Unit 9: Hawking

Wormholes: A wormhole is what Albert Einstein and Nathan Rosen called "bridges". They said that these theoretical passages between distant regions of spacetime were permissable by General Relativity. (source: lecture) Hawking has theorized that wormholes might connect our universe with other universes. (source: lecture)

Baby Universes: In Hawking's No Boundary model, there's a way for our universe to become warped in a manner which would mimic the creation of the No Boundary universe and could potentially create a daughter universe.

Alan Guth: USA, astronomer, MIT, originator of inflationary universe theory. "Inflation is a modification of the conventional big bang theory, proposing that the expansion of the universe was propelled by a repulsive gravitational force generated by an exotic form of matter." (source: http://web.mit.edu/physics/facultyandstaff/faculty/alan_guth.html )

Martin Rees: (b. 1942), British astronomer, Cambridge; a long-time friend of Hawking, Rees has been involved in a wide range of work, including the application of anthropic reasoning in cosmology. (source: White & Gribbin, p. 216) His departmental homepage can be found at: http://www.ast.cam.ac.uk/IoA/staff/mjr . A concise definition of "anthropic principle" is available from the Journey Through the Galaxy website: "we see the universe the way it is because if it were different we would not be here to observe it."

Michael Green: Cambridge, Superstring theorist. His departmental homepage can be found at: http://www.damtp.cam.ac.uk/user/mbg15/ . Superstring Theory combines String Theory with Supersymmetry (which is the theory that every fermion has a partner boson and vice versa).

Andre Linde: Russian, physicist, Stanford, associated with inflation theory. His departmental homepage can be found at: http://www.stanford.edu/~alinde/ .

Paul Steinhardt: In our reading, he is mentioned for his work on inflation theory and for a kerfuffle with Hawking over attribution. He also is known for his work on quasi-crystals - those cool things that resemble crystals but lack the repetitive patterns of crystal growth. His departmental homepage can be found at: http://www.phy.princeton.edu/~steinh/ and there's an interesting paper on quasi-crystals at: http://www.physics.princeton.edu/~steinh/quasi/ .

Kip Thorne: USA, physicist. He was the one who came up with a way to theoretically keep a wormhole open long enough to travel through it, after Carl Sagan asked him for help with this major plot device for his novel Contact.

Quantum Chromodynamics: See "quarks".

Strings: As I understand it, it's the idea that the things we think of as points (like electrons and quarks) are strings. (White & Gribbon, p. 257)

Quarks: Protons and neutrons are composed of smaller units called "quarks". The theory that describes their interaction is called "quantum chromodynamics" because the different types of quarks have been labeled with the names of colors. (White & Gribbin, p. 255)


Graviton: If there were a quantum theory of gravity, it would need to incorporate particles to carry the gravitational force (in line with the way in which photons relate to electromagnetism). The name for this proposed particle is a graviton. (White & Gribbin, p. 256)

Einstein-Rosen Bridge: From White & Gribbin, p. 294: "a wormhole that links two black holes" and a handy way to traverse the Universe - at least, that's the way it works in Contact .

Chronology Protection Conjecture: Hawking's term for the notion that the Universe might be set up so as to avoid the classic "time paradox" problem, just in case time travel were possible.

Photo above of Quark ( from Star Trek: Deep Space Nine) from website: http://www.startrek.com/startrek/view/series/DS9/character/1112445.html

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 )