"How is that possible?"

First off, let me clarify that this isn't "VADER SAYS HE'S LOOKING FOR SKYWALKER PLOT HOLE PLOT HOLE!" This is going from what we know in ESB, Saga Edition: Vader is obsessively looking for "Skywalker", the Emperor tells him Skywalker is the son of Anakin, and Vader asks "How is that possible?".

So, when this line was released, I think most of us assumed the most likely meaning at the time: Vader was playing dumb. He's thinking about getting Luke on his side and destroying the Emperor, so he pretends to know nothing of this "Skywalker" fellow.

ROTS, though, adds something to this. Vader thinks Padme died while still pregnant, and therefore the children are dead. So ANH comes, Luke destroys the Death Star, and Vader learns his name, just like we've always figured. What if he isn't sure it's his son, though? I mean, I can't imagine "Skywalker" is a common name, but it's a well-known fact that Padme died while pregnant - anyone could see that for themselves. Vader knows there's a Force-strong man named Skywalker, just about the right age, and so his quest is less about looking for his son and more about finding the truth. He has to know whether Luke is his son (which makes his obsessive drive to find him even more meaningful, IMO), and while everything he thought he knew tells him it's impossible, it makes too much sense not to be true. So when Palpatine confirms that it is actually his son, he has to know: "How is that possible?" Under this interpretation, he's being quite literal.

There's a third interpretation too, going with the above view. Palpatine tells Vader he killed Padme on Mustafar. So while Vader could hypothesize that Padme's funereal pregnancy was faked (and thus that his children might have survived), there's still the testimony of Palpatine that she died on Mustafar, obviously before she gave birth. And now Palpatine tells him the children survived, meaning Padme survived long enough to bear them. So in this case, "How is that possible?" is a dig at Palpatine. Vader knows Palpatine lied to him (which could well be what motiviates him to propose his coup to Luke on Bespin), and he's making a point: You told me I killed her, so how is it possible that the children survived?

Now, I was all for the "Vader is playing dumb" theory before ROTS, but now I really think that one of the latter two was what Lucas was going for. The new dialogue tells us little more than the original did, but it's worded differently. Before, the only reference to Luke being Vader's son was "the son of Skywalker", which was just casually slipped in there. This time, Palpatine distinctly states that Luke is the son of Anakin, making a clear point to Vader (which even warrants its own response, the one in question; this obviously isn't designed to be a throwaway line). I can't believe this is a coincidence, given what we know from ROTS about Anakin not believing his children could have survived. There's also that little bit about "I have no doubt this boy..." Well, that tag wouldn't really be necessary in another interpretation (i.e. they think the children could have survived): what reason would he have to doubt it's Anakin's kid? In fact, if they had no reason to think Anakin's children were dead, then I'd assume they'd just take it for granted that he was Anakin's son, as it was before the DVD changes. But if the characters think there's no way Anakin's kids could have survived, then that little tag makes a point: Yes, I'm sure this is his kid, no question about it.

This also answers the question of "Why add new dialogue?" Because in the older version, the characters all assumed there was no problem with Luke being Anakin's son. With ROTS, there would be, and it's not something they'd take for granted (and I really don't want to start an argument about whether it's right to change one movie to fit a later movie, etc., I'm simply throwing this out). The new dialog is something of a revelation for the characters: this is the first time that Vader and Palpatine are sure that Luke is Anakin's

 

I like the third interpretation, LH.

This actually adds a subtle but important plot point to the saga.

 

I see what you're getting at here but Palpatine didn't lie to Vader in ROTS. Vader did kill Padme, she was heart broken that he turned to the darkside. "What i told you was true, from a certain point of view".

My point is that i don't think he's having a dig at Palpatine with the line in question, just wondering, wanting more information than what he already knew.

 

Very interesting Lord_Hydronium. I like all your theories. I would like to add that the last time Vader is with Padme in ROTS he is convinced that Obi-Wan had this crazy complot to make her betray him (seems to me like in a jelouse way). 20 years pass by and Obi-wan returns with a kid who is so strong in the force that actually makes a shot of 1 in a million and looks very much like Anakin has the same tatoonie classic cloths and has the right age to be his son. This definatley has to feed Vader's imagination. Im pretty sure he was not sure that Luke was his son until the confirmation by Palpatine, but he already suspected it and I even think that he suspected that Padme somehow survived and runned away with Obiwan. My point here is that after the ANH events I think Vader has "a new hope".

 

At the beginning of ESB, Admiral Ozzel is skeptical about probe fragments from the Hoth System, but one look and Vader "knows" that is the right system. The force helped him divine the truth. Surely Vader could have "searched his feelings" upon learning of a force-strong Skywalker and known the truth of that as well? Perhaps the reason he tells Luke to do so in ESB is that it had worked for himself.

 

Awesome thread Hydronium! Finally, someone who understands the scene!

 

It's possible to interpret all of this as indicating that Vader initially thought that Padme Skywalker had a child with Obi-wan. I suppose it is also possible that Vader is in denial until Palpatine forces him to face the unvarnished truth. However, I like to think that Vader was mocking Palpatine, as was stated in the first pose (i.e., "I know you lied to me about when Padme died, you doddering old fool.")

 

"he's making a point: You told me I killed her, so how is it possible that the children survived? "

You know, that's not something I really thought about before. Certainly could have influenced his turning against palpatine.

 

I think Vader was not for sure that Luke was his son, so he probably wanted to look for him to find out for sure (but he probably thought that Luke wasn't). When the Emperor told him that Luke was the son of Anakin Skywalker, Vader was shocked (remember he still wasn't for sure) and he knew the truth. Vader originally thought that he killed Padme and she never gave birth to those twins, but he was wrong.