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Re: [Phys-l] Mass and Energy



Prof E. E. Baart wrote:

1. I believe Einstein's 1905 paper was entitled (in translation) "Does energy have mass"? This would put mass as a property of energy and not something different.

I assume we are talking about this paper:
Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?
Quite literally that reads:
Is the inertia of a body dependent on its energy-content?


2. Halliday and Resnick state "mass is simply another form of energy".

My take on the fundamental properties of mass are summarized at
http://www.av8n.com/physics/mass.htm

Relativistically speaking, energy is the zeroth component of the
[energy, momentum] 4-vector. It indubitably includes the mass
among other forms of energy.

However, in classical (pre-20th-century) physics, it is conventional
to speak of "the" energy as not including the mass.

This is a terminological inconsistency. It is not likely to be
resolved anytime soon.

3. I recently saw a statement by someone or other that "80 to 90% of the energy in the universe exist in the Kinetic energies of the gluons and quarks". How does this relate to rest mass ?

I have no idea what he's talking about. It's up to him to explain.

4. One frequently sees statements that matter is converted into energy.

That is an example of the aformentioned inconsistency. Nonrelativistic
language (mass distinct from energy) is being used to describe an
intrinsically relativistic process (annihilation). Despite the
inconsistency, everybody knows what the sentence means.