Introduction Background: Particles QCD Bosons Uncertainty Principal: Interaction Parton Variables Jets Psedorap. Next Previous

The uncertainty Principle

"The more precisely the position is determined, the less precisely the momentum is known in this instant, and visa versa"-Heisenberg. This succinct statement of something known as 'the uncertainty principle' made by the physicist Wener Heisenberg in his uncertainty paper in 1927 had enormous implications for a branch of physics known as quantum mechanics.

The implications of this statement are that it is impossible for us to know both the exact position and the exact momentum of a particular particle at the same time. The reason for this is because in order to determine a particles position, you need to fire another particle at it, and see where the particle you fired rebounds after it collides with the particle you are interested in. The problem with this is that when the particle you fire (i.e. a photon) collides with the particle your interested in, some of it`s momentum is transferred to the particle of interest. This has the effect of changing the momentum of the particle that been hit, so that you no longer know what the particles momentum was originally.

The uncertainty relation between position and momentum arises because of the fact that the greater the momentum of the particle you fire, the more accurately you can determine the position of the particle of interest (this is because of something called the De Broglie wavelength). However increasing the momentum of the particle you fire, means that more of it`s momentum is transferred to the particle you are interested in during collision. Hence you are more uncertain about what the particle of interest's momentum was before the two particles collided.

The obvious implication of this statement is that the reverse must be true. You can fire a particle with a very small momentum at another particle, thus disturbing it`s momentum by only a small amount, but by doing this you are more uncertain as to that particle exact position in space.

The mathematical implications of the uncertainty relations caused a large amount of controversy when they were first published. The idea that not all mathematics was definite and that there existed uncertainty within the universe was abhorrent to many physicists. Indeed many famous physicists were against the idea of uncertainty at the time, there is a famous quote by Einstein which was "God does not play dice with the universe!" However despite all the violent objections raised at the time of it's inception the uncertainty principle has become an integral part of quantum mechanics today, and is an important part of the theory upon which our project is based.