Particle physicists discover strongest ever evidence of dark matter http://www.extremetech.com/extreme/...scover-strongest-ever-evidence-of-dark-matter This is great! But I wonder.... "Which leads us neatly onto Cryogenic Dark Matter Search experiment, situated hundreds of meters underground in the Soudan mine in Minnesota and operated by a collaboration of American universities, including MIT, Stanford, and Fermilab. The CDMS basically consists of a silicon or germanium crystal (pictured above), covered a thin layer of aluminium and tungsten, and then cooled to just 50 millikelvin — 50 thousands of a Kelvin above absolute zero, or -273.1 Celsius (-459.58F). At this temperature, the silicon and germanium crystals are superconductive and incredibly sensitive — so sensitive that, in theory, one particle of dark matter hitting a silicon or germanium atom should create a measurable temperature change in the aluminium-tungsten layer. Now the CDMS experiment is reporting that one of its silicon crystals has detected three signals that appear to be WIMPs that are consistent with dark matter. These three signals occurred at a mass-energy of around 8.6 GeV (about 10 times the mass of a proton), which is far lower than most particle physicists would expect, but it is still consistent with some theories of dark matter, such as the dark sector. A mass of 8.6 GeV doesn’t correlate with findings from an underground experiment in Italy that pegged dark matter at 50 GeV a couple of years ago, but when dealing with something as flighty as dark matter, it’s not unheard of for experiments to have different results. It does mean that one of the experiments is wrong, though." How can this "dark matter" have so much mass and energy, and yet be so cool? Wouldn't the large amount of energy make it more hot and easier to detect? Unless it is very "diluted" in regular matter, but then there wouldn't be enough to account for it. Also, perhaps all this dark matter mass is behind the force of gravity? What do you think? Please Register or Log in to view the hidden image!
Cool stuff! I can't wait for the experiments to get precise enough to start making some definitive statements about dark matter, and it sounds like they're rapidly heading in that direction. I don't think the high mass-energy of dark matter has an effect on its temperature; at any rate, it's the silicon/germanium detectors that are absurdly cold here, not the dark matter particles. The reason dark matter is so hard to detect (at least according to the WIMP model) is that it only interacts via gravity and the weak nuclear force, which are tiny compared to the electromagnetic and strong nuclear forces at play in most of the matter we know and love. When the forces involved are so weak, dark matter can pass through ordinary matter while barely affecting it at all, and the detectors need to be super-cold or else the tiny dark matter signal will be swamped by thermal noise. As for whether dark matter is behind gravity, the whole reason dark matter was postulated in the first place is that there doesn't seem to be enough matter in the universe to explain how galaxies and other large structures hold together. In other words, dark matter contributes gravity to the universe, but it does so alongside (not in place of) regular matter.
Truthseeker: there's been some cynicism about this out in blogland. Like they've drawn a blank for years, they needed some kind of result, so they pulled one out of the hat. The timing is interesting. Planck has found large-scale inhomogeneity, and the ΛCDM model is built on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". Note that it's energy that causes gravity, not matter per se. Matter causes gravity because of the energy content. If dark energy was inhomogeneous it would have a mass equivalence and a gravitational effect. And it isn't made of particles.
Do you know the level of inhomogeneity? The Planck/WMAP/COBE data shows variations on the level of 1 part in 100,000. Furthermore the naive first formalisation of the FRW metric is about space-time and dark energy. The variations we see in the CMB are well captured by considering inflation dynamics on quantum fluctuations in the early universe. I'd tell you to go back and read your undergraduate cosmology lecture notes but then I remembered you're self taught on nothing but pop science and analogies. Obviously the universe isn't perfectly homogeneous, since there's galaxies and planets and people in it, clumps of matter. This doesn't mean that you immediately chuck the FRW metric. The applicability of the metric and the resultant universal dynamical is more robust than that, things such as the exponential increase of the FRW length scale term during inflation can still be applied to a clumpy universe, provided the clumpiness isn't too much. Of course if you're like to talk us through a detailed calculation of how the Planck data leads to a set of Einstein field equations which are sufficiently different from those of the FRW metric that the universal dynamics of the length scale during inflation and the current epoch are no longer valid then I'd be interested to see it. Hell, I'd be interested to see you show any ability to do any mathematical manipulation of things like the FRW metric. Actually I'd like to see you show you can do basic calculus, never mind something university level.
Don't try to hide behind an abusive mathematical shield, Alphanumeric. Talk physics. See the ESA Planck article and pay attention to Jan Tauber saying “We see an almost perfect fit to the standard model of cosmology, but with intriguing features that force us to rethink some of our basic assumptions". Note that your basic assumption is that inhomogeneity involves matter. Understand that the Lambda-CDM model is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". But in his Leyden Address Einstein said "'empty space' in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gμν)...". Look at the Einstein field equations. They are describing inhomogeneous space. So when you start with the assumption that space is homogeneous you've got an issue. You've already thrown gravity away and limited yourself to a flat universe. Then you spend the next twenty years down a mine. See work by Webb et al re spatial variation in the fine-structure constant and understand that α depends upon the energy at which it is measured, increasing with increasing energy. So it isn't actually constant. And if it varies spatially, then since the cosmological constant is "equivalent to an energy density in otherwise empty space", that isn't constant either. Think of the raisins-in-the-cake analogy and do not duck conservation of energy. Space expands between the galaxies but no within, so the energy density is going to vary. Google on inhomogeneous vacuum energy, read papers like this: http://arxiv.org/pdf/1203.6776v2.pdf , and expect more of the same ilk.
I doubt you will get to see any such thing. In fact, during an interesting discussion I have had with Farsight on another forum, he has made it quite clear what he thinks of people trying to learn and apply proper maths. Let's just say his arguments weren't pretty. That's a new one Please Register or Log in to view the hidden image!
Not really, it's pretentious crank speak that translates to:- "I'm a comprehensive clueless muttonhead who finds addition of single digit integers profoundly challenging"
Would you care to give a link to back up that specious accusation, Markus? No, because I haven't been disparaging about people trying to learn and apply proper maths. What I have said is that mathematics is a vital tool for physics, and we can't do physics without it. I've also said that it isn't the only tool in the box, that it's important to understand what the terms mean at the fundamental level and avoid circular definitions, and that it's important to pay attention to the scientific evidence and to what Einstein/Minkowski/Maxwell etc actually said. Now can we get back on topic please? And talk physics and cosmology?
It wasn't an accusation, just a statement of fact. Here's the link : http://www.thescienceforum.com/physics/30741-gravity-mass.html#post361231 Refer to post #75 for starters. To me this comes across as saying that doing the maths is a waste of time. Why else would you reply "What's the point ?" after having been asked for a simple demonstration of your ability to tackle classical mechanics ? That request was in response to your claim that your physics knowledge far surpasses ours ( post #70 ). If your understanding of physics is so superior, then those exercises should have posed no problem to you, because the maths involved are just high school algebra. You are of course correct in stating that maths is an indispensable tool in physics, yet at the same time I see no evidence of you making any effort to actually learn it, instead all you do is give wordy quotations. Why ?
If you divide by a fraction, such as 1 divided by 1/2 =2 you can violate energy conservation. I have one proton and divide it by 1/2, now I have two protons. In this case, the operation of division by a half takes at least the energy equivalent of a proton or else energy conservation is violated. The conceptual model is the horse, while math is the cart. If you let the cart lead the horse, you can make anything work out simply by ignoring the energy needed to do certain operations. Getting back to dark matter, one thing I don't understand is if dark matter is generating gravity, why is it still free within the earth's gravitational field and not contained like most of the matter? Is dark matter analogous only to a gas, but not liquid or solid?
In post 75 I said this: That's hardly the ugly argument that you suggested. Not so. Saying understand your terms is not the same as maths is a waste of time. The point is that to understand the physics, you have to understand the terms. I gave adequate demonstration in that post 75 and on previous posts. By the way, are you engaged in some kind of poaching exercise here? Setting me up so that you can refer to a competitor forum where you're a moderator? Don't bother answering that. Now let's get back on topic please.
Correction, you mean talk your definition of 'physics' which is devoid of mathematics since you cannot do any. Analogies and examples only go so far. Throwing a ball into the air isn't just about 'it comes down' but where, when and how fast. Details are essential. And you'd realise this if you tried to do what everyone else means when they say 'physics'. Mathematics isn't a shield to hide behind, it is a microscope, a hammer and a scaffolding which allows us to ensure a proper formal understanding of phenomena can be developed. You have such a negative view of it because you cannot do it. Suck it up. No matter how much you desperately try to avoid it you'll not be able to get away from details. Newton and Einstein both predict the precession of Mercury. Without details you cannot distinguish them on such grounds, their arm waving both leads to the same conclusions. Formalise the models, crunch the algebra, make quantitative predictions and you find Newton fails and Einstein doesn't. This is why your 'explained' stuff is so laughable. Firstly you have no experience with previous models in physics, secondly you don't consider actual experimental data and thirdly you can only provide arm waving. You're worse than 'not even wrong' and all your 'stop hiding behind your maths shield' attempts to convince yourself otherwise will not change that. Where did I say otherwise? No, I didn't say that. I know basic logical statements and implications are something you cannot grasp very well but I said that matter's clumpy nature shows there isn't perfect homogeneity, I never said 'inhomogeneity involves matter'. That would mean I (to quote you) 'assume' that if there is inhomogeneity then matter is the cause. That is different to what I said, which was matter causes inhomogeneity. Clumped matter is a sufficient but not necessary thing for inhomogeneity. Of course the practice of rigorously exploring 'if and only if' (or 'sufficient and necessary') logical relations is something someone competent at mathematics knows all about, something you clearly don't grasp too well. You reply as if I didn't acknowledge that. I specifically addressed this before you even said it. I guess you don't even bother to read what I say or don't understand it. Either way it's your problem. None of which you can understand, seeing as your the mathematically version of illiterate. Again, you show you don't understand. The EFEs are capable of describing an inhomogeous universe, that doesn't mean their application to a homogeneous system is (to quote you) 'an issue'. Rather homogeneity and isotropy impose particular symmetries on the metric. If something is homogeneous then it doesn't change under translations. If something is isotropic then it doesn't change under a change of orientation, ie rotations. Such systems are completely consistent with the EFEs but they are by no means ALL the possible setups. Again, you show you don't grasp particular subtle issues about such things seeing as you have never done any such calculations yourself. You don't understand the metric or the Einstein field equations, you just want to arm wave about what you think you understand about them and telling people you have some kind of insight into it. Thanks for telling me something I learn almost a decade ago. Something I have published work about. Something I've given presentations to research groups about in terms of coupling 'running' in QCD, holographic gauge duals of complicated metrics and in regards to moduli stabilisation, the core principle in my PhD. Something I've talked about time and time and time again on this forum and on PhysForums. Just ask Sylwester, he and I have had plenty of interactions in regards to asymptotic freedom. I've also talked about questions of spatial or temporal variation in coupling constants on this forum multiple times. You might think that kind of concept or result is rarely known but you're talking to someone who actually does particle physics related work. In the last year I've probably devoted 3~4 months looking at renormalisation principles but applied to engineering paradigms, outside of theoretical physics. Every other person whose done particle physics here and elsewhere knows of renormalisation, it's one of the core results in quantum field theory. And do I think you can do ANY of the mathematical physics pertaining to what you're talking about? Do I hell! This behaviour of yours, to try and deceive (and it is deception, attempted or otherwise) people into thinking you can do the sorts of mathematical physics you link to is pretty pathetic. You tell me I try to hide behind a maths shield and then you link to multiple things which touches on precisely the sort of mathematics I was referring to, clearly in an attempt to make it seem like you understand it. You cannot have it both ways, you cannot pretend to know this stuff while complaining when I or anyone else refers to it it is an attempt to 'hide'. It shows you don't really understand it, else you'd just dial up your conversation level appropriately. You hide behind it, linking to documents you cannot understand, hoping that if the thing you link to is complicated enough people will back off and assume you understand it. Too bad your notion of aiming high is laughably low by any remotely competent physics or maths graduate. But you'd know that if you learn some mathematical physics details and didn't just pretend to understand it. If you wish to claim you do understand it then I'm sure we can sort out a discussion/debate between us with clearly defined terms where you either step up or step out. Not necessarily, yet another subtle thing you don't get right because you don't know the details. Even your quote hints at it, saying it is an energy density, doesn't mean it is the only possible one. A spatially varying cosmological constant does not automatically lead to all coupling constants varying in a similar manner, I can outline example constructions which have such a property. Of course you'll dismiss them because they are theoretical models but that isn't the point, they illustrate your carte blanche statement isn't an undeniable truth, requiring you demonstrate that specifically in the case of the fine structure constant there is experimental evidence your conclusion is correct, that it is 'coupled' in some way to the cosmological constant. You have no such evidence nor do you understand any models which involve either of those things and so it is just opinion, an opinion you cannot provide a model for nor justify experimentally. Wow, again and again and again you show you don't understand it. Space expands within galaxies in such cosmological expansion models. The reason they aren't ripped apart is that they are gravitationally bound together, enough to overcome the incredibly weak separation tendency introduced by the cosmological constant. And so the cosmological constant does change everywhere in such cosmological models. Of course that doesn't preclude the possibility of things in Nature behaving differently from the current model but you have no such model to put on the table and you've shown you don't understand the model currently on the table anyway. This isn't even a matter of grasping the specific details of the metric's equations, it's a pretty simple qualitative concept. I guess you didn't understand or don't remember that from all those pop science sources you 'diet' upon. Gee thanks, I'll then go back in time and tell my past self from my PhD all about the running coupling and spatial variation of couplings, maybe that will help with the dozen or so computer programs I wrote to model exactly those concepts within simple cosmological models that year. Please Register or Log in to view the hidden image! You really have no idea....
