"The 1960s," I answered while peeling a carrot. (To be precise, the LASER was invented in 1960.)
She then showed me a passage in the book which, to her mind, sounded much like a laser: "some powerful wireless installation--a concentration of wireless energy far beyond anything so far attempted, and capable of focusing a beam of great intensity upon some given spot." Given that the theoretical work on optical coherence that led to the laser was completed in the early 1950s, this is not unlike H. G. Wells speculating about atomic weapons more than two decades before physicists had figured out that the atom could be split--which in fact he did.
Yet Wells is widely regarded as a precursor of science fiction as a genre, whereas Christie is most commonly associated with crime fiction, and specifically the subgenre of detective fiction. The reasons for this differentiation are probably better speculated upon by someone with more comprehensive knowledge than mine of the early 20th century landscape of popular fiction from which the genres we now tend to regard as distinct, established fields first emerged. In such an investigation, The Big Four would be necessary source of data.
Whether it is worth reading as literature is more debatable: My wife also informs me that the book uses the word "chink" multiple times, in connection with untrustworthy Chinese people rather than weaknesses in armor. Whatever her insights into future directions of physics, when it came to human biology she shared her time's and continent's obsession with now discredited race theory.
