Re: .Re: Why all the fascination with E = mc^2 ??
From: Leonard Pardin (leoppard_at_MailAndNews.com)
Date: 06/04/04
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Date: 4 Jun 2004 14:09:59 -0700
D.McAnally@i'm_a_gnu.uq.net.au (David McAnally) wrote in message news:<c9pdme$jok$1@bunyip.cc.uq.edu.au>...
> Firstly, I have to wonder how well you really understand the logical
> underpinnings of the Special Theory of Relativity. At least once below,
> you come dangerously close to stating that inertial frames of reference
> are distinguishable from each other. Such a statement would deny the
> Principle of Relativity (Einstein's First Postulate). This is also not
> the first time that I have seen you make such a statement.
If the frames are moving relative to each other, they must be
distinquishable.
>
> In the Special Theory of Relativity, it is invalid to describe a material
> body just as stationary or moving. In the Special Theory of Relativity,
> material bodies are described as stationary or moving with respect to a
> specific frame of reference. If a body is described just as being
> stationary or as moving, then that means that an inertial frame of
> reference has already been specified, and all discussion is implicitly in
> that frame of reference.
Good enough. I'll go along with the program.
>
> An inertial frame of reference is not system of bodies. An inertial frame
> of reference is a system of coordinates which satisfy certain conditions.
>
> This is an important point: an inertial frame of reference is a system of
> coordinates. It is not an experimental system, and it is not a system of
> bodies or particles.
O.K., it is imaginary, but it moves relative to other imaginary
frames. I can handle that. But once the reference frames have been
established, try to refrain from jumping from one to the other without
notice. We all want to keep track.
>
> Since you are obviously ignorant of the basics of the Special Theory of
> Relativity, as evidenced by many of the comments that you make below which
> betray your ignorance of these basics, then I would suggest that you learn
> the basics first, rather than trying something harder, where a knowledge
> of the basics (knowledge which you obviously don't have) is a necessary
> ingredient for understanding.
I try to make the the examples concrete, referring to such common
phenomena as stationary and moving to identify different sections of
the argument. If you postulate a reference frame, it exists for the
purposes of this argument. If you postulate a seconed frame, it also
exists apart from the other frame, especially if you assert that they
are moving relative to each other. I simply identify them in concrete
terms so we can keep them separate. If you are going to change from
one to the other in mid argument, just let me know.
<snip to get to the problem>
> This means that for v much smaller than c, the kinetic energy of the body
> relative to the second frame of reference is 1/2 M v^2 - 1/2 Lv^2/c^2
> plus other terms too small to worry, having decreased by 1/2 Lv^2/c^2
> plus terms too small to worry about. Since the speed of the body relative
> to the second frame of reference remains unchanged, but the kinetic energy
> relative to the second frame of reference drops, then there is a decrease
> in the mass of the object by an amount equal to L/c^2.
All that you say above is relative only to the second frame. There
is no decrease in mass relative to the first frame (the one in which
the body is stationary).
> Since the mass of
> a body is invariant (i.e. the same relative to ALL frames of reference),
> then the mass of the body decreases by L/c^2 in ALL frames of reference,
> including the frame of reference with which we started.
>
> David
>
The question: why is the mass relative to the first frame not
"invariant?" Why is only the change of mass relative to the second
frame "invariant?" Why is the lack of change in mass relative to the
first frame not "relative to all frames of reference?"
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