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Surpreendentemente acessível e divertido

22.12.12

 

Obrigado Gabino.

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Fear of the known

29.11.12

 

As a young theorist in Moscow in 1982, Mikhail Shifman became enthralled with an elegant new theory called supersymmetry that attempted to incorporate the known elementary particles into a more complete inventory of the universe.

“My papers from that time really radiate enthusiasm,” said Shifman, now a 63-year-old professor at the University of Minnesota. Over the decades, he and thousands of other physicists developed the supersymmetry hypothesis, confident that experiments would confirm it. “But nature apparently doesn’t want it,” he said. “At least not in its original simple form.”

With the world’s largest supercollider unable to find any of the particles the theory says must exist, Shifman is joining a growing chorus of researchers urging their peers to change course.

(...)

If nothing new turns up — an outcome casually referred to as the “nightmare scenario” — physicists will be left with the same holes that riddled their picture of the universe three decades ago, before supersymmetry neatly plugged them. And, without an even higher-energy collider to test alternative ideas, Falkowski says, the field will undergo a slow decay: “The number of jobs in particle physics will steadily decrease, and particle physicists will die out naturally.”

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"Seeing quantum mechanics with the naked eye"

09.01.12

 

 "Quantum mechanics normally shows its influence only for tiny particles at ultralow temperatures, but the team mixed electrons with light to synthesise supersized quantum particles the thickness of a human hair, that behave like superconductors.

Building microscopic cavities which tightly trap light into the vicinity ofelectrons within the chip, they produced new particles called ‘polaritons’ which weigh very little, encouraging them to roam widely.

Dr. Gab Christmann working with Professor Jeremy Baumberg and Dr. Natalia Berloff of the University of Cambridge, together with a team in Crete, produced the special new samples needed which allow the polaritons to flow around at will without getting stuck.

Injecting them in two laser spots, they found that the resulting quantum fluid spontaneously started oscillating backwards and forwards, in the process forming some of the most characteristic quantum pendulum states known to scientists, but thousands of times larger than normal.

According to Christmann: “These polaritons overwhelmingly prefer to march in step with each other, entangling themselves quantum mechanically.”

The resulting quantum liquid has some peculiar properties, including trying to repel itself. It can also only swirl around in fixed amounts, producing vortices laid out in regular lines.

By moving the laser beams apart, Dr. Christmann and his colleagues directly controlled the sloshing of the quantum liquid, forming a pendulum beating a million times faster than a human heart.

Dr. Christmann added:  “This is not something we ever expected to see directly, and it is miraculous how mirror-perfect our samples have to be.We can steer our rivers of polariton quantum liquid on the fly by scanning around the laser beams that create them.”

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Too cool for pics

14.07.10

It’s hard to imagine a more fundamental and ubiquitous aspect of life on the Earth than gravity, from the moment you first took a step and fell on your diapered bottom to the slow terminal sagging of flesh and dreams.

(...)

But what if it’s all an illusion, a sort of cosmic frill, or a side effect of something else going on at deeper levels of reality?

So says Erik Verlinde, 48, a respected string theorist and professor of physics at the University of Amsterdam, whose contention that gravity is indeed an illusion has caused a continuing ruckus among physicists, or at least among those who profess to understand it. Reversing the logic of 300 years of science, he argued in a recent paper, titled “On the Origin of Gravity and the Laws of Newton,” that gravity is a consequence of the venerable laws of thermodynamics, which describe the behavior of heat and gases.

(...)

Over the last 30 years gravity has been “undressed,” in Dr. Verlinde’s words, as a fundamental force.

(...)

This disrobing began in the 1970s with the discovery by Jacob Bekenstein of the Hebrew University of Jerusalem and Stephen Hawking of Cambridge University, among others, of a mysterious connection between black holes and thermodynamics, culminating in Dr. Hawking’s discovery in 1974 that when quantum effects are taken into account black holes would glow and eventually explode.

In a provocative calculation in 1995, Ted Jacobson, a theorist from the University of Maryland, showed that given a few of these holographic ideas, Einstein’s equations of general relativity are just a another way of stating the laws of thermodynamics.

Those exploding black holes (at least in theory — none has ever been observed) lit up a new strangeness of nature. Black holes, in effect, are holograms — like the 3-D images you see on bank cards. All the information about what has been lost inside them is encoded on their surfaces. Physicists have been wondering ever since how this “holographic principle” — that we are all maybe just shadows on a distant wall — applies to the universe and where it came from.

In one striking example of a holographic universe, Juan Maldacena of the Institute for Advanced Study constructed a mathematical model of a “soup can” universe, where what happened inside the can, including gravity, is encoded in the label on the outside of the can, where there was no gravity, as well as one less spatial dimension. If dimensions don’t matter and gravity doesn’t matter, how real can they be?

 

http://www.nytimes.com/2010/07/13/science/13gravity.html?pagewanted=1&_r=1

 

 

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