## Comments about "Faster than light" in Wikipedia

This document contains comments about the article Faster than light in Wikipedia
• The text in italics is copied from that url
• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
Faster-than-light (also superluminal or FTL) communication and travel are the conjectural propagation of information or matter faster than the speed of light.
This sentence is not very clear. It is a hypothetical sentence
On the other hand, what some physicists refer to as "apparent" or "effective" FTL depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal or undistorted spacetime.
To understand the sentence you need a clear definition of distorted versus undistorted spacetime. It also requires an explanation how time is measured, otherwise the concept more versus less time does not make sense.

### 1. FTL travel of non-information

In the context of this article, FTL is the transmission of information or matter faster than c, a constant equal to the speed of light in a vacuum, which is 299,792,458 m/s (by definition of the meter) or about 186,282.397 miles per second.
To understand that sentence you need a clear definition of 1 meter and 1 second.

### 1.6 Possible distance away from Earth

Since one might not travel faster than light, one might conclude that a human can never travel further from the Earth than 40 light-years if the traveler is active between the age of 20 and 60.
The distance that a human being can travel away from earth is a physical process and has nothing to do with the speed of light.
A traveler would then never be able to reach more than the very few star systems which exist within the limit of 20–40 light-years from the Earth. This is a mistaken conclusion: because of time dilation, the traveler can travel thousands of light-years during their 40 active years.
Time dilation has to do with a moving clock. A moving clock ticks slower, specific a clock which operates based on lightsignals. In general the reaction rate within certain container can be influenced (reduced) when the container a certain speed. For example an hourly glas will not function (maintain time) when the hourly glas is dropped.
However that does not mean that you can give a human being any speed you like and hope that the human being stays alive.
If the traveler returns to the Earth, she or he will land thousands of years into the Earth's future.
What can happen that the clock on board has aged 1 year and the clock on earth thousands of years, but that does not mean that the traveller is still alive.
Their speed will not be seen as higher than the speed of light by observers on Earth, and the traveler will not measure their speed as being higher than the speed of light, but will see a length contraction of the universe in their direction of travel.
What observers see is in some sense not important and can be very misleading.
What is important to measure everything from one frame.

### 8. Variable speed of light

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Created: 12 January 2018

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