Expanding Universe - Physics Demonstrations - Expanding Universe | Physics Undergraduate Labs

Purpose

Flashing LEDs on a stretching bungee cord model cosmic expansion. Students observe that all inter-LED distances increase proportionally when the cord is stretched, directly demonstrating Hubble's Law ( $$v = H_0 d$$ ) and showing that no point is the "center" of expansion.

Four flashing LEDs hanging from clips on an orange braided bungee cord at even intervals, positioned above a meter stick on a green lecture bench

Same four LEDs on the now-stretched orange bungee cord, showing increased spacing between all LEDs compared to the initial configuration

Figure 1: Initial configuration: four LEDs at measured intervals along the unstretched bungee cord, with a meter stick below for reference.

Figure 2: After stretching: all inter-LED distances have increased proportionally. More distant LEDs have moved farther apart — Hubble's Law in action.