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Comment Re:radiation shielding? bullshit (Score 1) 93

For neutron shielding, you want low-Z material, not low density material. Neutron shields are pretty much always made of concrete, water, or high density polyethylene (HDPE). All of those are relatively high density (compared to a metal foam anyway). What all those have in common is a high density of hydrogen (concrete less so, but it's cheap so you can put more of it). Metal foam is low density, low hydrogen content, so pretty much the worst thing you could think of for neutron shielding.

And of course gamma and x-rays only differ in the frequency, but that means the energy, and more importantly the radiation length / penetration depth. The mm-thick layer of lead in the aprons they give you at the dentist will block x-rays, and low energy gamma rays, just fine, but they won't do anything to >MeV gammas that are the real problem with radioactive sources.

Also just in case you want to be pedantic, x-rays and gamma rays are labeled as such not just by energy, but by emission source. X-rays are generated by atomic de-excitation, while gammas are generated by nuclear processes, so there are actually some gamma rays with lower energy than some x-ray lines.

Comment radiation shielding? bullshit (Score 1) 93

I do radiation shielding for a living, and there is no way 1 inch of low density _anything_ is going to give you any kind of useful radiation shielding. Maybe x-rays will be attenuated enough to talk about, but you may as well paper for all the neutron and high energy gamma shielding that will give you.

Comment Re:Temba ... his arms wide ... (Score 3, Insightful) 104

Yes. The idea is that Dark Matter particles interact via the same force (the Weak Force) as neutrinos.

Everything else you wrote is spot on, but WIMPs have been ruled out as truly Weakly interacting (where Weak with a capital W means "by the exchange of W or Z bosons) for almost a decade now. The original Weak Miracle posited WIMPs to be truly Weakly interacting, but now they are held to be sub-Weak, interacting most likely through Higgs exchange, but we kept the name. Really we should rename them wIMPs at this point.

Also I hate whoever decided to use Weak and Strong as formal names for those respective interactions.

Comment it's all about precision (Score 3, Interesting) 160

Sometimes three is just an inherent smarty-pants style to writing academic papers. I lose track of how many times I instinctively try to write something like "utilize" or "make use of" when a simple "use" will work.

But, at least in scientific writing, you use complicated language in order to be absolutely precise about your method and findings (as opposed in particular to scientific journalism...). As an example, I work in the field of direct experimental searches for evidence of interactions between particle dark matter and nuclei. That's a huge mouthful, but every single word in that phrase carries distinct meaning, and if you take any of them out, it is not a correct description of what I do, and may refer to another field entirely.

Now take that kind of precision and discuss an experimental result. "We find that, at 90% confidence level, there is no statistically significant evidence for X". Again, it sounds like buzzwords and jargon, but there is simply no way to turn that statement into "common" English.

Comment give this one a pass (Score 1) 153

Silly me, making the mistake of reading TFA on /. ( aside: what's the proper way to punctuate a sentence ending in /.?)
You want to know how we 'know' all of those things with such great precision? It's all about the scale of temperature fluctuations in the cosmic microwave background. The CMB is a snapshot of the universe some 30k years after the big bang, during the time of first neutralization, when the pathlength of photons quickly (on cosmic scales) went form very short in the hot plasma (think neon light tube) to mostly neutral hydrogen. The spectrum of density fluctuations there tells an incredible amount about how the small perturbations left over from inflation evolved during that early time, and is the main stick by which all of our cosmological models are tested. The incredible agreement with the standard cosmological model and the CMB using only 7 free parameters is probably the most successful accomplishment in scientific history.

Nowhere on the article's page of drivel is the CMB mentioned, nor the WMAP or Planck satellites which were responsible for bringing us that data. I didn't read much of the article, but there is simply no way to speak intelligently about early universe models without the CMB. If you actually want to learn about this stuff, take a look at some of the public stuff NASA has put together for WMAP at http://map.gsfc.nasa.gov/missi... ; some of the animations are really quite revealing, and I use them in seminars on the subject all the time. Then if you're still hungry for more and can handle the math, take a look at Dodelson's Modern Cosmology.

Bah, still too angry about this kind of crap. Not a good way to start the week.

Comment weakly interacting != the weak nuclear force (Score 5, Insightful) 93

I got about 1 paragraph into the article before it became obvious that the author had no clue what the hell he was talking about. Maybe the old paper was better, but I don't have the patience to try to find out. From TFA:

They would interact only through the feeble weak nuclear force—one of two forces of nature that ordinarily flex their muscle only within the atomic nucleus—and could disappear only by colliding and annihilating one another

So many things wrong just in that sentence
1) Weakly Interacting Massive Particles (WIMPs) do have very low interaction cross sections (read: rates). There's sometimes an unfortunate ambiguity in the fact that phycisists have no imagination and gave two of the fundamental forces the names Strong and Weak. To say something interacts Weakly means that it interacts by exchange of W or Z bosons, not just that it has a low rate. However the WIMP interaction cross section has been known to be sub-Weak by several orders of magnitude for decades.

2) The Weak force's most obvious manifestation is in the production or absorption of neutrinos (beta decay or inverse beta decay) in a nucleus, but that's certainly not the only place it shows up; it's the mechanism for neutrino-electron scattering, muon decay, and a whole bunch of other stuff up to driving supernova explosions

3) Self-annihilation is the vanilla model for WIMP transformation, but there are plenty of sundaes-with-cherries-on-top models like self-interacting dark matter, which is discussed about 2 sentences later. Also, the chi is the symbol for the supersymmetric neutralino, often equated to a vanilla WIMP, and is not at all specific to the self-interacting dark matter model.

In short, cbtfaij;dr (can't bother to find an intelligent journalist; don't read)

Comment complete and utter rubbish (Score 5, Informative) 225

I'm probably a bit biased here, but also an expert, since I am a physicist who studies dark matter for a living.

The title's question doesn't even make sense! Big bang theory, and in particular studying the exact power spectrum of the cosmic microwave background, is by far the strongest evidence we have for the existence of dark matter and dark energy. All those pie charts you've seen showing the divisions of baryonic matter, dark matter, and dark energy? If they're properly cited, I guarantee every single one of them comes from data from WMAP or PLANCK: CMB experiments! You can't say that dark matter gives you room to invalidate the big bang, because without that we don't have really any strong evidence for non-baryonic dark matter in the first place...

Comment Re:overrated, anyway (Score 4, Interesting) 732

You completely missed the point of the book if that's what you got. What made Ender the supreme commander wasn't his intelligence; he was brilliant, but not significantly more so than many of the other kids. Ender's gift was his empathy: what allowed him to overcome his foes was exactly that he DIDN'T see them as less than human, but that he respected, maybe even loved his adversaries, even as he set up to destroy them.

I won't argue about the rest of the series though

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