Season 4, Episode 5:
The Constant
"You answered, Penny."
Written by Carlton Cuse & Damon Lindelof.
Directed by Jack Bender.
"Every equation needs stability, something known. It's called a constant. Desmond, you have no constant. When you go to the future, nothing there is familiar. So if you want to stop this, then you need to find something there...something that you really, really care about...that also exists back here, in 1996."
— Daniel Faraday
As Lapidus flies Sayid and Desmond back to the freighter, they are caught in a storm, and Desmond wakes up in the army barracks of the Royal Scots Regiment. He believes that his experience on the helicopter was a dream, but just as suddenly finds himself back on the helicopter, frightened and confused, and does not recognise Sayid or Lapidus. They arrive on the freighter, and Desmond is brought to the sick bay where he finds Minkowski, who is suffering from similar symptoms. Sayid calls Faraday on the Island, who explains what is happening: as a side effect of travelling to and from the Island, Desmond's consciousness from 1996 is flashing back and forward in time. He tells Desmond to find him at Oxford University in the past.
Desmond finds Daniel at Oxford, and he tells him that he needs to find a constant in the future, something or someone that he cares deeply about that exists in both time periods, to stop the flashes. He chooses Penny, but is unable to contact her, as they have recently broken up and she is avoiding him. He goes to her house in 1996, and convinces her to give him her new number. He calls her from the freighter, and the two have an emotional conversation and promise to do whatever it takes to find each other. Daniel finds a note in his journal, stating that Desmond will be his constant if anything goes wrong.
Tropes in this episode include:
- Anachronism Stew: The number that Penny gives in 1996 has eight numbers. Before 2000, London telephone numbers were seven numbers long.
- Call-Back: Daniel asks if Desmond has been exposed to electromagnetism, theorising that it might be why he's "sick". Jack shakes his head, but the audience knows that Desmond was exposed during the Hatch implosion in "Live Together, Die Alone".
- Christmas Episode: Downplayed. The 2004 segment of the episode takes place on Christmas Eve, but this only comes into play at the end of the episode, and the only real element of a traditional Christmas episode comes in the heartwarming ending with Desmond and Penny making contact.
- The Constant: The Trope Namer. Daniel explains that in order to properly orient himself in time, Desmond must find a constant, something or someone that exists in both time periods. Desmond uses Penny as his constant, while Faraday discovers a note in his journal stating that Desmond will be his constant in case anything goes wrong at the end of the episode.
- Continuity Nod:
- Charles Widmore is seen buying artifacts related to the Black Rock.
- Penny references her conversation with Charlie in "Through The Looking Glass".
- Drill Sergeant Nasty: Desmond's commanding officer in the Royal Scots Regiment is a textbook example, screaming at his soldiers and giving the entire group punishment exercises whenever Desmond starts behaving strangely.
- Foreshadowing: After the doctor, Keamy and Omar lock Desmond, Sayid and Minkowski in the sick bay, the door is mysteriously opened and Minkowski comments that it looks like they have a friend on the boat.
- Laser-Guided Amnesia: It's implied that 2004 Daniel doesn't remember meeting Desmond in 1996 because his memory was damaged by exposure to the radiation from his time travel device.
- Mauve Shirt: Minkowski has appeared (albeit only as a voice on the radio to Daniel) in a handful of episodes earlier in the season and gets slightly more characterisation than a Red Shirt before being killed off to demonstrate what the consequences will be for Desmond if he fails to find a constant.
- Mental Time Travel:
- Desmond's consciousness from 1996 shifts back and forth between 1996 and 2004 for most of the episode.
- Minkowski also suffers the same effects, and dies of a brain aneurysm since he can't find a constant.
- Daniel in 1996 uses a device he built to send a rat's brain into the future, allowing it to instantly complete a maze that he hasn't taught it to run yet. It too, dies of a brain aneurysm.
- Obstructive Bureaucrat: The freighter's doctor is generally as unhelpful as possible towards Desmond, refusing to allow him to contact Faraday, the one person who actually understands what's happening to him, and locking him in the sick bay.
- Screw the Rules, I'm Doing What's Right!: Sayid breaks Desmond out of the sick bay and into the communications room to use the freighter's phone to cure him of his temporal displacement, while the freighter's crew are as unhelpful as possible. He also attacks the doctor to give Desmond a chance to talk to Faraday when the doctor refuses to let him do so.
- Snark-to-Snark Combat: Juliet and Charlotte trade barbs at the beach while discussing events on the freighter.Juliet: Why aren't you worried?
Charlotte: Should I wring my hands together and whisper a prayer on their behalf?
[...]
Charlotte: Dan, let's not confuse anyone.
Juliet: Well, Daniel, maybe if you talk real slow, we'll be able to follow. - Trust Password: 2004 Daniel tells Desmond to prove to 1996 Daniel that he was sent by his future self by telling him the correct numbers to input to get his time travel device working, and that he knows about Eloise, the rat he has been experimenting on.
- Unstuck in Time: Desmond and Minkowski both have their minds flashing between different time periods as a side effect of travelling to and from the Island. Minkowski ends up dying from being unable to properly orient himself in time, and Desmond comes very close to suffering the same fate.
- Year Outside, Hour Inside:
- Going to and from the Island has this effect on the helicopter, as Lapidus, Desmond and Sayid's trip takes only about 20 minutes from their perspective, but over a day from the perspective of the people still on the Island. Sayid also notes that they left at dusk and arrived on the freighter in the middle of the day.Daniel: Your perception of how long your friends have been gone, it's not necessarily how long they've actually been gone.
- As Desmond's consciousness jumps become more erratic, the difference between the amount of time he spends in one time period and the amount he spends unconscious in the other time period gets wider. Daniel notes that he was out for about 75 minutes, but Desmond has only been in the future for five.
- Going to and from the Island has this effect on the helicopter, as Lapidus, Desmond and Sayid's trip takes only about 20 minutes from their perspective, but over a day from the perspective of the people still on the Island. Sayid also notes that they left at dusk and arrived on the freighter in the middle of the day.
- You Already Changed the Past: 1996 Faraday questions why he doesn't seem to remember meeting Desmond in 2004, but when Desmond asks if they're changing the future by meeting, Daniel says this is impossible. The ending implies that their meeting "always" happened, and Daniel forgot about it because of his exposure to radiation.
