# Why do electrons repel?

1. Jul 22, 2006

### superweirdo

You know, these are basic questions, I never wondered why about there. Till a friend of mine told me that the speed of the info. for electrons that they are suppose to repel from each other is the speed of light, thus if two electrons travel faster than light, they wouldn't repel. But why? What causes them to repel from each other? What causes proton and electron to attract each other?

2. Jul 22, 2006

### mrjeffy321

Since electrons have mass, can never travel at the speed of light.

Two like charged particles will repel against each other due to a repulsive (or attractive, in the case of oppositely charged particles) force which is exerted between the two.

The force exerted on a particle with charge q_1 by another particle with charge q_2 at a radial distance r is given as,
F = (k * q_1 * q_2) / r^2
Where k is the Coulomb force constant 8.99 E9 Nm^2/C^2.
[Notice how similar this equation is to Newtonâ€™s law of universal gravitation...however electrostatic forces are much stronger than gravitational forces and can act both as attractive and repulsive forces, whereas gravity only attracts]

The resulting force is thus directly proportional to the magnitude of the charges on the two particles, and inversely proportional to the square of the inverse of the distance between each particles center of charge.
The force will cause the particle (electron) to accelerate.

The rest mass of an electron is: 9.10938188(72) E-31 kg
The charge on the electron is: 1.602176462(63) E-19 C

Last edited: Jul 22, 2006
3. Jul 22, 2006

### alias25

say if you had an isolated particle and just by observing it (if thats possible) you had to tell whether it was charged or not, without using electromagnitism or anything like that. Can that be done?

4. Jul 22, 2006

### superweirdo

Ok, you told me that repulsion is caused by electrostatic force. What causes electrostatic force? The Charge? What causes the charge? Why are electrons negative and protons are positive?

5. Jul 22, 2006

### 3trQN

I beleive it has something to do with subatomic particles, which have certain spin values based on quantum mechanics like stuff. The spin effects charge in some way.

And thats where my ignorance starts...or actually my ignorance started with this post..

6. Jul 22, 2006

### mrjeffy321

There are a whole slew of sub-sub atomic particles out there.
A proton is said to be made up of two "up" quarks and a "down" quark, giving it a positive charge, where as a neutrally charged neutron is made of two "down" quarks and an "up".
Electrons are a different category I believe, not made of quarks.

This part of it is defiantly not in my expertise, I cant do too well with why the particles have the size or magnitude of charge that they do.
This type of question should probably be in a different category than "chemistry".

7. Jul 22, 2006

### Gokul43201

Staff Emeritus
Actually, spin and charge and completely different and unconnected.

Sorry, but that's the last stop on the line. Ask again after a decade or two, and maybe there will be something to add.

Recognize that one can not indefinitely ask "why" and expect answers. The point of science is to be able to explain varied and complex phenomena based on a small set of fundamental truths. Perhaps, some day it can all be reduced to a single concept (there's a large number of scientists that challenge this point of view), but at that point, you could still ask "why" and have no answer.

As for the force (or field) traveling at the speed of light, it's almost the other way round. Light, being a disturbance in the electromagnetic field travels at the speed of propagation of the field.

How do you intend to go about "observing it"? The way we usually observe something is by bouncing light off of it and interpreting the information contained in this light. It doesn't always have to be light that gets used (you could use electrons, neutrons or even tennis balls, depending on what you want to observe), but the idea here is that an observation requires an interaction. So, it becomes meaningless to speak of observation "without using...anything".

8. Jul 25, 2006

### superweirdo

so what you are telling me is that there is not a single person on earth who knows what causes electrostatic force and what causes the charges in the subatomic particles?!

9. Jul 25, 2006

### Gokul43201

Staff Emeritus
What causes charge? What causes mass? These are active topics of research, but there is no definitive answer as yet.

10. Jul 25, 2006

### superweirdo

Does anyone here wanna take up the challange and share what they think?

11. Jul 25, 2006

### Gokul43201

Staff Emeritus
Superweirdo, maybe you're not familiar with the guidelines. This Forum doesn't look too kindly upon offhand speculation. If you want to know something about the currect extent of research in this area, you should start a new thread under the High Energy Physics subforum. If you want people to propose theories over their lunch break, you should ask outside PF.

12. Jul 26, 2006

### superweirdo

I apolozige gokul, i wasn't familiar w/ the guidelinis but thx to you. Just a random question, not worth creating a thread, I heard that photons travel twice as fast as light, well, when they collide each other, don't they speed up?

13. Jul 26, 2006

### Staff: Mentor

Photons are light, so how can they travel twice as fast as light?

14. Jul 27, 2006

### StoneBurner

You are quite correct, in a sense. The search for underlying causes is, so far, a never ending quest. Science DESCRIBES how things behave, and discovers the rules. Sometimes it explains how it one behavior occurs by going a layer deeper. Example: First the rules of planetary motion - planets move in elipses (plus perterbations.). Why? We discovered that an inverse-square attractive field (gravity) caused that behavior. Why does gravity behave that way... Well, Einstein added a deeper layer with spatial curvature. Why does space act like that? Or why do strings and quarks that make up the electron behave that way? At some point, you always say "I dunno - that's just what I've found. Ask God why." And that's always the answer to the last layer we've reached.

15. Jul 28, 2006

### superweirdo

thats what I heard, that particles inside light travel twice as fast as light in order for light to travel at that speed.

16. Jul 28, 2006

### Gokul43201

Staff Emeritus
Please provide a complete citation of the source that describes this.

Besides, this is clearly not what StoneBurner said.