Since that writing, we've lost Arecibo observatory, discovered gobs of exoplanets, started scrutinizing those exoplanets with JWST, and increased our radio sphere radius by another 19 lightyears.
[1] https://www.damninteresting.com/space-radio-more-static-less...
Bit of a plot point in Sagan's novel (and the movie adaptation):
Answer: No (which the article also mentions in so many words)
From <http://www.wbcq.com/>: WBCQ’s laser broadcasting service is available to beam your program into outer space via our high-powered, modulated, laser system. So in addition to broadcasting worldwide over shortwave radio, you can transmit into space over our high-powered lasers. It’s a lot of fun. The cost for this service is $50 an hour.
The oxygen has been here for far longer than us, sometimes at much higher levels.
So why no visitors? If there had been, we wouldn’t know. Any probes that dropped into our planet any further back than a few tens of thousands of years (and less if they landed in a hot wet region) might be gone by now. They’d have been eaten by corrosion and mechanical erosion and eventually by plate tectonics.
They also likely would have been small, meaning even if they got fossilized we’d have to get super lucky to find one. The energy required to accelerate something to meaningful fractions of light speed and then decelerate at the other side means a probe is probably an orbiter the size of a basketball and then a little drone the size of a golf ball or something.
We might have had dozens or hundreds of little visitors over the last billion years and we’d never know unless we got real lucky.
Flyby missions are also likely due to the physics. The energy for slowing down might instead be spent just going faster to get results faster. The probe just streaks past at 7% the speed of light and takes a bunch of pictures and measurements.
(And no, the dinosaur asteroid was not it. If an alien species is going to destroy Earth, they will destroy it, not slightly inconvenience the biosphere.)
2001 probably wasn't far off. I envision a small probe sent to each star system that finds a nice little hidey-hole inside an asteroid or moon and it burrows down in there and uses solar energy and local material to build more extensive infrastructure to replicate and send out copies to other bodies in the star system as well as to other local star systems.
I think we can rule that out.
But you don't get free oxygen on a planet without life to continually produce it.
It's a good indicator of some forms of life.
Actually humm maybe nukes are our brightest non directional transmission?
A civilization using only low power radio wouldn’t be detectable in the Centauri system.
Doppler shift would substantially change the wavelength, and frequency too.
Perhaps the number of light years a wave has traveled moving in the same direction that Earth is moving in, would be less distance than the side facing the direction that we are moving away from.
The Earth, and Solar System are always moving in motion; I would imagine doppler shift would also have a significant impact on the success of receiving such transmissions.
The civilizations who are "out there" may only have a narrow time window to pick up our signals. Like we've fashioned a poor man's Dyson sphere.
Well except for that one special time of year, but honestly Eurovision ought to be streaming online instead of broadcasting on TV already!
Shouldn't every cell in this column be the same?
