There's a famous experiment displaying Heisenberg's Uncertainty Principle


Where a beam of light is subject to increasingly narrow slit (constraining its position), eventually causing it's momentum to be increasingly unclear (to maintain the inequality) spreading it out.

If I wanted to do the inverse of this experiment, where I have particles, I constrain the particles' momentum (somehow), and see that their positions are increasingly undefined, how would I do that?

One idea:

If have a light beam originating from a source A to a target strip B,

the strip B is made increasingly small, so that if you spot a photon that landed on B, you would know the momentum to an increasing degree, thus the location of the photon at the source A should be increasingly unclear.

Now the question is how to measure this?


Momentum measurement is performed by observing the radius of curvature in a magnetic field.

As a practical matter many configuration require at least one collimator, but if you have spatially dense detection (say from a TPC, or a high resolution solid detector system) then you can even do without that.

Fun fact: the formula you learned in the intro class $$ r_c = \frac{p}{qB} \;,$$ remains correct for relativistic particles provided you use the momentum in the numerator rather than $mv$ (which—sadly—is the way many intro texts express it; tsk tsk).


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.