Phoning another world

(see: Interspex, by Clark Nida)

Radio signals move at the speed of light in free space. According to Special Relativity Theory, it is impossible to send a signal any faster, by whatever means. So we might as well think of our phone message being transmitted by either laser beam or radio waves. Both will travel at the same speed.

Nevertheless a radio signal still take an appreciable time to reach another planet. This inevitably means a delay between you saying something and hearing the answer. This delay will be at least twice the time taken for light to reach you from the target planet.

Light travels at approximately 186,000 miles per second. The moon is about 250,000 miles away from Earth. Say 500,000 miles for the round-trip. That means a delay of around 3 seconds between “How are you?” and “Fine, thanks”. Earth-Moon voice communication is a knack to be acquired only by practice.

Mars varies in distance from the Earth, but never comes nearer than 12 light-minutes or so. Thus the response-delay in a phone-call to Mars can be 24 minutes to over an hour. It’s not worth hanging on the line. Let them ring you back with their reply.

Titan is roughly nine times as far from Earth as Mars is at its closest. You won’t get a response to your call in much under three hours. It’ll take you all day to have the briefest of conversations with someone on Titan (or any of Saturn’s moons). Best say all you want to before they go.

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