"Communication by electromagnetic radiation suffers from the fact that the radiation diffuses indiscriminately in all directions."

While lasers technically do not need to be beam-like, I would point out that beam lasers do exist, as well as many other directional effects, as seen in flashlights and such.

It is a bizarre alien race that people are hypothesizing that apparently uses whatzamamagic communication that we currently can't even conceive of, but aren't capable of building the things we already know how to build that can provide very good directionality today. A very particular sort of powerful.

Beam lasers exist and stay narrow on the scale that we use them. They are tighter flashlights. Turn on any flashlight and the rapid diffusion of its light will be extremely apparent.

And I'll note that I responded to the comment "electromagnetic radiation basically has every characteristic you're looking for in a communications medium", with no mention of aliens at all. It is not true that electromagnetic radiation basically has every characteristic you're looking for in a communications medium.

There is a fundamental difference between a laser and a concentrated flashlight–lasers are coherent while ordinary light is not and cannot be made so no matter how much you focus it.

Lasers still diffuse; they are not fundamentally different in that sense. In the signaling sense of "is the light there or not?", whether it is coherent, or would be coherent if it was there, is not relevant to anything.

Lasers don't technically "diffuse", they spread out due to diffraction inside the beam itself. So they are much, much easier to better to in a reasonably directed beam.

Other than stars etc., I don’t think know any genuinely omnidirectional light sources. Even other substellar objects emit non-isotropically because they aren’t spherically symmetric. And at most frequencies, light doesn’t diffuse much.

To put it another way: lasers, lenses, parabolic dishes.

> Other than stars etc., I don’t think know any genuinely omnidirectional light sources. Even other substellar objects emit non-isotropically because they aren’t spherically symmetric. And at most frequencies, light doesn’t diffuse much.

In what cases does it matter that stars are not symmetrical enough to emanate light omnidirectionally? Stars are pretty close to isotropic.

That’s my point. They — stars and some stellar remants — are basically the only thing which are isotropic. Everything else is directed, has some gain over isotropic in the peak direction/s.