A bit about climate change
Save This Post as PDFRecently, an idea that sharp terrestrial climate change might be directly correlated to spiral arm passages of the Solar system became very popular. Namely, certain correlations of times of spiral arm passage with timing of ice ages and abundance of 
in fossils were claimed to be found (in the latter case, effective abundance of grows if gets locked up in ice). The basic idea is that if Solar system goes through spiral arms of the Milky Way, the event rate of cosmic rays in the Earth’s atmosphere greatly increases (since the number of supernovae in spiral arms is clearly much larger than in between the arms) and this presumably affects formation of clouds and therefore strength of greenhouse effect. However, in reality we don’t know very well when Solar system passed between the Galactic arms to make sufficiently strong statements about presence of such correlation.
In their recent paper “Testing the link between terrestrial climate change and Galactic spiral structure” Adrian Melott with collaborator debunk this hypothesis using new data about structure of the Milky Way (Englmaier et al., 2008 – see Fig. below from their paper).
Current location of the Solar system is shown by black dot; units on axis are kPcs.
The result of the study is that any such correlation as well as any periodic trend related to the rotation of the Galaxy is absent.
Via sergepolar.
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Susskind’s lectures on cosmology
Another amazing set of 8 lectures by Lenny Susskind – cosmology this time. Thanks for sharing this, Stanford!
P.S. If you were unable to see embedded video, here is the link to the playlist I’ve created for you.
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Other interesting things in ArXiv (12 Jun 2009)
Wayne Hu. Acceleration from modified gravity: lessons from worked examples. The main question Wayne Hu discusses in this minireview is “How can we distinguish dark energy from modified gravity theories if the former and the latter provide the same predictions for cosmological dynamics?” He is particularly focused on DGP and 
models. His answer is the presence of anisotropic stress for modified gravity models which is coupled directly to lensing potential – if we are able to measure this effect, we will be able to discriminate between IR modified gravity and dark energy. Another idea is to study behavior of theories in non-linear regimes, for example, by means of N-body simulation, and compare it to LSS.
M. Hermanns. Condensing non-Abelian quasiparticles. Maria Hermanns discusses physics of fractional quantum Hall effect at filling factor where elementary excitations (anyons) seem to possess non-Abelian statistics (
with odd 
). Corresponding wavefunctions are given by certain CFTs, and she is interested to understand the physics of daughter states in these CFTs.
H. Perets et al. A new type of stellar explosion. As we know, all supernovae explosions are divided into two classes: Type I (a,/b/c) and Type II (let me remind you that Type Ia are standard candles and are used to determine expansion rate of the Universe at large redshifts). This team claims to discover supernova of a new type which does not fit this classiication. Maybe, I’ll write about this result in more details later.
R. Williams et al., Skyalert: Real-time Astronomy for You and Your Robots. Skyalert.org is a web application which will be certainly useful for astronomers – professionals and amateurs. It collects data about time-critical astronomical transients and then pushes them to subscribers who, but setting their own trigger rules, can filter events according to the location, magnitude, etc. etc.
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How to use technology to teach undegraduate biology
Explanations by Stony Brook U. professor William Collins: it was fun to watch for me.
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The very meaning of socialism
Hehe, Lubos Motl will go crazy… 
I received a rather strange email message yesterday; since it was from unspecified person (spam in other words), I decided to share it with you – see below.
An economics professor at Texas Tech said he had never failed a single student before but had, once, failed an entire class. The class had insisted that socialism worked and that no one would be poor and no one would be rich, a great equalizer. The professor then said ok, we will have an experiment in this class on socialism. All grades would be averaged and everyone would receive the same grade so no one would fail and no one would receive an A.
After the first test the grades were averaged and everyone got a B. The students who studied hard were upset and the students who studied little were happy. But, as the second test rolled around, the students who studied little had studied even less and the ones who studied hard decided they wanted a free ride too; so they studied little..
The second Test average was a D! No one was happy.
When the 3rd test rolled around the average was an F.
The scores never increased as bickering, blame, name calling all resulted in hard feelings and no one would study for anyone else. All failed to their great surprise and the professor told them that socialism would ultimately fail because the harder it is to succeed the greater the reward but when a government takes all the reward away; no one will try or succeed.
That was the end of the message. So, I have two questions: a) what do you think about the story? and b) what are they trying to sell me?
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