Songfacts®:

• Grimes penned and recorded this song with Jack Antonoff of the band Fun. for the "Daddy Issues" episode of the HBO series Girls. After the pair came up with the tune, Girls creator and co-star Lena Dunham played the show's Music Supervisor Manish Raval a rough mix from her phone.
  
  "We instantly said, 'That's ours, don't give it to anyone,'" Raval recalled to Billboard magazine. "It ends one of my favorite episodes ever - a big party event leads us on a very melancholy note but there's something so awesomely fun and energetic about this track that really plays against the moment."
• Jack Antonoff is the boyfriend of Lena Dunham. "Jack is our secret weapon on the show," Raval said. "With him, we have access to so much: he's an amazing songwriter and producer, he has relationships… A lot of times, we'll just ask, 'What are you working on now? Taylor Swift?' I have no problem tapping into that connection."
  
  Grimes and Antonoff previously paired up in 2014 for "Take Me Away," a track from the fun. guitarist's solo side-project Bleachers
• Credited to Grimes and Bleachers, this breezy ode to one of the laws of nature finds Grimes crooning:
  
  Calculate the entropy
  Running out of energy
  A lack of love or empathy
  Leave me lonely
  
  The word Entropy came from the study of heat and energy in the second half of the nineteenth century. The entropy of an object is a measure representing the state of disorder of a system at the atomic, ionic or molecular level; the greater the disorder, the higher the entropy. At the lowest possible temperature, absolute zero, where all molecular motion ceases and order is assumed to be complete, entropy is zero.