Comment Re:Dissipation? (Score 1) 189
It's true that the beam will spread out as it travels. The diffraction effect doesn't even require an actual physical aperture like a hole. A collimated beam is the same as a beam that has been created by passing through an aperture, so diffraction effects apply.
Example of spread: a pencil-thick (say
Not sure where those numbers come from. When I studied laser physics the calculation using a 0.5cm beam produced a beam measuring many kilometres across at the moon. I think the beam was about 70m across at the moon when the initial diameter was 1m. This corresponds with standard diffraction principles in that the smaller the aperture, the greater the diffraction.
Thus, in order to communicate across interstellar distances they would have to start with a laser beam many kilometres in diameter if they wanted to minimise the effects of diffraction. With our current technology a laser this size just isn't going to happen, but that doesn't meant that it's impossible.
As for all the comments about how the lasers would have to be aimed specifically at the target, yadda, yadda, the article says that and says that the aliens would actually have to be trying to communicate with us, not necessarily simply firing out arbitrary bursts of information. ie. This search has a somewhat different focus to SETI, which is looking for communications, but also for arbitrary signals that could originate from an alien civilisation.
Using lasers would be preferable if you're just firing out in arbitrary directions hoping someone will pick it up, since laser beams have special properties that ordinary EM emitters do not possess, making them easier to distinguish from noise. But there are naturally produced laser beams coming at us from space, so the real deal is sorting out whether or not any laser sources are transmitting information.
Cheers Craigus
