December 19, 2008

Gravitational Wave Invesitigation ‘Nonsense’

In a move that would have any astrophysicist scratching his head, the U.S. Defense Intelligence Agency (DIA) commissioned a report to assess whether gravitational waves could threaten national security.

The JASON Defense Advisory Group was also asked to investigate other potential applications for high-frequency gravitational waves, such as imaging the Earth's core or uses in telecommunications.

Gravitational waves are wrinkles in space-time caused by the movement of objects with tremendously large mass, such as an extremely dense star. However, even waves from vast stellar events have been too weak to be detected by the most sensitive of detectors. Indeed, the best evidence of gravitational waves is indirect, based on observations of how very dense binary neutron stars lose energy.

Nevertheless, the JASON team was asked to evaluate a funding proposal that the firm GravWave had submitted to the DIA.  The proposal claimed that humans could generate strong gravitational waves on Earth, using something known as the Gertsenshtein effect, and describes how electromagnetic waves moving through a strong magnetic field can be transformed into gravitational waves.

However, the JASON team's analysis does not bode well for supporters of the plan. In fact, the technique was deemed so inefficient that it would take longer than the lifetime of the entire universe for every power station on Earth to create a gravitational wave with the energy of one ten millionth of a Joule.  By comparison, accelerating a spacecraft at 10 meters per second squared, a rate that barely exceeds the Earth's gravitational pull, would require 1025 times the electricity output of the entire world.

"These proposals belong to the realm of pseudo-science, not science," concluded the JASON team in their report.

Physicists seeking to detect gravitational waves were astonished that a committee needed a 40-page report to reach that conclusion.

"The proposal is utter nonsense," says Karsten Danzmann of the Max Planck Institute for Gravitational Physics in Hanover, Germany.  Danzmann is also a member of the GEO600 project, which seeks to detect gravitational waves.

"I'm a bit surprised the agency bothered to commission an investigation - it would probably have been enough to just ask an in-house science advisor," he told New Scientist.

MIT's David Shoemaker, a member of the LIGO project to detect gravitational waves, concurred, saying a simple phone call to any physicist would have sufficed to reach the JASON team's conclusion.

However, he adds that given the U.S. defense industry's history of funding faulty science, it might not be a bad thing that this particular idea was at least refuted at an early stage.

"The Department of Defense always have a few projects on the go that disobey the rules of thermodynamics, so I wish they would commission this kind of in-depth study in more cases."

Indeed, the Pentagon spent millions of dollars during the mid-1990s and early 2000s on the development a quasi-nuclear weapon called the hafnium bomb.  The project was ultimately based on junk science. 

In that context, perhaps the funding for the JASON report, which should prevent similar frivolous spending on a doomed gravitational wave weapon, was actually money well spent. 

The JASON team's full report can be viewed at http://www.fas.org/irp/agency/dod/jason/gravwaves.pdf.


Image Caption: Gravitational wave are propagating gravitational fields, "ripples" in the curvature of space-time, generated by the motion of massive particles, such as two stars or two black holes orbiting each other. Gravitational waves cause a variable strain of space-time, which result in changes in the distance between points, with the size of the changes proportional to the distance between the points. Gravitational waves can be detected by devices which measure the induced length changes. Waves of different frequencies are caused by different motions of mass, and difference in the phases of the waves allow us to perceive the direction to the source and the shape of the matter that generated them. Image Credit: K. Thorne (Caltech) , T. Carnahan (NASA GSFC)


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