That’s just what Cave Johnson WANTS you to think!
Also, regarding the ending (as this is a thread with the words “major spoilers” in it, I feel no qualms about spoiling, but will still warn ahead, just in case):
This is the same story universe as Half-Life (Black Mesa/Aperture Science). In Half-Life 2, the Combine have taken over and spoiled the world. At the end of Portal 2, you see Earth from two vantage points: One, after you put a portal on the Moon and you end up holding on for dear life to Wheatley and you can see the Earth from there…and two, once you’re “kicked out” of the testing facility, you see a lush field of wheat (I believe) surrounding a nondescript shed.
So, my view from this is: You see the field of wheat and the view of Earth from the Moon as you would expect them today. What I conclude from both of these (mere speculation, understand) is that the Combine, by whatever year that Portal 2 is set, is gone and that the Earth is “back to normal”. Whether this means that humanity has survived or not, however, is anyone’s guess, but I do believe that the Combine will be ultimately destroyed/driven off Earth.
Thoughts?