Science fantasy: Time travel isn't happening, get over it

Time travel is impossible. Hollywood needs to realize this.

By: Abid Mujtaba

Posted: 6/30/08

In a darkened theatre punctuated by the slow crunching of popcorn, the audience gazes in wonder as our hero steps in to a time machine to right the past and save the future, and I cringe. I have lost count of the number of times Hollywood has left me in a black depression when they decide to send someone back in time.

This is supposed to be science fiction, the stress should be laid on the first word: "science," not "fiction." The genre demands that we take leaps of fancy but that our imagination remains grounded in known fact, that we retain the baby as we throw out the bathwater. This is an essential element of any fiction, and much more so when it comes to sci-fi, that the story, the new ideas be connected with our common experience; that they grow upon them. Science fiction is supposed to be on the cutting edge, just on the verge of happening, give or take a few centuries.

Hollywood's problem is of course the light-hearted way in which they approach technical details - its penchant for providing for the lowest common denominator in the audience. When it comes to time machines the concept of causality seems to be alien to them. Causality, for the uninitiated, is one of the holiest physical principles that we think the universe obeys: that all causes precede their effects. Use time travel to violate causality and you have all sorts of nasty time-travel paradoxes on your hands.

Let us take "The Terminator" for instance. I am a huge fan of the second installment, but that doesn't change the fact that they took great liberties with the space-time continuum in the plot. Rest assured, if you are alive today then no one can go back in time and kill you in the past. Your being alive today means that any attempts to kill you in the past by cybernetic organisms sent by evil artificial intelligentsia have necessarily failed, otherwise how could you be here. This view of time travel revolves around the absoluteness of time. It says that what has happened, has happened; what will happen, will happen, nothing can change that, all time travel has already been incorporated in to this and it all works out in a nice self-consistent way.

The author Douglas Adams who initially was of this opinion summarized it rather deliciously when he wrote:

"One of the major problems encountered in time travel is not that of accidentally becoming your own father or mother. There is no problem involved in becoming your own father or mother that a broadminded and well-adjusted family can't cope with. There is also no problem about changing the course of history - the course of history does not change because it all fits together like a jigsaw. All the changes have happened before the things they were supposed to change and it all sorts itself out in the end."

Some authors can stick to this absoluteness principle. J. K. Rowling comes to mind in "Harry Potter and the Prisoner of Azkaban." Fanatical followers will recall how the book's protagonists earlier thought Buckbeak to be dead when they heard the sound of an axe swinging and Hagrid howling. In fact their future selves traveling back in time saved Buckbeak and it was the executioner swinging at a post in frustration and Hagrid howling in delight at the rescue. The rescue has always occurred, nothing was changed by the time travel, it had always happened.

Having negotiated this tricky bit of time warping Rowling then fell in to the classical subtle pitfall of time travel, what I like to call the paradox of original thought. Earlier Harry thinks his father has saved him from the dementors from across the lake. He later lies in wait for his father on the other end who fails to appear and he realizes that his past self had seen his future self from afar and mistaken him for his father. He then whips out his wand and conjures a spectacular patronus and saves all and sundry.

The problem is that the future Harry realizes he can conjure up the patronus because his past self sees himself do it. But this is a circular occurrence. His past self sees his future self do it, but his future self can only perform it because of the memory of it from his past self. Where did the original idea originate from? Seemingly from nowhere, but ideas must originate somewhere; the effects must have a cause.

This is a subtle violation of causality and one that physicists consider to be not allowed. The eminent physicist Stephen Hawkings has pondered over this issue and came up with several explanations. My least favorite one requires a cosmic censor who intervenes whenever causality is about to be violated. Circumstances will be created which disallow any violation.

The other explanation is even more far-fetched but much more elegant. Hawking suggests that every time someone travels back in time a parallel universe is created in to which the traveler is deposited. The original universe continues unchanged minus one time-traveler and all changes made to the past are incorporated in to the new parallel universe. This preserves causality because the cause of the change is preserved in the original universe.

This alternative raises philosophical questions about the rationale for time travel. You could go back and kill your enemy in the past but all that will achieve is the creation of an alternative universe and one with a very weird past at that. It is also possible that the time traveler is copied in to the parallel universe with no observable change whatsoever in the original. We wouldn't even know and we could be sending people back in time in what we consider to be failed experiments. Something to consider the next time we are about to create a black hole at CERN.