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Blobrana


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RE: Gravity Waves
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Penrose lecture highlights conference on gravity
How do physicists describe infinity? Does quantum mechanics make sense? What, if anything, does string theory have to do with the natural world?
Sir Roger Penrose, emeritus Rouse Ball professor of mathematics at Oxford University and Francis R. and Helen M. Pentz visiting professor of physics and mathematics at Penn State, has never shied from what he calls "the big fish." The author of "The Emperor's New Mind" and "The Road to Reality: A Complete Guide to the Laws of the Universe," Penrose is widely known for his work over the last 45 years in the areas of general relativity, cosmology, and the connections between fundamental physics and human consciousness. Last month, he returned to University Park to deliver a public lecture titled "Faith, Fashion, and Fantasy: How Big is Infinity?"

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Blobrana


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Gravity
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Title: Exponential Gravity
Authors: Eric V. Linder

We investigate a f(R) modification of gravity exponential in the Ricci scalar R to explain cosmic acceleration. The steepness of the dependence provides extra freedom to satisfy solar system and other curvature regime constraints. With a parameter to alleviate the usual fine tuning of having the modification strengthen near the present, the total number of parameters is only one more than LCDM. The resulting class of solutions asymptotes to w=-1 but has no cosmological constant. We also calculate the effect on the matter power spectrum.

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Blobrana


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Gravitational waves
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Using Dead Stars to Spot Gravitational Waves
A bunch of dead stars could serve as ready-made recorders for gravitational waves - subtle ripples in spacetime that if discovered would be the crowning achievement of Einsteins theory of general relativity, astronomers propose. Researchers have been spending billions of dollars to perfect sensitive, kilometre-long devices on the ground and launch even more sophisticated experiments in space to detect this cosmic symphony.
The new search technique would instead rely on radio waves generated like clockwork by millisecond pulsars - the collapsed remnants of massive stars that spin about once every one to 10 milliseconds. The speed at which these pulsars rotate enables researchers to measure the timing of the waves arrival at Earth with high accuracy.

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Blobrana


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Does gravity change with the seasons?
One question Newton didn't ask is whether apples or oranges fall differently. Or whether an apple would fall differently in the spring. They might seem peculiar concerns, but Alan Kostelecký, a physicist based at Indiana University in Bloomington, thinks they are important. He and his graduate student Jay Tasson have found that such flagrant violations of our best theory of gravity could easily have evaded detection for centuries.

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Blobrana


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Physicists in the US have devised a new way of making very precise measurements of gravity by bouncing atoms up and down off a laser beam. Unlike comparable techniques that involve dropping atoms about 10 cm, this new method only needs a drop of about 20 m . The team has also modified the experiment to perform atom interferometry, whereby quantum interference between atoms can be used to measure tiny accelerations.
Because of its compact size, the team believes the technique could be used to make precise accelerometers that could be used in navigation systems for aircraft, submarines and even spacecraft. The technique may also find use in experiments that look for deviations from Newton's laws of gravitation.

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Blobrana


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Holographic principle
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Driving through the countryside south of Hanover, it would be easy to miss the GEO600 experiment. From the outside, it doesn't look much: in the corner of a field stands an assortment of boxy temporary buildings, from which two long trenches emerge, at a right angle to each other, covered with corrugated iron. Underneath the metal sheets, however, lies a detector that stretches for 600 metres.
For the past seven years, this German set-up has been looking for gravitational waves - ripples in space-time thrown off by super-dense astronomical objects such as neutron stars and black holes. GEO600 has not detected any gravitational waves so far, but it might inadvertently have made the most important discovery in physics for half a century.

For a while, the GEO600 team thought the noise Hogan was interested in was caused by fluctuations in temperature across the beam splitter. However, the team worked out that this could account for only one-third of the noise at most.
Danzmann says several planned upgrades should improve the sensitivity of GEO600 and eliminate some possible experimental sources of excess noise.

"If the noise remains where it is now after these measures, then we have to think again".

If GEO600 really has discovered holographic noise from quantum convulsions of space-time, then it presents a double-edged sword for gravitational wave researchers. One on hand, the noise will handicap their attempts to detect gravitational waves. On the other, it could represent an even more fundamental discovery.

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Title: Emergent Electroweak Gravity
Authors: Bob McElrath

We show that any massive cosmological relic particle with small self-interactions is a super-fluid today, due to the broadening of its wave packet, and lack of any elastic scattering. The WIMP dark matter picture is only consistent its mass M \gg M_Pl in order to maintain classicality. The dynamics of a super-fluid are given by the excitation spectrum of bound state quasi-particles, rather than the center of mass motion of constituent particles. If this relic is a fermion with a repulsive interaction mediated by a heavy boson, such as neutrinos interacting via the Z^0, the condensate has the same quantum numbers as the vierbein of General Relativity. Because there exists an enhanced global symmetry SO(3,1)_space x SO(3,1)_spin among the fermion's self-interactions broken only by its kinetic term, the long wavelength fluctuation around this condensate is a Goldstone graviton. A gravitational theory exists in the low energy limit of the Standard Model's Electroweak sector below the weak scale, with a strength that is parametrically similar to G_N.

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Einstein Telescope project
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A team of scientists from Cardiff School of Physics and Astronomy are part of a Europe-wide project which could uncover the very origins of the universe.
The European Commission has allocated 3M Euros to a design study - the Einstein Telescope project which could finally find proof of one of the great scientists key theories.
Direct detection of gravitational waves tiny distortions of space-time first predicted by Einstein - is one of the most important and fundamental research areas of modern science.  The direct measurement of  waves has the potential to allow listening back as far as the very first trillionth of a second following the Big Bang. This could potentially provide completely new information about the universe and open up entirely new areas of science.

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Blobrana


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Gravitational Waves
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A team of gravitational wave researchers from four universities, including the University of Southampton, has been selected to exhibit at the prestigious Royal Society Summer Science Exhibition.
Researchers from the University of Southampton have joined forces with colleagues from the universities of Birmingham, Cardiff and Glasgow, designers from Milde Science Communication and associates from the Albert Einstein Institute in Potsdam, Germany, to showcase their exciting work looking at Einstein's general theory of relativity, black holes and gravitational waves.

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What on Earth is wrong with gravity?
Particle physicist and ex D:Ream keyboard player Dr Brian Cox wants to know why the Universe is built the way it is. He believes the answers lie in the force of gravity. But Newton thought gravity was powered by God, and even Einstein failed to completely solve it. Heading out with his film crew on a road trip across the USA, Brian fires lasers at the moon in Texas, goes mad in the desert in Arizona, encounters the bending of space and time at a maximum security military base, tries to detect ripples in our reality in the swamps of Louisiana and searches for hidden dimensions just outside Chicago.

Gravity



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