• The text in italics is copied from that url
• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Nomenclature

The article starts with the following sentence.

### 2 Conservation of mass and energy

Mass and energy can be seen as two names (and two measurement units) for the same underlying, conserved physical quantity. Thus, the laws of conservation of energy and conservation of (total) mass are equivalent and both hold true.
This law raises an issue because IMO the mainstream opinion is that both electromagnetic radiation and gravitational radiation represent energy while the mass of a photon is considered zero. I expect the same with graviton.

### 2.1 Fast-moving objects and systems of objects

When an object is pushed in the direction of motion, it gains momentum and energy, but when the object is already traveling near the speed of light, it cannot move much faster, no matter how much energy it absorbs.
I doubt if such an object can absorb energy, because when it does the object in some way or another should react. This reaction implies change.

### 3 Applicability of the strict mass–energy equivalence formula, E = mc2

The formula then required to connect the two different kinds of mass and energy, is the extended version of Einstein's equation, called the relativistic energy–momentum relation:
Er^2 - p_abs^2 * c^2 = m0^2 * c^4
Er^2 - (p * c)^2 = (m0 * c^2) ^2
or
Er = sqr ( (m0 * C^2) ^2 + (p*c)^2
• Mass in special realtivity paragraph 3.
For photons where m0 = 0, the equation reduces to Er = pc.
What does that mean? What does that say about the Energy of photons ?