“Some scientists are puzzled as to why no messages have been sent back even though humans have been transmitting radio and television signals for the last century.”
Don’t radio waves eventually fizzle out over time? I once heard that radio waves wouldn’t even reach Alpha Centari.
I guess it depends upon how much natural radio noise will drown out “I Love Lucy” broadcasts from the biggest possible broadcaster for all occupied regions of space within a 60-70 ly radius. Given that the current count of potentially intelligent alien lifeforms out there is zip, asteroid collisions, nearby supernovas, and global warming is more worth worrying about. Not that I think any of that crap is worth worrying about.
On the other hand intergalactic communications are probably conducted through control of "entanglement". Lot less noise that way, and it's FASTER!
No.
They don't. However the farther they go, the less energy per square inch of the wavefront they have. The wavefront is an expanding sphere (assuming an omni antenna.) The larger the sphere's radius gets (all the way to Alpha Centauri, for example) the larger its surface becomes. But the amount of energy you sent is the same; so less energy per unit of surface.
In the same vein, if the receiving antenna is a sphere that completely encloses the transmitter then it doesn't matter how far the wave travels, the antenna will capture *all* the transmitted power.
This holds true for optical frequencies too, that's why astronomers want larger telescopes - to capture more of the energy of the signal, given that the density of incoming energy is not under our control.
If your transmitting antenna is a beam antenna and not an omnidirectional radiator then the situation is exactly the same, just more power goes into a smaller cone of radiation. Since the cone doesn't know if you are radiating in other directions, the density of energy in the cone's wavefront follows the same laws as a sphere. You can find all the details here.
Also note that there is a popular belief that TV stations sent a lot of early TV shows into space. This is not exactly true. Antennas of TV stations are designed to radiate toward the customers (homes on the ground) and not into space. Some antennas have a very narrow beam and are designed to illuminate a very specific spot on the ground. You can see that very little is radiated toward 90 and 270 degrees in either plane. So most of the energy radiated by TV antennas goes into the ground, literally (it heats the soil) and only a tiny part of it is captured by receiving antennas.