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Contacting Aliens

Apr 30, 13 Contacting Aliens

Films such as Contact, one of my personal favorites, depict astronomers searching the skies using sophisticated radio telescopes, hoping to hear from intelligent life elsewhere in the Universe. In fact, virtually all contact with aliens seems to arrive as a radio signal from outer space, at least according to Hollywood. But, is this necessarily what we should expect?

In one sense, this seems to be contrary to what science would suggest. Specifically, the amount of information that can be transmitted in a fixed amount of time — known as bandwidth — is proportional to the frequency of light used. Radio waves, being the lowest frequency light, would then seem an odd choice.

X-rays and gamma rays would seem more logical as they reside in the opposite end of the electromagnetic spectrum. And strictly speaking this is certainly true, but there is more to consider than just bandwidth.

Specifically, we must also consider the ability to transmit and then detect the information, and finally, whether or not it would even be able to travel across the galaxy.

Radio waves are relatively easy to transmit and receive. We use them to send out radio and television signals, and communicate between all matters of communication devices. They also have the useful property of being able to propagate through our atmosphere without being absorbed or deflected.

In contrast, our atmosphere will absorb X-ray, gamma ray and even optical light to some extent. And the higher energy radiation is quite difficult to create, and even more challenging to detect. Therefore, the highest energy photos would be a peculiar choice as a signal transmitter by alien races.

But supposing an alien race of superior intellect, they may not be so concerned about our ability to accurately detect their gamma ray signals. Maybe they are only interested in communicating with us if we are of sufficient technological ability that we can manipulate gamma rays with ease. Certainly a reason to take a closer look at the data from the Fermi Gamma Ray Telescope, if you are so inclined. (The data is free to download and analyze.)

Given, though, that it is such a challenge to produce and receive high-energy radiation, we’ll assume for a moment that aliens would use other wavelengths of light. So, would optical be preferential to radio?

Probably not. The main reason is that optical light is easily scattered and absorbed by our atmosphere. Moreover, it is easily absorbed by interstellar gas and dust, making it difficult to penetrate various parts of our galaxy. This would severely limit the percentage of the galaxy that we, or other alien race, could potentially talk to.

So, while it seems strange, on one hand, that radio is the default choice for communications from potential alien races, the alternatives pose greater problems. Besides if we are really looking for intelligent life, wouldn’t we expect them to be about to get around the bandwidth problem?

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3 Comments

  1. Anonymous /

    You seem to be forgetting something quite obvious, Satellites. As they would provide a interface between deep-space and ground communications, thus eliminating the atmospheric degradation imposed by ground receivers, therefor solving the issue in the same way I bet an alien civilization would have.
    My proposal is a moon based communications array for deep space listening :-P

  2. Anonymous /

    What a neat idea. Being only a novice in these matters, this idea of using the moon a base for a communication array sound more doable despite the logistical problems of getting everything we need for the project on the moon. Granted we don’t have to develop the rocketry, but even if we have the launch technology it still remains a hard sell as the cost of getting everything on the moon would be enormous.

  3. Anonymous /

    But satellites have their own problems. They have very small collection areas, thus making it more difficult to find isolated signals. Also, they can miss some of the radiation because of the detection methods that we have to use, so you could, in theory, miss part of the message. (This is a bigger problem for gamma ray than for X-ray actually, but you get the point.) If we could build bigger space based detectors this would be less of an issue, but with cost considerations, and un-availability of larger rockets, this is simply not feasible. So unless we get really lucky, an instrument like the Fermi Gamma ray Telescope is unlikely to find a signal from aliens.

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