Update speculation - Portals

In the Portal trailer, when the character enters the portal it seems to take him/her/it to a different version of the planet they are on. Past - Present? Present - Future? Parallel universe?

What if the drab repetitive planets were always planned and in the original concept of the game, you had to find the portals to get to the worlds that they featured in the trailers? They just did not have enough time or money to get there.

If they are links to the past of those planets, what if you use the portals to go back in time to stop whatever is plaguing the abandoned buildings??

Maybe the fourth species that there has been speculation will be added is the one wiped out by the plagues and the ones that left the journal entries? You go through the portals on the planets and the abandoned buildings are no longer abandoned! Okay. I'm excited now.