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Looking into Atoms
Quantum physics is a branch of physics that works with the activities going on inside of atoms. They talk about subatomic particles interacting with each other. We're starting to talk about Albert Einstein and Max Planck's ideas here. In the early 1900's, scientists were beginning to examine the inside of atoms. They were wondering what was going on inside those things that were once thought to be solid. One big idea they came up with was that the energy of an electron depends on the frequency, or wavelength, of the EM radiation. Another interesting idea they discovered was that energy didn't depend on the intensity, or amount, of radiation.
Packets of Energy
During the early 1900's scientists also proved that EM radiation not only has packs of energy (quanta) but moves like a wave as well. It's like a stream of individual packets. If you apply this idea to the structure of an atom, there is a nucleus and there are rings (levels) of energy around the nucleus. Each wave that can exist is the orbit of one electron. No two electrons can be in the same orbit, or wave. Scientists say that those electrons move around the nucleus in clouds. Those clouds were once considered the shells.
The Uncertainty Principle
A German scientist named Werner Heisenberg came up with this idea called the uncertainty principle. He figured that the position and momentum of an atomic particle cannot both be observed accurately at the same moment in time. The idea shows that because these pieces are so small, whatever device you use to measure the particles will affect them. Think about it. If you use light to examine a piece of light, won't you knock it around? Well now you just lost the idea of position. What if you freeze it in place? That's all very well, but now you don't know where it was going, or how much momentum it had. When you increase the precision of one measurement, the other measurement will suffer.
Look at the Heisenberg uncertainty principle in a more general way using the observer effect. While Heisenberg looks at measurements, you can see parallels in larger observations. You can not observe something naturally without affecting it in some way. The light and photons used to watch an electron would move the electron. When you go out in a field in Africa and the animals see you, they will act differently. If you are a psychiatrist asking a patient some questions, you are affecting him, so the answers may not be truthful. Field scientists work very hard to try and observe while not changing the situation.
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