The Earth As a Gravitational Wave Detector 70
b30w0lf writes "Gravitational wave detection — i.e. the detection of propagating ripples in spacetime — is a hot subject these days, with ground-based interferometer experiments like LIGO active, and hopes for a space interferometer like LISA. However, physicist Freeman Dyson proposed back in 1969 that the earth itself could be used as a gravitational wave detector. The idea is behind the approach is that gravitational waves impact the earth's crust, causing potentially detectable seismic waves. Using Dyson's approach, Physicists at Harvard and NINP, Florence were able to put an upper limit on the intensity of gravitational background radiation based on a year of observational seismic data (abstract, full pre-print). The upper limit they found improved currently laboratory upper limits by 9 orders of magnitude."
Re:Are they finding the waves, or ruling them out? (Score:0, Interesting)
GW's can't be detected directly by the current crop of apparatus because the doppler shift caused by GW's is cancelled out by the DS of the compressed light stream by GR. It's been a fiasco. The announcement coming Monday is for indirect measurements of GW's from a telescope analyzing the CBR light polarity.
Use the Moon instead (Score:5, Interesting)
Since the moon is much more stable than the Earth, would it be a better detector? Have seismic readings been taken on the Moon?
Re:LIGO is a money pit (Score:4, Interesting)
LIGO is enormously more sensitive (~12 orders of magnitude), than this seismic measurement but in a different frequency band (~100Hz), so both are valuable measurements sensitive to different types of GW sources .
LIGO itself is a phenomenally difficult project, but with big payoffs. There is the basic physics of understanding how gravity works, but there are also technology spinoffs. The extremely low loss mirror technology developed for LIGO is not being used for other applications, including telecom. The high Q optical cavities are used in commercial measurement devices for measuring tiny concentrations of materials in gasses . There are likely many other spin-offs from the project.
Re:LIGO is a money pit (Score:4, Interesting)
I was on a LIGO review committed years ago (and worked on the precursor to the project many years before that). At the time of the review, LIGO had worked with a vendor to produce extremely low loss coatings. Based on that technology that vendor was able to move into the (at that time) rapidly expanding telecom optics business - and actually refused to make the parts LIGO needed) because the technology was more valuable to them for telecom. LIGO really was driving the optics business back then.
I believe there have also been spinoffs from their stabilization and vibration isolation work, and possibly from their ultra- stable frequency laser work (Maybe someone from the project will respond.... Stan???).
The value of basic physics like verifying, or disproving general relativity is of course much more difficult to measure. What is the value of understanding the large scale structure of the universe, or physics at very high energies? I don't know the coin to use to measure that. There was a time when number theory, quantum mechanics and relativity all seemed pretty esoteric and useless. That doesn't mean that all basic science is valuable, but there is no way to know in advance what is.
Coincidence? (Score:4, Interesting)
At 00:58:53 UTC on Sunday, 26 December 2004, an undersea megathrust earthquake occurred in the Indian Ocean which caused a tsunami which killed 250,000 people.