Tuesday, December 29, 2009

Change Blindness

Video of a dumbfounding Harvard experiment on "change blindness".

Here's another video on Youtube along the same lines.

Saturday, December 26, 2009

Parity Invariance

The Mystery of Parity
"And should I not take pity on Nineveh, that great city, with more than a hundred and twenty thousand inhabitants who do not know their right hand from their left, and many beasts besides?" [Jonah 4:11]
In this article we shall be concerned with microscopic parity invariance and a mystery which it presents. This consists of a marriage of internal and space-time symmetries, forbidden when the space-time symmetry consists of the whole Poincare group but permitted in this case because of the discrete nature of the parity transformation. We will argue that this marriage could point to regularities underlying the nature of quarks and leptons, and to extensions of particle interactions beyond those known today.

time reversal invariance violation

Large scale physical effects of T violation in mesons
An increasing number of experiments at the Belle, BNL, CERN and SLAC accelerators are confirming the violation of time reversal invariance (T). The violation signifies a fundamental asymmetry between the past and future and calls for a major shift in the way we think about time. Here we show that processes which violate T symmetry induce destructive interference between different paths that the universe can take through time. The interference eliminates all paths except for two that represent continuously forwards and continuously backwards time evolution. Evidence from the accelerator experiments indicates which path the universe is effectively following. This work resolves the long-standing problem of modeling the dynamics of T violation processes. It shows that T violation has previously unknown, large-scale physical effects and that these effects underlie the origin of the unidirectionality of time. It also provides a view of the quantum nature of time itself.

Missing Baryons

The Baryon Content of Cosmic Structures
We make an inventory of the baryonic and gravitating mass in structures ranging from the smallest galaxies to rich clusters of galaxies. We find that the fraction of baryons converted to stars reaches a maximum between M500 = 1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright galaxies in groups. The fraction of baryons detected in all forms deviates monotonically from the cosmic baryon fraction as a function of mass. On the largest scales of clusters, most of the expected baryons are detected, while in the smallest dwarf galaxies, fewer than 1% are detected. Where these missing baryons reside is unclear.

Flavor Physics

Brief Introduction to Flavor Physics
We consider the standard model (SM) quark flavor sector. We study its structure in a spurionic, symmetry oriented approach. The SM picture of flavor and CP violation is now experimentally verified, hence strong bounds on beyond the SM flavor structure follow. We show how to parametrically derive such bounds, in a model independent manner, via minimal flavor violation power counting. This min-review summarizes lectures given at the ISSCSMB '08 international school. It aims to give basic tools to understand how flavor and CP violation occur in the SM and its extensions. It should be particularly useful for non-expert students who have mastered other aspects of the SM dynamics.

Note: A spurion is the name given to a "particle" inserted mathematically into an isospin-violating decay in order to analyze it as though it conserved isospin. --- Wikipedia

Friday, December 25, 2009

Proton Spin

Understanding the proton's spin structure
We discuss the tremendous progress that has been towards an understanding of how the spin of the proton is distributed on its quark and gluon constituents. This is a problem that began in earnest twenty years ago with the discovery of the proton ``spin crisis'' by the European Muon Collaboration. The discoveries prompted by that original work have given us unprecedented insight into the amount of spin carried by polarized gluons and the orbital angular momentum of the quarks.

Thursday, December 24, 2009

Quantum Leaps

I just read the book Quantum Leaps by Jeremy Bernstein. He is an entertaining writer. The book discusses the history of the "Quantum Measurement" problem and also his expereiences as a physics student and journalist - he met many of the key historical figures over the years.
However, he did not actually meet the personalities in this ancedote (my paraphrase follows).
Beria was put in charge of the Soviet nuclear program. He complained to Stalin that the scientists were using quantum techniques, which were held to be in conflict with Marxism. Stalin allegedly told Beria "Leave my physicists alone. We can always shoot them later."

Wednesday, December 23, 2009

Modified Gravity

New Physics at Low Accelerations (MOND): an Alternative to Dark Matter
I describe the MOND paradigm, which posits a departure from standard physics below a certain acceleration scale. This acceleration as deduced from the dynamics in galaxies is found mysteriously to agree with the cosmic acceleration scales defined by the present day expansion rate and by the density of `dark energy'. I put special emphasis on phenomenology and on critical comparison with the competing paradigm based on classical dynamics plus cold dark matter. I also describe briefly nonrelativistic and relativistic MOND theories

Quantum Measurements and General Relativity

There are sticky issues when trying to understand how quantum measurement and general relativity might work together. Relativistic Model for Gravity-Induced Quantum State Reduction
A Lorentz invariant model for gravity-induced quantum state reduction is presented, which is mainly developed from the physical argument that the time translation operator in a superposition of macroscopic states is ill-defined. The model leads to a new approach how to overcome the basic problem of relativistic reduction models, the conflict between relativistic covariance and the assumption that state reduction leads to an abrupt change of the wave-function on a space-like hyperplane. Reductions are understood in the model as events on whole space-time regions instead on hyperplanes only. This view enforces a radical change for the formulation of the system's dynamics. A stochastic time flow running quasi orthogonal to the deterministic time evolution inside the four-dimensional space-time is proposed. It is shown that it is possible to formulate on the basis of this new view a meaningful physical model. The model is also checked for possible higher order effects, which provide new starting points for experimental research.

Tuesday, December 22, 2009

Dive Pictures

I went scuba diving in Grand Cayman last week - there were lots of turtles.

Reading the Mind in the Eyes

Reading the mind in the eyes is a test to determine how well can you tell what a person is thinking or feeling from a photograph of their eyes. I scored 28 out of 36. The typical range is 22-30 with over 30 indicating that you are exceptionally good at reading people and under 22 indicating that isn't one of your strengths. I would have guessed that I was about average at reading people's expressions, which this test confirms.
I took the test again on another web site, with a different format (you got immediate feedback after each question instead of at the end). This time I improved to 32/36 which isn't too surprising since they appeared to be the same pictures.