Dark Matter, WIMPS, and NASA's Alpha Magnetic Spectrometer Data 44
cylonlover writes "Recently the media has been saturated with overly-hyped reports that NASA's Alpha Magnetic Spectrometer may have detected dark matter. These claims may have some justification if the word 'may' is shouted, but they rest on a number of really major assumptions and guesses, some of which are on weak and shifting soil. So just what was seen in the experiment, and what are the possible explanations?"
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No, trust me, the media is saturated. I mean, shit, samzenpus posted an article about it on Slashdot and everything.
Never trust... (Score:5, Funny)
Never trust an Alpha Magnetic Spectrometer with important discoveries. I wouldn't even start considering it useful until it hit Beta.
Re: Never trust... (Score:1)
That is pretty goddamn funny no lie.
Funny and True (Score:2)
Never trust an Alpha Magnetic Spectrometer with important discoveries.
What makes this funnier is that it is true! Nobody will really believe that the AMS positron signal is from Dark Matter until we have discovered the Dark Matter itself. It may useful in giving us an idea of where to search. Indeed the earlier discovery by PAMELA of the signal AMS is studying already lead to new models for DM which can explain the lack of anti-protons.
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your phrase of "until we discover" is funny. most of the dozens of"exotic" subatomic particles we know of are from second, tertiary and high decay products that are more common ordinary things.
by your definition, we've mostly only discovered electrons and protons, even neutrons and neutrinos are detected by reactions that make electrons or protons do something.
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most of the dozens of"exotic" subatomic particles we know of are from second, tertiary and high decay products that are more common ordinary things.
Yes but in these cases we have the 4-momenta measured of most, if not all, the particle in the decay and so can reconstruct the invariant mass of the decaying particle along with other properties like charge and spin. Saying that a massively complex and not fully understood system like the galaxy is producing more positrons than we think it should is a very, very different from saying that we see a mass resonance at a particular value.
For example if instead of showing a mass peak when looking at Higgs t
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it is indeed "most", not all; for example those "little neutral ones" go flying out of the chamber/collision hall undetected at most labs.
you are right that far more evidence is needed, but the cool thing is that the data gathering started in the 1930s with stars in galaxies just not moving the right way. these are exciting times
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go flying out of the chamber/collision hall undetected at most labs.
Yes...and no. They can be indirectly detected by requiring conservation of momentum in a plane transverse to the beam. This is not as good as actually seeing them but we can easily reconstruct W boson decays which involve neutrinos and we can even measure the W boson mass although it is an incredibly complex analysis.
Treasure! (Score:2)
Nobody will really believe that the AMS positron signal is from Dark Matter until we have discovered the Dark Matter itself.
Maybe the proof is on an island you can only find if you already know where it is. [/piratesofthecarribean]
Blog Spam (Score:2)
Editors/moderators haven't had their coffee today?
Re:Blog Spam (Score:4, Informative)
Usually we don't discuss these things until they appear on the Bad Astronomy blog.
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How the source adds nothing to the discussion? I've seen this on slashdot when the story first appeared, and the media coverage was uniformly believing CERN's hype, without a shred of scepticism. This blog has a simple, correct explanation of the physics involved, and its interpretation of the data pretty much agrees with I've been hearing at the University.
Over-saturation is bad! (Score:2)
Recently the media has been saturated with overly-hyped reports that NASA's Alpha Magnetic Spectrometer may have detected dark matter
So here's another story about it. Brilliant.
These claims may have some justification if the word 'may' is shouted
The word is "emphasised." Try it now - read that out loud and shout the word "may."
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We demand that NASA's Alpha Magnetic Spectrometer may or may not have detected dark matter!
more antimatter near Earth than expected (Score:3)
The amounts are so small, dozens of protons for PAMELA and hundreds of thousands of positrons for AMS, that they would not be noticeable in human life.
Dark Matter and the Rest of Us (Score:2)
Is the article a bit "fluffy"? Sure. But if the link was
Old News With Smaller Error Bars (Score:1)
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It also goes to higher energy, and the longer the experiment lasts, the higher the energy range that will be explored (it is count-limited at the highest energies).
Of Particular Significance (Score:3)
People who are interested in these matters should follow Matt Strassler's science blog, Of Particular Significance [profmattstrassler.com], which covered these same points back at the beginning of April [profmattstrassler.com], and then again two weeks later [profmattstrassler.com].
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why no dark matter black holes? (Score:2)
We would definately notice dark matter signularities, since there is six times more of it than the non-dark kind.
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It wouldn't collapse into a blackhole if it never gets dense enough. And without electromagnetic interactions, it is much more difficult to form a dense object. If two charged particles collide, the acceleration they experience causes photons to radiate away some of the energy. If you have a pile of charged particles, the interactions will cause radiation of energy, cooling the pile of particles off and causing it to become more dense. Without that interaction, the particles would just all pass through
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Gravitational lensing surveys [harvard.edu] have pretty much ruled out [arxiv.org] this Dark Matter explanation for black holes (or any other dark compact objects) with masses > about 10^-7 Solar Masses, and it is very hard to see how smaller black holes could have ever formed.
Re:why no dark matter black holes? (Score:5, Insightful)
If dark matter only reacts to gravity, why doesnt collapse into hgh density clumps over the eons? Ordinary matter is stopped from doing this by the electronmagnetic repulsion of atoms for masses less than a few hundred Jupiters and by hadronic stong force for less than couple Suns.
It does, we call those clumps "galaxies".
Note that the virtue of interacting only a little bit with normal stuff (via only the weak and gravitational forces, not gravity alone) actually makes it harder for dark matter to pack in tightly. Why? it's hard for a distribution of dark matter particles to shed kinetic energy and settle down more deeply into the gravitational potential well. Ordinary matter has all sorts of electromagnetic ways to shed energy and cool down.
If this thermal argument is opaque, imagine one WIMP, with some kinetic energy. It falls down towards the center of a galaxy. But, it seldom interacts to lose any energy, so zooms right back out the other side. Sort of a tiny, frictionless pendulum with a galaxy sized amplitude.
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This is kinda putting the horse before the cart. The fact that galaxies exist as localized clumping of matter is postulated to be due to this "dark matter" substance that does not interact with anything else, including itself, in any way except by gravity. I.e., dark matter is the proposed explanation for galaxies, not the other way around.
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This is kinda putting the horse before the cart. The fact that galaxies exist as localized clumping of matter is postulated to be due to this "dark matter" substance that does not interact with anything else, including itself, in any way except by gravity. I.e., dark matter is the proposed explanation for galaxies, not the other way around.
Speaking of cart drawn horseages...
If gravity warps space time, then we agree space time can be warped. We observe that cosmic background radiation from the big bang isn't perfectly smooth. So, what if the structure of space is just slightly "warped?" Dark matter could just be space time curvature. Instead of the clustering up of galaxies being the result of more matter being present, the matter could just be pooling into places that are already more curved. In other words: You turn on a light, you
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Improperly worded summary (Score:5, Informative)
From the summary: "... reports that NASA's Alpha Magnetic Spectrometer ..."
AMS isn't a NASA experiment, it is an international collaboration and NASA is only one among many other collaborators. Source: http://www.ams02.org/partners/participating-institutions/ [ams02.org]
I believe this summary is badly worded letting people think the AMS experiment is even a NASA initiative while it isn't neither. It is a CERN experiment that is taking advantage of the ISS and hence the NASA collaboration. Even other space agencies have contributed in this experiment.
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NASA didn't even want to launch it, they had to have their arm twisted to schedule an extra Shuttle mission so it wasn't just left on the ground to rot.
dark matter (Score:1)