Unit 8: Hawking

Newton's Theory of Gravity: describes the gravitational force between two masses as a function of the distance between them. The strength of the force decreases in proportion to the distance squared. (source: http://en.wikipedia.org/wiki/Law_of_universal_gravitation )

Einstein's General Relativity: attributes the gravitational force to the way that matter curves spacetime. It unites Newton's gravitational theory to Einstein's Special Relativity. (source: http://en.wikipedia.org/wiki/General_relativity )

Special Relativity: Einstein's theory that says that the speed of light is the same for all observers, even when they are moving. (source: http://en.wikipedia.org/wiki/Special_relativity )

The Dynamics of Stars: The energy of stars comes from the process of nuclear fusion in which light nuclei are fused together to form heavier nuclei, in the process of which energy is released.

Black Holes (also: Event Horizon, Escape Velocity): A black hole is a body with such mass that the Escape Velocity is greater than the Speed of Light (hence, it's a "black hole" because not even light can escape from it. Escape Velocity is the minimum velocity required to escape a body's gravitational pull. The Event Horizon is the imaginary zone around a singularity where the escape velocity = the speed of light. (source: lecture notes)

Expanding Universe (Friedmann's Model): Alexander Friedmann used the Theory of Relativity to show that the Universe should be expanding. This was later supported by Hubble's observations.

"Big Bang": Hubble's work showed that the Universe is not only expanding but that the farther out a galaxy is, the faster it's moving. This suggests the behavior of fragments after an explosion. The idea that the Universe started started as an explosion was ridiculed by Fred Hoyle, who dubbed the notion the Big Bang. (source: lecture notes)

Contracting Universe ("Big Crunch"): The idea that a universe expanding from a singularity will ultimately collapse back into a singularity (mirroring the Big Bang). Hawking's No Boundary model eliminates the collapse while retaining the singularity by using the geometry of curved spacetime. (source: White & Gribbin, pp. 181-183)

Entropy (2nd Law of Thermodynamics): According to our text, "things wear out over time". Entropy is regarded as a measure of disorder. Within a closed system, entropy can only remain the same or increase. (source: White & Gribbin, p. 141)

Virtual Particles: Back in Unit 4, we saw how Heisenberg's Uncertainty Principle allowed for particles to be created out of nothing and not violate the Conservation of Energy. "An ephemeral particle allowed only by quantum mechanics; virtual particles carry the same charge as the corresponding true physical particles but have the wrong energy" (source: Randall, Warped Passages, p. 470)

Black Hole Radiation (aka "Hawking Radiation"): If pairs of virtual particles are created at the event horizon of a black hole and one of the pair falls into the black hole, the other might be able to escape as a real particle. This would be a way for a black hole to radiate and, hence, to contain entropy. (source: lecture notes)

Primordial Black Holes: This term refers to the small black holes which could have formed from free neutrons, right after the Big Bang. (source: lecture notes)

Anthropic Principle: "The reasoning that says, out of many possible universes, we could live only in a place where structure could have formed." (Randall, Warped Universes, p. 459) [By structure, Randall is referring to the constituents of matter.] Anthropic principle refers to an explanation of the universe in terms of the conditions which have given rise to and support life such as our own. As our text says: "The fact that we exist preselects, to some degree, the exact rules of physics that we will discover the Universe operates on." (source: White & Gribbin, p. 218)

Jacob Bekenstein: A Princeton researcher who, in 1947, applied the principles of thermodynamics to black holes and said that black holes had entropy. (source: http://en.wikipedia.org/wiki/Jacob_Bekenstein )

Alexander Friedmann: (1888-1925), Russian cosmologist, mathematician. His 1920s work on the expanding universe (which was derived from Einstein's general relativity) was backed up by Hubble's observations. (source: http://en.wikipedia.org/wiki/Alexander_Friedmann )


Edwin Hubble: (1889-1953), USA, astronomer; Working at Mount Wilson Observatory, Hubble did pioneering observations of distant galaxies. (source: http://en.wikipedia.org/wiki/Edwin_Hubble )