Something that's occurred to me is that radio is a bit more than a century old, and at the present time, we are still using EM radiation, but a huge portion of

Something that's occurred to me is that radio is a bit more than a century old, and at the present time, we are still using EM radiation, but a huge portion of our data bandwidth is being transported along enclosed waveguides, i.e., fiber optics, and transmission lines that have no long range dipole, such as coaxial and twisted pair cable. The net bandwidth of our open-air comms has increased by orders of magnitude, but all the while being designed to operate at ever lower power levels using modulation strategies that increasingly resemble noise, using antennas that avoid radiating into space for the sake of power savings. It could be that our civilization had a 1-2 century time window for being detectable from afar, before we effectively go dark. A superior method of communication might be a robot that, while it can't travel as fast, can engage in much more elaborate communication when it reaches its destination, e.g., carrying out trade, negotiations, cultural exchange, whatever. Also, the energy delivered by a robot, if it can steer itself to its destination, is not subject to the inverse square law of intensity. We have sent robots to visit the planets, because there's a limit to what we can learn by interrogating them with telescopes and antennas from Earth. Speaking of smoke signals, we may be inadvertently communicating our presence by the rapid change of the chemical composition of our atmosphere. Aliens equipped with a sufficiently sensitive spectrometer could scan the heavens for unusual chemical activity on known planets.