Equivalence Principle Demonstrator

As part of Einstein Year 2005, the Institute of Physics asked 42 Technology to develop a display to demonstrate the principle of equivalence at Cambridge Science Festival.

The equivalence principle, a vital stepping stone in Einstein’s development of the general theory of relativity, states that it is impossible to distinguish by experiment between an inertial force and the gravitational force acting on any body.

The brief for the demonstrator was to build a centrifuge with a pendulum clock in it, and compare the rate of passage of time as measured by this clock with an identical but static clock. Einstein’s equivalence principle dictates that the moving clock, subjected to both gravitational and inertial forces, should run faster than the static clock merely subjected to gravity. This establishes a link between inertial forces, gravitational forces, motion and the observation of time.

42 Technology designed a system of toothed belts and pulleys that allowed a metronome (our pendulum clock) to be rotated such that the plane of swing of the pendulum remained constant with respect to a static observer – an important but complicating design requirement.

Experiments showed that a repeatable difference was observed in the passage of time as measured by the stationary clock, compared with the constantly accelerating clock.