Slashdot Mirror
Gravity Wave Detector Ready For Business
Arthur Embleton writes "The BBC has an article about a Gravity Wave Detector. There are two L shaped set-ups. One in Washington, the other in Louisiana. They've got a Laser pointing at a mirror 4km away, watching for the reflection and if it is distorted then it shows that there has been a gravitational pulse, possibly by two Black Holes colliding. The detectors are apparently so accurate they can measure to one-thousandth of the width of a proton! How did they test that it works?"
John Baez has some really good info about LIGO in several of his "This Week's Finds in Mathematical Physics" columns. week198 is the most recent to mention it. Baez is a great place to start if you like understanding connections between all kinds of different areas of math & physics (which, of course, includes everything else :)
Here are the slides [pdf] from the Oct 2002 NSF review. Lots of pictures, graphs, technical details, etc. for anyone interested. In a nutshell they are aiming to measure strain on the order of 10^-21 over the frequency range of 100Hz - 1kHz. Using two facilities separated by 3000km allows them to search for correlated events and weed out localized noise. IANAP.
More slides here.
LIGO home page.
HTH.
Placing the tubes at a right angle makes perfect sense... because you don't know which way the gravity wave will come from.
What you are saying makes sense only if there were some way a gravity wave could make one tube shorter and one tube longer the same amount at the same time, AND the same photon had to travel through both tubes.
However, it seems that blue/red shift issues are moot anyway, since the device works by basically measuring a relative shift in arrival time between two photons, not my measuring spectrum shift.
=Smidge=
They don't. They damp out a certain amount of vibration via clever mountings, etc.
Then they make sure that all the rest happens at very specific frequencies. You can think of a guitar string. When you jolt a guitar, the string will "sing" at its tuned note. I think the LIGO mirror supports are incredibly precisely tuned.
Now they only look for gravity waves at other frequencies, mainly ones away from where seismic noise mostly is.
Finally, they compare respoonses from two remote detectors and look for "matching" events separated by the speed of light, instead of the speed of seismic waves.
Yes, but gravity waves travel at light speed, seismic waves travel, at a much smaller known speed (about twice the speed of sound is it??) As long as you keep perfect time sync between the stations its easy to measuse how fast the wave traveled and tell which it was.
Japan also has several semiconductor fabrication plants. These plants require really really low amounts of vibrations to get profitable yields. The foundations for these things are typically 1-2 miles deep, such that they are anchored in the second layer of the earth's crust. And then there's all sorts of vibration damping material everywhere. I figure the gravitational wave detectors use some similar methods, only more so. Besides, all they have to isolate is their laser source and detectors, not the whole vacuum chamber.
And there's this page on the site to which you linked.