What exactly is an electron?

  • Thread starter CF.Gauss
  • Start date
  • #1
8
0
HI,
Firstly I'd like to open with I know what an electron is and I know all about its charge and the role it plays in electricity, current, free electron model etc etc.
My question is what is an electron 'made' out of? My reasoning is that it cant be made out of anything physical as its charge would distribute evenly throughout its-self and would fly apart as every part of the electron would repel every other part of the electron.
In physics the electron is thought of as a mathematical point particle but in a 3-spacial dimensional universe a 1-d object cant physically exist so that rules that out.
If i could magically enlarge an electron to the size of a car what would i physically see?
or is there even any credence to asking a question like that?
 

Answers and Replies

  • #2
phyzguy
Science Advisor
4,650
1,586
I'd like to know, too. We don't have a model of elementary particles which gives them any structure. Many people have tried to build such a model (Lorentz, Poincare, Feynman ...), but no one has succeeded. Modern Quantum Field Theory assumes that elementary particles are pointlike entities with no internal structure. Whether this is true or whether this is only an approximation is an open question. "The Feynman Lectures on Physics" Vol 2, Chapter 28 gives a very readable history of these attempts.
 
  • #3
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
2019 Award
25,647
8,838
What exactly is a lion? If I pointed at one and said "that's a lion", wouldn't that be an acceptable answer?

What is unacceptable about pointing at an electron and saying "that's an electron?" Until you've answered that question, it will be difficult to write an answer that will satisfy you.
 
  • #4
vanhees71
Science Advisor
Insights Author
Gold Member
2019 Award
16,144
7,467
To conclude: To the best of our knowledge today (i.e., in this case the standard model of particle physics) the electron is an elementary spin-1/2 Dirac particle with one negative elementary charge and a mass of about [itex]511 \; \mathrm{keV}/c^2[/itex]. It's a lepton, i.e., participates only in the electroweak interaction (let alone gravitation, which acts universally on anything that has energy and momentum).
 
  • #5
Drakkith
Staff Emeritus
Science Advisor
21,009
4,828
When you ask what something is, the most accurate description is detailing the physical properties of it, such as mass, charge, etc. Asking what it "really" is simply doesn't make any sense, as there is no more available information. Any answer is simply speculation.
 
  • #6
A. Neumaier
Science Advisor
Insights Author
2019 Award
7,483
3,381
My question is what is an electron 'made' out of? [...]
In physics the electron is thought of as a mathematical point particle [...]
If i could magically enlarge an electron to the size of a car what would i physically see?
or is there even any credence to asking a question like that?
In enlarging quantum objects one makes their quantum properties disappear. Macroscopic objects behave classically.

The electron is an elementary particle, hence not composed of anything but itself. But it is not a point - only pointlike (which means, the formal, unobservable, bare electron in the defining action is a point). Due to radiative corrections stemming from the renormalization procedure for relativistic quantum field theories, an observable, renormalized electron has a positive charge radius (though far too small to be probed experimentally with current methods).
 
  • #7
Bill_K
Science Advisor
Insights Author
4,155
195
What is the charge radius of the electron predicted to be? Order of magnitude.
 
  • #8
1,352
90
CF.Gauss why do electrons not look like sparks/lightening?
 
  • #9
Khashishi
Science Advisor
2,815
493
CF.Gauss why do electrons not look like sparks/lightening?
I think the lightning you see is actually emission from partially ionized nitrogen and oxygen plasma.
 
  • #10
1,352
90
Yes, and when I "see" anything else what am I "seeing"? Say fire for example, am I seeing fire or what.

Simular to what Vanadium 50 said "What exactly is a lion? If I pointed at one and said "that's a lion", wouldn't that be an acceptable answer?"

an electron looks like a bzzt, and feels like a bzzt, so it must be a bzzt.
 
  • #11
17
0
This question is similar to asking what is a photon? Photons and electrons and other elementary particles are not actually little billiard balls that are flying around high speeds. They are both quantum excitations of their respective fields.

The entire universe is filled with a photon field, and it's mostly empty. You can think of it as an empty EM field as well. At every point in space there is a quantum harmonic oscillator for each possible spatial frequency, and thing about quantum harmonic oscillators is that only allowed energy levels come in steps of hw. The minimum energy of the oscillator is 3/2hw in 3 dimensions, and then it goes up to 5/2hw, then 7/2 hw, etc. One step above the zero-point level is considered one photon at that spatial frequency. The photon could have a range of frequencies, and be localized in some way, or be more spread out and less localized.

Just think of it of a field as an infinite set of harmonic oscillators at every point in space, and think of the particles as quantum vibrations of this field.

In a similar way, there is an electron field that fills of space with a zero-point energy, and it has certain linearly quantized energy levels above the zero level that indicate the number of electrons. This explains why every electron has exactly the same mass, charge, spin, and g-factor. Saying an electron is the same thing as saying a quantum vibration of the electron field, but the latter is too wordy. The electron vibration can be localized, as in a vibration around an atom, or more spread out like a free particle, or an electron in a double slit experiment.

The big difference between the electron field and the photon field is that with electron vibrations, they can't stack directly on top each other. This is described as the Pauli Exclusion rule. The electron field is a fermion field, described by the Dirac equation. Two electron vibrations can be in almost the same state very close to each other, but they can never occupy the same exact state.

I like to visual all quantum particles, whether they are photons or electrons, as 3 dimensional fuzz balls, and those fuzz balls oscillate and move around and sometimes disappear according the probabilistic laws of QFT. It's the sudden collapse of the fuzz balls that's most shocking to me, (wavefucntion collapse is mysterious).
 
  • #12
Drakkith
Staff Emeritus
Science Advisor
21,009
4,828
Fastman, while your explanations seems to make sense, I am hesitant to really accept it, as I've never heard of "photon fields" or "electron fields" and the like. What model is this from?
 
  • #13
17
0
You've heard of fermionic fields though right? I just sort of made it up the terms "photon field" and "electron field" on the spot.
http://en.wikipedia.org/wiki/Fermionic_field
The electron field is just a type of fermionic field governed by the Dirac equation. That's my definition anyway. It's what helps me envision quantum field theory better.

The most disappointing aspect of the field theory is that it predicts a large zero-point energy. It's been dismissed before, but now that dark energy is around, we need some explanation for why there is a negative energy field permeating the entire universe and causing cosmic acceleration. The zero-point energy of the QFs were a candidate, but the calculations were done and it's 120 orders of magnitude larger than the measured value! That's a terrible model error.

http://en.wikipedia.org/wiki/Zero-point_energy#Gravitation_and_cosmology
 
  • #14
Drakkith
Staff Emeritus
Science Advisor
21,009
4,828
You've heard of fermionic fields though right? I just sort of made it up the terms "photon field" and "electron field" on the spot.
Actually no. My knowledge of QFT is severely lacking. Thanks for the links by the way!
 
  • #16
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
2019 Award
25,647
8,838
False.

There is no prediction for the charge radius of the electron. There are experimental limits suggesting that any charge radius must be smaller than some number, but the number that A. Neumaier posted is neither a prediction nor a measurement.
 
  • #17
22
0
If you could magnify an electron to the size of a car,you would have to slow it down as well ,so as to observe the individual oscillations.
 
  • #18
A. Neumaier
Science Advisor
Insights Author
2019 Award
7,483
3,381
There is no prediction for the charge radius of the electron. There are experimental limits suggesting that any charge radius must be smaller than some number, but the number that A. Neumaier posted is neither a prediction nor a measurement.
I haven't seen the paper, but according to the abstract: ''indicate the validity of the SM down to the distance of order ~10^{-17} cm and the electron charge radius of ~ 10^{-16} cm.''
Thus there seems to have been a comparison between experiment and a prediction, though the number given is maybe only a bound.

I haven't found a calculation that I could have checked, But in principle, a prediction is possible: In his book

S. Weinberg,
The quantum theory of fields, Vol. I,
Cambridge University Press, 1995,

Weinberg defines and explicitly computes in (11.3.33) a formula for the
charge radius of a physical electron. But his formula is not
fully satisfying since it is not fully renormalized (infrared
divergence: the expression contains a fictitious photon mass,
and diverges if this goes to zero, as infrared corrections from soft
photons are not accounted for). See also Section V in the
review article

M.I. Eides, H. Grotch, and V.A. Shelyuto,
Theory of Light Hydrogenlike Atoms,
Phys. Rep. 342 (2001) 63-261.
http://arxiv.org/pdf/hep-ph/0002158

where the authors says:
''According to QED an electron continuously emits and absorbs virtual
photons (see the leading order diagram in Fig. 8) and as a result its
electric charge is spread over a finite volume instead of being
pointlike''. Then they give without proof the explicit formula (28)
for the charge radius, depending logarithmically on the charge of the
central field in which the electron moves.

But according to (7.12) in Phys. Rev. D 62, 113012 (2000),
the charge radius of neutrinos, another pointlike particle, computed
from the standard model to 1 loop order, is in the range of
4...6 10^-14 cm for the three neutrino species.
 
  • #19
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
2019 Award
25,647
8,838
I haven't seen the paper
Then maybe you should. You brought it up.
 
  • #21
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
2019 Award
25,647
8,838
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 point-like 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
A. Neumaier
Science Advisor
Insights Author
2019 Award
7,483
3,381
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.
I had given references that I read and understood (Weinberg Chapter 11.3, with an explicit formula for the renormalized charge radius, though in terms of a tiny photon mass, because this kind of computations have IR divergences). Only in response to the query for an explicit value, I referred to something I couldn't access but seemed to give such a value.

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.
I wasn't speaking of substructure in the sense of being composite, but of not having the properties of a point.
The electron is an elementary particle, hence not composed of anything but itself. But it is not a point - only pointlike (which means, the formal, unobservable, bare electron in the defining action is a point). Due to radiative corrections stemming from the renormalization procedure for relativistic quantum field theories, an observable, renormalized electron has a positive charge radius (though far too small to be probed experimentally with current methods).
This is the case for purely theoretical reasons, a direct consequence of QED, which is generally acknowledged to be reliable in this regime. (Corrections from the standard model would be tiny and not alter the general fact.)

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.
I didn't attribute it to electron substructure but to Weinberg's discussion in his QFT book. (One might attribute it to virtual substructure the physical electron being a composite of a bare electron and a cloud of bare virtual photons, but I don't like this sort of imagery.)
 
  • #23
A. Neumaier
Science Advisor
Insights Author
2019 Award
7,483
3,381
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 point-like 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.
Let me complement your experimental view with the theoretical side of the matter.

The deviations from pointlikeness are usually described by means of
form factors that would be constant for a point particle but become
momentum-dependent 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
970
3
CF.Gauss said:
What exactly is an electron?

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
 
Last edited:
  • #25
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
 

Related Threads on What exactly is an electron?

  • Last Post
Replies
12
Views
2K
  • Last Post
Replies
12
Views
2K
  • Last Post
Replies
7
Views
3K
  • Last Post
Replies
2
Views
720
  • Last Post
Replies
17
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
5
Views
3K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
7
Views
1K
Top