# Density of electrons and quarks

1. Jul 10, 2010

### jimjohnson

I recently noticed that the density of an electron, assuming it is a particle, was e21 gm cm3. This is e7 x more than a neutron star 2 x e14. I then looked up quarks. The up quark is the most dense (mass = 9 x e-27 gms, radius .5 x e-17 cm) with a density e5 x the electron or 1.7 x e25. Thus, a quark is e12 x more dense than a neutron star.
Is this correct??

2. Jul 10, 2010

### nicksauce

I don't know how you are calculating the density of electrons and quarks, but they are thought to be point particles, and are thus of infinite density so to speak.

3. Jul 11, 2010

### jimjohnson

No, I do not think they are point particles. My source for mass and radius is a chart on fundamental particles from cpepweb.org.

4. Jul 11, 2010

### nicksauce

For the electron and quark it says the size is <10^-18m and <10^-19m respectively. These numbers aren't what people think the sizes are, they are upper limits from experiments on what the sizes would be if there was any size at all. A size of 0 (point particle) is consistent with "<10^-18m".

5. Jul 11, 2010

### jimjohnson

Thanks for checking source and responding. I will have to research point particles.

6. Jul 11, 2010

### Naty1

Kip Thorne in his book BLACK HOLES AND TIME WARPS has some fascinating discussion on the density of white dwarf stars beginning on page 140, and continuing thru all of Chapter 4 and beyond.
Sirius B a well know white dwarf has a density of about 4 millions grams per cc, or about 60 tons per cu in based on modern astornomical observations. A formula called the Stoner-Anderson equation of state allows computation of the resistance to collapse (and formation of a black hole) as a function of density. For such astronomical bodies, electron and neutron degeneracy play major roles in resisting collapse, far more than thermal vibrations. His discuss will give you a good feel and some basic mathematics for astronomical bodies.

I do NOT know of any reasonable way to compute the density of an atomic particle, electron or any other, but my gut feel tells me its (a) quantum mechanical and (b) a probability type function. I think post #4 has the right idea....but there is more to why such an upper size limit exists.

Part of the physical measurement problem is that when one tries to confine any particle for measurement, Heinsenberg uncertainty comes into play as does wave-particle duality. This means when you try to hold an electron still and get a "size" measurement, it's wave becomes more and more frantic...you can't confine it to measure it's size....it's analogous to electron degeneracy which is a major factor resisting neutron star collapse into black holes. In an analogous way, when you try to probe an electron with ever larger experimental frequencies, that means additional energy, and to get a more accurate "picture" you end up adding energy to the particle.....increasing thermal vibrations and obscuring it....

I did a quick check of Wikipedia http://en.wikipedia.org/wiki/Electron
and the description of an electron has a lot of data but I did NOT see size nor density....

Last edited: Jul 11, 2010