# What exactly is an electron?

1. Mar 16, 2012

### CF.Gauss

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?

2. Mar 16, 2012

### phyzguy

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. Mar 16, 2012

Staff Emeritus
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. Mar 16, 2012

### vanhees71

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 $511 \; \mathrm{keV}/c^2$. 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. Mar 16, 2012

### Drakkith

Staff Emeritus
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. Mar 16, 2012

### A. Neumaier

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. Mar 16, 2012

### Bill_K

What is the charge radius of the electron predicted to be? Order of magnitude.

8. Mar 16, 2012

### nitsuj

CF.Gauss why do electrons not look like sparks/lightening?

9. Mar 16, 2012

### Khashishi

I think the lightning you see is actually emission from partially ionized nitrogen and oxygen plasma.

10. Mar 16, 2012

### nitsuj

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. Mar 16, 2012

### Fastman99

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. Mar 16, 2012

### Drakkith

Staff Emeritus
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. Mar 16, 2012

### Fastman99

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. Mar 16, 2012

### Drakkith

Staff Emeritus
Actually no. My knowledge of QFT is severely lacking. Thanks for the links by the way!

15. Mar 16, 2012

### A. Neumaier

16. Mar 16, 2012

Staff Emeritus
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. Mar 17, 2012

### derek101

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. Mar 18, 2012

### A. Neumaier

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
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
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. Mar 18, 2012