A Brief History of Time

A Brief History of Time

The laws of physics can be said to obey certain symmetries. Symmetry C is when the laws for particles are the same as their anti-particles, P is when the laws are the same in the mirror image of any situation, and T is when the laws remain the same if time were reversed.
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Symmetry Term Timeline in A Brief History of Time

The timeline below shows where the term Symmetry appears in A Brief History of Time. The colored dots and icons indicate which themes are associated with that appearance.
Chapter 5
Human Curiosity and Ingenuity Theme Icon
The laws of physics can obey certain kinds of symmetries. Symmetry C refers to the laws applying to particles and anti-particles in the same way.... (full context)
Human Curiosity and Ingenuity Theme Icon
...1956, Tsung-Dao Lee and Chen Ning Yang found the weak nuclear force does not obey symmetry P. This was proven true by Chien-Shiung Wu, who caused radioactive atoms to spin in... (full context)
The Search for a Unifying Theory of the Universe Theme Icon
Human Curiosity and Ingenuity Theme Icon
The weak nuclear force also does not obey the symmetry C, meaning it would cause a universe of anti-particles to not behave like our own.... (full context)
Human Curiosity and Ingenuity Theme Icon
The Danger of Stubbornness  Theme Icon
As the universe expands and cools, forces that do not obey the symmetry of T cause more anti-electrons to become quarks than electrons to become anti-quarks, creating the... (full context)
Chapter 9
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Scientific laws obey the combined symmetries of C, P, and T. C refers to particles acting as anti-particles do. P refers... (full context)
Chapter 10
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...allows time travel on a miniscule scale. As particles follow the C, P, and T symmetries, a particle going backward in time could be considered an anti-particle going forward in time.... (full context)