# Position of elementary particles

## Main Question or Discussion Point

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?

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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
Staff Emeritus
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.

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.

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