
#20
Mar1912, 05:04 AM

Sci Advisor
PF Gold
P: 1,942





#21
Mar2612, 11:22 AM

Mentor
P: 15,571

Normally when someone references a book or article that they haven't read, that pretty much ends the discussion. However, I don't want this thread to end on such a misleading note.
How does one quantify substructure? One can model an electron as a uniformly charged sphere of radius r. The sensitivity of an experiment is R if it can distinguish between a sphere of radius R and one of radius r, with r << R, but not any smaller than R. (In the interest of full disclosure, hard spheres have technical difficulties, so Today we know that for an electron r < 10^{18} or a few 10^{19} meters. These numbers come from both precision measurements at low energy and a search for deviations from a pointlike geometry in high energy scattering. Note that this isn't saying that an electron is a point; it's saying that it appears pointlike, but that we cannot resolve a distance smaller than about 10^{18} meters. So where does this 10^{16} number come from? That's the distance at which vacuum polarization becomes important and thus where the electric field starts to depart from a ~1/r potential. This happens for all charged objects: electrons, muons, quarks It would be profoundly misleading to attribute this to electron substructure because a) it is a property of every single charged particle, not just the electron and b) happens whether the electron is fundamental or composite. 



#22
Mar2612, 12:31 PM

Sci Advisor
PF Gold
P: 1,942





#23
Mar2612, 01:37 PM

Sci Advisor
PF Gold
P: 1,942

The deviations from pointlikeness are usually described by means of form factors that would be constant for a point particle but become momentumdependent for particles in general. The form factors contain everything that can be observed about single particles in an electromagnetic field. http://en.wikipedia.org/wiki/Electric_form_factor : ''The electric form factor is the Fourier transform of electric charge distribution in space.'' http://en.wikipedia.org/wiki/Magnetic_form_factor : ''a magnetic form factor is the Fourier transform of an electric current distribution in space.'' In particular, the charge radius is defined as the number r such that the electric form factor has an expansion of the form [tex]F_1(q^2) = 1(r^2/6) q^2[/tex] if [tex]r^2q^2<<1[/tex]. (Units are such that c=1 and hbar=1.) This definition is motivated by the fact that the average over exp(i q dot x) over a spherical shell of radius r has this asymptotic behavior. See Formula (11.3.32) in S. Weinberg, The quantum theory of fields, Vol. I, Cambridge University Press, 1995. QED (which treats the electron as pointlike in the usual sense of the word  that it appears as a fundamental field in the Lagrangian) imply a positive value for the charge radius of the electron. Indeed, this is Weinberg's conclusion from his calculations in Section 11.3, together with an estimate of infrared effects taken from (14.3.1). 



#24
Mar2612, 02:32 PM

P: 991

The electron is a elementary subatomic particle with a negative elementary electric charge. It has no known components or substructure. Observation of a single electron in a Penning trap shows the upper limit of the particle's radius is 10^−22 meters. [tex]r_e \leq 10^{22} \; \text{m}[/tex] I request to make a recommendation for the Physics Forums Science Advisers to simply cite and reference a Wikipedia webpage for layman original poster (OP) subject questions, instead of referencing high level physics science papers, in order to avoid a lot of confusion and hyperbole. Reference: Electron  Wikipedia 



#25
May312, 07:24 PM

P: 3

electron is electron only. we are still investigating that elementary "thing". we know some of it's properties, ie. particle property, wave property, charge, mass etc. we dont know what exactly it is, only can measure some of it's characteristics, thats all




#26
May512, 10:36 PM

P: 9

Well said lordsandman. If we ever come to understand what an electron really is then we won't need high energy machines anymore.




#27
May512, 11:11 PM

PF Gold
P: 11,013





#28
May612, 08:33 AM

Mentor
P: 10,791

How do you define "what an electron really is", without just describing its measured properties?
And even worse: How do you test this, if you cannot use any measurement by construction? 



#29
May612, 10:53 PM

P: 9

To Drakkith
Well, it depends on what understand means to those studying the issue. I suppose the words "understand" and "really" should banned from the world of physics. 



#30
May712, 12:09 AM

PF Gold
P: 11,013





#32
May712, 10:36 PM

P: 9





#33
May712, 10:55 PM

P: 9





#34
May812, 01:54 AM

P: 48

If the universe is governed by a number of laws, we can learn these laws, no matter how complex they are. Being so distant doesn't mean we will never reach.
About the OP's question, I believe he is asking about it's volume and shape, and other physical properties usually observed by eyes. 



#35
May812, 01:45 PM

P: 71

The electron is just a static waveform that selfreflects. The energy needed for this wave to form is the rest mass of the electron.




#36
May912, 01:03 PM

P: 117

An electron is a negatively charged sub atomic particle in an atom that is around the nucleus of the atom in the electron cloud. The electron is a very light mass subatomic particle and you can take away an electron from an atom or give electrons to an atom which will result in an ion(cation or anion).



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