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Communication Help (page 2)

By — McGraw-Hill Professional
Updated on Sep 17, 2011

Problems And Challenges

There are difficulties inherent in finding signals from extraterrestrials, as well as in sending signals to them. Here are some of the major challenges that SETI pioneers face.

First, only a tiny part of the sky can be scanned at any given time. A narrow field of reception is necessary because celestial objects generate a lot of radio noise, and this can be minimized only by “focusing in” on very small regions of the sky. Also, in order to get a signal to travel through the vast depths of interstellar space, it must be focused in a narrow beam. We cannot “spray” a signal all over the whole sky; it will become too diluted by the time it reaches the stars.

Second, the apparent direction of a distant star is not always exactly the same as its actual direction. All the stars are moving with respect to each other. The position of a star when its light leaves it, as compared with its position when a signal arrives from an Earthbound transmitter, can change (Fig. 12-5). The transmitted beam must be wide enough to get rid of the possibility that the signal might miss its target. We also must realize that the true target is not the star itself, but a planet in orbit around the star. Radio beams are wide enough so that this timing problem is not significant, but radio waves aren’t the only mode of communication that has been suggested. Lasers at visible and infrared wavelengths might be used to focus the beam into as narrow a shaft as possible. If the beam is narrow enough, communicators will have to calculate the actual position of the target planet when the signal is expected to arrive, and this will require precise observations as well as excellent computer programming.

The Search for Extraterrestrial Life What
Is Life? Problems And Challenges

Figure 12-5. When we aim an antenna at a distant star, we must take the star’s motion into account because the signals take years to get there. (The motion in this drawing is exaggerated for clarity.)

Third, we must decide which wavelength or wavelengths on which to listen and transmit. The resonant hydrogen wavelength at 21 cm is a natural marker in the electromagnetic spectrum and has been recommended as a wavelength near which interstellar communication can be carried out. Intelligent beings, knowing this wavelength and its significance, should be expected to send their messages at wavelengths near (but not exactly at) the resonant hydrogen emission signal. In any case, for signals to penetrate great distances in space, they must be concentrated at precise and stable frequencies. Otherwise, the electromagnetic noise generated by some stars, galaxies, and nebulae will overwhelm the communication signals.

All these problems make SETI a task akin to searching for the proverbial pin in a barn full of hay. Nevertheless, the quest goes on, with the hope that the pin is there and that if we roll around in the hay long enough and vigorously enough, it will sooner or later poke us.

Unknown Media

Some physicists, astronomers, and communications engineers think that there are modes of communication we have not yet discovered and that truly advanced extraterrestrial beings are signaling by such esoteric means. Radio signals, infrared waves, and light beams travel at about 299,792 km/s (186,282 mi/s) in space. This seems almost instantaneous in the immediate vicinity of Earth. People who regularly use geostationary satellites for twoway communications and Internet access know about the latency , or lag time, which can be upwards of half a second because of the time it takes for signals to travel to and from such satellites. When it comes to interstellar communications, however, latency will be measured in years, decades, centuries, millennia, or eons.

Suppose that we send a message by means of electromagnetic waves to a star system on the other side of our galaxy. If this signal is heard and a reply is sent, we will not receive the reply until 150,000 or 200,000 years have passed. This is, for all practical purposes, just about as good as no reply at all.

Are there particles or effects that travel faster than the speed of light in space? Some recent research suggests that there are. Is it possible to send signals in hyperdimensional levels, somehow short-circuiting the distances among stars and galaxies by cheating on time? This gets into the realm of science fiction, but today’s fiction has a way of becoming tomorrow’s fact. Some scientists have gone so far as to say that an advanced interstellar civilization would consider electromagnetic communications old-fashioned and quaint, in the same way we think of smoke signals or cannon shots.

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