# How does a collider know both the energy and position of the particle?

1. Apr 9, 2013

### jshrager

Presumably a collider has some sort of pinhole out of which particles get ejected in a particular direction, and the energy (momentum) with which they are ejected is supposedly known. So, the operators/designs of the instrument know both the position (at the ejection pinhole, or whatever) and momentum (energy) of these particles...uh...how?! Maybe they really don't know them both as precisely as one (or at least I) am lead to believe? (This is not to mention ejection time!)

2. Apr 9, 2013

### Lapidus

Colliders shoot particles at very *high* momentum at each other. The uncertainty principle is about the *spread* of momentum, related to position measurement and Planck's constant, a very *tiny* number.

So if you have high momentum particle, you have automatically very localized particles, since already very small deviations from their high momentum are large compared to Planck's constant which enters the uncertainty relation.

3. Apr 9, 2013

### jshrager

Ah. Great. Thanks!