# The volumn of the electron

1. Oct 3, 2011

### higgs1989

The volume of the electron

In the partical physics,it defines the electron has no volume but do have a radius,anybody can give me a detailed explaination?
The appreciation is mine！

Last edited: Oct 3, 2011
2. Oct 3, 2011

### Staff: Mentor

As far as I know, experiments have defined only an upper limit for the radius of the electron, which according to Wikipedia is about 10-22 m. This means that the electron could have a radius up to that size which is unmeasurable by current techniques; but there is no evidence that it actually does have such a radius.

3. Oct 3, 2011

### higgs1989

But does it has mass or to be checked later?It does not make any sense for the radius it has and the electric quantity.
if it does has no mass,then what composes it?

Last edited: Oct 3, 2011
4. Oct 3, 2011

### Mike Anderson

The electron has a mass. It is also approximate like the radius.

5. Oct 3, 2011

### G01

An electron could be a point particle with zero radius and still have mass. They are not mutually exclusive scenarios.

6. Oct 3, 2011

### haael

What would it mean for electron to have radius? I mean - what experiment could possibly show nonzero radius of an electron?

7. Oct 3, 2011

### Runner 1

It kind of comes down to -- what do you define volume as?

Wikipedia says "Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance [...] occupies or contains."

So we need to define that boundary.

An electron potentially "affects" every location in the universe. If we exclude any EPR-like correlations found to be a result of the electron, then its "effect" spreads at the speed of light. So we could say its boundary is expanding at the speed of light, which means its volume is growing.

A lot of times, the boundary is instead defined as the surface in which there is a 90% probability the electron will be found (whatever "found" means). 90% is arbitrary -- we could choose any number.

This is sort of ambiguous and probably not the answer you are looking for. The next question then, is an electron a point particle? No, not really. We can say that the electron is centered about some location, which is simply the average value for repeated measurements of its position.

Since energy is the same thing as mass, we can figure out the electron's distribution of mass. It's not all located in one zero-dimensional spot. How would we do this? Move a test mass around the electron and measure the gravitational force (not really possible in practice -- this is a thought experiment). If the electron's distribution of energy is a function of distance from its average position", then this measurement would give the same result as that of a point particle. To find the difference, one must keep moving closer and closer to that average position.

That last point may be a little hard to understand, so I'll give you an analogy. Say you were trying to determine whether the earth was a point mass or not. If you have a test mass in space and move it around, it will respond in exactly the same way as if all of earth's mass were concentrated in one spot (I forget what this phenomenon is called). But when you bring that test mass below sea level, then it begins to act differently. (Don't take this analogy too literally).

8. Oct 4, 2011

### higgs1989

i do appreciate all of your responses.
Now, I got another question,"once our physics professor told us that field is some kind of matter(such as electric field,etc)."
And my quetion is,"do field has a certain mass or volume?" so do wave?

9. Oct 4, 2011

### TrickyDicky

But in QFT it is supposed to be a point particle, isn't it? Otherwise you don't have Lorentz invariance and particle creation-annihilation.

10. Oct 4, 2011

### Runner 1

Is it? I don't know enough about quantum field theory to say, but the Wikipedia article states

Someone who actually studies in this area can hopefully provide further clarification.

11. Dec 11, 2011

### Naty1

12. Dec 11, 2011

### mraz

Anyone here read book of jan hebky gravity in minkowski space-time