Frame Dragging

Frame dragging is the prediction from Einstein's general relativity that a rotating mass twists the fabric of spacetime around itself, dragging nearby space and time along in the direction of its spin. It is one of the most counter-intuitive consequences of treating gravity as curved spacetime: a spinning object does not just attract things, it stirs the geometry around it like a spoon in honey.

Gravity that behaves like magnetism

In Newton's physics, gravity depends only on how much mass is present, not on whether it is moving. General relativity is different: moving and rotating masses produce additional gravitational effects, in a close analogy to how moving electric charges produce magnetism. For this reason frame dragging is also called gravitomagnetism. A gyroscope held near a rotating planet will slowly precess — its axis is dragged around — even if nothing touches it. This specific prediction is known as the Lense–Thirring effect, derived in 1918.

Measuring an almost imperceptible twist

Near the Earth, frame dragging is extraordinarily weak, causing a gyroscope to drift by only a few billionths of a degree per year. Detecting it required exquisite precision. NASA's Gravity Probe B mission, launched in 2004, carried ultra-precise gyroscopes into orbit and, after years of careful analysis, confirmed the Lense–Thirring effect to within about 20%. Independent measurements using the precise tracking of laser-ranging satellites have confirmed it as well.

Frame dragging at the extreme

Around a rapidly spinning Kerr black hole, frame dragging becomes overwhelming. Close to the horizon lies a region called the ergosphere, where spacetime is dragged so violently that nothing can remain still — everything is forced to rotate with the black hole. This extreme dragging is what makes the Penrose process for extracting energy from a black hole possible, and it shapes the swirling accretion disks and jets seen around real black holes.

A common misconception

Frame dragging does not mean the spinning mass physically grabs and pulls objects along with friction. Nothing material is touching them. What is dragged is the local definition of "non-rotating" itself: a freely floating gyroscope, feeling no force, still finds its orientation slowly carried around by the twisted geometry of spacetime.