I've been reading about this interesting topic today. So the first radio signals emitted from the Earth are about 110 light years away from Earth now. Most authors point out that an advanced alien civilization only 125 light years away would have no idea of our existence. Fair enough, but the assumption here is always that any intelligent life out there is far more advanced than we humans are. Let's say for argument's sake that there is a humanoid species living on the newly discovered Centauri planet just four light years away and that this civilization has achieved the level of technological advancement that humans on Earth had achieved in the year 1850. Am I correct to presume that neither civilization would be aware of the other's existence?