I learned this today. Signals from intelligent life are so difficult to hear because of the sheer vastness of space and the fact that we change the technologies we use.
It is possible to look at a distant planet and reason that it has intelligent life because of the gases that are coming off the planet. There are gases that wouldn’t be there if something on the planet wasn’t replenishing them. Oxygen is a good example. Oxygen on Earth is only there because life is producing it. However, the problem with this is that you don’t have to have life to create oxygen. If a planet had water in its upper atmosphere, ultraviolet light from the planet’s sun could split the water into hydrogen and oxygen and the hydrogen could escape into space, leaving the oxygen.
This is why scientists hope that alien life will send out another type of signal that could be in the form of radio waves. These could be an intentional signal or just information pollution. For example, Earth sends out two kinds of signal. In 1974, an intentional signal was beamed into space from the Arecibo Observatory in Puerto Rico. It was a radio wave that contained information about Earth and humans encapsulated in a binary code. It was beamed toward the M13 globular cluster, which is 25,000 light years away.
The second kind of signal that we send is constant and from all over the Earth. Every radio and TV signal sent since the first radio program in 1906 has been travelling out into space. This is a bubble of rapidly expanding information noise.
There are two things that we can learn from this that show how difficult it will be to find a signal from an alien civilization. The first is that radio waves travel at the speed of light, which is incredibly fast, but the universe is simply enormous. The first radio program broadcast has been travelling into space for 116 years. It has left our solar system, but it has barely crossed the Milky Way. There are 59,722 stars within 100 light years of us. There are 100 billion stars in the whole Milky Way. The universe is just so big that any signal from another intelligent life would have to travel so far that the alien life that broadcast it may no longer exist when it is received.
The second problem is that the strength of these radio waves is not enough for them to be picked up as intelligent signals. Over the vast distance, they will weaken to become the same as the cosmic background radiations. The signal sent from Puerto Rico in 1974 was a much stronger radio signal, but it was concentrated in only one direction. If there is nothing to receive it, it will not be heard. And these are the problems that people listening for Signals from outer space have to deal with.
There are two other problems that need to be considered in regards to signals from an alien planet. Firstly, civilizations don’t use radio as a form of communication for very long. We started using it in the late 1800s and we are already cutting down on the technology because fiber optics and other forms of technology are far more reliable. If all civilizations do this, then there may only be a two-hundred-year window when we can detect radio signals. Before that and after that the civilization may be silent. The chance that a civilization evolved at just the right time to broadcast signals that we can pick up now is so infinitesimally small as to be almost zero.
And, secondly, why would a civilization broadcast such a signal. To transmit a high beam of information to a distant solar system would require huge amounts of energy and organization. This is incredibly unlikely. After all, we are capable of doing it but we don’t. Why would we expect other civilizations to?
It is far more likely that our first contact with alien life would be probes. We cannot send people to the nearest stars because it takes too long, but if a camera was light enough and could be given enough acceleration, it is possible that it could reach the closest stars to us in thirty years or so. It could then beam back pictures. That is a project that is currently undergoing planning. If we are at the stage when we can do this, perhaps other civilizations have or will at some point, making it most likely that our first contact with another civilization would be observing their probes. What then? Who knows.
So, radio signals from other intelligent civilizations are difficult to detect because they are just too far away and the chances of them evolving to broadcast at the exact time we listen is too remote. And this is what I learned today.
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Photo by Derpy CG: https://www.pexels.com/photo/light-sea-art-space-7462340/
Sources:
https://en.wikipedia.org/wiki/Breakthrough_Starshot
https://en.wikipedia.org/wiki/BLC1
https://arxiv.org/ftp/arxiv/papers/0707/0707.0011.pdf
https://seti.berkeley.edu/FAQ.html
https://www.livescience.com/59153-how-to-search-for-extraterrestrial-life.html
https://www.seti.org/seti-institute/project/details/broadcasting-message
https://thenextweb.com/news/yes-exoplanets-can-have-oxygen-without-alien-life-syndication