This document contains comments about the article Absolute space and time in Wikipedia
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• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
Absolute space and time is a concept in physics and philosophy about the properties of the universe.
It can not be both. The sentence explains 'nothing'
In physics, absolute space and time may be a preferred frame.
The wording may be is to vaque. IMO a better sentence is: In physics, absolute space and time are related to reference frames.

### 1. Before Newton

Robert S. Westman writes that a "whiff" of absolute space can be observed in Copernicus's classic work 'De revolutionibus orbium coelestium', where Copernicus uses the concept of an immobile sphere of stars.
What Copernicus wrote is extremely clever. IMO what Copernicus mentions is that the position of the stars is fixed versus the positions of theplanets, which are moving.
To compare that with absolute space you first need a definition.

### 2 Newton

According to Newton, absolute time and space respectively are independent aspects of objective reality:
Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time ...
Recapitulation:
Absolute time is the real physical time.
Relative time is the measured duration by means of the motion 'of a clock'.
According to Newton:
Absolute space, in its own nature, without regard to anything external, remains always similar and immovable. Relative space is some movable dimension or measure of the absolute spaces; which our senses determine by its position to bodies: and which is vulgarly taken for immovable space ...
Recapitulation:
Absolute space is the whole of all of space.
Relative space is small part of absolute space.
Accordingly to Newton:
Absolute motion is the translation of a body from one absolute place into another: and relative motion, the translation from one relative place into another ...
Recapitulation: Absolute motion is the speed calculated in absolute space. Relative motion is the speed calculated in relative space.
These notions imply that absolute space and time do not depend upon physical events, but are a backdrop or stage setting within which physical phenomena occur.
I would rewrite this sentence as:
These notions imply that absolute space and time do not describe specific physical events, but serve as a stage setting within which individual physical phenomena occur.
Thus, every object has an absolute state of motion relative to absolute space, so that an object must be either in a state of absolute rest, or moving at some absolute speed
Using the above definitions that is 100% correct.

### 3. Differing views

Gottfried Leibniz was of the opinion that space made no sense except as the relative location of bodies, and time made no sense except as the relative movement of bodies.
Leibniz lived from 1646 to 1716. Newton from 1642 to 1727
What is the definition of no sense?
Newton discussed the behaviour of the planets around the Sun which is all based on relative space, relative location and relative velocities.
George Berkeley suggested that, lacking any point of reference, a sphere in an otherwise empty universe could not be conceived to rotate, and a pair of spheres could be conceived to rotate relative to one another, but not to rotate about their center of gravity,an example later raised by Albert Einstein in his development of general relativity.
You cannot discus any form of physics based on one object in a completly empty universe, because such an object does not exist. You can discus the behaviour of two isolated objects rotating around there center of gravity in an otherwise empty universe.
Even within the context of Newtonian mechanics, the modern view is that absolute space is unnecessary. Instead, the notion of inertial frame of reference has taken precedence, that is, a preferred set of frames of reference that move uniformly with respect to one another.
At the end you need one reference frame. in order to combine all observations.
As a practical matter, inertial frames often are taken as frames moving uniformly with respect to the fixed stars. See Inertial frame of reference for more discussion on this.
The concept of fixed stars, as being stars in our galaxy, is wrong.

### 4 Special relativity

Absolute simultaneity refers to the concurrence of events in time at different locations in space in a manner agreed upon in all frames of reference.
Before you can understand this sentence, you must first understand what does it mean that two events are simultaneous in one reference frame.
The theory of relativity does not have a concept of absolute time because there is a relativity of simultaneity.
This sentence is not clear because it hinges on two concepts which both are not clear.
An event that is simultaneous with another event in one frame of reference may be in the past or future of that event in a different frame of reference, which negates absolute simultaneity.
How do you define that two events are simultaneous in one reference frame. Reflection 2 - Reference frame.

### Reflection 1 - Isaac Newton

Based on what is written in paragraph 2. Newton it can be recapsulated that absolute refers to the total of something. Relative refers to a part of the total.
As such in absolute space you have absolute positions, absolute velocities and absolute accelerations.
In relative space you have relative positions, relative velocities and relative accelerations.
The whole problem that this difference between absolute and relative in practice does not make sense when you want to calculate the positions of the planets in our solar system, or of the stars in our galaxy.
Newton studied the first.

### Reflection 2 - Reference frame

When you read all what is written about "Absolute Space and Time" the question pops up: Why do you need different reference frames in order to unravel the laws of nature? Why can not you use one (universal) coordinate system for all?
This question is important if you want to define what means simultaneous.
A slightly different question is: Does the whole of the universe has a present (a now) a future and a past.
1. If the answer is Yes than all the events that happen anywhere in the universe at present are simultaneous.
2. If the answer is No than the next question is: Does each reference frame has its own present, future and past.
I expect the answer will be: Yes.

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Created: 22 February 2019

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