Scientific American has a piece on speculation that dark matter may be behind diffuse radiation in the galactic center. Beginning in 2003, researchers led by Douglas Finkbeiner noticed a curious excess of microwave radiation in the WMAP data, after all known sources of such radiation were accounted for. Data from NASA's Fermi Gamma-Ray Space Telescope resulted in a similar anomaly in gamma rays. "A paper posted to the physics preprint Web site arXiv.org on October 26 and submitted to the Astrophysical Journal points to a possible signature of dark matter in the Milky Way, although the study's authors are careful to keep their observations empirical and table such speculation... In the new paper [the researchers] describe the Fermi gamma-ray haze and make the claim that it confirms the synchrotron origin of the WMAP microwave haze. And as with the microwave haze, the authors argue that the electrons responsible for the gamma-ray haze appear to originate from an unknown astrophysical process. ... 'We are absolutely in the process of exploring the Fermi haze in the context of dark matter physics,' [one of them] says."
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Black hole and dark matter have very precise meanings in physics. In fact, black holes aren't strictly black due to Hawking radiation and dark matter is transparent, not dark.
Close. Black holes emit hawking radiation in so far as physics is concerned however, the more massive a black hole is the less bright it is. A black hole with twice the mass of another black hoel will be 1/8th as bright as the smaller black hole. For blackholes largers than the sun, the hawking radiation is so miniscule that the lifetime of the black hole is on the order of 10^60+ years before it "evaporates." Dark matter O.T.O.H. is merely undetectable with current instrumentation outside of indirect gravitational effects.
If dark matter is "undetectable", then why are they attributing microwave radiation to dark matter, instead of, say, the energy given off by normal matter falling into the black hole at the center of the galaxy? (What happens when dark matter falls into a black hole, anyway?)
It looks like they're claiming that the radiation from these electrons indicates that a process of higher energy than a supernova caused the phenomena. I presume that the process they're talking about is the decay of WIMPs and other dark matter candidates. The dark matter its self hasn't been directly detected unless you're counting this paper as an example of the contrary. The problem is that this is a very new paper in arxiv and as such requires much more peer review before we can say with reasonable c
Not decay annihilation, the WIMP has to be stable and so not decay otherwise we'd have none left by now. What they are hoping to detect is when two WIMPs annihilate and form a ??????? that then decays and emits the radiation they are detecting.
Well shoot. You got us all figured out. We're all just a bunch of charlatan priests. I guess we'll just give up and go home now.
You want scientists to consider their theories falsified, question their premises, and come up with new ideas, eh? OK, when I find that galactic rotation curves don't line up with what I've predicted, I'll consider my theories (standard model with, as best we can manage, general relativity) falsified. I'll question my premises (for instance, the premise that I know exactly what particles exist in the universe). I'll come up with some new ideas (for instance, that there might be some type of particle that I don't know about). Looks OK so far, right? At what point do you have an objection to this?
One objection that I can see is that you might think that no other avenues of investigation have been explored. However, they have. Instead of questioning the standard model (giving us dark matter), we could question general relativity. This gives us a theory called MOND. It doesn't really work very well, but a lot of very smart people spent a great deal of time and effort investigating it.
In the end, in order to be a good scientist, you've got to come full circle. You take all the new ideas (new theories) that you've come up with, and you make predictions with them. Turns out that dark matter predicts something different from, say, MOND for a collision between two galaxy clusters which contain gas, stars, and dark matter. Well, we found such a collision (Bullet Cluster), and dark matter made the correct prediction, whereas MOND made the wrong prediction.
But that's not all. When you start to enumerate all the properties that dark matter ought to have in order to fit what we've observed in galactic rotation curves, the bullet cluster, etc, it turns out that there are not too many different ways in which to fit dark matter onto the standard model. And those ways in general predict different things about what astroparticle experiments like Fermi, ICECUBE, etc should see. Give it a few (~10) years, and these experiments will either have indirectly observed dark matter (and the characteristics of that observation will narrow down the particular type of dark matter dramatically), or they will have ruled out a large number of the candidate dark matter models, leaving even fewer. Give it long enough, and we'll have either made the indirect observation or ruled out all the models.
If we rule out all the models, then it's back to the drawing board. We'd have a falsified theory, we'd question our premises, and we'd come up with some new ideas. But until then, dark matter is a very good avenue for investigation. You shouldn't "believe" in it until it's been observed, but neither should you claim it's bad science. It isn't.
FWIW, I don't really expect to convince you of this, as you seem to be quite firmly decided that it is bad science, even though it fits your apparent criteria for what science should be. But hopefully I can prevent others who read both of our comments from being infected by you.
Instead of questioning the standard model (giving us dark matter), we could question general relativity. This gives us a theory called MOND.
Actually, no. It gives you an "I don't know." That's unacceptable, so MOND emerges to fill the gap.
Seriously, you actually believe that? It's useless, not unacceptable. If all scientists did is say "I don't know" they wouldn't get much done would they? Think about it for a minute. Or, they do what scientists do best (i.e. science) and come up with new theories (e.g. MON
Seriously? darkmatter has been theoriticaly predicted and experimentaly detected in three observations at three largely different scales. Your two options with the observation is to change newtowns and einsteins laws of gravitation so that they fit these results and get left with seriously fudged laws of gravity (I'm not even sure if anyone managed to do this in a consistent way) or you infer the pressence of dark matter, which given our understanding of particle physics is highly plausable that such matter
So what you're saying is that you don't actually believe the nonsense you're spouting - you're simply trolling? Fun. Does that make you feel like a big man?
Far from it, good sir. It means I believe it whether or not others need to disagree or even ridicule me for it. I believe that this is one of those polarizing things where you either see it for yourself or you don't and bickering about it is infinitesimally unlikely to change anyone's mind. So I won't. The indifference means I am not bothered when things I believe don't find ready support, for that is a type of insecurity based on bandwagon appeal and I see the error in it. It also means I don't need to think ill of people, not even of those who can't disagree with my viewpoint without also judging me to be inferior in some way or inferring an ulterior motive such as trolling or egotism when my actions are mysterious to them. I am thankful to not carry that burden, for it's a heavy one.
If you would accept a suggestion from me, never confuse consensus agreement with truth. Not even when you find yourself on the side of the majority consensus.
No, "dark matter" and "dark energy" are just discrepancies in two particular aspects of astrophysics. Empirical observations suggest that there's more matter out there than we can see. However, because they sound vague and they're active areas of research (that is, they're mentioned often and it's clear we don't know what they are), people who have no real understanding of physics jump to the conclusion that it's some general hand-waving. Perhaps this makes them reinforces their belief that they're so much
Why do we keep invoking "dark matter" to explain that which is adequately explained by the massive black hole at the center of this and almost every other galaxy?
Why do we keep invoking "dark matter" to explain that which is adequately explained by the massive black hole at the center of this and almost every other galaxy?
Because the massive black holes don't adequately explain things.
Rotation speeds of stars about the center of the galaxy don't behave as they should in the case where the massive black hole is the only thing acting on them other than nearby bits of galaxy.
The difference is that dark matter and dark energy can be tested for in various ways; a deity can't be. When physicists can't explain something they may use a place holder at times but there's no chance of just giving up like the "god did it" explanation does.
The difference is that dark matter and dark energy can be tested for in various ways; a deity can't be.
When physicists can't explain something they may use a place holder at times but there's no chance of just giving up like the "god did it" explanation does.
It's worth echoing that. Even the really iffy, amorphous parts of physics like superstring theory will eventually have empirical evidence shaping (and perhaps falsifying) it. OTOH, we have no idea whether it is even possible to test the theory of "God exists."
That's just not a logical conclusion. It leaves out the much more likely answer that our understanding of the equations of motion is wrong.
So, you take a WHOLE YEAR of Physics in school, and suddenly, you are ready to say with confidence that all the formulas of physics (which, coincidentally, are correct enough to land a robot on Mars and propel a satellite out past the Solar System) are wrong?!?!? Further, you even state that it's MORE LIKELY that they are wrong?
Simulations of stars in galaxies are approximations because: 1) there isn't an equation for an exact solution to any gravitationally bound system containing more than 5 objects. 2) stars in a typical galaxy are not uniform so the simulations must take this into account as a best guess. br/>3) newton's equations are indeed incorrect however, Einstein's equations only dominate to a significant degree under unusual conditions.
In so far as dark matter is concerned, you are incorrect. Experiments like the Cryogenic Dark Matter Search are attempting to detect dark matter particles directly, we've got neutrino detectors looking for evidence of annihilation events... Particle accelerator experiments attempting to actually synthesize dark matter candidates.. To claim that there isn't a way to test the dark matter hypothesis would be grossly inaccurate. Disclaimer: Physics isn't my major but I did study quite a bit of it in high school and college.
This is more along the lines of "our equations don't explain the observed motion of galaxies, therefore, there's matter there we can't see or touch."
Wow! I never thought they would do things like that! I would have expected things to go like this:
"our equations don't explain the observed motion of galaxies, therefore, it's reasonable to hypothesize that there's matter there we can't see or touch, let's test it."
And then they'd go and look for evidence or something. Thanks for correcting me!
That's just not a logical conclusion. It leaves out the much more likely answer that our understanding of the equations of motion is wrong.
So all that stuff I heard about MOND [wikipedia.org] was just in my head? Thanks for grounding me in reality!
Most galaxy motion simulations are based on either Newtonian mechanics or "modified Newtonian" mechanics, even though both are known to be wrong. Einstein showed them to be wrong over a hundred years ago!
You're right! It's quite likely that thousands and thousands of astrophysicists have spent decades researching a problem that has such an obvious solution. You're a veritable font of wisdom!
I studied physics at University, and both me and a friend of mine noted during our studies that Physics seems to overuse simplified equations... Those simple equations are the ones we learned about also. They're wrong. In many practical cases, the error can exceed 30%!
O M G ! - W T F ! Low level physics classes use lots of simplifications? That explains why I can't find massless ropes and frictionless pulleys on E-Bay!
This is what computers were designed to do, but instead of just doing a numerical simulation, physicists insist on waving their hand and dismissing the error term like it's not even there, so they can keep using nice pretty exact solutions that... don't agree with reality.
I think these people [dur.ac.uk] may disagree with you.........
You'll find most of those simulations are Newtonian. I just checked some of their latest papers, and they all use Newtonian or modified Newtonian (MOND) codes. The code they run is called "GADGET-3" (they also used earlier versions in the past), and according to this [www.aip.de] high level description, it's Newtonian. Admittedly, it's an impressive simulator, but it seems to concentrate on scale (many particles) and on including many effects like gas interactions, magnetohydrodynamics, etc... but not a relativistic met
"god did it" is a little different from, "there seems to be a source of gravitational attraction, we're not sure what it is, but it seems distinct from 'regular' matter; let's call it 'dark matter' while we continue to investigate."
Clearly, God lives in the FFth dimension. Dimensions numbers are designed to be two byte fields. God never though anyone could ever need to use more than four dimensions.
I second that, I would even add that God must have F fingers.
Proof: if you want to know the n-th number of pi, you have to calculate all numbers up to n-1 to calculate n. However, in binary, octal, hexadecimal and any base 2^n you can calculate that number independently [maa.org]. So, to know the last "3" of "3.141592653" we need to calculate all numbers before. To know the last "0" of "3.243F6A8885A308D313198A2E0" we do not have to calculate all numbers before it. As we see here, God of course has his shortcuts
Can't explain something, Dark Matter is the reason! Can't find a cause, Dark Matter is it!
This is completely incorrect. This work is the result of looking for Dark Matter. Dark Matter is the best explanation for galactic rotation curves and the cosmic microwave background. Depending on what the Dark Matter is it may annihilate with itself and produce, amongst other things, electron-positron pairs. In fact the paper is really a very beautiful and elegant bit of work since the first bit of evidence which lead to this comes from the background 'noise' of one of the major pieces of evidence for Dark Matter - the WMAP data! As such, far from noticing something and then attributing it to Dark Matter, this is actively looking for something that suggests evidence for Dark Matter. True the evidence does not show that it HAS to be Dark Matter but if you cannot attribute it to anything else which is known and you have models which suggest that Dark Matter might produce such a signal it is very interesting.
Arkani-Hamed et al have a model which may explain this and which, if correct, predicts jets of leptons (electrons or muons) at the LHC. This is actually one of the things which my colleagues and I are looking for on the ATLAS Experiment [atlas.ch]. If we do observe them then this will be further evidence for Dark Matter and not a "oh, something else we cannot explain and put down to Dark Matter". Until we have enough bits of evidence that, combined, show that Dark Matter is the only possible cause there will always be some doubt but that should not be construed as flailing around and using Dark Matter to explain every observation that is inexplicable. Indeed, the fact that we are using Dark Matter models to suggest observations and experiments to perform and then finding that these return "inexplicable" results is very, very interesting!
Try an engineer's perspective here, not just the pure science one. A geer would say:
"When we add the Dark Matter fudge factor, our equations tend to get better, and we haven't found many (if any) equations that break in major bad ways because of it so, we will build our next bridge using this fudge factor and be confident it will be the best inter-galactic bridge built in 2009."
To see what engineers have to deal with on a daily basis, have a look at any of the links off of this page: lmnoeng.com [lmnoeng.com]. All
There appears to be something out there that interacts gravitationally with normal matter but does not glow or reflect light. Doesn't glow:-> dark. Has gravity: -> matter. Therefor we call it "dark matter", for now.
That's actually not such a bad idea. Maybe we could refocus all of those creation "scientists" on something worthwhile. You know, take their argument and turn it around: "Well, if you proved Colorless Jesus Powder exists then we'd have to believe in God" and then once they do we can switch to "Oh come on, only crazy people didn't believe in Colorless Jesus Powder, to really prove science wrong, you'd need to show exactly how the Jesus Explosion occurred". And so on..
Actually, they try to avoid the subject of dark matter. It is simply an unknown astrophysical phenomenon. Since they ran out of other possibilities, one could say that what ever remains, however unlikely is surely the truth (hence said a wise man). However, there are probably other researchers who will be able to further this discovery, determine the cause of the phenomenon and provide a non-darkmatterish explanation...just for your satisfaction of course.
Like "gravity", dark matter is the name given to a phenomenon or set of phenomena that appear related, not necessarily an actual thing or force. We don't know what gravity actually "is" under the hood; we only know what it does. Gravity is a model that explains observations nicely. But the actual workings behind it are still elusive. We've yet to successfully break it down into sub-mechanisms or sub-models, like knowing that cars move and the patterns of their movements, but not why they move.
Dark matter may actually be many different forces or causes, and perhaps in the future may be split up or re-assigned to other "forces" (models). At this point in time it's merely a guess that it's all one thing. Gravity may also turn out to be multiple things that only appear to be one in the same from our limited perspective and observations. We have to peel the onion one layer at a time, and may never reach the final center layer (if there is such a thing).
It's a black hole! (Score:5, Funny)
Of course it's dark matter in the middle
Re:It's a black hole! (Score:5, Informative)
Black hole and dark matter have very precise meanings in physics. In fact, black holes aren't strictly black due to Hawking radiation and dark matter is transparent, not dark.
Parent
Re:It's a black hole! (Score:4, Interesting)
Close. Black holes emit hawking radiation in so far as physics is concerned however, the more massive a black hole is the less bright it is. A black hole with twice the mass of another black hoel will be 1/8th as bright as the smaller black hole. For blackholes largers than the sun, the hawking radiation is so miniscule that the lifetime of the black hole is on the order of 10^60+ years before it "evaporates." Dark matter O.T.O.H. is merely undetectable with current instrumentation outside of indirect gravitational effects.
Parent
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It looks like they're claiming that the radiation from these electrons indicates that a process of higher energy than a supernova caused the phenomena. I presume that the process they're talking about is the decay of WIMPs and other dark matter candidates. The dark matter its self hasn't been directly detected unless you're counting this paper as an example of the contrary. The problem is that this is a very new paper in arxiv and as such requires much more peer review before we can say with reasonable c
Re:It's a black hole! (Score:4, Interesting)
Parent
Re:It's a black hole! (Score:4, Funny)
Just like woosh has a very precise meaning on Slashdot.
Parent
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Well, to continue the Slashdot tradition:
Just like whoosh has a very precise meaning on Slashdot.
Fixed.
Re:It's a black hole! (Score:5, Funny)
Of course it's dark matter in the middle
Dark matter is sort of like violence. If it doesn't work, just use more of it.
Parent
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You have a profound understanding of Physics. That's exactly what physicists do.
Of course it's dark matter in the middle
Dark matter is sort of like violence. If it doesn't work, just use more of it.
Re:It's a black hole! (Score:5, Insightful)
You want scientists to consider their theories falsified, question their premises, and come up with new ideas, eh? OK, when I find that galactic rotation curves don't line up with what I've predicted, I'll consider my theories (standard model with, as best we can manage, general relativity) falsified. I'll question my premises (for instance, the premise that I know exactly what particles exist in the universe). I'll come up with some new ideas (for instance, that there might be some type of particle that I don't know about). Looks OK so far, right? At what point do you have an objection to this?
One objection that I can see is that you might think that no other avenues of investigation have been explored. However, they have. Instead of questioning the standard model (giving us dark matter), we could question general relativity. This gives us a theory called MOND. It doesn't really work very well, but a lot of very smart people spent a great deal of time and effort investigating it.
In the end, in order to be a good scientist, you've got to come full circle. You take all the new ideas (new theories) that you've come up with, and you make predictions with them. Turns out that dark matter predicts something different from, say, MOND for a collision between two galaxy clusters which contain gas, stars, and dark matter. Well, we found such a collision (Bullet Cluster), and dark matter made the correct prediction, whereas MOND made the wrong prediction.
But that's not all. When you start to enumerate all the properties that dark matter ought to have in order to fit what we've observed in galactic rotation curves, the bullet cluster, etc, it turns out that there are not too many different ways in which to fit dark matter onto the standard model. And those ways in general predict different things about what astroparticle experiments like Fermi, ICECUBE, etc should see. Give it a few (~10) years, and these experiments will either have indirectly observed dark matter (and the characteristics of that observation will narrow down the particular type of dark matter dramatically), or they will have ruled out a large number of the candidate dark matter models, leaving even fewer. Give it long enough, and we'll have either made the indirect observation or ruled out all the models.
If we rule out all the models, then it's back to the drawing board. We'd have a falsified theory, we'd question our premises, and we'd come up with some new ideas. But until then, dark matter is a very good avenue for investigation. You shouldn't "believe" in it until it's been observed, but neither should you claim it's bad science. It isn't.
FWIW, I don't really expect to convince you of this, as you seem to be quite firmly decided that it is bad science, even though it fits your apparent criteria for what science should be. But hopefully I can prevent others who read both of our comments from being infected by you.
Parent
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Instead of questioning the standard model (giving us dark matter), we could question general relativity. This gives us a theory called MOND.
Actually, no. It gives you an "I don't know." That's unacceptable, so MOND emerges to fill the gap.
Seriously, you actually believe that? It's useless, not unacceptable. If all scientists did is say "I don't know" they wouldn't get much done would they? Think about it for a minute. Or, they do what scientists do best (i.e. science) and come up with new theories (e.g. MON
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Re:It's a black hole! (Score:4, Interesting)
So what you're saying is that you don't actually believe the nonsense you're spouting - you're simply trolling? Fun. Does that make you feel like a big man?
Far from it, good sir. It means I believe it whether or not others need to disagree or even ridicule me for it. I believe that this is one of those polarizing things where you either see it for yourself or you don't and bickering about it is infinitesimally unlikely to change anyone's mind. So I won't. The indifference means I am not bothered when things I believe don't find ready support, for that is a type of insecurity based on bandwagon appeal and I see the error in it. It also means I don't need to think ill of people, not even of those who can't disagree with my viewpoint without also judging me to be inferior in some way or inferring an ulterior motive such as trolling or egotism when my actions are mysterious to them. I am thankful to not carry that burden, for it's a heavy one.
If you would accept a suggestion from me, never confuse consensus agreement with truth. Not even when you find yourself on the side of the majority consensus.
Parent
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No, "dark matter" and "dark energy" are just discrepancies in two particular aspects of astrophysics. Empirical observations suggest that there's more matter out there than we can see. However, because they sound vague and they're active areas of research (that is, they're mentioned often and it's clear we don't know what they are), people who have no real understanding of physics jump to the conclusion that it's some general hand-waving. Perhaps this makes them reinforces their belief that they're so much
And it went a little something like this: (Score:4, Funny)
CAPTAIN KIRK: Spock, come in here, can you make sense of these readings?
SPOCK: Captain, it appears that dark matter may be behind diffuse radiation in the galactic center.
CAPTAIN KIRK: It's the most magnificent thing I've ever seen!
SPOCK: It is...fascinating.
CAPTAIN KIRK: But why would diffuse radiation need a starship?
DR. MCCOY: Come on over here, boys! This galactic dick ain't gonna suck itself!
Thanks for reading and supporting fan fiction.
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Purple Haze (Score:2)
Call me an astrophysics noob, but (Score:2)
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Because the massive black holes don't adequately explain things.
Rotation speeds of stars about the center of the galaxy don't behave as they should in the case where the massive black hole is the only thing acting on them other than nearby bits of galaxy.
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Because it isn't.
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because you're an astrophysics noob and don't realize that blackholes do not explain it at all.
I like my coffee... (Score:2, Funny)
...like I like my cosmological hypotheses. Dark, with a nice distribution of heat.
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While I prefer my coffee like I like my women... cold, and bitter.
Can we please just call it by its traditional name (Score:5, Funny)
Magic?
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Technically dark magic. [-5 overly pedantic]
Re:Explanation Impossible (Score:5, Insightful)
The difference is that dark matter and dark energy can be tested for in various ways; a deity can't be.
When physicists can't explain something they may use a place holder at times but there's no chance of just giving up like the "god did it" explanation does.
Parent
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The difference is that dark matter and dark energy can be tested for in various ways; a deity can't be. When physicists can't explain something they may use a place holder at times but there's no chance of just giving up like the "god did it" explanation does.
It's worth echoing that. Even the really iffy, amorphous parts of physics like superstring theory will eventually have empirical evidence shaping (and perhaps falsifying) it. OTOH, we have no idea whether it is even possible to test the theory of "God exists."
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GOD: I am defrosting my dinner.
Re:Explanation Impossible (Score:5, Funny)
The difference is that dark matter and dark energy can be tested for in various ways; a deity can't be.
Well, technically you can test for existence of a deity.... you just can't come back to tell the rest of us about it afterwards.
Parent
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>> you just can't come back to tell the rest of us about it afterwards.
You can. You just need to pick the right deity.
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That's just not a logical conclusion. It leaves out the much more likely answer that our understanding of the equations of motion is wrong.
So, you take a WHOLE YEAR of Physics in school, and suddenly, you are ready to say with confidence that all the formulas of physics (which, coincidentally, are correct enough to land a robot on Mars and propel a satellite out past the Solar System) are wrong?!?!? Further, you even state that it's MORE LIKELY that they are wrong?
You and your friend were astute enough to n
Re:Explanation Impossible (Score:5, Informative)
Simulations of stars in galaxies are approximations because: />3) newton's equations are indeed incorrect however, Einstein's equations only dominate to a significant degree under unusual conditions.
1) there isn't an equation for an exact solution to any gravitationally bound system containing more than 5 objects.
2) stars in a typical galaxy are not uniform so the simulations must take this into account as a best guess. br
In so far as dark matter is concerned, you are incorrect. Experiments like the Cryogenic Dark Matter Search are attempting to detect dark matter particles directly, we've got neutrino detectors looking for evidence of annihilation events... Particle accelerator experiments attempting to actually synthesize dark matter candidates.. To claim that there isn't a way to test the dark matter hypothesis would be grossly inaccurate.
Disclaimer: Physics isn't my major but I did study quite a bit of it in high school and college.
Parent
Re:Explanation Impossible (Score:5, Insightful)
This is more along the lines of "our equations don't explain the observed motion of galaxies, therefore, there's matter there we can't see or touch."
Wow! I never thought they would do things like that! I would have expected things to go like this:
"our equations don't explain the observed motion of galaxies, therefore, it's reasonable to hypothesize that there's matter there we can't see or touch, let's test it."
And then they'd go and look for evidence or something. Thanks for correcting me!
That's just not a logical conclusion. It leaves out the much more likely answer that our understanding of the equations of motion is wrong.
So all that stuff I heard about MOND [wikipedia.org] was just in my head? Thanks for grounding me in reality!
Most galaxy motion simulations are based on either Newtonian mechanics or "modified Newtonian" mechanics, even though both are known to be wrong. Einstein showed them to be wrong over a hundred years ago!
You're right! It's quite likely that thousands and thousands of astrophysicists have spent decades researching a problem that has such an obvious solution. You're a veritable font of wisdom!
I studied physics at University, and both me and a friend of mine noted during our studies that Physics seems to overuse simplified equations ... Those simple equations are the ones we learned about also. They're wrong. In many practical cases, the error can exceed 30%!
O M G ! - W T F ! Low level physics classes use lots of simplifications? That explains why I can't find massless ropes and frictionless pulleys on E-Bay!
Parent
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This is what computers were designed to do, but instead of just doing a numerical simulation, physicists insist on waving their hand and dismissing the error term like it's not even there, so they can keep using nice pretty exact solutions that... don't agree with reality.
I think these people [dur.ac.uk] may disagree with you.........
You'll find most of those simulations are Newtonian. I just checked some of their latest papers, and they all use Newtonian or modified Newtonian (MOND) codes. The code they run is called "GADGET-3" (they also used earlier versions in the past), and according to this [www.aip.de] high level description, it's Newtonian. Admittedly, it's an impressive simulator, but it seems to concentrate on scale (many particles) and on including many effects like gas interactions, magnetohydrodynamics, etc... but not a relativistic met
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"god did it" is a little different from, "there seems to be a source of gravitational attraction, we're not sure what it is, but it seems distinct from 'regular' matter; let's call it 'dark matter' while we continue to investigate."
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Clearly, God lives in the FFth dimension. Dimensions numbers are designed to be two byte fields. God never though anyone could ever need to use more than four dimensions.
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Proof: if you want to know the n-th number of pi, you have to calculate all numbers up to n-1 to calculate n. However, in binary, octal, hexadecimal and any base 2^n you can calculate that number independently [maa.org]. So, to know the last "3" of "3.141592653" we need to calculate all numbers before. To know the last "0" of "3.243F6A8885A308D313198A2E0" we do not have to calculate all numbers before it. As we see here, God of course has his shortcuts
Explanation Very Possible (Score:5, Informative)
Can't explain something, Dark Matter is the reason! Can't find a cause, Dark Matter is it!
This is completely incorrect. This work is the result of looking for Dark Matter. Dark Matter is the best explanation for galactic rotation curves and the cosmic microwave background. Depending on what the Dark Matter is it may annihilate with itself and produce, amongst other things, electron-positron pairs. In fact the paper is really a very beautiful and elegant bit of work since the first bit of evidence which lead to this comes from the background 'noise' of one of the major pieces of evidence for Dark Matter - the WMAP data! As such, far from noticing something and then attributing it to Dark Matter, this is actively looking for something that suggests evidence for Dark Matter. True the evidence does not show that it HAS to be Dark Matter but if you cannot attribute it to anything else which is known and you have models which suggest that Dark Matter might produce such a signal it is very interesting.
Arkani-Hamed et al have a model which may explain this and which, if correct, predicts jets of leptons (electrons or muons) at the LHC. This is actually one of the things which my colleagues and I are looking for on the ATLAS Experiment [atlas.ch]. If we do observe them then this will be further evidence for Dark Matter and not a "oh, something else we cannot explain and put down to Dark Matter". Until we have enough bits of evidence that, combined, show that Dark Matter is the only possible cause there will always be some doubt but that should not be construed as flailing around and using Dark Matter to explain every observation that is inexplicable. Indeed, the fact that we are using Dark Matter models to suggest observations and experiments to perform and then finding that these return "inexplicable" results is very, very interesting!
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"When we add the Dark Matter fudge factor, our equations tend to get better, and we haven't found many (if any) equations that break in major bad ways because of it so, we will build our next bridge using this fudge factor and be confident it will be the best inter-galactic bridge built in 2009."
To see what engineers have to deal with on a daily basis, have a look at any of the links off of this page: lmnoeng.com [lmnoeng.com]. All
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There appears to be something out there that interacts gravitationally with normal matter but does not glow or reflect light. Doesn't glow:-> dark. Has gravity: -> matter. Therefor we call it "dark matter", for now.
Re:Explanation Impossible (Score:5, Funny)
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Actually, they try to avoid the subject of dark matter. It is simply an unknown astrophysical phenomenon. Since they ran out of other possibilities, one could say that what ever remains, however unlikely is surely the truth (hence said a wise man). However, there are probably other researchers who will be able to further this discovery, determine the cause of the phenomenon and provide a non-darkmatterish explanation...just for your satisfaction of course.
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First, he was a fictional character. One who would not characterize himself as wise, I think, based on the stories I've read.
Second, that's not actually what he said.
Re:Explanation Impossible (Score:4, Informative)
Like "gravity", dark matter is the name given to a phenomenon or set of phenomena that appear related, not necessarily an actual thing or force. We don't know what gravity actually "is" under the hood; we only know what it does. Gravity is a model that explains observations nicely. But the actual workings behind it are still elusive. We've yet to successfully break it down into sub-mechanisms or sub-models, like knowing that cars move and the patterns of their movements, but not why they move.
Dark matter may actually be many different forces or causes, and perhaps in the future may be split up or re-assigned to other "forces" (models). At this point in time it's merely a guess that it's all one thing. Gravity may also turn out to be multiple things that only appear to be one in the same from our limited perspective and observations. We have to peel the onion one layer at a time, and may never reach the final center layer (if there is such a thing).
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> Evolution is the answer to everything and the answer to nothing at the same
> time.
What is your answer?
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Welcome to the internet, how long will you be staying?