Cue the Dr. Who theme music because The Constant should shatter any lingering doubts about whether Desmond actually time travels. As we discussed after Flashes Before Your Eyes, the obvious analogy is to Billy Pilgrim, the time-traveling protagonist of Slaughterhouse Five. Like Billy, Des has become unstuck in time -- his consciousness can jump through the fourth dimension to any point along his timeline. Also like Billy, Desmond can't change the future, which presumably course corrects to stop him if he tries. He can, however, influence the past to effectuate the present, creating what's called a predestination paradox.
That's where effects precede their causes in time, necessitating time travel or some other form of reverse causality to complete the chain of events. The Constant actually featured two of these predestination paradoxes. One was Eloise the rat knowing her way around the maze before being taught the correct route -- her apparent foreknowledge was actually the result of time travel. Another such paradox was Penny's decision to keep the same phone number for eight years before Desmond called her to be his Constant. If Des hadn't made contact with Penny in the past through time travel, she wouldn't have waited around for his call.
The examples of Eloise and Penny are important because they highlight two larger predestination paradoxes, both stemming from activation of the Fail-Safe, that are at the very heart of the show. The first is the characters' strange attraction to various Island elements (e.g., the Numbers) in their flashbacks. I argue in Cause and Effect that this attraction results from the Fail-Safe blasting their thoughts and memories back in time. Just as Eloise "remembers" the correct route through the maze because she will learn it in the near future, our Losties are drawn to the Island and its symbols by their subconscious "recollection" of future events.
The second big predestination paradox explains our Losties' rescue. I've suggested before (e.g., in The Cancer Man's Con) that Desmond's conversation with his physicist friend Donovan set in motion events culminating in the Freighter expedition. Charles Widmore somehow learned of Desmond's time travel rant, recognized his description of the Swan button, and waited for the discharge to find the Island. As with Penny's constant phone number, the effect paradoxically precedes its cause in time. If Des had never traveled into the past via the Fail-Safe, the Freighter would not have known to look for the electromagnetic anomaly.
Still with me? Good, because I'd like to raise one more related but distinct paradox clearly depicted in The Constant. An ontological paradox involves the spontaneous creation of objects and information through time travel. The classic illustration is actually pretty close to what we saw in the episode. A scientist is visited by his future self, who provides him with plans for a time machine he will later invent. The scientist builds the machine and travels back in time, closing the loop by providing the plans to himself in the past. The ontological paradox results because it's unclear where the plans for the time machine came from in the first place.
Ask yourself: how did Daniel know to set his machine to 2.342 and 11 Hz? Future Dan got those numbers from his notebook, then gave them to Desmond, who traveled back in time. While in the past, Des gave the figures back to Dan, who wrote them down in his notebook, apparently completing the loop. But that really doesn't explain anything -- we're still left with the ontological puzzle of how the information originally came into being. It's unclear what the significance of this twist will be, but at least one grim possibility occurs to me. What if the course correction for such ontological paradoxes is the total elimination of everyone affected?
Here are some other thoughts and questions I had about The Constant:
* As the foregoing analysis suggests, I absolutely adored this episode! I am, however, a little concerned that they've depicted time travel in a way that complicates things unnecessarily. Apparently, when your consciousness jumps through time, your physical body collapses in the time you've left like some kind of narcoleptic. But what happens to the consciousness you replace when jumping to a new time? Where do those displaced thoughts and memories go? A more logical solution would be for your past and present selves simply to switch places, avoiding these thorny questions...
* Well, now we know why Daniel has memory loss issues. At first, I figured the amnesia was just so Dan would have an excuse for not remembering Des despite meeting him in the past. The clear implication, however, is that Daniel exposed himself to his machine and is now unstuck in time. This presumably explains why Dan needs a caretaker and perhaps why he cried upon seeing the wreckage of Oceanic 815 -- he subconsciously remembered the future.
* Sayid mentioned that the helicopter took off at dusk and landed in the middle of the day, which is a much larger time differential than the 31 minutes reported by Dan's rocket. This actually points to the second of three scenarios that I proposed after Eggtown. The trip to and from the Island always covers the same distance from the perspective of the traveler, but may take varying lengths of time from the perspective of observers on the Island or Freighter.
* Who the heck is Tovard Hanso? Is he some relative of Alvar and Magnus that we haven't heard of previously? Or is this a sign that Desmond's trips to the past can change things more than Ms. Hawking and Prof. Faraday would have us believe?
* I'm guessing that Sayid and Desmond's friend on the Freighter, the one who unlocked the Sick Bay door for them, is Michael or Walt...
* Now we know why the Looking Glass console connected to Penny Widmore after Charlie deactivated the jamming signal. She probably had that number, like the Freighter's, on continuous auto-dial just waiting for someone to answer...
* Minkowski mentioned that he and Brandon became unstuck in time after they took the helicopter out for a flyby of the Island. What's curious about that is they're the only two we know of who became unstuck without exposure to large doses of radiation or electromagnetism. Mere continuity error or clue to something more?