## Comments about "Lorentz factor" in Wikipedia

This document contains comments about the article Lorentz factor 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.
The Lorentz factor or Lorentz term is the factor by which time, length, and relativistic mass change for an object while that object is moving.
The problem lies in the definition of moving. All objects are moving.
Due to its ubiquity, it is generally denoted with the symbol "lowercase gamma". Sometimes (especially in discussion of superluminal motion) the factor is written as "uppercase-gamma" rather than "lowercase gamma"
Discussions about superluminal motion are highly speculatif.

### 1. Definition

where:
• v is the relative velocity between inertial reference frames,
• Beta is the ratio of v to the speed of light c.
• tau is the proper time for an observer (measuring time intervals in the observer's own frame),
• t is coordinate time
• c is the speed of light in a vacuum.
See Reflection 1

### 2 Occurrence

• Time dilation: The time (dt') between two ticks as measured in the frame in which the clock is moving, is longer than the time (dt) between these ticks as measured in the rest frame of the clock:
dt' = gamma * dt
The only way you can perform this experiment that you have a clock A at rest in front of you.
Secondly you have an identical clock B which you move towards the right with a constant speed v and backwards with the same speed.
The result could be something like: Clock A has counted 10 ticks and clock B 5 ticks in a time dt in the rest frame.
That means the time dt' for clock B to make 10 ticks is 2*dt or gamma is 2.
• Length contraction: The length (dx' ) of an object as measured in the frame in which it is moving, is shorter than its length (dx) in its own rest frame:
dx' = dx / gamma
The simplest way to do this experiment that you place two lights at both ends of your rod (a train) which has a rest length l0. Next you move a rod (a train) with the same length with speed v in front of the rod or train at rest.
You as an observer you position your self at a certain distance midway between the two lights.
When you observe the two lights simultaneous, with the moving train inbetween the two lights, you know there is length contraction involved.

As far as I know no one has actual performed such an experiment.

### 5. Applications in astronomy

Subatomic particles called muons, have a relatively high lorentz factor and therefore experience extreme time dilation. As an example, muons generally have a half-life of about 2.2µs which means muons generated from cosmic ray collisions at about 10km up in the atmosphere should be non-detectable on the ground due to their decay rate. However, it has been found that ~10% of muons are still detected on the surface, thereby proving that to be detectable they have had their decay rates slow down relative to our inertial frame of reference
There is nothing wrong with this text. The only problem is that this has nothing to do with time dilation but more with reacting speed. The point is that the reaction speed of processes can be influenced by there own speed through space. The fact that a moving clock slows down is the same.

### 6. See also

Following is a list with "Comments in Wikipedia" about related subjects

### Reflection 1 - Lorentz factor

The Lorentz factor is used to decribe three different physical concepts: Time dilation, Length contraction and Relativistic mass.
Time dilation is defined as: t = to * gamma.
Length contraction is defined as: l = l0 / gamma
The problem is that both are based on the parameters v and c and it is important to define them properly.

### Reflection 2 - Does SR describe a physical experiment.

Time dilation starts from the physical experience that a moving clock runs slower than a clock at rest. The problem is that this is the result of the physical behaviour of a moving object or process but by itself does not say anything about the concept time. In fact the lesson learned from this experiment is that we should not use moving clocks in any experiment or when you do you should adjust (continuosly synchronise) its reading.

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Created: 1 July 2017

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