## Programming the Universe: A Quantum Computer Scientist Takes On the Cosmos – Seth Lloyd

**Thoughts:** It’s been a while since I read this one. I remember feeling a bit lost among all the discussion of entropy and quantum effects, but I recall Lloyd doing a good job explaining all the quantum weirdness. Worth reading if you’re already interested in simulation and/or quantum computation, but probably not otherwise.

(The notes below are not a summary of the book, but rather raw notes - whatever I thought, at the time, might be worth remembering.)

Lloyd, Seth. 2006. *Programming the Universe: A Quantum Computer Scientist Takes On the Cosmos*. Alfred A. Knopf.

- 17: striking way to open a class as a lecturer: “First… you ask questions and I’ll try to answer them. Second, if you don’t ask questions, I’ll ask you questions. Third, if you don’t answer my questions, I’ll tell you something I think you ought to know.”
- 19: English system of weights and measures is a binary system: 8 oz. in a cup, 16 oz. in an (American) pint, 32 oz. in a quart, 128 in a gallon.
- 22: Meter: originally conceived of as 1/10 000 000 of the distance from the north pole to the equator (so, circumference of the earth ~= 40 000 km)
- 36: “It is just when we behave rationally, moving logically, like a computer, from step to step, that our behavior becomes provably unpredictable. Rationality combines with self-reference to make our actions intrinsically paradoxical and uncertain.”
- 72: “Temperature is a measure of the trade-off between information and energy: Atoms at a high temperature require more energy to register a bit of information, and atoms at a low temperature require less energy to register a bit. Temperature is energy per bit.”
- 80: flow of information in the universe: “unknown bits infect known bits.”
- 91: “A convenient way to think about up or down spin is to curl the fingers of your right hand in the direction the ‘particle’ is spinning.” Your thumb points in the direction of the spin.
- 106: the double slit experiment reveals that every electron goes through both slits at once
- 184: assume some computer program has generated a string. Statistically, says Ray Solomonoff, the most likely program to have produced it is the shortest (among randomly generated computer programs)
- 189: mentioned: Seth Lloyd, “Measures of Complexity: a Non-Exhaustive List”
- 191: entropy consists of random, unknown bits; neck entropy consists of structured, known bits

Posted: Jul 25, 2022. Last updated: Jul 25, 2022.