Comments about "How Einstein Discover Relativity" by John Stachel

This document contains comments about the essay "How Einstein Discover Relativity" by John Stachel
In the last paragraph I explain my own opinion.

Contents

Reflection

Introduction

The article starts with the following sentence.

1. If you have read

For SRT we have the paper "On the Electrodynamics of Moving Bodies", in which the theory was first set forth in 1905 in its finished form, indeed a rather polished form (which is not to say that it bears no traces of its gestation process).
The title of the paper is strange. Electrodynamics and Moving Bodies have "nothing" in common, specific when free floating objects are considered as influenced by gravity. Electrodynamics at the same can be the cause that bodies move, but IMO this are physical different subjects.

2 Contrary to my original, naive expectation

Given the nature of the available documentation and the difficulty of understanding any creative process -let alone that of a genius- this really is not surprising.
Understanding the creative process of any person is difficult, except(?) if the person himself or herself has continues written down in some sort of diary what his or her thoughts are.
I have in mind from another remark of Einstein:
"A new idea comes suddenly and in a rather intuitive way. That means it is not reached by conscious logical conclusions.
New ideas come by logical reasoning and conclusions. This reasoning is often started based on discussions with others (who do not "understand" or have objections), on articles or books by others or on errors by yourself.

3. The main methodological hypothesis

Intellectually, Einstein was an exceedingly self-absorbed person, willing to go over and over the grounds for the theory again and again.
That is a very professional habit.
It follows from these methodological assumptions that I must preface my conjectures with a brief resume of the "logical schema of the theory of relativity" as it was first published in the 1905 paper
Okay.
In this paper, as in almost all subsequent accounts, Einstein bases SRT on two fundamental principles:
  • the principle of relativity and
  • the principle of the constancy of the velocity of light.
We are discussing here the Special Theory of Relativity
This theory should be a description of certain physical phenomena.
The principle of relativity originated in Galilean-Newtonian mechanics: Any frame of reference in which Newton's law of inertia holds (for some period of time) is now called an inertial frame of reference.
It is strange that the principle of relativity is based on Newton's law, and is not derived from some more basic principles.
Immediate next:
From the laws of mechanics it follows that, if one such inertial frame exists, then an infinity of them must: All frames of reference (and only such frames) moving with constant velocity with respect to a given inertial frame are also inertial frames.
That maybe true, but what is the purpose?
If you want to describe the movement of objects using Newton's Law than you need one (fixed) reference frame which encapsulates all objects studied.
Immediate next:
All mechanical experiments and observations proved to be in accord with the (mechanical) principle of relativity: the laws of mechanics take the same form in any of these inertial frames.
I would expect something more profound.
The principle of relativity, as Einstein stated it in 1905, asserts that all the laws of physics take the same form in any inertial frame-in particular, the laws of electricity, magnetism, and optics in addition to those of mechanics.
Okay.

4. The second of Einstein's principles

The second of Einstein's principles is based on an important consequence of Maxwell's laws of electricity, magnetism, and optics, as interpreted by H. A. Lorentz near the end of the nineteenth century.
Okay.
Since light waves easily propagate through the vacuum of interstellar space, it was assumed that any vacuum, though empty of ordinary, ponderable matter, was actually filled by such a medium, to which our senses did not respond: the ether.
IMO to discuss that the reality is more than what "we" humans see, smell or sense is makes sense. The word ether has a bad connotation, but to assume that from a physical point of view space can be empty is wrong.
The question then arose, how does this medium behave when ordinary matter is present?
In fact this question is wrong. The real question is to what are extend are physical processes we can observe, influenced by physical processes we can not observe.
In particular, is it dragged along by the motion of matter?
Better is:
In particular, is the path of a photon that travels into our position influenced by photons which do not travel in our direction?
Various possible answers were considered in the course of the nineteenth century, but finally only one view seemed compatible with (almost) all the known experimental results, that of H. A. Lorentz: The ether is present everywhere.
In the next sentence its become clear what Lorentz meant:
Ordinary matter is made up of electrically charged particles, which can move through the ether, which is basically immobile. These charged particles, then called "electrons" or "ions", produce all electric and magnetic fields, which are nothing but certain excited states of the immovable ether.
A direct consequence of Lorentz's conception of the stationary ether is that the velocity of light with respect to the ether is a constant, independent of the motion of the source of light (or its frequency, amplitude, or direction of propagation in the ether, etc.).
The biggest problem with this sentence is to what extend the speed of light is constant. That means always and every where the same. Specific in relation to gravity, which is also part of "the inivisible ether".
Einstein adopted a slightly-but crucially-modified version of this conclusion as his second principle: There is an inertial frame in which the speed of light is a constant, independent of the velocity of its source.
An inertial reference frame is at rest with the observer or has a constant speed. Such an inertial frame posses a problem when gravity is involved.

5 Now I shall begin my conjecture

In much later reminiscences, he reports that during the following year (1895-1896) he conceived of a thought experiment: what would happen if an observer tried to chase a light wave?
Thought experiments are always tricky. You must really ask yourself the question can I learn something about the physical reality.
Could s/he catch up with it? If so, s/he ought to see a non-moving light wave form, which somehow seemed strange to him.
Suppose I'm a photon moving with the speed of light. Parallel from me other photons are moving in the same direction which I cann't see (detect). From the opposite direction photons engulfing and interfering with me. What is so strange? Nothing is strange its my normal dayly physical life as a photon.
This is not somuch a thought experiment as a description of the physical reality.
IMO it is impossible to catch such a description in a mathematical form See also #ref2"> Reflection 2 - Moving as a bird with the speed of light

6. By the time he gave up the ether concept

7. To return to the main thread

Einstein seems to have wrestled with the problems of an emission theory of light for some time, looking for a set of differential equations describing such a theory that could replace the Maxwell-Lorentz equations; and trying to explain a number of optical experiments, notably the Fizeau experiment, based on some version of the emission theory.
For more about the Fizeau experiment read this: Albert Einstein and the Fizeau 1851 Water Tube Experiment by Galina Weinstein
A little further we read:
As noted then, the Maxwell-Lorentz equations imply that there exists (at least) one inertial frame in which the speed of light is a constant regardless of the motion of the light source.
It is important to mention that we are discussing here the Maxwell-Lorentz equations which from a physical point have nothing to with the movements of objects through space i.e. gravitation.
One issue is if the speed of light depends about the speed of the source. The answer is no.
A different issue is if the speed of light, emitted from a light source, in both directions is identical? Observed by two different observers this can't be the case.
From a physical point of view, this can only be in one reference frame.
Einstein's version of the relativity principle (minus the ether) requires that, if this is true for one inertial frame, it must be true for all inertial frames. But this seems to be nonsense.
Seems this nonsense, or is this nonsense? By who?
The problem is: Is this constant the same in every inertial frame.
A more bassic question is: Why this discussion? Is it not more practical to only consider one reference frame at rest?
How can it happen that the speed of light relative to an observer cannot be increased or decreased if that observer moves towards or away from a light beam?
The first question to answer is: What has an observer to do with the speed of light?
IMO nothing.
When an observer increases or decreases its speed, the speed of light from a physical point of view does not change.

Reflection 1 - Moving as a bird with the speed of light

When I was at high school, around the age of 18, my physics teacher thought me that nothing could go faster than the speed of light, more specific with the speed of lightning, as produced in a thunderstorm.
I dared to discuss this things with my fellow students so the only thing I could do is think about this issue only in my mind.
In my mind I thought what happens if you travel with a light ray and specific what happens if a lightray approaches you from the opposite site. The approaching speed should be larger as my speed, raising the issue that speeds larger than the speed of light are possible. I did not know the answer.

Later in my life I learned that General Relativity also handles this same problem. The solution of GR was a mathematical solution. In fact GR ignores the physical problem by claiming in some sense that when I travel with the speed of light my speed is zero.

Feedback

If you want to give a comment you can use the following form Comment form
Created: 8 January 2017

Go Back to Wikipedia Comments in Wikipedia documents
Back to my home page Index