Out of the billions of stars it would seem some would have planets with the same conditions that gave rise to life on earth. Considering the huge number of solar systems, it seems likely that many extra terrestrial civilizations have evolved throughout the universe. By chance many civilization would have started before earth's civilization. Those early starters would likely be more technically advanced than we are. So why haven't we gotten radio messages from alien civilizations? There are several apparent possibilities.
Our history has examples of two cultures coming together with the more advanced group overpowering and subduing the weaker group. The clash between Europeans and Native Americans is an example. Perhaps aliens on planets in other star systems are keeping silent to escape the notice of more advanced civilizations who might have reasons to take advantage of a weaker civilization.
Another reason for no alien messages is the possibilty that once a civilization becomes sufficiently advanced to communicate interstellarly, the civilization has the technical capability of destroying itself through a variety of means. One of those self destructive mechanisms gets triggered before the civilization is in existance long enough to send any significant amount of interstellar communications.
A third possibility is that the cosmos is awash in interstellar communications from any number of civilizations. Our communication technology is based largely on electromagnetic radiation - radio waves. We know how to use lasers to transmit information. We also have the knowledge to use pulses of atomic particles to send information. If seems very likely that there are other methods of transmitting communications that we have no knowledge of. Perhaps one or more such advanced methods are much more effective modes of signal sending and are being used on a large scale throught the universe. We just are not aware of the messages.
Sending and receiving information to distant civilizations could be extremely beneficial to humanity. Civilizations somewhat more advanced than ours could be expected to have knowledge that would be of great benefit to us. That knowledge could include ways to efficiently collect the energy of sunlight and how to use that energy for transportation and other uses. We might learn of technologies that could be used to prevent human diseases and technologies that would in other ways greatly improve our lives.
Should we send out radio messages beamed toward other earth-like planets to elicit an exchange of knowledge? Should we remain silent, not disclosing our existance to any more advanced civilizations that could have a reason to exploit us? Just as with any other complex issue, there are proponents of both opposing positions. It seems that no reason that decides the issue has thus far been proposed.
An argument in favor of sending information: Any extra terrestrial civilization approximately at our level of advancement would not be technically able to cause us harm. Interstellar distances are so great that travel from one solar system to another is not possible. A civilization far enough advanced to be capable of traveling such distances, would likely be able to take care of their own concerns without intervening in our affairs.
The argument against sending messages: Civilizations farther advanced than ours that are located in solar systems a few tens of light years away might be capable of travel to earth. We could be the closest likely prospect for their relocation or for expansion of their homeland. They might regard us as we regard lower life forms - which might include the attitude that it would be okay to use a device such as a neutron bomb to exterminate humanity so they could easily populate the planet.
There are operations taking place to listen for extra terrestrial communications. Funding has largely been from private individuals and organizations. Governments have at times also provided funding. No signal has been detective that has conclusively been from an alien intelligence. It seems wise to continue listening and there are presently in operation several systems listening for signals of extra terrestrial origin. Several outgoing signals have been generated and sent out in hopes that they will be detected by far away civilizations. Those few signals were largely symbolic. No sustained attempts have been deployed.
A good souce of a basic overview of this topic is the wikipedia article titled SETI.
Alan Detwiler grew up on a small farm. The weather and the natural world are very much a part of living on a farm. On a farm, everyday observations demonstrate how plants and animals grow and develop and how weather and climate interact with living things. Alan and anyone growing up a farm knows that our food supply is very much dependant on how much it rains, when it rains, and how warm or cold it is.
Genetics and disease are topics of special concern to anyone living on a farm. Farm crops and farm animals are not the plants and animals of the wild. They have been genetically altered by human intervention. Farmers are especially aware of those differences and how genetics produce those differences. Farm animals are in constant threat of disease. It is not uncommon for farmers to loose substantial numbers of their animals to disease.
Farm living, plus an interest in science gave Alan the background for writing Earth's Edge which examines drastic global warming, epidemic, and future science. Those two threats are very serious and are perhaps likely to drastically affect our lives. The consequences of either of those calamities are bound to be unpleasant, but why react with anxiety? Wouldn't a better reaction be to take action to be prepared and feel good that you have done so?
Alan writes to explore ideas and to discover ways to more enjoy life. His method is to use the ideas of others, add anything his own experiences and observations can contribute, and finally to use imagination to add new ideas for appreciating all that is good. His hope is that the readers of his books will do the same.
Alan is the author of the ebook, Earth's Edge, a speculative science fiction novella describing a pandemic, global warming, future science, and alien contact. Earth's Edge is available as a Kindle ebook at http://www.amazon.com/dp/B004UMP1HQ/ and as a Nook book at http://search.barnesandnoble.com/Earths-Edge/Alan-Detwiler/e/29400123798...