Hi Ok so checking the math to make sure I’ve got it. They start with a path that is (in effect) 1600 KM long. That’s 1.6x10^6 meters. They resolve something that is in the 1x10^-23 range. That would be 1x10^-17 meters.
Wikipedia confirms that a proton is at 0.87x10^-15 meters. The resolution would be right at 1/100th of a proton in that case. The signal is at 1x10^-21 or so. That comes out to roughly one proton. Yes the numbers are different if you look only at a single path. I’d suggest that’s not the signal they actually used. Ok so far? Bob > On Feb 13, 2016, at 3:12 PM, Tom Van Baak <[email protected]> wrote: > >> 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<ligo-timelab-2.gif>_______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
