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I have been wondering why doesn't the uncertainty principle prevent the LHC experiment as if one want to collide two particles together one must accelerate a particle to certain speed and aim it at another particle thus requiring the scientist to know both the velocity and the position in microscopic world, violating the uncertainty principle?

Thanks in advance

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No, the LHC doesn't violate the uncertainty principle. The principle only affects position and momentum (not actually velocity) in the same direction, but in a particle accelerator, you don't have to constrain both position and momentum in any one direction. It's only important to constrain the position in the transverse direction (perpendicular to the beam) and the momentum in the longitudinal direction (along the beam).

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  • $\begingroup$ You might also mention that a particle accelerator doesn't normally collide two particles exactly but a small finite width beam of many particles $\endgroup$ – Triatticus Jun 16 '13 at 9:15
  • $\begingroup$ I did not realize that the uncertainty principle has to satisfied the x y and z vectors of momentum and position to held effect, so technically you can know the x and y vectors for momentum and x y and z vectors for position for any microscopic particle without violating uncertainty principle? $\endgroup$ – user1433153 Jun 18 '13 at 18:32
  • $\begingroup$ @user1433153 there is one copy of the uncertainty principle in each direction. So the precision to which you can constrain the x momentum of a particle is entirely unrelated to the precision to which you can constrain its y position, for example. $\endgroup$ – David Z Jun 18 '13 at 18:56
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I was just reading a discussion about this exact thing Naked Scientists thread: Does CERN violate the uncertainty principle?.

In the final post, an answer to this question is that

the uncertainty in the particles position and momentum are smaller than the observed track. We can know the path the particle takes to within those limits.

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