At times, the glass bulb on your bookshelf is filled with violet sands; at others, it is completely empty. You’ve watched the fine powder emerge from nowhere on several occasions, swirling outward from a needle’s-eye hole in space. You’ve also observed the grains sliding through one another until none are left, leaving it hollow once more. This is apparently no illusion; the bulb is far heavier while it appears to be full.

As a child, you used to ask your grandfather what it was. “It’s a reminder of something very important,” he’d say, then make you guess what you thought it was. You had lots of ideas, and asked him if it was a baby planet, or a desert-making machine, or even an alien aquarium. He especially liked that last one, but heartily replied “nope” to all of the above. In retrospect, your imagination seemed to put him at ease.

Since then, the bulb has become one of the few things left to you in his will, along with a collection of research documents from the University Beneath Chicago’s Chronodynamics lab. You’ve never found any other record of such an institution’s existence, but apparently he worked there for many years as a technician, along with his brother, who you never knew existed either. “You always wanted to know what this was,” he left in a personal note. “But I could never bring myself to explain it. I wanted it to be something better than it was for you. If you’re still curious after all these years, this binder contains everything there is to know about that little bookend of mine. Love, Grandpa.”

Over the past few months, you’ve slowly pieced together his work. According to his findings, it is one of two-hundred and fifty-six such orbs believed to exist throughout the solar system, together constituting a six-dimensional hourglass network. Sand pours in and out of each one through a series of knots in space, eventually accumulating in some unknown gravitational sink. While there is no clear calculation of when the dust will finally settle, your grandfather ultimately concluded that it seemed to be timed against the death of the sun, and lamented that most of the orbs discovered had long since stopped refilling themselves.