Concepts in Unit 4

The following is a list of concepts, terms, etc. that were discussed in Unit 4:

Dual Particle/Wave Nature of Matter: Given that we can't know both and object's velocity and its position (See Uncertainty Principle), when we consider the minute constituents of matter we can see how they exhibit both the properties of particles (if we look for their location) and those of waves (if we measure their energy/momentum).

Heisenberg Uncertainty Principle: We can't measure both the exact location of an object and its momentum at the same time.

Determinism: A mechanical view of the universe in which future events can be predicted on the basis of past events.

Quantum Theory: The quantum theory of atoms describes an electron as a probability cloud in the atom, rather than as a discreet particle (as in the Bohr model).

Sum-over-histories: Feynman's approach to quantum theory. The example given in the lecture involved a photon emitted from a candle's flame. Rather than thinking of it as having traveled a straight path from the flame to the observer's eye, consider that what we see is the sum of all of the possible paths that the photon could/did take.

Quantum Electrodynamics (QED): In the electrical force that exists between charges, the process by which virtual photons are exchanged. (QED is not to be confused with Q.E.D. "quod erat demonstratum". I am soooo much more familiar with the Latin phrase that it used to confuse the daylights out of me when I worked at a bookstore and kept seeing QED used in Physics titles. I kept thinking "What nerve!")

Nuclear Fission: The method by which nuclear energy is produced. For example: If Uranium is split into two unstable daughter elements, both will need to find a more stable state. In the process of which, energy is released.

Chain Reaction: When the Uranium is split (see above) you get the two daughter elements plus energy plus a few extra neutrons. If each of these neutrons can cause another fission (and so on) in a sustainable fashion, you'd have a critical chain reaction of the type used for nuclear power. If you were to get more than one additional fission reaction, it would be super-critical and that's when the Manhattan Project comes into the picture.

Nuclear Fusion: This is the process that runs our Sun. The idea is that two light nuclei are fused together, forming one heavy nucleus and a lot of energy.

Nuclear Weapon Design: The Manhattan Project resulted in two different designs used against the Japanese. "Little Boy" was a gun-type, with one sub-critical mass being fired at another and the fission process set off by neutrons introduced by an initiator. The design of "Fat an" had a hollow Pu core and this was compressed by using the explosive charges arrayed around it.