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Experimental Physicists Close in on the Detection of Gravitational Waves

Experimental Physicists Close in on the Detection of Gravitational Waves

As we approach the centennial of Albert Einstein’s publishing of his General Theory of Relativity (1915), physicists spread across the globe continue to search for a method that would allow them to detect a phenomenon predicted by the theory and fundamental to many of its groundbreaking ideas about the laws governing the physical universe: the existence of gravitational waves.

Gravitational waves

Scientists have been hunting gravitational waves for years, and may finally be on the verge of a breakthrough. Illustration: Pete Guest

If you’ve never heard of gravitational waves before or forgot anything you once knew long ago, don’t worry you’re not alone. Physicists have, for some time now, come to accept the existence of these waves, due in large part to their ability to observe their indirect effects (mostly based on the 1974 discovery and observation of the Hulse-Taylor Binary Pulsar, which also resulted in the two-star system’s namesakes, Russel Hulse and Joseph Taylor, being awarded the 1993 Nobel Prize in Physics).

Gravitational Wave Detector

While the existence of gravitational waves may not be a subject of much debate amongst physicists, discussion concerning exactly how and when direct observation may be possible has been ramping up over the past few years as leaps and bounds have been made in the technology necessary to increase the sensitivity of detectors being employed to measure the waves presence here on Earth. In essence, just as direct observation of the atom and subatomic particles after that required the development of a microscope that was powerful enough to magnify matter that small, scientists must create a device that can detect the minuscule amount of energy that gravitational waves are generating by the time they reach Earth.  But before looking at what they’ve come up with, it’s probably a good idea to get a better understanding of exactly what gravitational waves are and where they come from.

ligo_interfermometer

Gravitational waves can be thought of as ripples in space-time.  More specifically, they represent a curvature in space-time that propagates like a wave as it moves outwards from its source.  The energy allowing the waves to curve space-time as they move along is called gravitational radiation (it is this energy that scientists are hoping to detect).  The source of the waves was part of what Einstein’s theory helped to explain.

A Singularity

One phenomenon that Einstein’s general relativity theory explained was how events involving energy converging in space quickly and in enormous quantities are able to cause changes in the fabric of the universe that would, under any other circumstance, be outside the realm of what is physically possible – known as a singularity (The Big Bang being the most commonly known occurrence of the phenomenon).

singularity

While the Big Bang was unique, singularities occur regularly in the universe whenever a large star reaches the end of its life cycle.  Expanding at first, a star will then succumb to gravitational forces and start to collapse inwards. For many stars, this process leads to the creation of a White Dwarf; a small, dead star a fraction of the size of what it once was. Only stars that are approximately 3 times the size of the sun or larger will produce an adequate amount of energy to create a singularity.

The amount of gravitational energy necessary to cause the collapse of such a large star is strong enough to actually break apart individual electron orbitals, resulting in what, can be best described as matter being ripped apart at its seams. Once the energy of a collapsing star is able to overcome electron degeneracy pressure, there is nothing left to stop gravitational force from pulling the matter of the star infinitely closer.

einstein

What Einstein realized was that such a situation was far too unstable to continue for any significant period of time. Therefore something must happen that would allow stability to return, in other words, a singularity. In the case of a collapsing star, the infinitely increasing energy and decreasing size of the matter of the star is powerful enough to alter the fabric of space-time and produce 2 lasting results:

1.)   A Black Hole – visit http://science.nasa.gov/astrophysics/focus-areas/black-holes for more information on black holes.

sygnux-black-hole

2.)   Gravitational Waves

While the black hole that results from the collapsing star remains (relatively) fixed in space, the gravitational waves created move away from their source in all directions, steadily losing energy at a rate (equivalent to the inverse relationship between the magnitude of the gravitational force and the distance between the two objects, meaning as distance increases, gravitational attraction decreases). Because no singularity has occurred relatively close to Earth (thankfully, as the result would not be a good one for those of us who would enjoy existing), the distance between us and the nearest occurrences of the singularities that produce gravitational waves is also what makes them so hard to detect. So, even though the energy present when they were created was incredibly large, by the time the waves reach Earth it is so minute that current detectors, powerful enough to detect energy at quantum levels, still have had no luck.

ligo

However, researchers working at detection sites such as LIGO (Laser Interferometer Gravitational-Wave Observatory – www.ligo.org) think they are closer than ever to making this monumental discovery. While technological advances increasing the sensitivity of current detectors as well as employing innovative new approaches are part of the reason physicists are more optimistic, an increased understanding of the properties of the waves themselves is what is leading experimenters to design more precise detectors. Two of the more important properties of the waves fueling recent innovations are:

1.)“Burst Signals” – allows for an increased ability to predict when and where gravitational waves are most prevalent and more likely to be detected.

2.) “Quantum Squeezing” – the particles in gravitational waves (gravitons), given enough time, become extremely polarized literally “stretching” them out physically, making them easier to detect.

continuous gravitational waves

Most physicists working in the field now feel that their detection is imminent, causing an influx of excitement and enthusiasm in their efforts. When exactly they will be successful is unclear, what is clear is that it will not only mark a monumental achievement in experimental physics, but also add to the already impressive amount of evidence gathered that is helping to cement Einstein’s century-old theory as one of the greatest examples of scientific thought in history.

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About Jeffrey Shalda

Jeffrey Shalda graduated with a B.S. degree from the University of Georgia with a major in psychology and a minor in history. He obtained his M.S. degree from Villanova University in psychology, concentrating on cognitive psychology. Jeff's interests cover a wide range of topics including cutting-edge trends in science and technology, complex systems, number theory, music and literature. He is currently completing his first novel while working on several larger non-fiction projects as well. JeffShalda@TheHighTechSociety.com