2012-03-22
On Strong Magnetic Fields
Robert Duncan, Strong Magnetic Fields:
Many fascinating physical effects occur in magnetic fields with strength exceeding the “quantum electrodynamic field strength” of BQ=4.4×1013 Gauss. (This field-strength given by a combination of fundamental constants: BQ = me2c3/he, where me is the mass of the electron, c is the speed of light, h is Planck’s constant divided by 2 π, and e is the charge on an electron.) In fields stronger than BQ, electrons gyrate at nearly the speed of light around magnetic field lines, even in their lowest quantum energy states. Consequently, the ultra-magnetized vacuum — which, according to quantum mechanics, seethes with virtual electron-positron pairs and other particles — becomes birefringent like a calcite crystal, capable of distorting and magnifying images (“magnetic lensing”). X-ray photons traveling through such strong fields readily split into two, or merge together; and many other novel physical effects come into play.
There’s more on extremely strong magnetic fields at this arxiv paper. (via science.tumblr.com’s post on magnetars)
2012-02-23
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Google’s doodle for the 155th anniversary of the birth of Heinrich Hertz, who expanded on Maxwell’s work and experimentally detected electromagnetic waves.
2012-02-19
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Kristian Birkeland’s terrella, as pictured in an article about his use of the models at Sphæra, the newsletter of the Museum of the History of Science, Oxford:
Birkeland’s largest experiment was carried out in 1913 in a large vacuum chamber of 1,000 litres capacity with terrellas of 24 and 36 cm in diameter. This apparatus became very well known for its ability to recreate Aurora effects and in Norway its fame is such that it is depicted on the Norwegian 200 kroner banknote.
That banknote is one of the most attractive I’ve seen from any country. Sadly, as this excerpt of Lucy Jago’s excellent book The Northern Lights recounts, Birkeland’s theoretical explanation of the aurora, based on observational work in the far north of Norway during long, cold winters failed to convince the influential British scientific establishment:
Arthur Schuster, a Fellow of the Royal Society and a prominent scientist in the field of terrestrial magnetism, dismissed Birkeland’s huge volume with a terse comment in the Society’s Proceedings:
“Even originally well-defined pencils of cathode rays from the sun cannot reach the Earth. For Birkeland’s theories to be correct, the existence of such cathode rays is clearly presupposed to be necessary… and this assumption is untenable.” Birkeland was furious, for he knew that, if his theories were ever to be widely disseminated, it was necessary for the British scientific establishment to accept them. Over the next five years, Birkeland’s life fell apart.
It was only in the 1960s that the “cathode rays”, or what we’d now call the solar wind (a stream of charged particles, both electrons and protons) were observed and his theories about the cause of aurora were vindicated.
(inspired by Dan W’s post of a different image of a terrella)
2011-05-06
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Physics and compsci are almost level. Interestingly (to me, anyway) astronomy/astrophysics is a bit further towards a 50/50 split. (via Gender Composition of Academic Disciplines: PhDs in 2009 at Sociological Images)
2010-11-08
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Figure 14: Followers of τism seek the way of the τ
from The Tau Manifesto by Michael Hartl, which argues that τ (= 2π) would be a more useful physical constant.
2010-02-22
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Jez Paxman, in That’s the story, talking about a talk at The Story conference Matt Locke organised that I attended on Friday.
Spooner’s talk, which was early in the day (when most people were still shocked at arriving at Jackanory Live rather than How To Convey A Narrative) probably left me feeling more annoyed than any other.
It started off straightforwardly enough, with a slightly boiled down but essentially correct description of the neutrino, but then started to try and connect the particle with “coincidences”, claiming that when - if - a neutrino interacts with the matter in your body, a coincidental happening is the result. This instantly got my back up; it’s close to the sort of “quantum homeopathy” rubbish that New Scientist’s Feedback so often criticises, and left me wondering if Spooner just didn’t understand the science.
As his talk progressed, though, and got more outlandish, I realised that we’d turned a corner, from truth to fiction. I’m so used to people being (unknowingly?) incorrect about physics and science that my first response was not to assume storytelling, but misunderstanding. Evidently I hadn’t yet mentally adjusted to the tone of the conference.
Afterwards, I mentioned this to some of my friends, who spotted the transition from more-or-less correct physics to a story instantly. That’s probably because they don’t share my hangups. Reading Paxman’s quote now, though, I’m wondering if I wasn’t right to feel annoyed at launching a story - a fiction, or even a pack of lies - from a foundation of truths, as it seems to have caused confusion between the science and the story.
On the other hand, maybe I’m reading Paxman wrong, and he too knows that the “complex scientific theories” portrayed weren’t real. As I’ve indicated above, it would hardly be the first time I’ve been too literal-minded.
