How Fast Does the Fabric of Space Move?

This excellent question gets to the heart of some deep concepts in relativity and cosmology. The short answer is: The fabric of spacetime itself doesn't "move" in the way objects move through space. Spacetime isn't a material substance with a velocity; instead, it's the stage on which motion happens, and this stage can itself change in shape and scale.

However, there are three specific phenomena that people often think of as the "fabric of space moving," and we can assign meaningful speeds to them.

1. The Expansion of Space (Cosmological)

This is the most famous example. Space itself is expanding, causing galaxies to move apart.

How fast? The rate is given by the Hubble Constant (H₀). Currently, the best measurement is about 70 km/s per Megaparsec.

What that means: For every 3.26 million light-years (a Megaparsec) two galaxies are apart, the space between them grows at a rate of 70 kilometers per second.

Key Point: This is not a speed through space, but a recession velocity due to new space being created between them. At great enough distances, this "velocity" can exceed the speed of light—this does not violate relativity because nothing is moving through space faster than light.

2. Ripples in Spacetime (Gravitational Waves)

When massive objects accelerate (like merging black holes), they create ripples in the fabric of spacetime called gravitational waves.

How fast do they travel? Precisely at the speed of light (c), which is about 300,000 km/s.

Analogy: This is like asking how fast a wave travels through the ocean. The wave (the distortion) propagates at a specific speed, but the water itself doesn't travel with the wave. Similarly, a gravitational wave is a traveling distortion of spacetime itself.

3. Frame-Dragging (The "Lensing" of Spacetime)

A massive rotating object, like a planet or black hole, literally drags the surrounding spacetime around with it as it spins. This is similar to a spinning ball in a thick fluid pulling the fluid around it.

How fast? The "dragged" spacetime rotates at a speed that depends on the mass and spin of the object. Near Earth, the effect is tiny—NASA's Gravity Probe B measured Earth's frame-dragging as causing a rotation of spacetime of about 39 milliarcseconds per year. In practical "speed" terms at Earth's surface, this is extremely slow (on the order of millimeters per year).

Near a rapidly spinning black hole, however, the effect is so strong that nothing can resist being pulled around.

Philosophical/Physical Clarification

Asking "how fast does spacetime move?" is like asking "how fast does a meter move?" or "how fast does the background grid on a graph move?" Spacetime is the coordinate system, the arena. We measure the motion of objects and the evolution of geometry within that arena.

Important Caveat: In general relativity, there is no fixed, absolute background. Spacetime is dynamic and curved, but its "motion" is not a velocity in the traditional sense. We instead talk about its dynamics—how it expands, curves, ripples, and rotates.

Summary of Spacetime Dynamics

Phenomenon	What's "Moving"?	Speed / Rate
Cosmic Expansion	New space being created between galaxies.	Hubble Rate: ~70 km/s/Mpc (not a traditional velocity).
Gravitational Waves	A wave-like distortion of spacetime.	Speed of Light (c): ~300,000 km/s.
Frame-Dragging	Spacetime being twisted by a rotating mass.	Varies: From mm/year near Earth to near-light-speed near black holes.

So, while the "fabric" itself doesn't have a speedometer reading, the changes and distortions in that fabric propagate and evolve at very specific, measurable rates—most famously, at the speed of light for its ripples (gravitational waves).