Since our discovery of the radio in 1895, we have been beaming radio transmissions into space. Most scientists believe the invention of the radio and radio telescopes would be a natural technological evolution by any intelligent life. Therefore, it would be reasonable to conclude that advanced aliens may have transmitted proof of their existence. The timeframe of their transmissions would depend on when they evolved. If their evolution were concurrent with ours, their transmissions would have started about a century ago. However, if they evolved millions of years ahead of us, their transmissions could have started millions of years ago.
In fact, the whole notion of listening for radio transmissions from aliens dates back to 1896, when Nikola Tesla promoted the idea that the radio could be used to contact advanced extraterrestrial life. In the early 1900s, Guglielmo Marconi, the inventor of the radio, claimed to have picked up Martian radio signals. Other iconic scientists, like Lord Kelvin, credited with inventing the telegraph, added fuel to the radio search for advanced aliens by publicly stating that the radio represented a possible way to detect and even contact them.
When scientists of the stature of Tesla, Marconi, and Kelvin speak, the world listens. In 1924, Mars was closer to Earth than any time in the last 100 years before or since. Obviously, this would be an excellent time to listen for radio transmissions from Mars. To avoid cluttering the Martian signals with our own, a “National Radio Silence Day” was promoted by the United States. For a 36-hour period, during August 21-23, 1924, all radios were silent for five minutes at the beginning of each hour. Concurrently, a dirigible was used to lift a radio up in order to receive signals 3 kilometers above the United States Naval Observatory. A select few listened, including the chief cryptographer of the U.S. Army, William F. Friedman. No radio transmissions from Mars were reported.
The most famous human enterprise listening for alien radio transmissions is SETI, which is not a single organization, but rather a group of organizations that employ radio technology to search for advanced extraterrestrial life. This includes Harvard University, the University of California, Berkeley, and the SETI Institute. Astronomer Frank Drake, using a small radio telescope, undertook the first SETI experiment in 1960. In 1961, the first SETI conference was held at Green Bank, West Virginia. From this humble beginning, SETI was launched. It is still highly active in its search for extraterrestrial radio transmissions as of this writing.
SETI technology has improved vastly. They are searching more frequencies than ever before. However, to date we have no confirmable evidence. SETI researchers have intercepted signals twice, once in 1977 and once in 2003, that may have been alien in nature, but they were not able to confirm the results. In fact, after more than five decades of searching, no confirmable radio transmission evidence of advanced aliens exists. However, to be fair to SETI, we need to examine their two greatest obstacles.
1. Scale Problems—The universe is enormous, and SETI has had to confine its search to sun-like solar systems within about 200 light years of Earth. Our galaxy is about 100,000 light years across. This may appear as if they have examined about 20% of our galaxy, but that would be incorrect. They focus on high-probability solar systems (ones similar to our own), and thinly slice space looking for the radio transmission. Therefore, the real number is much less than 20%. If it is viewed in terms of the volume, SETI has covered one-fifteen millionth of our own Milky Way galaxy. This, however, is likely to improve. If we add the recent upgrades that SETI made in 2007, namely the Allen Telescope Array, located in northern California, SETI is able to extend its search radius to 25,000 light years. This enables SETI to examine the 40 billion solar systems closer to the center of our galaxy. Still though, we are looking for a needle in a very large galactic haystack.
2. Technical Hurdles—Our transmitted radio and television signals disperse relatively rapidly in space. They would require extremely sensitive radio telescopes to detect. To understand this, imagine someone holding a candle at night a few feet from you. You are able to see it clearly. This is because numerous photons from the candle are reaching your eyes. Next, imagine that person moves farther away from you. The farther away the person moves, the dimmer the candle becomes. After a while, you will not be able to see the candle at all. The photons of the candle spread out over distance. Initially, when you were close to the candle, numerous photons reached your eyes. As the candle moved farther away, the photons spread out over a larger area, and fewer of them reach your eyes. This is why the candle became dimmer. Eventually, the candle was so far away, too few photons were reaching your eyes for your eyes to sense them.
SETI estimates that even with a sensitive radio telescope, as the extremely large Arecibo Observatory radio telescope in Puerto Rico, the Earth’s radio and televisions transmissions would only be detectable at a distance within 0.3 light years. Therefore, unless the advanced aliens used highly directed transmissions, we would likely not detect them. In addition, if the advanced aliens compressed their data, similar to data downloads from the Internet, the compressed data would appear as noise to us. In addition, advanced aliens may be using frequencies we are not monitoring or do not penetrate our atmosphere. The list of technical hurdles is numerous. Their sheer number and complexity has cast doubt on the entire SETI methodology. Critics believe the SETI efforts are futile, since the technical hurdles regarding the interception of advanced alien radio transmissions are enormous.
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