This document contains comments about the article Conservation of energy in Wikipedia
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In the last paragraph I explain my own opinion.

Introduction

The article starts with the following sentence.

4 Relativity

With the discovery of special relativity by Henri Poincaré and Albert Einstein, energy was proposed to be one component of an energy-momentum 4-vector.
It should be made clear why this distinction between Energy and momentum.
Each of the four components (one of energy and three of momentum) of this vector is separately conserved across time, in any closed system, as seen from any given inertial reference frame.
What this means that there cannot physical be any physical exchange between the objects that have Energy versus the objects that have momentum.
Thus, the rule of conservation of energy over time in special relativity continues to hold, so long as the reference frame of the observer is unchanged.
The question is what specific has to happen to invalidate this rule. Suppose my reference frame is based on the Sun, does that invalidate this rule?
This applies to the total energy of systems, although different observers disagree as to the energy value.
Why?
In general relativity, energy–momentum conservation is not well-defined except in certain special cases.
What is the use of this whole 'exercise' when it cannot be used (I assume) to predict the future of our Solar system.
However, since pseudotensors are not tensors, they do not transform cleanly between reference frames.
Solution? Use only one reference frame.?
If the metric under consideration is static () or asymptotically flat (), then energy conservation holds without major pitfalls. In practice, some metrics such as the Friedmann–Lemaître–Robertson–Walker metric do not satisfy these constraints and energy conservation is not well defined.
https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

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Created: 15 June 2019

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