Era of astronomical discovery

Jul 08, 2014 by Leda Zimmerman
Nergis Mavalvala (pictured) aims to detect elusive gravitational waves. Credit: Len Rubenstein

For much of her professional life, MIT professor Nergis Mavalvala has been devoted to a singular goal: creating a device to detect gravitational waves. These ripples in the fabric of space-time—the signature of violent cosmic events—are "extremely aloof," Mavalvala says. In fact, gravitational waves have been dodging elaborate efforts by scientists to track them down since Einstein predicted their existence a century ago.

But last March brought a possible breakthrough: Astronomers at the Harvard-Smithsonian Center for Astrophysics discovered what appears to be the first direct evidence of . For Mavalvala, the Curtis and Kathleen Marble Professor of Astrophysics, the news could not be more thrilling. She believes it may herald a new era of astronomical discovery. "It will be exciting beyond measure, and the greatest excitement will be finding things we can't yet imagine," she says.

Mavalvala is certainly ready. Since her graduate school days in the early 1990s at MIT, she has been helping design and build the Laser Interferometer Gravitational-Wave Observatory (LIGO). For helping design this complex and finely tuned scientific tool for detecting gravitational waves, Mavalvala won a MacArthur Fellowship in 2010.

Many large heavenly bodies and events in the universe, such as the birth and death of stars, generate energy in different wavelengths of light, which existing telescopes can find, she says. But compact astrophysical objects—such as neutron stars and light-eating black holes, which are believed to produce energy in the form of gravitational wave radiation—remain concealed from human view. These waves, unlike light, she says, "flow through everything, because matter is basically transparent to them. They come to us unobstructed right from the source." For Mavalvala, gravitational waves are "a clean messenger bearing information about how the universe is put together."

LIGO's instrument for detecting the extremely faint signature of gravitational waves is "an exquisitely sensitive interferometer," Mavalvala says. It measures the time it takes for light beamed from a laser to strike a mirror four kilometers away and reflect back. Theoretically, a gravitational wave arriving on earth and passing between laser and mirror will slow down the light as it bounces, thus changing the distance between the two infinitesimally. LIGO is built to identify a change in distance of 10 to 18 meters—1,000 times smaller than a proton.

Members of an international team, Mavalvala, and her lab colleagues have been refining the laser interferometer, specifically the optical sensing and control system. In the past several years, two observatories have started up—one in Washington state and the other in Louisiana—but have not yet yielded results. LIGO researchers are now sharpening their focus by a factor of 10. "This allows us to be sensitive either to weaker gravitational waves, or to the same sources, such as a pair of colliding, but farther out," Mavalvala says.

Engaged with LIGO's second-generation detectors, Mavalvala is contending with a critical problem involving the instrument's measuring precision. But she has some clever tricks to sidestep these constraints. One deploys "squeezed light sources"—laser beams whose quantum properties are manipulated to reduce noise fluctuations—that may improve the sensitivity of the LIGO detectors and render more accurate measurements.

"The big picture mission drives you. When you work in the lab, [it's like] you bang your head against the wall for weeks at a time, working on a state-of-the-art circuit, for example," Mavalvala says. "Yet this is what enables scientific discovery, when the smaller to bigger pieces of experiments succeed, when the whole thing does what it is supposed to, and then you hope nature gives you the event you've been waiting for."

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User comments : 6

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Technico
1.7 / 5 (6) Jul 08, 2014
Rigorous general relativity (GR) doesn't allow the gravitational waves (GWs). It can be understood in many ways. First of all, the time dimension serves in GR for description of space-time curvature. The GWs are formed with such a curvature, so they cannot move and propagate in another time (afer all, as any other artifact of GR).
At second, the reference frame in GR is defined only with space-time curvature, without it the space-time is flat, void and empty and all speeds and reference frames are relative (as the name of this theory implies). But the GWs are formed with space-time curvature, they're defining their own reference frame. As Eddington pointed out before many years, the speed of the alleged waves is coordinate dependent. A different set of coordinates yields a different speed of propagation.

Therefore in four-dimensional GR GWs cannot exist, or they would appear like stationary objects (common gravitational lenses) or like the noise with no relative speed defined.
Technico
1.7 / 5 (6) Jul 08, 2014
Both above variants of GWs were already observed and they're not difficult to detect. The stationary GWs are common gravitational lenses or recently observed B-mode of CMBR anisotropy. They don't move, so that everything's OK with GR here.

The GWs in form of noise are routinely observed as a CMBR noise. They're formed many miniscule GWs, which don't propagate by itself, as their reference frame remains undefined. They do correspond the Brownian noise in the space-time analogy of water surface, where the time dimension represents the density gradient forming the water surface.

So there's no need to build and maintain expensive detectors, as every analog TV set is already detecting them (and filters out as a noise). The noise which you can see at the TV during night or lack of signal is the visible manifestation of GWs. This noise does contain a quadruple component of gravity field too. But such a waves aren't apparently interesting for mainstream physicists.
Technico
1.7 / 5 (6) Jul 08, 2014
What the physicists are looking for are quadruple ripples with co-moving coordinates. Such a ripples can exist at the water surface too, but only under special occasions. For example, the underwater SOFAR channel is the density gradient, which enables the propagation of underwater sound waves at the distance (whales like to swim in it). When such a gradient would penetrate the water surface, it would enable to propagate the longitudinal component of sound waves across water surface. Therefore the GWs could propagate along surface of gravitational lenses.

Another source of waves similar to GWs can serve the dark matter (DM) filaments. The DM filaments are hyperdimensional objects, so they do allow the propagation of true waves across four-dimensional space-time. Recently some new model has been published, which considers such a waves. But such a waves cannot propagate outside of DM filaments anyway.
Technico
1.7 / 5 (6) Jul 08, 2014
Also, it's not true, that Einstein has predicted the gravitational waves. He actually disliked this concept in similar way, like the existence of space-time, expanding universe or black holes (1,2,3). After long discussions he got convinced with his referee in consideration of pseudotensor at the case of cylindrical coordinates, which indeed introduce an extradimensions into GR (only fully spherical 3D sphere is 3D object in 4D space-time). In accordance with it, the spherically symmetric source of GWs cannot exist in GR.

This is just the problem with contemporary formal physics, it often introduces a terms and geometries which aren't consistent with dimensionality of underlying physical model, which indeed leads into unphysical artifacts and predictions.
IMP-9
5 / 5 (4) Jul 08, 2014
Rigorous GR does allow for gravitational waves.

Ah Zephr, you never give up and you never learn. You post the same crap time and time again, even when show it's false. It's no longer just ignorance it's lies.

As Eddington pointed out before many years, the speed of the alleged waves is coordinate dependent.


Lie, the paper does not say that. His paper makes it quite clear that does not apply to all wave solutions. Therefor your argument is bogus.

which indeed introduce an extradimensions into GR. In accordance with it, the spherically symmetric source of GWs cannot exist in GR.


Wrong. Cylindrical coordinates do not introduce extra dimensions. Their argument showed plane wave solutions exist, it did not prove spherically symmetric solutions don't exist. The type these detectors are looking for are not spherically symmetric anyway. A sphere is not the only 3D object.

So again there is nothing to prove direct detection attempts will not wok.
Tangent2
not rated yet Jul 09, 2014
This article said a whole lot of nothing except that they haven't yet succeeded. No kidding. If the waves were detected, it would be all over the news like the Higgs particle.