I'm too lazy to google a source right now, but actually, yes, we could detect Earth out to a few tens of lightyears. Not far in the scale of things, and the onl

I'm too lazy to google a source right now, but actually, yes, we could detect Earth out to a few tens of lightyears. Not far in the scale of things, and the only thing we'd really be able to detect are the most powerful radars, but it is theoretically possible to detect ourselves at nearby stars.