Distant galaxies are receding faster than light — and we can still see them

Nothing can travel through space faster than light — that rule is ironclad. And yet the most distant galaxies are receding from us faster than light. Both statements are true, and the resolution is a subtlety that trips up almost everyone.

The galaxies aren’t moving through space at superluminal speed. Space itself is expanding, and they are being carried along with it. The faster-than-light limit governs objects moving through space; the stretching of space between objects obeys no such cap. Add up enough expanding space between us and a remote galaxy and the gap grows faster than light can cross it.

This isn’t fringe speculation. A peer-reviewed analysis by Tamara Davis and Charles Lineweaver states plainly that “we can observe galaxies that have, and always have had, recession velocities greater than the speed of light,” and that this does not violate Einstein’s relativity. Essentially every galaxy above a redshift of about 1.5 crosses that line.

So how do we see them at all? Light they emitted long ago has been crawling toward us for billions of years. As the universe ages, the boundary of what’s reachable shifts, and those ancient photons eventually win the race to our telescopes — delivering an image of a galaxy that was, even then, fleeing faster than light.