He notes the satisfaction he, Hanks and the crew felt about having the rare opportunity of shooting a movie in sequence, a process generally negated by the need to film certain actors, locations and light-dictated scenes within the same constrained time period.
"When I told them I would do another film during the hiatus, that sweetened the pill," says Zemeckis. "When we returned to Fiji to shoot the second half of Cast Away I noticed that a kind of spark had gone out of Tom's eyes, which was perfect because of what happened to Chuck. It was wonderful - and a little eerie - to see."
That look was the result of four months of dieting and exercise which Hanks found generally monotonous. "The story of Chuck on that island was all I thought of for all the time we were off," Hanks says. "It never went away. Bob had put the first half of the movie together and we watched it while we figured out how to balance the second half. I started growing all this hair and losing all this weight. After doing a workout I would stand on the scale, and there in front of me in the mirror would be this man I was preparing to play again. "I was constantly cataloguing all the things Chuck hadn't seen for four years - everything, like a cheeseburger or the rear view mirror of his car. He hasn't turned on an electric light. He hasn't picked up the telephone. He hasn't heard kids playing in a playground. All these stimuli that surround you every day, and then you start subtracting them all until you're left with almost nothing. By the time we got back down to Fiji after the break I looked like a piece of beef jerky with a goat head on. We were just prepared. It was instantaneous."
Uncompromising to the end, Cast Away proves an enthralling philosophical film which allows the stranded Chuck - and the viewer - ample time to reflect on the human condition in all its vulnerability, fallibility and dependency, and on all we take for granted in our lives.
"I think this happens to anyone beyond the age of 30," Zemeckis comments, "but, usually, not in such a dramatic way, of course. Re-evaluating aspects of our lives is part of the growth process we unfortunately all have to go through."
To Hanks, the concept of loneliness is an instantly explorable one, and he believes everyone would have their own perspective on it: "The gap between solitude and abject loneliness is bottomless, but it can be just a very narrow crack that's hard to get out of if you happen to fall down into it. It's also extremely relative. You can be in the middle of the busiest airport in the world and feel like you're all alone in the world, and that usually happens for very specific reasons that have a flux to them.
"As Vincent Dowling says, all the great stories are about loneliness. Whether it's Hamlet or The Godfather, I see some sort of battle against loneliness. The way you feel about Michael Corleone (the Al Pacino character) at the end of The God- father, Part II is that this guy has killed everyone and is in a room all by himself. This is no way to live, and it's no way to have power. It's also the single driving force in all of human history.
"There are some people who want power, and I think they want power because it's the best defence against loneliness. I think people want riches because it's a fabulous defence against loneliness. You can seek out love for the same reason, and there are all sorts of loneliness - probably as many as there are souls in the world."
Hanks cites some of the characters he plays as examples of this, such as the 12year-old boy trapped in a man's body in Big, the emotionally disconnected Forrest Gump who runs away from reality after his mother dies, and Jim Lovell, the astronaut he played in the factually based Apollo 13. "When Jim's going around the moon I don't think he's so concerned with the nature of what his own loneliness is, but I think he projects what's going to happen to his wife and family if he becomes just a corpse floating in this tin can around the moon and never gets back. So it's not necessarily your own individual battle against loneliness but how it affects everyone else you know."
Is it ever lonely at the top for Tom Hanks, who's regarded as the most bankable actor in movies today? "I can tell you, I've been wonderfully married for 12 years and I've got four kids, but there have been times when I've found myself alone in a hotel somewhere and I just feel sad. I ask myself, `Why am I knocking myself out like this?' And even though I've never been to the level of abject despair or hopelessness, there have been times when I've experienced an absence of feeling that I am truly connected to the world. We've all felt that.
"I think as you get older you develop a degree of faith, faith in whatever theology, or faith in serendipity, you know. The battles of conscience I or any of us face at 24 are different to those we face when we're 44."
The huge commercial success of Cast Away in the US - where the $85 million production took over $143 million on its first 17 days on release - has justified the confidence of Hanks and Zemeckis in their "rule-busting" project, but Hanks refuses to take individual credit for the achievement.
"There were no shortage of battles about how much it was going to cost," he says, "because it was an expensive movie to make, but as for how it was going to be made and how the story was going to turn out, they were nothing but supportive for the creative alliance of Bob, Bill and myself. If I as an actor said I wanted to make a film like this, I would still need someone to write it and someone to direct it, and unless you align yourself with people who are going to constantly test you and the material, chances are it's going to be a recipe for disaster.
"You could get anyone to write or direct it, because they are going to want the money, the influence and the proximity to you. But there's a good chance that such a movie is going to stink, and you can guess who's going to take all the flak if that happens. You might get some people to show up at the cinema on the first day because of your name, but by the second day the word-of-mouth is out there, and if they don't want to come, you can't make them."
Inevitably, Hanks's riveting performance has made a front-runner for an Oscar nomination next month. He has been nominated as best actor four times and has won the award twice, on consecutive years for Philadelphia and Forrest Gump. "Being nominated is an extremely personal thing from the get-go, and then you hold on for dear life for the next six weeks until the ceremony finally comes round," he says. "It's like the world stands still. Now, particularly now, it exists on this whole other level of competition and attention. It's almost like pari-mutual betting goes on, and you know, not only that, because now the Oscar season begins in March.
"Of course, it means an awful lot to me. That award represents such a force in society that is undeniable - otherwise you wouldn't be asking me about it. Win or lose, it plays itself out in front of three billion people."
Hanks is about to follow Cast Away by starring in the new film from Sam Mendes, the director of last year's Oscar-winner, American Beauty. Hanks describes the film, The Road to Perdition, which is based on a graphic comic novel, as "almost Shakespearean in its mythic genre and the way it captures the Depression era. It's one of those great sagas of justice and retribution, and bad things happening to bad people with good reason. I play an American Irishman named Michael O'Sullivan who has made some very serious rationalisations in his life that, in all honesty, he has to pay for."
And if Hanks needs any coaching with his Irish-American accent, he can always call up his old mentor, Vincent Dowling.
Cast Away is now on general release