[time-nuts] LIGO detects gravitational waves

[Bob Stewart]

Hi Tom,

Thanks for posting this.  I'm looking at the timelab plot, and the only thing I can relate that to is a musical note played backward.  IOW, the decay seems backwards to me.

Bob - AE6RV

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On Sat, 2/13/16, Tom Van Baak <tvb at LeapSecond.com> wrote:

 Subject: Re: [time-nuts] LIGO detects gravitational waves
 To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
 Date: Saturday, February 13, 2016, 2:12 PM
 
 > How much of a shift did they
 actually see in their 2.5 mile long laser paths?
 >
 > The news article I saw talked about a distance change
 of “1/10,0000 the size 
 > of a proton”.  That didn’t seem to make much
 sense.
 > 
 > Bob
 
 Hi Bob,
 
 The unit of measurement that gravity wave folks use is
 "strain" which is unit-less meters per meter. It's analogous
 to how we T&F people use unit-less Hz per Hz for
 oscillator frequency offset and stability measurements. Plus
 they have their strain spectral plots like we have our phase
 noise plots.
 
 From what I understand, the GW signals they're looking for
 create a distortion on the order of 1e-21 so they want a
 detector that's in the 1e-22 or 1e-23 range; in a 20 to 500
 Hz bandwidth. This level of precision is just mind-blowing.
 But as you read the wealth of PDF's out there about LIGO,
 and drool at photos of the optics, and understand the plots
 showing strain sensitivity as a function of frequency, you
 start to believe that this is actually possible. Ok, given a
 thousand PhD's, a billion dollars, and a couple of decades.
 
 Yes, the interferometer is 4 km in length but they bounce
 the beam back and forth 400 times so the effective length is
 more like 1600 km. They keep the mirrors stationary to
 "picometers". They use hundreds of clever tricks to pull
 this off.
 
 Since the press is averse to using scientific notation they
 tend to make up units. So it's common to read units like
 Rhode Island, football field, human hair, and now, proton. A
 proton diameter is about a femtometer so 1/10,000th of that
 is about 1e-19 meter.
 
 LIGO publishes the raw and processed data -- and this is
 time nuts -- so attached is a TimeLab plot for you showing
 the chirp of the century. The LIGO/Hanford and
 LIGO/Livingston data is from:
 
 https://losc.ligo.org/s/events/GW150914/P150914/fig1-waveform-H.txt
 https://losc.ligo.org/s/events/GW150914/P150914/fig1-waveform-L.txt
 
 For TimeLab, set scale to 1e-21 and tau to 6.1035e-5 s
 (1/16384 s). The time axis is relative to 2015-09-14
 09:50:45 UTC plus about 0.25 s. 
 
 /tvb
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