Revista Scientific American Febrero 2017. Inglés

Revista Scientific American Febrero 2017. Inglés

ISSN: 0036-8733

Descripción

The Exercise Paradox
Studies of how the human engine burns calories help to explain why physical activity does little to control weight and how our species acquired some of its most distinctive traits

Still no giraffe. Four of us had been walking half the day, tracking a wounded giraffe that Mwasad, a Hadza man in his late 30s, shot the evening before. He hit it in the base of the neck from about 25 yards with a steel-tipped, wood arrow smeared with powerful, homemade poison. Hadza are traditional hunter-gatherers who live off wild plants and animals in the dry savanna wilderness of northern Tanzania. They know the landscape and its residents better than you know your local Trader Joe’s. Mwasad had let the giraffe run to give the poison time to work, hoping to find it dead in the morning. An animal that size would feed his family and his camp for a week but only if he could locate it.

Cosmic Inflation Theory Faces Challenges
The latest astrophysical measurements, combined with theoretical problems, cast doubt on the long-cherished inflationary theory of the early cosmos and suggest we need new ideas

By Anna Ijjas, Paul J. Steinhardt, Abraham Loeb
On March 21, 2013, the European Space Agency held an international press conference to announce new results from a satellite called Planck. The spacecraft had mapped the cosmic microwave background (CMB) radiation, light emitted more than 13 billion years ago just after the big bang, in better detail than ever before. The new map, scientists told the audience of journalists, confirms a theory that cosmologists have held dear for 35 years: that the universe began with a bang followed by a brief period of hyperaccelerated expansion known as inflation. This expansion smoothed the universe to such an extent that, billions of years later, it remains nearly uniform all over space and in every direction and “flat,” as opposed to curved like a sphere, except for tiny variations in the concentration of matter that account for the finely detailed hierarchy of stars, galaxies and galaxy clusters around us.