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Newsgroups: sci.physics.relativity
Subject: Re: Energy?
From: nospam@de-ster.demon.nl (J. J. Lodder)
Reply-To: jjlxa31@xs4all.nl (J. J. Lodder)
Date: Wed, 31 Jul 2024 10:02:01 +0200
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The Starmaker <starmaker@ix.netcom.com> wrote:

> Ross Finlayson wrote:
> > 
> > On 07/29/2024 05:14 PM, The Starmaker wrote:
> > > There is no one person on earth that can even define correctly the
> > > word...Energy.
> > >
> > >
> > >
> > > Stefan Ram wrote:
> > >>
> > >>    In a chapter of a book, the author gives this relation for a
> > >>    system with mass m = 0:
> > >>
> > >> E^2/c^2 = p^"3-vector" * p^"3-vector"
> > >>
> > >>    . Then he writes, "This implies that either there is no particle
> > >>    at all, E = 0, or we have a particle, E <> 0, and therefore
> > >>    p^'3-vector' <> 0.".
> > >>
> > >>    So, his intention is to kind of prove that a particle without mass
> > >>    must have momentum.
> > >>
> > >>    But I wonder: Does "E = 0" really mean, "there is no particle."?
> > >>
> > >>    300 years ago, folks would have said, "m = 0" means that there is
> > >>    no particle! Today, we know that there are particles with no mass.
> > >>
> > >>    Can we be confident that "E = 0" means "no particle", or could there
> > >>    be a particle with "E = 0"?
> > >>
> > >>    Here's the Unicode:
> > >>
> > >> EÂ"/cÂ" = pâ∞˜ · pâ∞˜
> > >>
> > >>    and
> > >>
> > >> |This implies that either there is no particle at all, E = 0, or we
> > >> |have a particle, E â≈  0, and therefore pâ∞˜ â≈  0.
> > >
> > 
> > Entropy has two definitions, sort of opposite each other,
> > "Aristotle's and Leibniz'".
> > 
> > The energy or energeia then relates to the entelechiae,
> > content and connectedness, what results to dynamis/dunamis,
> > which are the same word, one for power the other potential.
> > 
> > So, energy is defined by other definitions, the least.
> 
> What is Einstein's definition of...Energy?

Einstein did not need to define energy.
He, and all physicists who mattered, knew what it was.
Ever since Huygens, who first cleared it up.

A somewhat jocular, but practical working proper definition is:
Energy is 1/2 m v^2, and everything else that is missing from the law of
conservation of energy.

It is operational, and properly circular,
as it should be.
It is adequate as long as general relativity is not involved.

Jan