Introduction

In a modern world inhabited with robotic dogs, the Internet, and cloned mice, science fiction is quickly becoming science fact. One of the most intriguing science fiction technologies is time travel. Who wouldn't want to go to the past to relive the best day of their life or travel to the future to witness the first colony on Mars? Time travel involves more than merely jumping into a time machine and entering the desired date of arrival. Even though the reality of time travel is theoretically possible, it cannot be fully implemented in the near future due to massive energy requirements. In addition, the existence of time travel creates paradoxical issues that need to be resolved. However, time travel is not totally out of the question.

Definition of Time Travel

To better understand the possibility of time travel, it is important to first define it. In our world, we can move freely in three spatial dimensions (Gott): forward and backward; left and right; up and down. We can accomplish movement in any of these directions without a second thought. For example, I can travel to my professor's office by walking down one street, making a left onto an intersecting avenue, and then taking an elevator up to the second floor. Every object's position around the world can be described by these three dimensions. There also exists an additional dimension, that of time, which physicist Albert Einstein established as the fourth dimension (Kaku 10).

Traversing in the fourth dimension is vastly different than moving in the previously mentioned three. We simply cannot will ourselves to move forward five minutes or back ten days. In other words, time only moves forward, and we are stuck moving in that direction like corks bobbing helplessly in a river (Gott). Thus, the end goal of time travel is to enable us to control where we go in this fourth dimension. Much like moving back and forth, time travel involves moving to either the past or the future. However, our actions in the fourth dimension are cause for concern. What we do now in the present affects our future. In the same manner, our actions in the past should have affected our present lives. Changing the outcomes of past events leads to what physicists and philosophers refer to as the "Grandfather Paradox," an issue that needs to be addressed in any serious discussion of time travel.

The Grandfather Paradox

Suppose time travel to the past does one day become possible and some time travelers make a journey to 1960s Texas to prevent the assassination of President Kennedy. Another time travel group brings back blueprints of the latest SUV to a young Henry Ford. Logic dictates that these meddling time travelers just altered the future. What if by changing the future world, they prevented themselves from being born? This would mean that they should cease to exist, but if they were not born, then how did they change the past in the first place? These seemingly mind-numbing problems are variations on the Grandfather Paradox.

The Grandfather Paradox involves the question: If a person traveled to the past to murder his grandfather, thus preventing his father and subsequently himself from being born, what happens to that person? Does he simply fade away into non-existence? If he is not born in the first place, how did he manage to travel back in time to kill his grandfather? A solution to this paradox is necessary before even considering the possibility of time travel. There are a number of suggestions of ways to resolve the paradox. Philosophers present a simple solution. They reason that when the grandson attempts to murder his grandfather, he fails on all accounts because it is logically impossible to change the past (Riggs). This is because the grandson still exists in the present and when he goes back in time. Any number of things could go wrong: he misses on every shot or the gun doesn't work. By virtue of his own existence, no matter how hard he tries, he cannot kill his grandfather. This can also be applied to other cases where time travelers attempt to change the past. They simply cannot succeed due to the nature of the timeline from which they came.