It's a Wonderful Life

It's A Wonderful Life (1946)


Concept featured in film: Turn-off time

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Summary of clip: This clip shows the two angles in It's a Wonderful Life, depicted as galaxies, talking to each other. The galaxies are blinking on and off rapidly during the conversation. Clarence, the angel who wants to get his wings, is not quite a galaxy yet. He is merely a star. In this conversation, his star is shown as a point of light, then as a bright star burst.

Connection of flick to concept: Light is information. The speed limit imposed on light is also imposed on information. Information cannot travel from point A to point B faster than 3x10^8 m/s. The theory of special relativity simply will not allow it.

In a typical astronomy class, students are asked to consider if galaxies could shut off instantly, as in the flick of a switch. The answer is no, they cannot. Take a galaxy that is 10,000 ly across. If one side of the galaxy were to shut off, it would take 10,000 years for the other side of the galaxy to shut off.

Galaxies are typically used to introduce the condept of turn-off time. However, galaxies do not "turn off." Quasars, however, do vary in luminosity on rather short timescales. Since the speed of light is known, the "turn-off"time may be used to determine the diameter of quasars. This flickclip provides a good image of what this might look like. In this flickclip, the two galaxies are changing their brightness rapidly. They are also turning on and off quickly. Could this happen in real life?

In Clarence's case, his star appears to blink brighter, then dimmer as he talks. This would be a good clip to introduce pulsars . Since, from Earth, pulsars do look like they are turning on and off, could this really happen? This could then be used to discuss the lighthouse model that explains how a pulsar appears to turn on and off.