No ET! Ever?

[Jehanne]

It may be better to express things simply in joules.  Fact is that stars are basically point sources which is why they, unlike planets, twinkle on clear nights (planets, unlike stars, have angular size on the night sky); this fact, called scintillation, is going to impact any source of light, and so, assuming that you could produce a narrow, coherent form of laser light and aim such perfectly, it is virtually certain that such will get scattered somewhere in the interstellar medium.

The visible twinkling comes from the atmosphere.  Point sources don't twinkle when viewed outside the atmosphere.  There is scattering by interstellar medium.  But around the vicinity of earth significant scattering takes >>50 light years worth of interstellar medium.  We can actually measure the amount of scattering by distance by measuring exoplanet transits.

You're absolutely correct, however, we are talking about stars and planets, the diameters of which are many magnitudes greater than some sort of radio transmitter, which means that a narrow band signal, such as laser, would be still subject to scattering in the interstellar medium.  Stars are, of course, much more powerful than are interstellar laser beacons, and being omnidirectional, the scattering that they experience is much less.  However, their light still does get scattered:

https://en.wikipedia.org/wiki/Lyman-alpha_forest

Once again, I think that the "Wow! signal" may have been authentic:

https://en.wikipedia.org/wiki/Wow!_signal

But, if was authentic, it was, at the Wiki article states, likely some beacon that was sweeping the (alien) sky in more or less random directions.

What I am railing against here is what was stated in the BBC link in the OP, that is, that "absence of evidence" is grounds for concluding evidence of absence; hence, given the laws of Nature, it is completely understandable why we have not heard from ET or why ET has not visited our solar system.  Other than a powerful, sweeping beacon, the challenges, in my opinion, for direct radio communication are likely either impossible, or at least practically infeasible.  The only evidence that we are likely to get for ET will be indirect evidence, the type that came in the Wow! signal, or perhaps, KIC 8462852:

https://en.wikipedia.org/wiki/KIC_8462852


In short, the BBC article is just plain wrong.