Communication Help (page 3)
Each and every time a signal escapes into space from our planet, it can be thought of as saying, “CQ alien life”! The expression “CQ” is used by amateur radio operators and means “Calling anyone.” CQ signals sometimes are followed by modifiers indicating a preference for the type of station with which communication is desired. An extraterrestrial being, if intercepting one of our standard radio or television broadcast signals, would be smart enough to know that it was not especially intended for his or her (or its) civilization, but the fact that we had allowed the signals to escape into space could be interpreted as an invitation to reply, a call of “CQ extraterrestrial.”
Of course, any good search for other stations in a communications medium involves a combination of transmitting and receiving. The equipment for receiving long-distance signals is less expensive than the equipment for sending them, and results can be anticipated sooner. Thus SETI astronomers did their listening first, and reception continues to take priority over transmission. To adopt an age-old principle: We can learn more by listening than we can by talking.
The first serious attempt to find signals from another civilization was initiated by Dr. Frank Drake using a radio telescope at Green Bank, West Virginia, in 1959. Drake and his colleagues called the undertaking Project Ozma , named after the fantasy land of Oz. The scientific establishment regarded Project Ozma with interest, amusement, and some skepticism. But Drake believed that if enough stars were scanned with the sensitive radio receivers and large antennas at Green Bank and other radio observatories, it was only a matter of time before signals from an extraterrestrial civilization were picked up.
Some of the stars that Drake investigated were Tau Ceti in the constellation Cetus and Epsilon Eridani in the constellation Eridanus. Various frequencies were checked, but especially those in the vicinity of the well-known hydrogen emission energy that takes place at a wavelength of 21 centimeters (cm) and corresponds to a frequency of about 1400 megahertz (MHz). This “signal” is prevalent throughout the Universe. Frequencies just above and below it are logical choices for interplanetary and intergalactic radio calling channels. The results were negative, but the amount of time spent on the project was limited. Campaigns similar to Project Ozma continue today as part of SETI.
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.
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.
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.
A New Kind Of Patience
Regardless of the mode, be it radio signals, infrared, visible light, or some thus-far-unknown technology, Homo sapiens will have to cultivate great patience to make interstellar communications possible. We will have to be willing to send out signals and realize that they might not be heard until many human generations have come and gone. It is difficult to imagine putting down notes that we do not expect will be read for 50,000 years. But there is no way, as far as anyone knows, that our descendants 500 centuries from now, reading our instructions and adjusting their communications equipment accordingly, can reply to us and ask, “What if your software doesn’t run on our computers?”
It is hard enough right now, in most Earthly societies, for parents to communicate with their children. Imagine this generation gap multiplied by several thousand times! If ever a civilization from some distant star system sends its representatives to meet us here on our humble little planet, we will know that they have attained a degree of patience we can only dream about. However, it will inspire us, because the instant we know who they are and where they came from, we will realize that if they can attain such a lofty state of existence, so can we. We will realize that Earth is not a miracle. Or if you prefer, we will come to know that miracles are common in the Cosmos.
Communication is an economical way to search for life on other worlds, and it is also the method that we can expect to produce results, if there’s anyone out there listening and transmitting with the same intentions. However, communication is not much of an adventure, and if we ever find another civilization “on the radio,” we’ll want to meet those beings face to face. This can happen in three ways: We can go to them, they can come to us, or we’ll run across each other in the vastness of interstellar space.
We Do The Traveling
Interplanetary travel, within the limits of our own Solar System, has already been done by robotic space probes. We know it’s possible for machines to do it, and given reasonably good economic and political conditions in the next several decades, astronauts will someday visit some of the planets and moons, especially the planet Mars and Saturn’s largest moon, Titan. It is not necessary to attain fantastic speeds to get to the other planets in our Sun’s family. To reach the stars, however, we will have to accelerate our space ships almost to the speed of light.
If the Earth were the size of a marble, the Moon would be a small pea approximately 300 mm (about 1 ft) away. At present space-ship speeds, it takes 2 or 3 days to get to the Moon. On this same scale, the Sun would be about 120 m (or 400 ft) away, roughly the distance from home plate to the center-field fence in a major league baseball stadium. The distance from the Sun to Pluto would be on the order of 5 km (3 mi). We have the ability to span these distances, although it takes years to reach the outermost planets. The nearest star to our Solar System, Proxima Centauri , would be more than 32,000 km (20,000 mi) away on this same scale. Even if we can build a ship that will travel at half the speed of light, a round trip to this star will take 18 years. Our Milky Way galaxy is 25,000 times wider than the distance to Proxima Centauri.
If we humans are ever to attempt interstellar travel on a galactic scale, our space vessels will have to reach speeds so high that a peculiar phenomenon, relativistic time dilation , takes place. Maybe you’ve heard about this: the slowing down of time for beings in a vessel traveling at near the speed of light. This would make it possible, in theory, to reach almost anywhere in the known Universe within the span of one human lifetime. Relative to the rest of the Cosmos, however, including the planet of origin (Earth), such space travelers would be hurled irrevocably into the future by hundreds, thousands, or millions of years.
Long-distance space travel presents all kinds of obstacles and dangers, and we’ll look more closely at this subject later in this book. We’ll study relativistic time dilation and other effects of extreme speed as well.
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