On "Lost," time is always of the essence — for the show's characters, its writers and its viewers.

After dazzling viewers with its character flashbacks and flash-forwards, the ABC mystery drama (season finale, 8 tonight Hawai'i time) has shaken the space-time continuum this season by exploring the temporal variance between the island and the outside world and the possibility of traveling vast distances rapidly, or traveling through time.

Viewers able to maintain their equilibrium will be rewarded with tonight's finale, in which Locke (Terry O'Quinn) seeks to "move the island" to save it. "When you see it, you will be able to see much more clearly what the possibilities are when it comes to space-time on the show," says executive producer Carlton Cuse.

Time is central both to "Lost"'s story and in how the show is presented to the audience. "The Constant," arguably the most highly praised episode of a well-received fourth season, saw island castaway Desmond (Henry Ian Cusick) connect via his consciousness to a younger version of himself in England.

It took five weeks, rather than the usual two, for the writers to put that story together, because they needed to determine its ramifications on future stories. Executive producer Damon Lindelof says "The Constant" may be the most important episode of the series in laying out "Lost"'s rules for time travel.

"I remember in the writers room saying, 'I wish we could travel into the future, read the script and then come back and just go: This is what it's going to be,'" he says.

Space-time questions have popped up in recent episodes, as when the body of the doctor from the offshore freighter washes up on the island apparently before he was killed, and when a parka-clad Ben (Michael Emerson) appears in the Tunisian desert seemingly out of nowhere.

Andrew Morrison, a "Lost" viewer who teaches physics at Illinois Wesleyan University, says the producers have so far avoided the physically impossible.

They "have seemingly not (yet) violated any laws of physics, although the technology for how the effects would be accomplished are way beyond present-day engineering capabilities."

"Lost"'s rules for space-time are a mix of real physics and the show's internal mythology. "We try to use enough science to give a sense of credibility," Cuse says.

Producers have dropped clues to scientific connections by naming characters Faraday (a scientist conducting experiments relating to time on the island) and Minkowski (a freighter victim of time-travel sickness) after, respectively, an English physicist known for work in electromagnetism and a German mathematician who theorized about the space-time connection.

Fans have theorized about wormholes, a bending of space-time that theoretically allows faster-than-light-speed travel, and the effects of electromagnetism on "Lost" space-time.

Those theorists will learn more tonight via the Orchid Station, a Dharma Initiative site. The episode will expand on an Orchid orientation film that producers showed at last year's Comic-Con (and still available on YouTube) that featured a scientist mentioning the Casimir Effect. The Casimir Effect is believed to demonstrate "negative energy," which would be considered necessary to stabilize a wormhole for safe travel, Morrison says.

Regarding story rather than science, a cornerstone of "Lost" space-time is that characters cannot change their own futures, Lindelof says. "Once you tell the audience that they can (do that), nothing they've seen in the flash-forwards has any emotional stakes," he says.

The rule was proven last season when a precognitive Desmond knew Charlie (Dominic Monaghan) was going to die, tried to stop it but ultimately couldn't, Cuse says. "What that story proved was he couldn't change that fate."

Although one "Lost" writer does keep track of the physics that underlies the show's theory of space and time, the staff can't get too wrapped up in it.

"If we sat in the room and talked all day about physics and wormholes, we would never get any story telling done," Lindelof says.