13 One interesting example of many speculations on spacetime foam: John Ellis, N. E. Mavromatos, D. V. Nanopoulos, “Derivation of a Vacuum Refractive Index in a Stringy Space-Time Foam Model,” Phys. Lett. B 665 , 412 - 417 (2008). 14 Joseph Silk, “The Cosmic Microwave Background.” arXiv:astro-ph/0212305v1 15 For history of quantum mechanics: Hans C. Ohanian, “Principles of Quantum Mechanics,” (Prentice-Hall, Englewood Cliffs, N. J. 1990), see section 1.4 on the Heisenberg microscope. A classic in quantum theory is: D. Bohm, “Quantum Theory,” (Prentice-Hall, Englewood Cliffs, N. J. 1951), see chapter 5. An online reference is: en.wikipedia.org/wiki/Introduction to quantum mechanics. 16 For quantum theory in general: R. Shankar, “Principles of Quantum Mechanics,” second edition (Plenum Press, New York and London 1994), see chapter 3 on history. 17 M. Born and E. Wolf, “Principles of Optics,” seventh edition (1999) (Cambridge Press, Cam- bridge UK 1959), see chapter 10. 18 Also see section 5.3 of Ohanian in 15 19 E. R. Taylor and J. A. Wheeler, “Spacetime Physics,” (W. H. Freeman, San Francisco 1963), see chapter 1. 20 R. J. Adler, M. Bazin, and M. Schiffer, “Introduction to General Relativity,” (McGraw Hill, N. Y. 1965, second edition 1975), chapter 9. 21 C. W. Misner, K. S. Thorne, and J. A. Wheeler, “Gravitation,” (W. H. Freeman, San Francisco 1970), chapter 39. 22 B. F. Schutz, “A first course in general relativity,” (Cambridge University Press, Cambridge UK 1985) chapter 1 on special relativity and chapter 8 on Newtonian limit. 23 C. Will, “Theory and experiment in gravitational physics,” (Cambridge University Press, Cam- bridge UK 1981, revised edition 1993), chapter 4. 24 See section 6.2 of 20 25 See chapter 14 of 20 26 See chapters 33 and 34 of 11 27 Ronald J. Adler and David I. Santiago, “On gravity and the uncertainty principle,” Mod. Phys. Lett. A 14 , 1371 V 1381 (1999), F. Scardigli, Generalized uncertainty principle in quantum gravity from micro black hole gedanken experiment, Phys. Lett. B 452 , 39 - 44 (1993). Also see 11. 19