Re: When can we use special relativity?

Edward Green wrote:
Sue... wrote:
Bill Hobba wrote:
"fitz" <zeusrdx@xxxxxxxxx> wrote in message

When can we use special relativity?

When no, or at the most only weak, gravitational fields are present.

Does gravity change retarded potential or the speed of light?

We can use SR locally in any old case, provided "local" is defined as
"not on such scales of time, distance and precision where SR begins to
fail"; in other words, we can use it, except when we can't. ;-)

That's the sort of non answer I'd expect from Hobba or Roberts...but
then
I posed the question to Hobba so I'll give you a B+ on pinch hitting.
;-)


Hmm... though what does that say about laboratories not in free fall?
I dropped my pencil... oops! Gravitational effect! Can't use SR!
Perhaps we can continue to use SR in some situations with significant
gravitational effects (like falling pencils), under an approximation of
Newtonian gravity; i.e., where a gravitational force is added by hand.

The question is not when can you *abuse* SR. It is important
that we don't attach inertial effects where the term "uniform motion"
is used in the 1920 paper. The 1923 Gothenburg lecture offer some
insight why. The Tajmar / de Matos experiment is another clue.


And what do _you_ think about the connection between Unruh and Hawking
radiation, Sue? The question is vexing me: together can they smugly
say, yes, we've resolved the question of whether uniformly accelerated
charges radiate, and the seeming contradiction with the equivalence
principle...?

You are questioning the validity of GR's pseudo-space?

In SR, does Einstein get away with dumping the nearfield
effects of coupling structures into farfield regions of free space ?
As a formalism for a few specific calculations it suceeds but
on the whole it distorts more than it clarifies and leads to
well known paradox when misapplied.

EM is a radiative mechanism so 377 ohms seems
complete and is much less ambiguous.
http://en.wikipedia.org/wiki/Wave_impedance
http://en.wikipedia.org/wiki/Free_space


In GR, does Einstein get away with dumping the nearfield
effects of coupling structures (Mach) into farfied regions of
free space ? While the the excuses for employing such
sleight of hand may seem better than the SR case, the
distortion and confusion are even more severe.

Gravity is as much inductive as radiative and nearfield
reigons aren't so easy to define. We don't even know
a frequency or mode so it is a bold assumption that
we can homogenize some particular region of space
and employ a gravitational equivalent to the 377 ohms
that EM sees. Mercury's orbit and galactic orbits would
suggest it is a bad assumption.


For most physicists, the business of spatially moving mass
and energy comes at a high price. A jar of jam at your favorite
grocer is not the same as a jar of jam in your fridge. Suppose
we spread the jam evenly on a path between your grocer and
your house, baste it with gasoline and lay a steel tape alongside
with its metres interpreted as seconds. For some limited
calculations, a square metre of this fuel and jam flavored real
estate actually represents the time and energy difference
between jam in your fridge and jam at the grocer. A grocery
conglomerate might even use the model to strategiclly
place new stores. But if we take the construction too far
and try to attach fuel and jam properties to an ordinary square
metre of real estate the model breaks down.

GR is like that. The mass responsible for inertia is not
evenly distributed so we have to take care about what
we consider the "vacuum" or a pseudo-space and what
we consider a representative region of real space.

So, I don't pay too much attention to black hole physics
unless the theorist lays enough foundation to demonstrate
that he knows the difference in a jar of jam in the fridge
and a jar of jam on the way to the fridge, because neither
is well represented by a path covered with jam and
gasoline. ;-)

Sue...



SR references:
http://farside.ph.utexas.edu/teaching/em/lectures/node98.html
http://farside.ph.utexas.edu/teaching/em/lectures/node50.html
http://www.conformity.com/0102reflections.html

GR references:
http://nobelprize.org/nobel_prizes/physics/laureates/1921/einstein-lecture.html
http://www.iisc.ernet.in/currsci/dec252005/2009.pdf
http://www.bartleby.com/173/

Experimental Unruh Radiation?
http://www.phys.lsu.edu/mog/mog17/node8.html

.

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