To the bewilderment of scientists, the Pioneer 10 spacecraft–which left the solar system in 1983–is slowing down:

Scientists eliminated all possible causes — gravity, radiation, equipment problems — and have now apparently concluded that the craft have been affected by a previously unknown force that’s about 10 billion times weaker than the gravitational force.

What is this new force, and how is it we haven’t encountered it before? Explanations aren’t forthcoming just yet, but the research is due to be published in an upcoming issue of The Physical Review, a physics journal. After that, expect a lot of arguing among researchers about how to verify this force, why it exists and what to call it. Or as scientists call it: fun!

I won’t be reading that journal article, but I look forward to hearing about the reaction to it. I enjoy these reminders that so much of our existence can be summed up with the word “mystery.”

By the way, I’m reading a great book — “Twilight of the Clockwork God” by John Ebert, an editor with the Joseph Campbell foundation. He explores how metaphysics and physics are growing closer.