Comments about "Compton ***" in Wikipedia

This document contains comments about the article Compton *** in Wikipedia
In the last paragraph I explain my own opinion.




The article starts with the following sentence.
In the theory of general relativity, the equivalence principle is any of several related concepts dealing with the equivalence of gravitational and inertial mass, and to Albert Einstein's observation that the gravitational "force" as experienced locally while standing on a massive body (such as the Earth) is the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.
This implies all the test performed in a laboratory frame on earth are performed in principle in a non-inertial reference frame.

1. Einstein's statement of the equality of inertial and gravitational mass

See also:

2. Development of gravitation theory

This is why an accelerometer in free-fall doesn't register any acceleration; there isn't any.
I think the reverse is also true: If an accelerometer registers any acceleration then the object is not in free-fall.
In reality when an accelerator registers long enough or is very accurate it will always measure an acceleration: Free fall is a theoretical concept and in some sense applies to an empty Universe which does not exist.

3. Modern usage

3.1 The weak equivalence principle

  • The trajectory of a point mass in a gravitational field depends only on its initial position and velocity, and is independent of its composition and structure.
The idea of a point mass is to calculate the strength of the gravitational field at a certain position. Point masses are used because they will not influence the strength of the gravitational field of a massive object. The deeper thought about the sentence is that a point sized object has no mass.

3.1.1 Active, passive, and inertial masses

By definition of active and passive gravitational mass, the force on M1 due to the gravitational field of M0 is:
F1 = M0act * M1pass/r^2
Along that same line: the force on M0 due to the gravitational field of M1 is:
F0 = M1act * M0pass/r^2
Why should not F1 be the same as F0?
That being the case we get M0act * M1pass = M1act * M0pass or M0act / M0pass = M1act / M1pass
The importance of this assertion is not clear,

3.1.2 Tests of the weak equivalence principle

3.2 The Einstein equivalence principle

Here "local" has a very special meaning: not only must the experiment not look outside the laboratory, but it must also be small compared to variations in the gravitational field, tidal forces, so that the entire laboratory is freely falling. It also implies the absence of interactions with "external" fields other than the gravitational field
This place hugh constraints on its applicability.

3.2.1 Tests of the Einstein equivalence principle

3.3 The strong equivalence principle

The strong equivalence principle suggests the laws of gravitation are independent of velocity and location. In particular,
The gravitational motion of a small test body depends only on its initial position in spacetime and velocity, and not on its constitution.
The outcome of any local experiment (gravitational or not) in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime.
The question is what has all of this to do if you want to study the movement of objects through space. When you study that the concept "Local" has no usage.

3.3.1 Tests of the strong equivalence principle

The strong equivalence principle can be tested by searching for a variation of Newton's gravitational constant G over the life of the universe, or equivalently, variation in the masses of the fundamental particles.
This is a very tricky exercise.
To determine variation in the masses of the fundamental particles you must be able to measure its trajectories.

4 Challenges

5 Explanations

6 Experiments

7. See also

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

Reflection 1 - Implications equivalence of inertial mass and gravitational mass

On of the first questions to ask is what exactly is the definition and the difference between inertial mass and gravitational mass(accordingly to Einstein). Secondly how is each measured or calculated.
The interesting thing is that using Newton's Law mass is calculated based on observations using Newton's Law. Newton's Law starts from the concept that the sum of all the forces is zero and based on that concept (law) the masses are calculated with best fit observations.


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Created: 22 October 2017

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