ITHINK 09/29/2008
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After going through this circus, one may ask…is there anything out there that is real?
Niels Bohr says no. There is nothing actually “out there” at the quantum level. Somehow, reality emerges only in relation to the result of “measurements”.
This view embraced by the majority of physicists, is called “Copenhagen Interpretation”. Copenhagen Interpretation of quantum mechanics implies that quantum mechanics is as good as it gets. There is nothing really “out there”, which means that detecting an electron at a certain position “creates” the position of this electron. -
In order to measure the present position of a particle, the obvious way is to shine light on the particle. Some of the waves of light will be scattered by the particle and this will indicate its position. However, one will not be able to determine the position of the particle more accurately than the distance between the wave crests of light, so one needs to use light of a short wavelength in order to measure the position of the particle precisel. Now, by Planck’s quantum hypothesis, one cannot use an arbitrarily small
amount of light; one has to use at least one quantum. This quantum will disturb the particle and change its velocity in a way that cannot be predicted. Moreover, the more accurately one measures the position, the shorter the wavelength of the light that one needs and hence the higher the energy of a single quantum. So the velocity of the particle will be disturbed by a greater amount. In other words the more accurately you try to measure the position of the particle, the less accurately you can measure its speed, and vice versa. Heisenberg showed that the uncertainty in the position of the particle times the uncertainty in its velocity times the mass of the particle can never be smaller than a certain quantity, which is nothing but Planck’s constant. Moreover, this limit doesn’t depend on the way in which one tries to measure the position or velocity of the particle, or on the type of particle. Heisenberg’s uncertainty principle is a fundamental inescapable property of the world.
