Big Bang: unexpected discovery

An unexpected discovery may see physicists heading back to the drawing board in order to update models representing the Universe immediately after the Big Bang. In an experiment not previously possible, physicists have created the state of matter thought to have filled the Universe just a few microseconds after the Big Bang. To their astonishment, physicists found that instead of a gas, the substance was more like a liquid. Understanding why it is a liquid should take physicists a step closer to explaining the earliest moments of our Universe.

The liquid is said to exhibit characteristics like nothing else physicists have observed before, and its collective movement is rather like the way a school of fish swims "as one". In fact, physicists' tentative calculations suggest that its extraordinarily low viscosity makes it the most perfect fluid ever created.

The new state of matter was forged in the Relativistic Heavy Ion Collider, situated at the Brookhaven National Laboratory. Colliding the central cores of gold atoms together, head-on at almost the speed of light, the researchers created a fleeting, microscopic version of the Universe a few microseconds after the Big Bang. This included achieving a temperature of several million million degrees (about 150,000 times the temperature at the center of the Sun). They then detected and analyzed the explosive rush of particles that this miniature Big Bang created. Researchers had confidently believed that they would observe something like "steam", made up of free quarks and gluons, but instead the researchers saw evidence of collective movement as the hot matter flowed out of the collision site. This indicated stronger interactions between the particles than expected, leading to the belief that the quark-gluon plasma is similar to a liquid.

This latest development is much more unusual than anyone expected. "No one predicted that it would be a liquid," said Professor John Nelson from the University of Birmingham, who heads the British involvement in the multinational experiment.

"This aspect was totally unexpected and will lead to new scientific research regarding the properties of matter at extremes of temperature and density, previously inaccessible in a laboratory."

The liquid defies physicists' current understanding of how matter in the universe behaved microseconds after the Big Bang. According to previous models there should be no evidence of matter - as we know it - in existence mere microseconds after the big bang, because the extreme temperatures generated would have been far to high for any matter to exist. There is a suggestion that certain versions of string theory may be able to explain the liquid behavior of the quark-gluon plasma. "Although these findings did not fit with expectations, the theories are slowly coming into line," said Nelson.

[Based on scienceagogo]

[Picture from Brookhaven National Laboratory]

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MythBusters Spoof - Time Travel

Good parody on MythBusters show. Just funny.

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Hidden variables of reality

Returning to Einstein's nagging doubts about quantum mechanics, Nobel laureate Gerard 't Hooft of Utrecht University has begun to outline a way in which its apparent play of chance might be underpinned by precise physical laws that describe the way the world works.

Despite being physicists' most fundamental theory of the properties of matter and energy, quantum mechanics holds that there are things we just cannot know. For example, it forbids us from knowing everything about a subatomic particle: its exact speed, position, mass and energy. We can only put limits on the probable values of all these things at any instant.

Albert Einstein did not like this idea, and suspected that another theory - another layer of reality - might underlie quantum mechanics, in which everything is spelled out precisely. These deeper properties of objects became known as 'hidden variables'. According to this view, our ignorance about the nature of a quantum object is illusory; we just haven't found the right theory to describe it yet.

Today, most physicists adhere to a different reading of quantum theory, called the Copenhagen Interpretation, as advocated by the Danish nuclear physicist of the 1940s, Niels Bohr. This says that there is no deeper reality, that hidden variables don't exist and that the world is simply probabilistic. It holds that we are not ignorant about quantum objects, it's just that there is nothing further to be known.

Indeed, in the 1980s, the Copenhagen Interpretation was put to an experimental test based on a theorem devised by the Irish physicist John Bell - and it stood up. Hidden variables had to go.

't Hooft is not about to resurrect hidden variables. But neither is he convinced that quantum uncertainty has to be the final word. "Contrary to common belief," he says, "it is not difficult to construct deterministic models where quantum mechanics correctly describes stochastic behaviour, in precise accordance with the Copenhagen doctrine."

Here, stochastic means that things seem governed by fuzzy, rather than precise, probabilities. And deterministic means that one thing leads definitely to another, not simply to a range of other things with various probabilities.

"The key, " says 't Hooft, "is information loss. At the smallest conceivable size scale - the Planck Scale, many trillions of times smaller than the nucleus of an atom - there exists complete information about the world. This information gets lost very quickly. By the time we start trying to probe and measure a system, we are like archaeologists trying to make sense of ancient Babylonia: we have only the scantiest of information to go on. We can say only what the system was probably like."

This might sound like sleight of hand to introduce quantum uncertainty, but 't Hooft has outlined a way to turn it into a predictive mathematical theory. But because the Planck Scale is so far below the resolution limit of any conceivable experiment using current technology, it will be very difficult to put his ideas to the test. Richard Gill, who is also based at Universty of Utrecht suspects that the real answer may turn out to be eternally elusive.

"Perhaps, " he speculates, "the world was built according to quantum mechanics but quantum mechanics itself prevents us from ever being sure."

[Based on Nature, picture from Membrana]

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Light can travel faster than the speed of light?

The textbooks say that information can't travel faster than light, but researchers at Rochester University have uncovered tantalizing evidence that this may not be the case. To put Einstein to the test, they're planning new experiments based on their work to date that shows that light can travel faster than the speed of light… if it's traveling backwards. If it sounds confusing, don't worry, you're not alone. Robert Boyd, Professor of Optics at the University of Rochester says:

"I've had some of the world's experts scratching their heads over this one. Theory predicted that we could send light backwards, but nobody knew if the theory would hold up or even if it could be observed in laboratory conditions."

To understand Boyd's reverse-traveling light pulse, think of a big-screen TV and video camera. When passing such a display in a store window, as you walk past the camera, your on-screen image appears on the far side of the TV. It walks toward you, passes you in the middle, and continues moving in the opposite direction until it exits the other side of the screen. Boyd's negative-speed pulse of light acts much the same way. As the pulse enters the material, a second pulse appears at the far end of the fiber and flows backward. The reversed pulse not only propagates backward, but it releases a forward pulse out the far end of the fiber. In this way, the pulse that enters the front of the fiber appears out the end almost instantly, apparently traveling faster than the regular speed of light. In our store-front analogy, it's as if you walked by the shop window, saw your image stepping toward you from the opposite edge of the TV screen, and that TV image of you created a clone at that far edge, walking in the same direction as you, several paces ahead.

In the Rochester experiment, detailed in Science, the scientists sent a burst of laser light through an optical fiber that had been laced with the element erbium. As the pulse exited the laser, it was split into two. One pulse went into the erbium fiber and the second traveled along undisturbed as a reference. The peak of the pulse emerged from the other end of the fiber before the peak entered the front of the fiber, and well ahead of the peak of the reference pulse. But to find out if the pulse was truly traveling backward within the fiber, Boyd and his students had to cut back the fiber every few inches and re-measure the pulse peaks when they exited each pared-back section of the fiber. By arranging that data and playing it back in a time sequence, Boyd was able to depict that the pulse of light was moving backward within the fiber.

"It's weird stuff," says Boyd. "We sent a pulse through an optical fiber, and before its peak even entered the fiber, it was exiting the other end. Through experiments we were able to see that the pulse inside the fiber was actually moving backward, linking the input and output pulses."

Does this violate one of physics central creeds - that nothing can travel faster than the speed of light?

"Einstein said information can't travel faster than light, and in this case, as with all fast-light experiments, no information is truly moving faster than light," says Boyd. "The pulse of light is shaped like a hump with a peak and long leading and trailing edges. The leading edge carries with it all the information about the pulse and enters the fiber first. By the time the peak enters the fiber, the leading edge is already well ahead, exiting. From the information in that leading edge, the fiber essentially 'reconstructs' the pulse at the far end, sending one version out the fiber, and another backward toward the beginning of the fiber."

Boyd's team are already working on ways to see what will happen if they can design a pulse without a leading edge. According to Einstein, the entire faster-than-light and reverse-light phenomena will disappear. Boyd is eager to put Einstein to the test.

Check out an animation of BFTL from Rochester.

[Based on scienceagogo and University of Rochester]

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Evading quantum barrier to time travel

Ruling out the possibility of traveling back in time has turned out to be trickier than many physicists had supposed. Two researchers of Princeton University have shown that quantum effects do not necessarily prevent the occurrence of loops in time.

Einstein's special theory of relativity unifies space and time as aspects of a single, four-dimensional entity known as space-time. His general theory of relativity describes how the presence of matter warps the fabric of space-time. Physicists have found that general relativity equations yield many solutions representing different space-times. Sometimes, sufficient warping of a particular space-time makes possible the existence of paths known as closed timelike curves. A traveler moving along such a path would find that his or her watch always runs forward, even though the traveler eventually ends up where - and when - he or she started.

In 1982, William Hiscock and Deborah Konkowski calculated the quantum state of the space, or vacuum, pervading a simple type of space-time called Misner space, which includes closed timelike curves. Their result indicated that such a combination of gravitational space-time and vacuum quantum state could not exist. Noting that result, Stephen Hawking (University of Cambridge) proposed the chronology protection conjecture, stating that physical laws do not permit the appearance of closed timelike curves. For example, quantum theory could conspire to prevent time travel by ruling out the existence of space-times with such paths.

Misner space can exhibit more than one type of vacuum state, however. Li-Xin Li and J. Richard Gott III of Princeton University demonstrate now that one of these states permits the occurrence of time loops. That state is self-consistent, meaning that going back in time doesn't alter what happens later in the system.

"We have found a counterexample to Hawking's conjecture," Gott says. "Quantum effects do not automatically enforce chronology protection in every case."

That doesn't mean a person could build a machine to travel back in time. The amount of space-time warping required for such a feat would lead to all sorts of practical problems. The calculations also involve crucial approximations and may not apply to the "real" cosmos. However, the possible existence of closed timelike curves under certain extreme conditions may offer a solution to the problem of what came before the Big Bang, which most cosmologists believe started our universe.

Li and Gott explore the question of whether anything in the laws of physics would prevent the universe from creating itself. "The universe wasn't made out of nothing," Gott suggests. "It arose out of something, and that something was itself. To do that, the trick you need is time travel." The researchers speculate that a universe undergoing the rapid early expansion known as inflation could give rise to baby universes, one of which (by means of a closed timelike curve) would turn out to be the original universe.

As they did for Misner space, the two physicists found a self-consistent vacuum state, demonstrating that closed time loops can occur under inflationary conditions in certain space-times. Hence, the researchers say,

"the laws of physics may allow the universe to be its own mother."

[Based on sciencenews]

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