Thursday, July 28, 2005

General Relativity Resolves Galactic Rotation Without Exotic Dark Matter

by F. I. Cooperstock, S. Tieu, Preprint in the physics archive.

The stars in galaxies are observed to have "flat rotation curves", the velocity of the stars is the same, independent of their distance from the center of their galaxy. However, when we look at the distribution of luminous matter in the galaxies, Newtonian gravity predicts that the velocity of stars should fall off. Hence all the buzz about "Dark Matter", that there must be non-luminous matter in galaxies which is causing the stars to rotate uniformly.
However, Newtonian gravity is not the final word. Einstein's 1915 theory of gravity, General Relativity, makes more accurate predications. It was thought though, that because gravity is very weak in galaxies (apart from black holes and the small supermassive region at the very center of the galaxies) that the differences between Newton's theory and Einstein's theory would be insignificant.
To the contrary, the authors point out that the differences are very significant. They claim to reproduce the observed rotation curves with a quite reasonable distribution of matter, consistent with the observed distribution of luminous matter using General Relativity instead of Newtonian gravity.
There's been a veritable industry of Dark Matter research with all kinds of exotic proposals for new, hereto unobserved forms of matter. This now appears superfluous.

Monday, July 25, 2005

The Arrow of Time and the Initial Conditions of the Universe

by Robert M. Wald. preprint at the physics archive.

Wald is critical of "inflation" the standard explanation for some of the key features of the Big Bang.

Thursday, July 21, 2005

In This Corner, in the Flouncy Skirt and Bowler Hat...

Published: July 21, 2005 article in the New York Times

Noah Friedman-Rudovsky for The New York Times

Wrestlers warming up in El Alto, Bolivia, near La Paz. Indigenous women, dressed in their traditional garb, are the stars of the increasingly popular bouts, Bolivia’s version of the World Wrestling Federation

Friday, July 15, 2005

Thickness of ventromedial prefrontal cortex in humans is correlated with extinction memory

Article published online in PNAS.

The ventromedial prefrontal cortex is a part of the brain which has been show to be involved in fear extinction. In this study, the subjects were conditioned to associate a light with an electric shock. Then they were shown the light without the shock - the extinction phase. The next day they were again shown the light with no shock, to test "extinction retention". Skin conductivity was used to measure fear. There was a correlation between the thickness of the medial orbitofrontal cortex and lower skin conductivity.

Jack in "24" could be pretty thick.

Flying Snakes

Check out the web site for images and movies of the flying snakes of Asia. They jump from trees and then glide of course, they don't truly fly.

Brain Under Surveillance: The Microglia Patrol

Perspective in Science Magazine.

Microglia patrol the brain and shield it from injury. Microglia continually extend (green) and retract (yellow) processes, surveying their immediate environment within the brain. The processes move rapidly toward a site of injury, such as a damaged blood vessel in the brain, in response to the localized release of a chemoattractant (gradient of orange) from the injured sited. Once at the target site, the processes form a barrier to protect healthy tissue.

Researchers have used two-photon microscopy on living mouse brains to image microglia (common brain immune cells) in motion. They genetically engineered the mice so that their microglia were fluorescently labeled.

A previous microglia post

Tuesday, July 05, 2005

The Pioneer Anomaly

from NASA

The Pioneer and Voyager spacecraft are furthest from the Sun of any spacecraft launched so far. They are experiencing a small but apparently significant unexplained sunward acceleration. There's a proposal to launch a new mission to understand this phenomenon: A Mission to Explore the Pioneer Anomaly

Saturn's Rings

Waves and Small Particles in Ring A

See the full explanation and an even larger version of this gorgeous image at JPL/NASA

Friday, July 01, 2005

Stephan’s Quintet

Stephan's Quintet as imaged by the Gemini Observatory using the Multi-Object Spectrograph on Gemini North. The interacting members of the cluster are almost 300 million light years away. The galaxy NGC 7320 (top–center) is thought by most astronomers to be in the foreground (about 8 times closer) and is distinguished in this image by multiple red blobs indicating hydrogen clouds where stars are forming. Orientation: North–bottom, East–right.
Galactic Contortionists Captured by Gemini

From the image gallery at the National Optical Astronomy Observatory.

New Pillow from Japan

TOKYO - A new product on the Japanese market has been designed for the single girl in need of some manly comfort while she sleeps.

The “Boyfriend Arm’s Pillow” is shaped like a giant arm which will hold you all night without the need for the real thing.

The almost life-size boyfriend pillow is the product of the Japanese bed linen maker, Kameo Corp., located in the Japanese city of Fukuoka. The company already sold more than 1,000 pillows since its launch last year. It costs $80 dollars (8,500 yen) and is currently only sold in Japan on the Internet.
Kameo is now planning to upgrade the pillow by producing different models, including a muscular one. And the company is also working on the prototype for a fake female lap shaped pillow targeting male users.

The company says the shape of the pillow does not just provide the illusion of having someone sleeping next to you. Tomoki Kakehashi of Kameo says the unique structure keeps the human body balanced by supporting the sleeper from both sides.

“My grandmother used to say that there is nothing more comfortable pillow than human,” says Kakehashi. “I always thought someone’s lap is the best pillow for me. So, I thought that maybe women want to sleep on the arm shaped pillow. As a fact, my kids always like to sleep on my arm. Human pillow seems to be warm and healing. This is why I made this arm shaped pillow.”