Is The Speed of Light Fast Enough?

Very often, anyone who is making a long-distance telephone call outside the state of Alaska is communicating over at least one satellite link. While the benefits of space-age communication are enormous, they may also be frustrating. In a transcontinental call, one may often notice that there is an agonizing overlap in the conversation. People on one end of the line will begin a sentence at the precise instant that the person on the other end does the same. Then there are a few seconds of silence while everybody tries to get the thing sorted out, and the process repeats.

The confusion usually results because of the time lag involved in the transmission of the signals to a communications satellite and back to Earth. These satellites are in stationary, or synchronous orbit over 22,000 miles above various points of the earth's surface. Because the waves carrying the transmission travel at the speed of light, or about 186,000 miles per second, the round trip takes about a quarter of a second.

This may not sound like a lot, but considering that the same effect applies from both ends, and that people are generally disinclined to spend more time than they must on long-distance conversations, the half second gap amounts to quite a bit--and to the resulting overlap in conversation. People on one end of the conversation will begin to say something before they realize that whoever is on the other end has already started.

While we may find the basic laws of elementary physics mildly annoying in our everyday lives, they are all-important in the realm of science. From the observer's standpoint, who could not have been awed in December of 1968 by hearing the voices of astronauts Borman, Lovell and Anders, orbiting the Moon, knowing that the words we were hearing had actually been said more than a second before? Or that the magnificent pictures that we received from our probes to Jupiter and Saturn took an hour or more to reach the earth?

Closer to home, one of the impacts that this travel-time delay has on us is in the gathering of scientific data relating to the state. A good example is the recording of earthquake waves recorded by the seismographic stations operated by the Geophysical Institute. Many of the signals from these stations are transmitted to a satellite and back to Fairbanks where they are recorded. Because earthquakes are located by observing the travel times of the waves as they spread out from the source, a precise knowledge of their arrival times at the various recording sites is essential.

Some signals from Geophysical Institute stations take not only one "jump" from a satellite, but two, resulting in a delay of the reception of the signal for about a half-second.

Because earthquake shocks travel through the earth at about five miles per second, this delay must be accounted for in order to obtain accurate locations. At the Institute, this adjustment is made automatically by the computer program used in epicentral locations.