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# Faster Than Light Travel

Note: There are several theories on faster than light travel, this is only an overview.

## Introduction

It is commonly known from Einstein's Special Theory of Relativity that “No object may move faster than the speed of light.” However, for a long time both Scientists and Science Fiction Authors have been pondering the idea of Faster-Than-Light (FTL) Travel and it’s consequences.  It is known that in order to get out and explore beyond even our own Solar System, we have to have technology to propel ourselves at Faster Than Light speeds.  Our nearest Star, Proxima Centauri, is roughly 4 light  years from our solar system.  At sublight speeds of 253,000 kilometers per hour, a mere 0.0235% the speed of light, which is the fastest speed we have achieved, it would take about 17,000 years to reach the star.  If we could even reach 10% the speed of light would shorten the travel time to only 40 years, but we are not likely to achieve that kind of speed until we are far more advanced in our space technology.1

### 1.1 Classical Physics

#### Newton’s Law’s of Motion

Isaac Newton discovered three things when he was observing motion, which are now commonly known as “Newton’s three laws of motion”

His First Law of Motion states that “An object at rest or in uniform motion in a straight line will remain at rest or in the same uniform motion unless acted upon by an unbalanced force” and is also known as the Law of Inertia.

His Second Law of Motion relates to force; “The acceleration (a) of an object is directly proportional to the total unbalanced force (F) exerted on the object, and is inversely proportional to the mass (m) of the object (in other words, as mass increases, the acceleration has to decrease). The acceleration of an object moves in the same direction as the total force” and is also known as the law of acceleration.  This theory can also be expressed in the formula “F = M * A”

His Third Law of Motion is the most widely know, it states that “Every action has an equal yet opposite reaction”, also known as the Law of Interaction.  A classic example of this law in every day life is moving a box.  When you push on a box you provide an action, the equal and opposite reaction is the box starts sliding across the surface it is on.  The force of the action is always equal to the force of the reaction.

### 2 Special Relativity

Special Relativity doesn't play a role in our daily life. Its impact becomes apparent only for speed differences that are considerable fractions of the speed of light, c. They are also known as "relativistic speeds". The effects were first measured near the end of the 19th century and explained by Albert Einstein in 1905.

The Entire theory is based upon:2

1. The laws of physics are the same for all observers in uniform motion relative to one another (Galileo's principle of relativity),
2. The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.

The resulting theory has many surprising consequences. Some of these are:2

• Time dilation: Moving clocks tick slower than an observer's "stationary" clock.
• Length contraction: Objects are shorter along the direction in which they are moving.
• Relativity of simultaneity: two events that appear simultaneous to an observer A will not be simultaneous to an observer B if B is moving with respect to A.
• E=mc²: energy and mass are equivalent and interchangeable.

### 2.1 Time Dilation3

Time dilation is the phenomenon whereby an observer finds that another's clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. This is often taken to mean that time has "slowed down" for the other clock, but that is only true in the context of the observer's frame of reference. Locally, time is always passing at the same rate. The time dilation phenomenon applies to any process that manifests change over time.
Time Dilation, according to the Theory of Special Relativity, occurs when an object travels near, at, or faster than the speed of light.

The twin paradox is about twins of whom one travels to the stars at a relativistic speed while the other one stays on Earth. It is obvious that the example assumes twins, since it would be easier to see if one of them actually looks older than the other one when they meet again. Anyway, it should work with unrelated persons as well. What happens when the space traveler returns to Earth? Is he the younger one, or maybe his twin on Earth, or are they equally old?
To anticipate the result, the space traveler will be the younger one when he returns. The solution is almost trivial. Time dilation only remains the same, as long as both observers stay in their respective frames of reference. However, if the two observers want to meet again, one of them or both of them have to change their frame(s) of reference. In this case it is the space traveler who has to decelerate, turn around, and accelerate his starship in the other direction. It is important to note that the whole effect can be explained without referring to any General Relativity effects. Time dilation attributed to acceleration or gravity will change the result, but it will not play a role in the following discussion. The twin paradox is no paradox, it can be solved, and this is best done with a space-time diagram.

A Predestination Paradox, also known as a Causality Loop, is a paradox of time travel that can result from interaction with others due to the fact that traveling faster than light might send you back in time.

A Predestination Paradox exists when a time traveler is caught in a loop of events that predestines him/herself to travel back in time and participate in an event in the past.

Here is an example of a predestination paradox:

A man travels back in time to discover the cause of a famous fire. While in the building where the fire started, he accidentally knocks over a kerosene lantern and causes a fire, the same fire that would inspire him, years later, to travel back in time.

References:
All Information sourced from Real Physics and Interstellar Travel. (2006). Ex Astris Scientia. Retrieved March 20, 2007, from http://www.ex-astris-scientia.org/treknology/warp1.htm unless stated otherwise.  Permission to duplicate content granted by Ex Astris Scientia webmaster on the date of Saturday, the 31st of March, 2007
1. Interstellar Travel, Sub-light-speed Travel. In Wikipedia. Retrieved March 20, 2007, from http://en.wikipedia.org/wiki/Interstellar_travel
2. Theory of Relativity, Special Relativity. In Wikipedia. Retrieved March 27, 2007, from http://en.wikipedia.org/wiki/Theory_of_relativity
3. Time Dilation. In Wikipedia. Retrieved March 27, 2007, from http://en.wikipedia.org/wiki/Time_dilation/