1 Edmond Halley: Mr Newton! I have some strange astronomical observations I can make neither head nor tail of. Perhaps you would be so good as to peruse them?
2 Isaac Newton: Mr Halley, these figures indicate a confluence of historical junctures. Time itself is being unravelled!
2 Edmond Halley: Where?!
3 Isaac Newton: Not where, when. In the distant future. The 1940s to be precise.
4 Edmond Halley: A world-shaking event in the 1940s? Some new form of musical entertainment, perhaps?

The dominant popular music of the 1940s was swing, which evolved in the pre-war years of the 1930s.

There in fact wasn't any particularly notable form of new musical entertainment in the decade. Rhythm and blues had begun the evolution that would turn it into rock and roll in the 1950s, but it wasn't there yet.