OK I'm going to try and jump inside The Joker's head for a minute to answer this one. I really think this may be the one thing The Joker didn't lie about. Like he said, it was a "social experiment." If one group actually chose to kill the others it would prove what he said in the interrogation scene; "When the chips are down, these civilized people will eat each other." That's the theme of all of his crimes; to turn people against each other. Getting the goons to kill each other during the bank robbery, holding the "tryouts" for his organization, sending the citizens of Gotham after Mr. Reese, turning Harvey against Gordon and Batman, almost tricking SWAT into slaughtering the hostages, these are all his ways of "introducing a little anarchy" and "upsetting the established order."
I agree with most of this post but even if wires were crossed (so you blow up your own boat) the Joker would still have his "social experiment." I think the detonators were wired to the same boat, and they were rigged not to go off until the time was up. If one button blew up both boats how would the Joker know who pressed the which button? And if the detonators weren't timed together one boat would blow up before the other people had time to press their button.
But there's no way to know. Either scenario is equally legit. This is another layer of how Nolan has created a thinking man's Batman... it all depends on how you personally view the Joker's motivations and methods... and each of those scenarios are perfectly plausible and equally open to debate.
The Joker lied because he wanted Harvey to live and knew Rachel would die because Batman couldn't get to her. He wanted Harvey to live with the death of Rachel and become bitter. Joker also knew that Batman had a thing for Rachel and with Rachel dying, you get 2 bitter men that will do rash things after loosing a loved one.
Yeah this sums it up. It's clear from the movie that he switched the addresses based on his analysis of Batman so that Rachel would die. He also made SURE that Rachel and Dent knew it would be Batman who would choose... again guessing that Dent would then blame Batman for choosing wrong and killing Rachel.
But everything the Joker does in this movie are little tests. In the end I dont really think the Joker cares who dies as long as he gets to see what everyone's (Batman, Harvey etc) reactions are. If Dent had died instead of Rachel I think the Joker would have gone "hmm chaos!" and move on with a next plan adjusted with that information. The main thing would be the fun of making Batman make that decision and testing his hypothesis and insight against what Batman would actually choose to do.
Sounds odd, but to me Joker is almost scientific in his madness. He is a powerful observer and manipulator and tactician, and when he has enough information he gambles it all to see if he was right. He keeps a clinical distance. I get the sense that he's too narcacistic to get too too personally invested in anyone else. It's all about HIS plan, HIS stories, HIS manipulations not someone ELSE'S pain. When he tells Harvery "nothing personal" he means it. He's more interested in pushing buttons and seeing what happens.
A couple of examples. When he stands in the street daring Batman to run him down. I dont think he has a deathwish exactly, more like a total
indifference to his own life (as kevin smith said in an interview). Based on what we saw, Joker has the brains to be a world-class psychiatrist or a millionaire corporate strategist... and he's terribly bored with himself. Whether he lives or dies is
not as interesting to him as pushing Batman's buttons and seeing what he will do. He basically guesses that the Batman wont kill him based on earlier interactions, but it's fun to put his own life on the line to see if he was right
Same thing when he's in Harvey's room and puts his own gun to his head and Harvey's finger on the trigger. Of course you can argue that the gun was UNLOADED and it was 100% manipulation of Harvey (which is legit) but I think Joker truly gave him a loaded gun to see what Harvey would do. Mind you I think he basically
knew he had worked Harvey over enough psychologically to displace guilt from himself to Gordon and "schemers" but he also truly wanted to see what Harvey would do. If Harvey had pulled the trigger I can see the Joker thinking in his last moments an amused 'hmm... I was wrong" and laughing manically before he crumples over
The only thing Joker truly misjudges in the entire movie is how Batman would get the better of him by sacrificing himself for the city by accepting Dent's guilt, thereby destroying Joker's grand plan for the entire movie. Joker
thinks he has Batman's number with the one rule and his affection for Rachel etc... but in fact he truly has no clue about what drives Batman. That's why I think Joker really has no clue that Batman is Bruce Wayne... Joker has a hubris that he truly understands Batman and the Batman needs him but in truth all Batman does, he does for the city (an altruism that Joker can never fathom because he thinks such a thing doesn't even exist).