Origin of Cosmological Redshifts

This animation gives a 2-dimensional analogy to the expansion of 3-dimensional space and to the stretching of wavelengths leading to cosmological redshifts. As the balloon expands, all points move away from all other points. Therefore, an observer viewing from any one of the points will appear to be the "center", with all other points moving away with a velocity proportional to the distance from the observer. In reality, the surface of the balloon has no "center", since any point looks like any other point.

As the balloon expands, a light wave is "stretched" to longer wavelengths, which corresponds to a spectral redshift. The longer the light wave travels in the expanding spacetime the more it will be stretched. Therefore, the redshift is a measure both of distance traveled and of time since emission. Usage: Click "Play" to begin and "Stop" to halt. "Step" moves forward one step and "Back" moves backwards one step. "Home" returns to the beginning from any point.