repulsion. A cloud of electrons would disperse, not coalesce.
Gravity is even weaker than the so-called "weak" force in quantum physics. It is the weakest of all.
Re:Occam's Razor - Dark matter is nothing special (Score:4, Informative)
Maybe, but the gravity is also the only force which works beyond subatomic distances.
Electromagnetism is not short-range. It only seems like it is normally because most materials are electrically neutral.
It's effect is also additive so enough electrons held together would eventually be massive enough to overcome the electromagnetic repulsion (just like protons).
Yes, it's being additive which is why gravity dominates the large-scale structure of the universe (not accounting for dark energy). Electromagnetism likes to cancel out, while gravity likes to build and build.
Weather it's actually possible to condense a cloud of electrons in order for them to exhibit a strong enough gravitational pull, I have no idea.
I don't think so, since the cloud wouldn't exist in the first place. It would disperse long before there was anything like a 'cloud'.
However if you started with something else, like a cloud of hydrogen gas, that could condense, eventually creating a situation where gravity has overcome the electron's repulsion. Something like what our sun will become [wikipedia.org].
These kinds of objects don't make good dark matter candidates. At least for the majority of the unseen mass, and the observations supporting its existence.
Re:Occam's Razor - Dark matter is nothing special (Score:5, Informative)
wouldn't all matter collapse into a common gravitational center?
Yes, assuming it's not ripped apart by the expansion of space and assuming there is enough mass in the cloud for gravity to eventually dominate the other forces. Note that some of these filiments are long enough that the two ends are not gavitationally bound (due to the exansion of space).
As I understand it the reason that DM comes in filaments between galaxies rather than seperate blobs has something to do with quantum fluctuations when our observable universe was compresed into a point particle, it also appears that the bulk of the normal matter (galaxy clusters) occurs where these filaments meet (although I don't know of a explaination as to why), the rest of the normal matter (lone galaxies and primordial gas) coincides with the dark matter filaments. In simplistic terms the matter in the universe is arranged like swiss cheese but the space containing the cheese is expanding to rapidly for the cheese to sucumb to gravity and lump together at a central point. Supercomputer models of the 14Gyr evolution of the universe that include dark matter are consistent with observations, models that only use normal matter are not as skillfull in reproducing ALL the observations.
And for all the metaphysics types out there it's been pointed out a map of the universe at the largest scale [sciencemag.org] looks remarkably like the nuron network in a brain [typepad.com]
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Doesn't matter lead to gravity the way love leads to marriage?
Indeed, once married, gravity doesn't matter any more, with pregnancy, mortgage, kids' school, etc becoming more critical. Gravity starts to matter again closer to retirement age, but then manifests itself more like a burden.
Except we'd still see evidence (Score:5, Informative)
Well, except that if 80% of the mass in our galaxy was simply non-luminous, we'd still see the "haze" from it, just as we can see evidence of the existing hydrogen haze by it's characteristic absorbtion spectra, especially when starlight passes through nebula where the diffuse matter density is extremely high. Perhaps the vast majority simply formed gas giants and the like that were two small to "ignite", recent evidence does suggest wandering planets may be far more common than star-bound ones, but to get the 5:1 ratio still we'd be talking about 5000 Jupiters for every sun, and the sun is actually pretty tiny as stars go - with that many dark planets whizzing around it seems likely we'd see some evidence of them, likely of the frequent "Gas giant zooms through solar system, multiple planetary orbits disrupted, news at 11" sort. If the planets were smaller the "invasions" would be even more frequent, and if they were much larger (we're not sure of the exact limit) they'd spontaneously ignite
Then again - if using general relativity rather than Newtonian gravity actually does explain the odd rotational characteristics of our galaxy without reliance on massive amounts of additional matter then you may be right. There's still things like the Bullet Cluster that show evidence of something very weird going on though - the gravitational lensing seems to have become partially disconnected from the visible matter - if "dark matter" was simply non-luminous you would expect it to still have distribution and gravitational-collision properties similar to the glowing stuff, which is not the case there. Whatever is causing the lensing is behaving in a manner fundamentally different than the matter we can see, in fact it appears to be largely unaffected by the collision at all, which would seem to at odds with many "simple" dark matter theories as well (i.e. it's like normal matter, except light passes right through it).
Re:Except we'd still see evidence (Score:4, Interesting)
It seems to me that conclusions based on lensing effects are making a rather large assumption about the homogeneity of both interstellar and intergalactic space. The interstellar medium especially is supposed to be composed of so many atoms per cubic meter, and the assumption is those atoms are almost exclusively hydrogen and are evenly distributed
That may be an unwarranted assumption.
We've been staring at the sky for a long time now, but only recently have we been doing very large sky surveys, and only very recently have we had the processing power available to do something useful with wide swaths of that data at once. Seems to me there might be some Ph.D's to be had in using data from things like the Sloan Sky Survey to try to validate assumptions about the interstellar medium in greater detail. There may be thin filaments (on interstellar scales) of finely distributed matter that are denser than the overall medium. Or less dense. Or clumps. Nebulas are typically very diffuse. Might it be possible for there to be nebula-like formations that are even more diffuse? So diffuse that they appear largely transparent to most frequencies? So diffuse that their only affect on light is lensing?
I remember astronomers locating nebulas that were previously invisible because they don't emit visible light, but do emit in other parts of the spectrum. The explanation was they are older, cooler formations. But they don't just vanish as they continue to age. That gas is still around, getting ever cooler and more diffuse. Considering how much nova and supernova debris we've already identified in the galaxy, it doesn't seem too big of a leap to consider the long term (as in gigayears) ramifications of nova debris on the general interstellar medium.
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Why do you think that astrophysicists assume that the matter lensing the light is uniformly distributed? They're the most sophisticated experts in the actual distribution of the matter, which they say is uneven.
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in fact it appears to be largely unaffected by the collision at all, which would seem to at odds with many "simple" dark matter theories as well (i.e. it's like normal matter, except light passes right through it).
How is that at odds?
When you grab a door knob, why don't your fingers pass right through it? For that matter, why doesn't your hand just fall apart, or gravitationally collapse into a black hole?
The answer is that the electrons in your hand are repelled by the electrons in the door knob, and that the various atoms in your hand are held together by chemical bonds, but repel each other as well to hold themselves roughly rigidly in place.
Why does that happen? Electrons interact with the electromagnetic force
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At odds because when you're talking about colliding galaxies you're not talking about physical collision - the instances of individual stars actually colliding with each will be fairly rare - the collision is gravitational - stars pass by each other and mutually deflecting their paths, exchanging momentum in the process. Since such collisions are almost entire gravitational you would expect "simple" dark matter to behave in a similar manner. Photon pressure would have some effect, but probably not much,
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They totally convert into the equivalent mass of ballpoint pens you have that you have but never bought.
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More specifically, non-working ballpoint pens.
Evolution in action (Score:3)
Re:bleh (Score:5, Funny)
first post
Dark post; doesn't matter.
Re:Dark Post (Score:5, Insightful)