Little Green Men revisited.

Offset Gregorian antenna used in the Allen Tel...
Offset Gregorian antenna used in the Allen Telescope Array, a radio telescope at the University of California at Berkeley, USA. (Photo credit: Wikipedia)

I’m going to continue the LGM theme. I don’t plan on doing multiple posts on a single subject very often, but there were some things that I want to add to my previous post.

It seems to me that the difficulties of point to point interstellar communication are such that it makes it unlikely that we will be able to find LGM by searching for intentional broadcasting or unicasting of signals, for the reasons that I raised in the previous post. There are other reasons that I haven’t touched too.


Radio Transmission Towers Atop Mt. Wilson
Radio Transmission Towers Atop Mt. Wilson (Photo credit: FastLizard4)

One big question is one that occurs to me, probably because I am a computer professional. Why would a civilisation want to be found? If you broadcast something on the Internet, you attract all sorts of undesirables trying to access your systems, your data, your private stuff.


US Mail
US Mail


Some of the undesirables might be governments of course, depending on your point of view and political affiliations. On a more personal level, people have told friends on social networking sites of a private party and hundreds of people have read this and gatecrashed. As a consequence the party gets overrun and the house gets trashed, the police get called.


A party at Colorado State University -- yeah, ...
A party at Colorado State University — yeah, that’s a riot. (11pm on April 27) …item 2.. a combination of Woodstock, ‘Animal House’ and Girls Gone Wild. (08/30/2011) … (Photo credit: marsmet553)

If you broadcast to the Universe the same sort of thing might happen. The LGM might not be friendly and with benign intent. Why would you risk attracting undesirables? Of course, the civilisation sending the signals may not be benign. Such a signal could be a honeypot, designed to attract unwary civilisations.


Lavender Attracting Bees
Lavender Attracting Bees (Photo credit: rutthenut)

So, it seems that it might be unwise to respond to alien signals. Murray Leinster’s novelette “First Contact” explores the issues, albeit in a first contact away from the origins of the contactees.


Two technologically equal species are making first contact in deep space. Both desire the technology and trade the other can provide, but neither can risk the fate of the home planet based on unfounded trust.

Another danger would be encountering a more advanced civilisations. In all cases where this has happened on earth, this has always resulted in disaster and absorption of the less advanced civilisation. This usually starts with disease, both sexual and non-sexual, which may be common in the more advanced civilisation but which the less advanced civilisation has no defence against. However, ultimately it is foreign ideas that cause the destruction of the less advanced civilisation and there’s no vaccine against that.


With masks over their faces, members of the Am...
With masks over their faces, members of the American Red Cross remove a victim of the Spanish Flu from a house at Etzel and Page Avenues, St. Louis, Missouri. (Photo credit: Wikipedia)

So, maybe we should avoid alien civilisations, at least until we can be sure that contact will not harm us. But how will we know that they are there, so that we can avoid them? Can we detect them before we blunder into something we can’t handle?


One possible way would be to observe the rate of emission of radio waves from a stellar system. If the electromagnetic spectrum emission in the wavelengths that are used for TV and radio is unusually high, it may indicate that a civilisation exists in the stellar system.


United States radio spectrum frequency allocat...
United States radio spectrum frequency allocations chart as of 2003 (Photo credit: Wikipedia)

So if an otherwise unremarkable star should suddenly (in astronomical terms) start emit radio waves it might indicate that an advanced civilisation might have discovered radio on a planet orbiting the star. Or, rather, that it did discover it, a long time ago. If we did discover such a star (and I’ve no idea if it is remotely possible to detect such an anomalous production of radio waves), it may be thousands of light years away, which means that the waves have been on their way for thousands of years.


A supernova remnant about 20,000 light years f...
A supernova remnant about 20,000 light years from Earth (Photo credit: Smithsonian Institution)

If we then send an expedition to a star at, say 20,000 light years, it would take us 20,000 years at least to get there, and probably many, many more. That 40,000 years that would have passed since the wave were generated and no civilisation that we know off has lasted for more than a few hundred. They might have all died out or reverted to savagery or evolved into something that we can’t understand. We might have done similar in the 20,000 years that it would take to get there.


Cycle of paintings History of civilisation in ...
Cycle of paintings History of civilisation in Poland. (Photo credit: Wikipedia)

It’s unclear why we would want to contact them anyway. A conversation that takes millennia would be a strange one. About all we could say would be “Hi from Earth. Here are some snaps from our family album”. Of course, when we decode their signals, as XKCD notes, we would most likely find that they are unintentionally broadcasting the alien equivalent of cheesy TV shows like “I Love Lucy” or contrived  “reality” shows. After all, that’s what we have been broadcasting.


Fox Reality Channel
Fox Reality Channel (Photo credit: Wikipedia)

All of the above is moot as is my previous post if the LGM do not exist. The most famous attempt to estimate the likelihood of there being other civilisations other than ours out there is the Drake Equation. As I mentioned in my previous post, this equation irritates real mathematicians, since it is not derived from anything, but is merely a string of terms strung together to look like an equation. Plausible values for the components of the equation can give answers ranging from almost zero (there are no other civilisations other than ours in our galaxy) to 38 million or more.


"Where is Everybody?", or "Why ...
“Where is Everybody?”, or “Why am I so Lonely?”: Fermi’s Paradox / the Drake Equation, Logocentrism and Gabriel Garcial Marquez (Photo credit: timtak)

The SETI Institute concludes that “The importance of the Drake Equation is not in the solving, but rather in the contemplation”. Certainly the values of most of the terms of the equation are not really known, though estimates can be made. Investigation of one term may throw up information which throws some light on the other terms.


Drake Equation
Drake Equation (Photo credit: Merritt Boyd)

The crucial term is, I feel, “L”, the length of time that a civilisation will be able to and desire to make radio signals. Looking at how we have used radio waves, there seems to be a trend from the low end to the high and very high end of the broadcast spectrum. Early experiments and usage was in the VLF (very low frequency) band, but the frequencies used for most radio broadcasting moved to medium frequencies. TC, both digital and analog use VHF (Very High Frequencies) and UHF (Ultra High Frequencies). Satellite broadcasts use even shorter wavelengths (higher frequencies). So our radio usage has changed over the 100 years or so that we have had radio receivers and transmitters.


Aerials (Photo credit: ettlz)

All in all I think that it is unlikely that we will contact LGM. We may stumble over some, if we ever manage to go Interstellar, and it may be that some as yet unknown technology might enable us to easily spot advanced civilisations from a distance, so that we can signal or visit, but although I applaude the SETI effort I don’t think that the search will be fruitful.


SETI@home logo
SETI@home logo (Photo credit: Wikipedia)

It may be that we can never visit other stars because no way exists for us to do so. In a story that I once read, but can no longer remember the name of, one character referred to star systems as “God’s test tubes”. I recall that at the end of the story the human race had just found a way to escape its “test tube”.


A,B,C - test tubes
A,B,C – test tubes (Photo credit: Wikipedia)
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Little Green Men


SETI is short for “Search for Extraterrestrial Intelligence”, or in other words, a search for the “Little Green Men”. The main thrust of SETI is to examine the light from other stars for signs of intelligent life, often on well known wavelengths such as wavelengths near the “water hole“,  a section of the electromagnetic spectrum associated with hydrogen and hydroxyl ions emissions lines. Hydrogen and hydroxyl together make water and water is supposedly necessary for life, so the thinking is that technically advanced life would possibly use this frequency to initiate contact with other civilisations.

Denomination of atomic shells and of character...
Denomination of atomic shells and of characteristic emission lines (Photo credit: Wikipedia)

The trouble is that this is just a guess and there are many possible frequencies that might seem plausible to technically advanced civilisations. If the little green men are not made of water, as we essentially are, they might pick a different frequency band to search. XKCD, my favourite web site has a cartoon which makes this point:

XKCD - the search
The Search

Suppose a remote civilisation did decide to broadcast in that waveband. If they are just announcing their presence, they would need to broadcast their signal in all directions, or they would need to pick out some likely looking star systems and send a directed signal in just a few directions.

If they broadcast in all directions, the power that they would require would be huge. The problem is that in any average stellar neighbourhood, there aren’t many stars. In the sun’s neighbourhood there is an average of 0.004 stars in a cubic light year. So the probability of finding a star one light year from a star in a neighbourhood like the sun’s is four in 1,000. If you look two light years out from the star, you will enclose a volume of eight times the volume of the search area up to one light year, meaning that the probability of finding a star in that volume is 0.032. You would need to look further than five light years out for there to be a fifty-fifty chance of finding a star in that volume, which would be 125 time the size of the original volume of one cubic light year. At 15 lightyears, there would likely be at least 10 stars within the search area.

Globular Cluster NGC 6397
Globular Cluster NGC 6397 (Photo credit: Hubble Heritage)

That’s all very well, but most if not all of these stars will be of the wrong type to support planets of the type that will have free water on them. In fact it is extremely unlikely that a suitable star with suitable planets can be found within, say 200 light years of our hypothetical advanced civilisation. (That’s an out and out guess, but see later).

The remnant of a supernova located 6000 light ...
The remnant of a supernova located 6000 light years from Earth in the constellation Taurus. (Photo credit: Smithsonian Institution)

The trouble is that the signal gets weaker and weaker the further it travels. If you use the signal strength at one light year as the yardstick, the strength is reduced to one quarter at two light years, one ninth at three light years and one sixteenth at four light years and so on because the signal is spread over an area proportional to the square of the distance from the source.  So if the signal strength at 200 light years will be 1/40,000th of the strength of the signal at one light year. If the signal has to travel further it will be correspondingly weaker.

My second attempt at illustrating the Inverse ...
My second attempt at illustrating the Inverse Square Law. S represents an ideal source of electromagnetic radiation and A represents an arbitrary segment of the surface of a sphere of radius r. (Photo credit: Wikipedia)

So likely systems are rare and the signal strength will be weak at the distance of a suitable system. This means that the signal needs to be very strong to be detectable.  Very strong means lots of energy. To broadcast to the Universe at large the civilisation would have to expend a considerable amount of its available energy to only potentially contact another civilisation. Imagine trying to get a project like into the planetary budget!

Clark's accompanying book to Civilisation
Clark’s accompanying book to Civilisation (Photo credit: Wikipedia)

So the hypothetical civilisation is probably desperate to make contact. That may be because either they are in trouble themselves, or they want to warn all local civilisations about something. They are unlikely to do it on a whim, as they must know that the chances of success are pretty close to zero. There’s a faint possibility of a sort of “vampire civilisation” that must prey on other civilisations and so chooses to broadcast in the hope of finding a new victim. I consider that highly unlikely, since as I said the chances of success are nearly zero, and such a civilisation would need to find a new host in a relatively short period of time, astronomically speaking.

Mark of the Vampire
Mark of the Vampire (Photo credit: Wikipedia)

If a broadcast signal is very unlikely to find a receiver, how about a directional signal, maybe driven by a laser. The spread of a laser signal is much less than a broadcast signal, but the signal does spread. An advanced civilisation would still have to divert significant resources into sending the signal but it might be possible.

The civilisation would have an issue, though. If they wanted to get a signal to us and they used a ground based laser, their ground station would be in line with us once each local day, and our receiver would be in line with them once in every day too. Since it is unlikely that the day lengths would match, so the window for transmission would be short, even down to a minute or less.

Window of opportunity
Window of opportunity (Photo credit: GioPhotos)

The hypothetical aliens would most likely opt for an orbital laser. That could be pointed in our direction all the time, for every hour of every alien day, unless some local object got in the way. However we have a problem now. We would need to detect that a signal is coming from a point in space, in spite of all the extraneous noise that might mask it, and then we would need to concentrate our resources looking in that direction for a length of time. The hard part would probably be convincing ourselves that a signal is from LGM (little green men).

Littler Green Men
Littler Green Men (Photo credit: JD Hancock)

There’s an equation that purports to estimate the possible frequency of extraterrestrial civilisations, called the “Drake Equation”. It’s the sort of “equation” that gives mathematicians the heebie-jeebies, since it is derived from nothing and nothing is derivable from it. XKCD cruelly lampoons the equation, and while I don’t much like the sentiment expressed, I can understand why the Drake equation raises his ire – it is ad hoc, probabalistic, and presents as constants things which are fundamentally unknown. In other words, your guess is as good as mine, and both will fit comfortably in the Drake equation. I may return to the equation in a later post.

XKCD - the Drake Equation
The Drake equation as extended by XKCD


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