AdamDZ

But since distances are measured in tens and hundreds of light years it's very hard to knock on the neighbor's door. We might eventually receive radio signals from a civilization only to find out that it's long gone since it took a few hundred years for the signal to reach us.

And seriously, we waste too much resources on wars to have any real chance to break away from our solar system. Until the planet unifies and ends wars the progress of individual nations will remain too slow to enable space exploration on a large scale.

I mean, NASA is back to rockets and parachutes from space shuttles. And until we burn chemicals we won't get anywhere anyway. Nations would have to put togehether all they have to have a shot at developing meaningful propulsion technology and spacecraft capable of carrying a large number of people and cargo across significant distances. And even that will require gazillion of other accompanying technologies to make the space travel possible: materials, life support systems, communication, navigation, energy storage and conservation, food processing and storage, health and emergency medicine, psychology, etc. None of these are at the level that will enable a large crew to travel across interplanetary space. Sending 4 people on a 4-year trip in a 10' wide can, hoping they won't freak out and eat one another, to bring back some rocks from Mars is not "space exploration".