Position of elementary particles

[Helicobacter]

My teacher told me that elementary particles don't have position. Well, I don't understand this; it's like an oxymoron to me. Anyone with a easy-to-understand explanation?

 

[interested_learner]

What your teacher is talking about is something called the uncertainy principle. What that says is that for a subatomic particle (uncertainy of location X uncertainy of momentum) >= constant. In other words, you can't know the exact location or momentum of a particle. And as the uncertainy of momentum goes down, the uncertainy of location goes up and visa versa.

This means that we can't peg a subatomic particle at exactly one location. There is a limit of uncertainy that can't be passed. Sure they have position, but the position is smeared.

 

[ZapperZ]

Actually, we need to be careful with this. Your teacher is describing the uncertainty principle, which is often misunderstood. The reason why I say this is because many elementary particles, such as an electron, CAN have a definite position. When an electron hits a screen, it makes a DOT, and you have already determined that the electron had that position.

The uncertainty principle indicates our ability to PREDICT the relevant measurement under identical conditions. It doesn't say that a particle doesn't have a "position". It does. It is just how well we can tell the position measurement would turn out if we happen to know its momentum before hand.

Zz.

 

[Anonym]

My teacher told me that elementary particles don't have position. Well, I don't understand this

Your teacher told you that the particles in QM (every particle, not only elementary) are fields and therefore in general have infinitely many positions. As interested_learner and ZapperZ explain to you, in the specific physical situation it may be just a single point in space(position). Today experimenters may show to you the detailed picture of the single electron/photon with any precision you will require.

Dany.