Kakalios, James (4 de outubro de 2005). The Physics of Superheroes. New York: Gotham Books/Penguin Group, Inc. ISBN978-1-59240-146-8 The author, James Kakalios, is a physics professor. Pages 254-255: "With our improved understanding of physics, we can now more accurately describe Kitty Pryde's mutant power as being able to alter her macroscopic quantum wave function, increasing her tunneling probability to near 100 percent at will." Page 255: "How, when she's is 'phasing' and immaterial, can she walk?"
