How can you aim without knowing the precise position and velocity of a particle?

[berty]

The uncertainty principle states that you can never know with any accuracy the precise position and velocity of a particle, because the measurement of such will alter them in an unknown way.
Therefore, if you do not know either the position or speed of a particle, how can you a) aim another particle at it? And b) gather any data?

 

[ChrisAvery]

I don't think they aim at any particular particle...they shoot a swarm at a swarm :) and the data is a swarm of particles that can then be measured...I think...Forgot to add that in increasing the count increases the probability.

 

[Edgardo]

Hello berty,

I remember sitting in a lecture where one student asked the professor the same question. The answer was that indeed you don't let collide only 2 particles but many, as Chris Avery said.

Here's a nice animation:
http://www.gsi.de/portrait/Broschueren/Wunderland/Au+Au_2AGeV_b=0fm.mpg

http://www.gsi.de/portrait/Broschueren/Wunderland/05_e.html

 

[selfAdjoint]

You have a large number of particle in a beam, and the beam has a cross section, and theory let's you calculate the probability that that cross section will interact with anything. With colliders you have two cross sections and a mutual probabiity.

The number of particles in the cross section is called the luninosity, and one of the main things beam physicists do is to increase the luminosity, maybe by improving the focussing. Thinks of controlling the spray from a hose with an adjustable nozzle.

 

[misogynisticfeminist]

The physical picture is 2 probability clouds hitting each other. As long as your probability cloud of the first particle hits anywhere in the cloud of the target particle, it has hit it.

 

[marlon]

The uncertainty principle states that you can never know with any accuracy the precise position and velocity of a particle, because the measurement of such will alter them in an unknown way.
Therefore, if you do not know either the position or speed of a particle, how can you a) aim another particle at it? And b) gather any data?

In QM, you don't aim just one particle in order to make it interact with another particle. You need to think of an interaction as a beam of particles that interacts/scatters onto a beam of other particles. Quantities like the cross-section/scattering-amplitude of such a beam will give you a notion of what the probability of interaction is.

marlon