|A black body. Public domain image. SOURCE.|
The name quantum comes from the Latin word for "how much". This field was developed because classical (or Newtonian) physics doesn't apply to atomic particles; radiation from black bodies (a black body absorbs and then emits all radiation that reaches it) could not be explained by it, or by electromagnetic theory. In 1900, Max Planck came up with a theory that explained the radiation from observed black bodies, and it proposed that electromagnetic radiation comes in quanta.
There are several important ideas to quantum physics:
1. The Copenhagen Interpretation. Created by Niels Bohr, it states that nothing exists until it is measured.
2. The collapse of the wave function. The wave function--which was created by Erwin Schrodinger--of a particle "collapses" into one of all possibilities when observed.
3. The Heisenberg Uncertainty Principle. Invented by Werner Heisenberg, the principle explains that either the momentum or the position of a particle, but not both, can ever be determined.
4. The EPR Paradox. Named after Albert Einstein, Boris Podolsky, and Nathan Rosen, it was an attempt to dismantle the Copenhagen Interpretation; the basic idea is that if a pair of particles have opposite spin and you measure one of the two, the other particle immediately acquires the opposite spin, faster than the speed of light.
5. The infinity problem. This is a mathematical hang-up where in quantum electrodynamics (QED), if you try to solve Schrodinger's aforementioned wave function, you end up with an electron with infinite mass, energy, and charge, a clear impossibility.
But that's not all. Due to problems with the Copenhagen Interpretation, there is another, competing quantum theory. The Many Worlds Theory, presented by Hugh Everett III in 1957, proposes that there are as many universes as there are possibilities; that every time a measurement is taken, the universe splits into one where the measurement occurred, and many more where the measurement resulted with all the other probabilities. In the case of a particle with two possible states, the universe would divide twice.
Brian Greene is a professor of physics and mathematics at Columbia University who obtained a Ph.D. from Oxford University. He made a series of discoveries in superstring theory (which tries to bring together quantum theory and general relativity into a single unified theory) and topology change (the idea that the fabric of space can split). He is the author of The Elegant Universe, The Fabric of the Cosmos, The Hidden Reality, and Icarus at the Edge of Time. He was the host of the PBS NOVA programs The Elegant Universe and The Fabric of the Cosmos, both based on his books. He also co-founded the annual World Science Festival in 2008.
A short video of Brian Green explaining quantum physics:
So, which do you champion: the Copenhagen Interpretation or the Many Worlds Theory? Do you think we'll ever find a definitive answer?
-----The Golden Eagle