No ET! Ever?

[Jehanne]

But, they would be pointing it at a moving target that is going at 675 times the speed of sound, and then, they would also have to track that target across intergalactic space.  In addition, the radio signal, even if it was a laser, could end-up being scattered away by the zillions upon zillions of atoms, molecules, dust particles, etc., scattered throughout intergalactic space.  In addition, the energy requirements, given the inverse law, would still be enormous, likely, the entire energy output of the US over the course of a year, assuming, that ET wanted their signal to picked-up by something other than the Arecibo telescope, which means, of course, that Arecibo would need to be looking at the right spot at the exact time.

P.S.  Arecibo is not equipped to pick-up laser light.

Details. Details.

It's one thing to say something couldn't possibly exist. But to say something couldn't possibly be done is to cut off the future before we get to it.

Arecibo is a radio telescope, and so, it would have to be redesigned.  There are, of course, optical searches for ET going on:

http://www.planetary.org/blogs/bruce-bet...earch.html

Of course, the shorter the wavelength of light that one uses for interstellar communication the more likely that it will get absorbed and/or scattered by interstellar matter.