Well, I could comment a bit on gravity waves vs. lasers.
Consider wavelength, and how that limits narrowness of a beam.
If I wanted to be noticed by someone on a planet 30 lightyears away, I would get the biggest Nd:YAG ("YAG") laser that I could get and fire it through a large telescope.
Let's see what happens if I get a 25 megawatt peak pulse YAG laser (1064 nm) and fire it out a telescope whose objective is 3 meters in diameter. I try Google and find 25 MW YAG lasers have been made, and Earth's biggest telescope is about 5 meters last time I checked (long ago).
If I don't have things terribly wrong, good optics can get the beamwidth in radians down to not much more than the ratio of wavelength to objective diameter. With a micrometer and 3 meters, that's 1/3 microradian or a bit more, with cross section of the beam being about 1E-13 steradian. 25 megawatts into this is 2.5E20 watts per steradian.
Maybe that will be weak compared to output from the sun... Let's see...
I am figuring the sun to give us 1380 watts per square meter from
1.497E11 meters away. That's about 3.1E25 watts per steradian...This does mean that a pulse train fired from a 25 MW peak power YAG laser through a 3 meter telescope will be about 51 dB below the sun's output.
Now, suppose aliens are checking us out with a narrowband filter or having a computer monitor a spectral power distribution of our solar system for patterned spikes? If we are not doing the same, then I think we should! I certainly know that a spectrometer costing only a few thousand $ has resolution down to a few nanometers. It appears to me that not too many megabucks are needed to have a computer-monitored spectrometer with resolution of 1/10 nanometer and checking by the microsecond, and with alerts beeped out and spectral power distribution curves logged if a discernably non-random pattern of a spectral spike is detected. If we are not doing this, I don't think it's much of a waste of taxpayer money to get a few of these up and running to monitor at least parttime the main sequence stars within maybe 30-50 light-years and of spectral class lower or middle F to upper K or so. And I also think it's worthwhile to have a setup or a few firing pulse trains of laser radiation towards such stars.
But back to calculating numbers:
Portion of solar output in a 1 nm wide band at 1064 nm: .048% of 3.1E25 w/sr, which is about 1.5E22 w/sr. I am proposing 2.5E20 w/sr competing against that, which is about 17 dB down.
Now, I will assume that better-achievable high power lasers will have wavelength known to the .1 nm range and that monitoring of a spectral power distribution of "optical band" output of a star system can watch for this. Now we only have to watch for non-random patterns at selected wavelengths to be monitored having patterns 7 dB below the output in same bandwidth from a sun-like star, assuming their capabilities for producing patterned laser bursts are what I mentioned above.
Now for an alternative spectral region to monitor: Radio bands. Possibly it might be worthwhile to see if nuclear explosives get detonated in the outer atmospheres of other planets - for whatever purpose!
- Don Klipstein ( snipped-for-privacy@misty.com)