Physics explains this impossibility

Jan 23, 2009 18:42 GMT  ·  By

Traveling back and forth in time has been a topic so widely spread, that there's hardly any possibility left uncovered by fiction. Books, comics, feature films and TV shows have all addressed the aspects of time travel, and have proposed various theories on how this can be accomplished. And it's not only them who have done so – physicists have also attempted to determine scientifically if time travel is possible, and, if so, what theories would apply to the changes a traveler would make through his or her actions.

There are a number of paradoxes that could come true if someone was to return in time. One of them states that the same being cannot be in two places at the same moment. Of course, the opposite is also true, meaning that two instances of the same being cannot be in the same place. You touching yourself in the past could mean that the course of history has been altered.

The same holds true for speaking, breathing, or even walking over an insect in the past. The repercussions of our deeds remain unknown even in the present, but in the past they can wreak havoc in the world as we know it today.

Physically speaking, time is the fourth dimension, alongside height, depth and width. When you walk from a place to another, you move through coordinates such as length and width, but you also move ahead through time. “Space and time are tangled together in a sort of a four-dimensional fabric called space-time,” Charles Liu, an astrophysicist at the City University of New York's College of Staten Island, said.

“When something that has mass – you and I, an object, a planet, or any star – sits in that piece of four-dimensional spandex, it causes it to create a dimple. That dimple is a manifestation of space-time bending to accommodate this mass,” he explained. The bending of this dimple influences the trajectory of objects in it, and this is what we've come to know as gravity.

But time isn't subject to the same freedom width, height and depth are. One can only move forward in time, and, even then, the traveler has no control over the speed with which he or she is moving.

Perhaps the most well-known idea for time travel involves a concept known as a “wormhole.” Proponents of this theory say that time flows in sinusoidal waves, which fold alongside each other in an endless stream. They hypothesize that, by creating a hole in the fabric of space-time, one could theoretically short-circuit the sinusoidal loops, and end up somewhere in the future (see picture).

“Many people who study the subject doubt that that approach has any chance of working. But the basic idea if you’re very, very optimistic is that if you fiddle with the wormhole openings, you can make it not only a shortcut from a point in space to another point in space, but a shortcut from one moment in time to another moment in time,” string theory expert Brian Greene, who is also a physicist at the Columbia University, revealed.