radius of an electron?
Marshall Carroll
Hi. Does an electron have a radius? If so, what is it?
Thanks for any info., Cheers, M.Carroll
email: mcar...@access.mbnet.mb.ca
tnte...@sfu.ca
Marshall Carroll (mcar...@mbnet.mb.ca) wrote:
: Hi. Does an electron have a radius? If so, what is it? Dear Mr. Carroll,
yes, electron have a radius. The value of so-called
classic electron radius is 2.81 Fermi.
Regards, Dr. Andy Inopin
AdrianX
Hi,
The electromagnetic force is transmitted by photons, yes?
OK. I call to mind an experiment I did 30 years ago in which I deflected a
trickle of water with a plastic comb I'd dragged through my hair.
Are there photons flying back and forth between the comb and the water,
and if so, what is their frequency/wavelength?
All the best,
Adrian...
Matt McIrvin
<tnte...@sfu.ca> wrote:
> Dear Mr. Carroll,
> yes, electron have a radius. The value of so-called
> classic electron radius is 2.81 Fermi.
This is a classically calculated quantity obtained via theories no
longer believed to apply. The quantity still has certain applications in
physics, but is not held to be the electron's actual radius.
Distances much smaller than a fermi have been probed, and the electron
seems to be smaller than anyone's measurements can discern.
--
Font-o-Meter! Proportional Monospaced
^
Physics, humor, Stanislaw Lem reviews: http://world.std.com/~mmcirvin/
Gilles Orazi
On 6 Sep 1997, Marshall Carroll wrote:
> Hi. Does an electron have a radius? If so, what is it?
> Thanks for any info., Cheers, M.Carroll
> email: mcar...@access.mbnet.mb.ca
Hello,
As far as we know, the electron has no spatial extension. It is believed
to be a pointlike particle.
Cheers,
Gilles
E-mail : Gilles...@cern.ch
Home page : wwwcn.cern.ch/~orazi
ralph sansbury
In pre Cern scattering experiments the proton and electron had various
radii depending on the experiment all near the classical electron radius
of about 10^-15 or 10^-16 meters. The dimensions of the electron also
depend on temperature so at liquid nitrogen and liquid helium pressures
there is reason to believe electrons and protons are smaller than at room
temperature etc.
That is the electron is not an indivisible particle but rather a
composite particle. Consider that the apparent increase in the mass of
an electron with its velocity is due to an inelastic decrease in the rate
of increased charge polarization and so magnetic responsiveness of the
moving particle as the elastic limit-the velocity of light- is
approached. This is shown to be a an equally valid interpretation of
Kaufmann's demonstration in 1903 of the effect of a crossed electric
field and magnetic field at right angles to one another on beta
electrons ejected from a radium nucleus at velocities near the speed of
light. The faster of the already fast electrons should have been more
deflected by the magnetic field than they were. That they were not can
be ascribed to an increase in the inertial mass of the beta electrons to
infinity or to a decrease in its rate of increase in responsiveness to a
magnetic field as its finite limit of elasticity is approached. If the
latter interpretation is assumed, the corallary of course is that the
conservation of matter principle Lavosier used so successfully in a. 1770
to infer the chemical combinations of the elements need not be revised
into a conservation or transformation principle of mass-energy. Such an
ambiguous principle extant in 1770 might have prevented Lavosier's
discoveries.
The related conversion of mass into energy can be explained also
without recourse to relativity.The evidence for the materialization of
electrons and positrons from a gamma ray photon of frequency f, and
energy hf, where h is Planck’s constant can also be interpreted without
the assumptions of special relativity as follows: the interaction of an
oscillating charge - or photon source- and a neutral particle comprised
of two masses about the size of a positron and an electron but of twice
the positive charge of a positron, +2e, and twice the negative charge of
an electron,-2e and four much smaller masses orbiting these larger ones
of charge, -e,-e,+e, and +e in a figure eight configuration.
The interaction of the oscillating charge- or photon source- with the
orbiting charge of about the same frequency produces an increasing
amplitude of the orbiting charge until some of the orbiting charge
escapes and the neutral particle comes apart with a positron composite
and an electron composite moving with the velocities they had as part of
the larger neutral configuration leaving in this example two oppositely
charged particles of much smaller mass behind. These charged masses could
combine into a neutral particle also of much smaller total mass without
leaving the tracks of moist air condensed on the other charged particles
as they move through a cylindrical container which can be viewed and
photographed from a window in the top end of the cylinder; illumination
is usually provided by a window in the wall of the cylinder.
In this experiment gamma radiation (originating from another container
of fluorine gas bombarded with protons) and a magnetic field are applied
to a region in the cylinder filled with moist air and it is possible in
the photograph to detect the difference between tracks of electrons and
positrons so produced from heavier charged particles like nuclei and
partially ionized atoms that may be produced in secondary reactions
between the atoms of the water vapor and the gamma radiation; Among the
various patterns of tracks it is possible to observe one pattern of only
two tracks emerging from a single point that curve in opposite directions
in the applied magnetic field whose thickness and trajectory identify
them as an electron and a positron. (see Intro to Atomic Physics ,
R.Semat, Rinehart Co. 1958, p434)
The equivalence between the total rest masses of the electron and
positron and the energy of the gamma radiation supposedly producing them
can be understood by first noting that the kinetic energy expended in one
complete orbit of the proposed small charged mass around the much larger
charged core mass of an electron or positron is equal to the product of
the duration of the orbit -the reciprocal of the frequency of the orbit-
times the instantaneous kinetic energy of the orbiting particle; and that
this product is analagous to the one for the orbit of an electron around
the hydrogen nucleus which is equivalent to Planck’s constant, h » 10^-34
in mks units.
When we multiply, h, times the frequency of the hydrogen electron’s
orbit, about 10^16, we obtain the instantaneous kinetic energy of the
hydrogen electron in its orbit. The corresponding constant for this much
smaller faster orbit with a much smaller mass m*=10^-56 kg is ((1/2)
m*v*^2)(1/f*) =10^-48 and when we multiply this constant times the much
faster frequency f*=10^36 we obtain the same instantaneous kinetic
energy, (1/2) m*v*^2 of the very small mass we would obtain by
multiplying Planck’s constant by some value f* and measuring not the
wave length corresponding to f* but the kinetic energy hf* of particles
produced as in this case or from secondary radiation. Note that v*^2 =
(9)(10^9)e^2/Rm* ; we assume R=(9)(10^9)e^2 /mc^2 , and m denotes the
rest mass of the electron so that m*v*^2 = mc^2. In words the gamma
radiation that produces pair production is of a much higher frequency
than previously thought and the production mechanism is the effect of a
resonant sympathetic oscillation of charge on charged particles of much
smaller mass than the electron or positron inside a neutral composite as
described above.
The figure eight model of the neutral particle just described can be
applied to neutrons, protons and combinations of neutrons and protons in
atomic nuclei. Just as there are discrete elliptical orbits in hydrogen
atoms there could be discrete figure eight, elliptical orbits etc inside
atomic nuclei associated with Coulomb excitation levels etc of atomic
nuclei. Such a model of the nucleus could resolve the curious dichotomy
of the nucleus behaving sometimes as a liquid drop, sometimes as an open
structure with well defined shells. This would lead to a clearer
understanding of nuclear fission,fusion, the strong force and the weak
force. Instead of relying on gluons and other humorous mysteries, the
nucleus would be held together by electrostatic forces between charged
masses as small as 10^-56kg moving at superluminal speeds within the
10^-15 meter perimeter of the nucleus and a central heavier composite
core. Short lived pieces of nuclei and other similar unstable particles
(leptons, mesons, baryons) either positive, negative or uncharged, could
be similarly formed.
The reason we can avoid such awkward and procrustean concepts as
gluons and quarks etc. is that we have shown the possibility of particles
moving at speeds that exceed the speed of light usually inside perimeters
like those of protons and electrons. The scattering experiments of high
energy electrons penetrating various nucleons indicate that the electrons
are scattered by interactions with point particles distributed within the
nucleon. These particles may be combinations of quarks called partons or
they may be the particles within the orbiting systems described here. So
a high energy electron close enough to the negative charge orbiting the
core at 10^22 meters per second would be turned back or to the side and
back or to the side and front. The positions of the orbiting negative
charge would be uniformly distributed over the perimeter of 10^-15 meters
approximately would move one tenth of this perimeter in 10^-38 seconds.
Another problem to consider is that when an electron is accelerated to
great speeds it increases in size before the negative charge orbiting the
electron flies off.
The assumption that the stationary room temperature electron radius
is R=(9)(10^9)e^2 /mc^2 is suggested by the Maxwell Lorentez theory of
electromagnetic waves. The wave front of the wave emanating at the speed
c from a moving electron has a specific energy and as it passes and
interacts with a secod electron it produces a force due to the
longtudinal electrostatic field (E1,E2,E3) and the transverse in phase
magnetic field (B1,B2,B3) due to the first electron. In general the
velocity of the moving electron we regard as the source of the field is
part of an oscillatory motion and the magnitudes of the vectors are B and
E where B=E/c.
The result is the excitation of particles of very small mass whose
kinetic energy is mc^2 inside the electron-positron composite producing
these results as first observed by Thibaut, Crane & Lauritsen and
described above from Semat’s atomic physics text.
It may appear at first that our interpretation of these experimental
results diverges more from the observed data than the interpretation that
simply assumes the convertability of mass into energy and avoids any
detailed model of the mechanism. But it should be noted that we are not
insisting on some specific model but rather on a genus of models that
does not require the addition of axioms to the axiom set of physics
prior to the acceptance of Maxwell’s theory of radiation. This earlier
axiom set includes the axiom of the conservation of mass which made
possible Lavosier’s discovery of the atomic elements and the axiom of the
conservation of mechanical thermal and radiant energy. This axiom set
does not include the axioms or implications of special relativity of the
interconvertability of mass and energy and the increase of mass to
infinity of a moving object as its speed approaches the speed of light.
It is these later axioms that lead to circumlocutions for explaining
Bell’s theorem, Quasars, etc., that diverge even more from common
experience and experimental physics as well.
Trond Myklebust
ralph sansbury <r...@concentric.net> writes:
>
> In pre Cern scattering experiments the proton and electron had various
> radii depending on the experiment all near the classical electron radius
> of about 10^-15 or 10^-16 meters. The dimensions of the electron also
CERN was founded about 45 years ago: we weren't building 12GeV
accelerators back then.
At LEP, we're currently using e+e- collisions to probe at 183GeV
(distances of around 7x10^-18m). So far, no electron substructure has
been observed.
Trond
Dries van Oosten
One should realize that the photons transmitting the em-force are virtual
photons. They are allowed to have mass and they cannot be detected. But
ultimately it's the virtual photons that "pull" the electrons from the
comb to the water.
Dries van Oosten
***************************************************
Disclaimer: What I said in the lines above here
does not necessarily reflect the opinions of
the university whose computer I am using right now.
***************************************************
Runner up in our competition for most depressing
line in pop-music:
"When I am king, you will be first against
the wall." - Radiohead
***************************************************
ralph sansbury
Trond Myklebust <mykl...@vuoep1.uio.no> wrote:
>
>ralph sansbury <r...@concentric.net> writes:
>
>>
>> In pre Cern scattering experiments the proton and electron had various
>> radii depending on the experiment all near the classical electron radius
>> of about 10^-15 or 10^-16 meters. The dimensions of the electron also
>
>accelerators back then.
>
> At LEP, we're currently using e+e- collisions to probe at 183GeV
>(distances of around 7x10^-18m). So far, no electron substructure has
>been observed.
>
>Trond
>
>ralph sansbury <r...@concentric.net> writes:
>
>>
>> In pre Cern scattering experiments the proton and electron had various
>> radii depending on the experiment all near the classical electron radius
>> of about 10^-15 or 10^-16 meters. The dimensions of the electron also
>
>accelerators back then.
>
> At LEP, we're currently using e+e- collisions to probe at 183GeV
>(distances of around 7x10^-18m). So far, no electron substructure has
>been observed.
>
>Trond
You may not be observing the collision of particles of mass
about 10^-30 kg but rather particles of much smaller mass as previously
described and of much smaller cross section at energies of 183 GeV. That
is you are probably observing electron substructure but dont realize
it. At these energies the electron and positron are stripped of the outer
orbiting particles of charge - e or +e and the inner parts of charge -2e
or +2e are observed first although these parts may also be stripped of
analagous orbiting masses that are much smaller than the core masses of
about 10^-30. The smaller masses referred to are about 106-56 kg..
I have read in textbooks and journals that scattering at such high
energies suggest substructure because of the non uniformity of the
scattering in various directions etc. Are you aware of this?
Trond Myklebust
ralph sansbury <r...@concentric.net> writes:
> You may not be observing the collision of particles of mass
> about 10^-30 kg but rather particles of much smaller mass as previously
> described and of much smaller cross section at energies of 183 GeV. That
> is you are probably observing electron substructure but dont realize
> it. At these energies the electron and positron are stripped of the outer
> orbiting particles of charge - e or +e and the inner parts of charge -2e
> or +2e are observed first although these parts may also be stripped of
> analagous orbiting masses that are much smaller than the core masses of
> about 10^-30. The smaller masses referred to are about 106-56 kg..
> I have read in textbooks and journals that scattering at such high
> energies suggest substructure because of the non uniformity of the
> scattering in various directions etc. Are you aware of this?
What non-uniformity? There is no evidence of any anomalous angular
dependence in any analysis I can find at LEP (and believe me, if we
had found it we're desperate enough to publish it 8-). Please quote your
sources.
For the latest published limits, read the various papers from the LEP
experiments on the subject, such as Phys. Lett. B393 (1997) 231-244
(DELPHI), or Phys. Lett. B391 (1997) 197-209 (OPAL).
Trond
Paul Draper
Gilles Orazi wrote:
>
>
> As far as we know, the electron has no spatial extension. It is believed
> to be a pointlike particle.
>
This isn't quite right. As far as we know, we have not *seen* any
structure to the electron, and we know its size is smaller than roughly
10^-19 m, but there is no theoretical requirement that I know of that
suggests that it is pointlike.
Paul Draper
Trond Myklebust
Paul Draper <dra...@uta.edu> writes:
> This isn't quite right. As far as we know, we have not *seen* any
> structure to the electron, and we know its size is smaller than roughly
> 10^-19 m, but there is no theoretical requirement that I know of that
> suggests that it is pointlike.
It is perhaps more correct to say that the Standard Model *assumes*
the electron to be pointlike. Any measurement of structure would
therefore be 'new physics' beyond the Standard Model.
Trond
Edward Meisner
>
> On 6 Sep 1997, Marshall Carroll wrote:
>
> > Hi. Does an electron have a radius? If so, what is it?
> > Thanks for any info., Cheers, M.Carroll
> > email: mcar...@access.mbnet.mb.ca
I am not sure, but this may be a valid way to determine the radius of
an electron. Take a pith ball of known radius and charge it with a
certain amount of Coulombs. Then extrapolate from this charge to the
10^-19 Coulomb charge of the electron. IOW take the ratio of the charge
of the pith ball to the charge of the electron and set this equal to the
the ratio of the radius(known) of the pith ball to the radius(unknown)
of the electron and then solve for the electron's radius. Then GR can be
used to confirm the results. The energy density, radius and curvature of
the pith ball can be extrapolated towards the energy density, radius and
curvature of the electron. You can solve for the radius of the electron
in the same way as the first method. The radii given by the two methods
can then be compared.
Edward Meisner
E
Sorry this is wrong. You must combine the two methods to get the
radius. You take a pith ball of a known radius and charge it with a
certain number of Coulombs. It is known that the charge of the electron
(10^-19 Coulombs) is equivalent to 10^-15 joules. So the pith ball will
have a known radius and therefore a known energy density. You can then
calculate the curvature. The charge of the electron is 10^-19 Coulomb's
and its energy equivalent is therefore 10^-15 joules. In order to find
the energy density of the electron you must know its radius. To get the
radius take the ratio of the charge of the pith ball to the charge of
the electron and set it equal to the ratio of the curvature of the pith
ball(calculaterd as above) to the curvature of the electron and then
solve for the curvature of the electron. You now know the curvature and
energy of the electron. Using these two quantities, you can use
Einstein's equations to solve for the radius of the electron.
Trond Myklebust
Edward Meisner <ode...@injersey.com> writes:
> Sorry this is wrong. You must combine the two methods to get the
> radius. You take a pith ball of a known radius and charge it with a
> certain number of Coulombs. It is known that the charge of the electron
> (10^-19 Coulombs) is equivalent to 10^-15 joules. So the pith ball will
> have a known radius and therefore a known energy density. You can then
> calculate the curvature. The charge of the electron is 10^-19 Coulomb's
> and its energy equivalent is therefore 10^-15 joules. In order to find
> the energy density of the electron you must know its radius. To get the
> radius take the ratio of the charge of the pith ball to the charge of
> the electron and set it equal to the ratio of the curvature of the pith
> ball(calculaterd as above) to the curvature of the electron and then
> solve for the curvature of the electron. You now know the curvature and
> energy of the electron. Using these two quantities, you can use
> Einstein's equations to solve for the radius of the electron.
Is this a complicated way of saying that the electromagnetic and
gravitational potentials have to balance in order to prevent collapse?
Using Newtonian gravity as an approximation that gives a radius of
the order of 10^-27m. This is a region in which neither G.R. nor
Newtonian gravity have been tested for validity, so your argument is
inconclusive.
Trond
ZTellman
>Hi. Does an electron have a radius? If so, what is it?
>Thanks for any info., Cheers, M.Carroll
The electron is considered a point particle with no radius.
MFergerson
ZTellman wrote:
Hmmm....... electrons have nonzero angular momentum...so what is the
length of the moment arm for an electron?
Jon Bell
MFergerson <mferg...@aol.com> wrote:
> ZTellman wrote:
>
>>The electron is considered a point particle with no radius.
>
>Hmmm....... electrons have nonzero angular momentum...so what is the
>length of the moment arm for an electron?
The "orbital" angular momentum of an electron, in quantum mechanics, is
defined on analogy with the classical angular momentum, that is as R x P
(using vector notation), and substituting the appropriate q.m. operators
for R and P.
The "spin" angular momentum is an intrinsic property of an elementary
particle, and has *no* classical analog. Although it is sometimes useful
to think of the "spin" as analogous to the angular momentum of an extended
object which is rotating about its own axis, this is not correct, strictly
speaking.
Note that the classical "spin" angular momentum of an object can be
thought of as the sum of the orbital angular momentum of the object's
parts, as they revolve around the axis of rotation. One cannot do this
with quantum-mechanical "spin".
--
Jon Bell <jtb...@presby.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA
[for beginner's Usenet info, see http://web.presby.edu/~jtbell/usenet/ ]
Douglas A. Singleton
In article <EGwyz...@presby.edu>, Jon Bell <jtb...@presby.edu> wrote:
[stuff cut]
>The "spin" angular momentum is an intrinsic property of an elementary
>particle, and has *no* classical analog. Although it is sometimes useful
>to think of the "spin" as analogous to the angular momentum of an extended
>object which is rotating about its own axis, this is not correct, strictly
>speaking.
The statement "spin has no classical analog" while mostly OK is not
the whole story. It is in fact possible to show that the spin of the
electron arises from the circulating flow of energy in the Dirac
field. For a more familiar example it is possible to obtain the
angular momentum carried in an electromagnetic field by integrating
r x (E x B) over all space (modulo factors of 4 \pi c). Doing some
integration tricks it is possible to split the integral of r x (E x B)
into two parts : one that looks like the orbital angular momentum
of the EM wave (photon) and one that looks like the spin of the EM
wave (photon). This is problem 7.19 in Jackson. Now if instead of
E&M fields (Maxwell's equations) one wants to discuss the Dirac field
(Dirac equation) a similiar thing can be done. Ohanian does the math
and gives a nice discussion in an Am. J. Phys. article (Vol. 54, pg. 500
(1986)). While the picture of the electron as a tiny spinning ball
is certainly untenable, Ohanian's article shows that spin is
nevertheless not so distantly removed from our "classical" intuition
as most texts would have one believe.
Doug
Kevin Sterner
> The "spin" angular momentum is an intrinsic property of an elementary
> particle, and has *no* classical analog. Although it is sometimes useful
> to think of the "spin" as analogous to the angular momentum of an extended
> object which is rotating about its own axis, this is not correct, strictly
> speaking.
How strictly are you speaking? The spin of an electron is the same
conserved current--corresponding to the same spatial symmetry (isotropy)--
as the angular momentum of a macroscopic object. The spins of quantum
objects and the angular momenta of orbiting or rotating macroscopic
objects are not conserved independently of one another. You can
flip the spin of an electron by emitting a photon; that same photon (or
rather, a sufficient ensemble of identical photons) can be used to
induce a measurable rotation in a macroscopic object.
I am not saying that the spin of an electron can be described as an
extended object rotating about an axis; I am merely pointing out that
the angular momentum of a baseball is the same quantity as the spin
of an electron. They differ only in amount.
> Note that the classical "spin" angular momentum of an object can be
> thought of as the sum of the orbital angular momentum of the object's
> parts, as they revolve around the axis of rotation. One cannot do this
> with quantum-mechanical "spin".
Rather, if you look very closely at the angular momentum of an extended
object, you will (in principle) observe it to behave in ways that
cannot be explained by summing up m(r X v) for its components. Angular
momentum for any object is quantized; m, r and v are not.
-- K.
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Kevin L. Sterner | U. Penn. High Energy Physics | Smash the welfare state!
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