Tonight I watched the debut of FlashForward, which is based on the novel of the same name by Rob Sawyer, an SF writer from my hometown whom I have known for many years. However, "based on" is the correct phrase because the TV show features Hollywood's standard inability to write a decent time travel story. Oddly, just last week I watched the fairly old movie "Deja Vu" with Denzel Washington, which is also a time travel story.

Hollywood absolutely loves time travel. It's hard to find a Hollywood F/SF TV show that hasn't fallen to the temptation to have a time travel episode. Battlestar Galactica's producer avowed he would never have time travel, and he didn't, but he did have a god who delivered prophecies of the future which is a very close cousin of that. Time travel stories seem easy, and they are fun. They are often used to explore alternate possibilities for characters, which writers and viewers love to see.

But it's very hard to do it consistently. In fact, it's almost never done consistently, except perhaps in shows devoted to time travel (where it gets more thought) and not often even then. Time travel stories must deal with the question of whether a trip to the past (by people or information) changes the future, how it changes it, who it changes it for, and how "fast" it changes it. I have an article in the works on a taxonomy of time travel fiction, but some rough categories from it are:

• Calvinist: Everything is cast, nothing changes. When you go back into the past it turns out you always did, and it results in the same present you came from.
• Alternate world: Going into the past creates a new reality, and the old reality vanishes (at varying speeds) or becomes a different, co-existing fork. Sometimes only the TT (time traveler) is aware of this, sometimes not even she is.
• Be careful not to change the past: If you change it, you might erase yourself. If you break it, you may get a chance to fix it in some limited amount of time.
• Go ahead and change the past: You won't get erased, but your world might be erased when you return to it.
• Try to change the past and you can't: Some magic force keeps pushing things back the way they are meant to be. You kill Hitler and somebody else rises to do the same thing.

Inherent in several of these is the idea of a second time dimension, in which there is a "before" the past was changed and an "after" the past was changed. In this second time dimension, it takes time (or rather time-2) for the changes to propagate. This is mainly there to give protagonists a chance to undo changes. We see Marty Mcfly slowly fade away until he gets his parents back together, and then instantly he's OK again.

In a time travel story, it is likely we will see cause follow effect, reversing normal causality. However, many writers take this as an excuse to throw all logic out the window. And almost all Hollywood SF inconsistently mixes up the various modes I describe above in one way or another.

Spoilers below for the first episode of FlashForward, and later for Deja Vu.

Update note: The fine folks at io9 asked FlashForward's producers about the flaw I raise but they are not as bothered by it.

In FlashForward (both book and show) at one moment, everybody in the world blacks out for a short period, and sees a vision of themselves in the future. (6 months ahead in the TV show, 20 years in the book.) The blackout causes major disasters (cars crash, etc.) but the real story is the visions. It becomes clear quickly that the visions are of a specific future. People who were meeting together both see the same meeting, people watch the same TV shows, read the same newspapers.

However, the show diverges from the book in an important and mistaken way. Most people see a vision of some random snippet of life. They are in a meeting, or on the toilet, or asleep and dreaming, or watching a regular TV show. However, the lead characters see scenes that are the direct result of the FlashForward catastrophe. One is an FBI agent who sees himself working on the FlashForward case. His wife has a meeting with somebody she only meets because she treats his son for injuries from the catastrophe.

This makes no sense. If the visions are of a world after the FlashForward, then the magic day, 6 months in the future, would be the most anticipated day in the history of the world. Forget the moon landing, forget Canada-vs-USA for Hockey Gold. Nobody would be doing something mundane. Everybody would be awake, no matter what time it is. Everybody would be either gathering with others, or watching TV, with many trying to act out their now misremembered memory of the vision they had, and others working prevent it.

So we see a world where most people are seeing the future which would have been, a mundane future. But that future is clearly not true, it is at most an image of what might have been had there not been a big world event. Yet a few characters are seeing the world with the big event. It's the same world, but it can't be.

In the novel, people learn quickly that the seen future is not certain. For example, people who saw visions of the future die -- sometimes because of the bleak future they saw. With the first such death it's obvious that the vision is not an assured future, and people can work to change it (or bring it about) as they see fit. The TV show future is neither, it just makes no sense.

A few other quibbles: A thousand planes crash. In reality, planes are all on autopilot, even when landing and taking off. Only a few would crash. Even planes not on autopilot would not hit the ground in 137 seconds in most cases. It is reported that Hong Kong is devastated -- but it would be around 4 in the morning there, so in fact the effect would be quite mild, and most people might not even remember it. 1/3 of the world would be asleep, and thus face minor trouble -- and as such perhaps come to dominance in the injured world. Based on the regular death rate, we would have seen the proof that the viewed future was not set within minutes, not weeks.

But can they get past the big one, and move more to the novel's story where the visions are just a warning? It's hard to see that happening, since the main plot is the FBI agent trying to determine the cause of it all.

Update: The producers, when asked, suggest that a character might be on the toilet because "sometimes you just have to go." While that's true enough, he would not be idly reading and sitting, he would be very annoyed. And having seen the toilet scene and been disappointed by it, he would make sure he didn't have to go. But many other characters are having totally mundane experiences that could easily be avoided. And all the people watching TV are seeing ordinary TV shows, not the "live coverage of the big event" that would be on every channel.

Deja Vu

Deja Vu has a similar problem. In this film, after a terrorist attack, we get a great plot... The spooks have a device that can look back just over 4 days, and they need to use it to solve the crime. This would have made a great story, but they decided to make it two-way and allow first a message, and then a man, to go back in time.

The problem is that some of what they experience is the result of those trips back in time, but some of it is not. In the movie, Denzel goes to the murdered woman's house, and sees bloody swabs and a message on the fridge that, it turns out, were left by him when he went back in time. The problem is that the future created by his trip in time, which has that message and bloody swabs, has no murder and has no terrorist attack. There is no reason for him to be in the house or investigating the crimes at all in that future.

The movie has this problem because it wants to tease you and make you wonder if it's of the Calvinist sort above, or the modified form where you try to change things but they happen anyway. This creates some suspense, "is it all going to happen again, in spite of his time travel?" But as soon as he saves her, it no longer can, since the whole investigation starts because he discovers that she died before the terrorist bomb. Once she doesn't die then, the new future can't be the old one. And yet bizarre coincidences keep coming, to tease the audience, not to make any sense.

Indeed, even the first note sent back has this problem. Denzel's partner's car is found parked at the Ferry. This is because he saw a note sent back in time and went to investigate the ferry, and was killed. He also damaged the terrorist's car, making him need a new one -- but he's already set up an appointment to steal the car from the woman he will murder. And that's the car he uses anyway.

It's sad because the movie started out well, and might have ended well had he been unable to get the Hollywood ending and save the girl and stop the bomb. But it's really sad because the story with the device that spies into the past would have been a great consistent story, one that doesn't violate the laws of physics at all, and one which has been explored in the past in some great SF. (There are a number of privacy concerns with such technology of course, which are brought up in some of that SF.) The movie is well made and has gripping moments, which makes it doubly sad because it could have been great.