The Voyager Golden Record: Earth's Mixtape to Aliens
The two gold-plated copper phonograph records each put into Voyager 1 and Voyager 2 and launched in 1977 are the denizens of Earth's attempt to make at least one-way contact with any advanced space-faring alien worlds that may exist. Personally I think using the electromagnetic spectrum to communicate is more practical than a drifting time capsule but I am an amateur radio operator so I am biased.
Chances are neither record will ever be encountered and played by aliens. The Voyager spacecrafts are on interstellar missions. Neither spacecraft has sufficient velocity to leave the Milky Way galaxy. Due to the vast emptiness of space I think it's far more likely at least one if not both spacecraft will still be aimlessly traveling billions of years after the Milky Way and Andromeda collide and merge.
Of course, since the recordings are on a phonograph NASA included a stylus to play the record. Any alien that recovers one of the two records would literally have found a needle in a cosmic haystack.
The contents of the Voyager record were selected for NASA by a committee chaired by Carl Sagan. Dr. Sagan proposed his version of the Kardashev scale in his 1973 book The Cosmic Connection: An Extraterrestrial Perspective several years before the Voyager probes were launched.
This is what I think the truth is:
Hip hop mixtapes first appeared in the mid-1970s according to Wikipedia. Sagan was aware of this and decided Earthlings should make their own mixtape of images, speech, music and his paramour's EEG brainwaves because Carl Sagan was that kind of a freak.
Sagan inferred that if an alien species was ever going to find either Voyager 1 or Voyager 2 they would be at least a Type I civilization. Majestic, intelligent and global. Even their medicine would be more advanced. After finding the probe and viewing its random stream of consciousness the aliens would send their best doctors to Earth and offer the best psychiatric treatments the galaxy had to offer.
Or maybe Earth just made a mixtape for aliens just for the sake of making a mixtape.