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Relativity - Physics Forum

Relativity - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 05-08-2005, 08:25 AM
David Dixon
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Default Relativity



Here is an example of how classical physics clashes with modern physics:

http://stark-effect.com/tehcrab.jpg

How would *you* explain how this paradox can be resolved? Be specific and
precise.


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  #2  
Old 05-08-2005, 03:07 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Relativity

Dear David Dixon:

"David Dixon" <[Only registered users see links. ].com> wrote in message
news:F1kfe.45934$[Only registered users see links. ]-kc.rr.com...

In the moving charge's frame, there is no length contraction, and
hence no magnetic force.

David A. Smith




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  #3  
Old 05-08-2005, 08:00 PM
Josef Matz
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Default Relativity

Thats pure nonsense. The forces might depend on the frame, indeed but not
this way. The result of the forces is an obvious trajectory in each frame
which are connected by a frame transform. If you consider radiation
exchange, there might be more than one possible trajectories, but only on of
them realized in the concrete problem. Therefore classically as well as as
quantum mechanically there is at each time point a well defined state
realized, not two different.

If the crab is alive or not does not depend on the frames you describe the
problem. But there might be a chance that the crab survives your
experimental set up.
It is a sort of schrödingers cat your crab. The probability to be alive or
not depends on the nature of forces nothing else. And the "forces" or
probability of occurances are independent on the frame you select for
description. This is valid for classical and quantum mechanical decriptions.
The death of the crab is a well defined thing classically as well as quantum
mechanically. If it occurs the crab is dead forever. Also quantum
mechanically the crab dies at a well defined time but this time is a little
unsharp when you measure it.

So your main error is that your frames are selected wrong. And the moved
crab frame also has moved charges ! The paradox is constructed. If you treat
your problem with correct special relativity electrodynamics (classical
treatment as described for example in Landau Lifschitz) you will see that
depending on the starting conditions the result crab alive or dead is the
same in both frames. That is essential to all classical field theories
(except GR).

So it just looks that this is another trial to construct fictive paradoxes
which have nothing to do wether with classical physics nor with quantum
physics.
It is just bluff or ununderstood principles. Believe me: The crab problem is
not at all a problem of interest at all. It is a problem of your skills not
more.


Josef


"David Dixon" <[Only registered users see links. ].com> schrieb im Newsbeitrag
news:F1kfe.45934$[Only registered users see links. ]-kc.rr.com...


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  #4  
Old 05-09-2005, 01:37 AM
Morituri-|-Max
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Default Relativity


"David Dixon" <[Only registered users see links. ].com> wrote in message
news:F1kfe.45934$[Only registered users see links. ]-kc.rr.com...

Apart from anything else, as well as your continuous misspelling of "the",
you do realize, don't you, that a crab won't actually see individual
protons?


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  #5  
Old 05-09-2005, 04:59 AM
RP
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Default Relativity



David Dixon wrote:


There are several ways to resolve this paradox:

First let's assume the proton's speeds wrt lab frame approach c.

1) We can instigate photon exchange, then note that as the speed of the
protons wrt lab frame increases that the rate of photon exchange
decreases, that is, since the photons must propagate farther between the
protons than when the protons are at rest. The force is thus reduced. At
c the force is zero since the protons will have reached the end of the
accelerator tube before the first photon is exchanged. In the frame of
the protons (crab's frame) the force is repulsive, but the length of the
accelerator has reduced to zero, thus though the force is present, it
has no time to act. The same end result occurs in either frame, i.e. no
separation is accrued from one end of the accelerator to the other.

2) We can assume that in the context of Maxwell and the wave model of
the em interaction, that the field lags the charges more and more as the
speed of the particles approaches c, and in fact at c the field lines
will all trail the protons in a line directed back toward the starting
point. Thus the flux density at the position of the other charge will be
zero. No force is exerted between the charges when they are moving at c
wrt lab frame. In the frame of the charges, again, the accelerator
length has reduced to zero, and thus there is no time for the charges to
separate.

In both of these solutions SR is invoked, but they are actually just two
different yet equivalent interpretations of the same sequence of events.

3) There simply is no force acting between charges at rest wrt each
other, which is a model that better fits the data, since charged
particles need not be moving at c to fail to interact. Cooper pairs is
an obvious example of this. In a coherent electron beam the particles
fail to diverge. The electrostatic interaction is a result of the
motion of charged particles relative to each other, in exactly the same
way that the magnetic interaction is the result of the motion of charges
relative to each other. Both the E and B fields are macroscopic fields
constructed of the superpositon of electron fields that are in motion
relative to each other, the former being the result of randomized
polarities of the particles, and the latter of an ordering of the
polarities of the particles. The polarity in this sense isn't that of
the magnetic field of the particles, but of a field more fundamental
than either E or B.

Special relativity still applies in this model and thus in this solution
to the paradox presented, but in a fashion much different than 1 and 2
above. In the context of SR, when an object approaches c all thermal
activity within it must cease. Because of this the electrons in an
electron beam must cease their random motions wrt lab frame when the
beam velocity is c, and thus the electrons cease to have motion relative
to each other and hence cease to exert a force on each other. Force
requires relative motion between the particles. In the frame of the
electrons the Brownian motions of their neighbors still exists, and thus
there is still a force acting between them, but as in 1 and 2 above, the
accelerator has reduced to zero length and there is no time for the
force to act.

In all three cases special relativity was required to resolve the
paradox, but only argument 3 correctly accounted for the thermodynamic
details. It is quantified without even appealing to SR, and is derived
deductively directly from empirically derived equations, in the
following paper:

[Only registered users see links. ]

Electrons, and especially their em fields, cannot possibly be physically
altered by the mere changing of ones observational frame of reference.
Number 2 above thus runs into direct contradiction with the entire
purpose of special relativity, which was to render such interactions
frame invariant, or IOW to render them independent of frames of
reference. That it works in certain cases (those that typically ignore
the obvious absurdities) is immaterial, because it provides for entirely
different structures of the particle's fields wrt the two frames. The
PoR, in my logical assessment, must render everything frame invariant,
including em fields. If the E and B fields cannot attain to this, then
they are necessarily nonexistent, or IOW, mere macroscopic effects,
which is of course precisely what is derived in the paper linked above.

Number 1 above is proving a bit more difficult to counter, in that the
photon can be assumed to have whatever properties it needs to have in
order to conform to 3, and/or to the empirical data. That's quite a
novel approach to theory I must say, although IMHO it's not far removed
in concept from the invocation of pixies.

Richard Perry

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  #6  
Old 05-14-2005, 08:05 PM
PD
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Default Relativity


David Dixon wrote:
physics:
specific and

I would read Chapter 5 of Purcell's book on Electricity & Magnetism,
available for about $50 used on Amazon, and be done with it. This, by
the way, would have taken far less time than drawing the stuff that
went into your link.

PD

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  #7  
Old 05-15-2005, 11:00 PM
RP
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Default Purcell Chapter 5 (was Re: Relativity )



PD wrote:

Purcell is simply incorrect.

For online reference:
[Only registered users see links. ]

In the intro to this article you will find that in order to account for
zero force on an electron at rest wrt a conductor, the line density of
negative and positive charge within the conductor must be equal wrt the
frame of the external charge (electron). However the stopping of this
electron current would then result in an decrease in line density of
negative charge wrt the external charge, and thus the conductor would
become net positive wrt the external charge. This change in electrical
potential of the conductor is nowhere addressed by Purcell. Conversely
a neutral closed circuit composed of a battery, switch, and loop
conductor, should become net negative when the switch is closed. Thus
either this extra negative charge must then leave the system in order to
provide Purcell's initial condition of a neutral current carrying
conductor, or no change in the line density of charge occurs between the
two states of the circuit --conducting and nonconducting. This begs the
questions, "Assuming that no change in line density occurs, what force
exists wrt the conductor, or wrt the electrons in the conductor, that
would force some electrons to exit the conductor to provide the
necessary neutrality of the conductor wrt the external charge? But more
importantly, how could electrons leave the circuit and simultaneously
leave the original number of electrons unchanged?" Obviously we are
forced to conclude that the line density of negative charge doesn't
occur between the two states of the conductor, wrt either the protons in
the conductor or wrt the external charge.

Empirically we observe a pinch effect on the current, that is, the
drifting electron current is drawn toward the center of the conductor.
This effect requires, according to Purcell, that the electrostatic force
acting between the components of charge within the conductor is
increased, but without a change in line density of these charges wrt
each other we can ask "How can this increase in force between the
components of charge be accounted for?"

The empirical evidence thus rules out Purcell's premise of a neutral
current carrying conductor, more specifically, the charged state of a
current carrying conductor is frame dependent, and non-neutral wrt
either component of charge within the conductor. Since it is however
neutral wrt an external charge at rest wrt it, then it must follow that
the positive component of charge within the conductor is not at rest wrt
the conductor, but is drifting counter to the negative component. The
two-current model that was voted out long ago is necessarily incorrect.
Since the remainder of Purcell's arguments center around the now
disproven one-current model, it is automatically incorrect in that no
such initial condition exists. His velocities are incorrect by the
difference of 1/2 the drift rate that he assumes. This is however a
very small correction since the drift rate is incredibly slow, and for
all practical purposes it can be ignored when

v_external charge >> v_drift

His arguments can however be readily adapted to the two-current model,
and some versions of the argument do in fact assume this model as a premise.

Having corrected the faulty premise of the linked article, let's move
onward toward ever more perplexing paradoxes.
Let's take into account the Brownian (thermal) motions of the particles
of charge within the conductor. Purcell posits that the magnetic force
is just a relativistic change in the electrostatic force, which in turn
increases as the speed of the charges wrt each other increases. We can
segregate the charges within the conductor into four sets of charges in
any small interval of time, those being the electrons that are drifting
to the left as a group, those to the right, and likewise for the
protons. There are thus four currents flowing within the conductors, and
this is true even when there is no net drift on the whole. Thus there
must be an increase in the Coulomb force exerted between the components
of charge in the opposing conductors, such that if equal small charges
are distributed along their lengths then the force acting between them
would be the Coulomb force between the excess charges plus the magnetic
component arising from their relative motions in the form of the
sub-currents described above. OTOH, empirically there is only the
Coulomb force given by the Coulomb equation:

F/length = 2kq^2/d

It is required then, in the classical approach, that the electrons
composing the excess charge remain perfectly at rest wrt their
conductors, which is of course absurd. It follows that the Coulomb
equation already takes into account the thermal motions of the electrons
wrt each other, that is, that the Coulomb equation represents a magnetic
force between the charges, or IOW a force that arises from the motion of
electrons wrt each other. If then the electrostatic force is itself the
vector sum of many magnetic interactions, then how can it possibly apply
to two electrons at rest wrt each other? The empirical evidence also
shows us that coherent electrons comoving at much less than c wrt lab
frame will not interact.

In summary, the empirical evidence rules out Purcell's model, or rather
it limits its domain of applicability to the macroscopic. It is valid
for macroscopic charges (composed of very many charged particles in
random motions wrt their combined center of mass), but not for bare
particles of charge. The model must however be reinterpreted, that is,
since we have found that the classical magnetic force is really due to
an increase in the already existing relative motion of the charges, or
IOW it is just the compounding of a more fundamental force due to an
increase in the relative speed of the particles, dropping to zero as the
relative speed drops to zero, and not as Purcell supposes "due to an
increase in the line density of electrostatic charge". The classically
described magnetic force between parallel conductors can be treated as
an increase in the *assumed* electrostatic force between the components
of charge, as long as it is recognized that the electrostatic charge is
not a property of the particles, but rather of the assemblage of thermal
particles.

When the relativistic factor gamma is applied by Purcell to the line
density of the charges in the conductors, it is correct in the
mathematical sense, but not in the interpretive sense. It is a
relativistic adjustment not to the line density of the electrostatic
charge in the conductors, which as shown above doesn't even exist in
actuality, but rather it is an adjustment to a particular component of
velocity of the particles of the charges wrt each other, that component
being the tangential component of the velocity of the particles wrt each
other. This adjustment is in turn due to the fact that the magnitude
of the force between two charged particles is a function of their
relative velocity, a function that includes the relative angle of motion
of the particles as well as the magnitude of that motion. The field of
the charged particle is a vector field, and it is neither
classical-magnetic nor classical-electrostatic, it is simply *the* em
field. This field produces a mutual force between particles that is
proportional to the tangential component of their relative
velocity...squared, proportional to the product of the charges, and
inversely proportional to their separation squared. Integrating, using
this relationship, over any two populations of charges, mixed or
unmixed, will provide the net force between those assemblages of
charges, with a caveat; the average speed of the fundamental charges
must be c. This corresponds to the quantum mechanical electron
probability cloud, since statistically, an electron moving about at c
could easily assume an average distribution equal to that predicted by
QM. Another possibility is that the electron *is* the cloud while the
charge of the electron is something yet more fundamental and that
propagates at c.

This reply has also been sent to sci.physics.relativity for the prospect
of a more fulfilling intellectual engagement. Keep in mind that I fully
accept Lorentz invariance as a logical necessity; here I'm simply
disagreeing with it's application to the real world.

Richard Perry

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  #8  
Old 05-15-2005, 11:41 PM
xxein@bellsouth.net
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Default Purcell Chapter 5 (was Re: Relativity )


RP wrote:
Magnetism,
by

for
of...

xnip


xxein: Nice, but have you considered that an equilibrium process is
always taking place in the near and far?

I am not deliberately trying to muddle your work, but maybe physics is.
Don't forget that thermodynamics seems to work - but - at some odds to
+,- attraction.

Just a thought. Continue on.

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  #9  
Old 05-16-2005, 12:16 AM
tadchem
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Default Purcell Chapter 5 (was Re: Relativity )


"RP" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...
<snip>


PARADOX ALERT!

You have said (1) "an electron at rest wrt a conductor" and (2) "the
stopping of this
electron current".

You cannot have it both ways. Either the electron is at rest WRT to the
conductor, *OR* it is moving as part of a current.

Empirically, the moving electron is subject to a force which works
(Force*distance) on the electron as it travels to provide the energy lost to
electrical resistance.


Tom Davidson
Richmond, VA


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  #10  
Old 05-16-2005, 02:20 AM
RP
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Default Purcell Chapter 5 (was Re: Relativity )



tadchem wrote:


LOL, I'm certain that you're attempting to capitalize on either a typo
or an misunderstanding of the context.
If the electron is drifting, this doesn't prevent it from being at rest
wrt the remainder of the electrons, though I don't subscribe to that
fact, and this was covered in some depth.

BTW, one typo found of importance: The two-current model was "correct".
(original passage said "incorrect"). This is of course also supported
somewhat by the Hall effect.

I'm aware that the article seems disconnected and hard to follow, but
this is only due to the fact that it's a quick summary of the logical
sequence from which it originated. The seemingly missing logical
connections should be apparent to anyone who has muddled with this
problem at length.

Richard Perry

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