They just don’t strike me as something you’d really want to build, for a whole variety of reasons.

So, to clarify – you’d have to wonder how intelligent ET is if you can’t decode the message. We’ve thought about how to encode a message in such a way that it’s reasonably easy to decode without any knowledge of who or what we are.

(OK, I’ve only read as far as the mid-twenties so far, so there might be something enlightening that I just haven’t reached yet.)

First, IIUC, nearly all natural sources of radio waves have broad bandwidths. Artificially-produced radio waves (except in perhaps the first 20 – 30 years of our use of radio) have narrow bandwidths. Certainly a suffciently narrow-band signal would be worth following up with additional observation.

Second, if a radio signal encodes information, there are only a very few ways of varying a radio signal. On/off keying, for instance (as in Morse code transmissions) would be pretty obvious, even if we couldn’t hope to decode the message’s content. Similarly, modulation of the frequency or amplitide of a signal would be obvious. A narrow-band signal with some kind of modulation on it would be a pretty good sign of ETI, but you’d have to question how intelligent ET is. After all, we’ve considered how we might encode a message to transmit to the stars, and we’ve concluded that the encoding would need to be pretty obvious (how about a repeating sequence of bits, where a positive frequency deviation represents one and a negative frequency deviation represents zero, in which the number of bits is the product of two primes – with this, we have encoded an image).

What are rocks made of? Metal and semi-metal oxides. Plus, only the crust of planets is rocky – the interior of the Earth is basically a big ball of Iron and Nickel. This is because early in Earth’s formation when everything was molten, the heavier elements sank down to the bottom and the lighter ones (oxygen, silicon, etc.) floated on top.

Plus, metal isn’t even the best construction material. Carbon fullerenes and graphene are superior building materials and carbon is relatively abundant in the Universe.

The main objection to a Dyson sphere is, as Chris said, the sheer *amount* of material you’d need. Considering the solar system, you’d need to break up every planet to get enough material for even a thin shell.

However, it’s quite possible that other star systems out there have a wealth of building materials. We’ve seen systems with a large number of huge planets. Plus, there’s always the possibility of towing in material from outside the star system.

Personally I think it’s likely that at least a few alien civilizations have built Dyson spheres, but probably not enough for us to have a high chance of detecting.

I think it is an acceptable margin of error because it’s within a single order of magnitude.

Having in mind that it was possible that the probability was around 0.001 or 0.0000001 (or even less… we had no idea after all), being sure that the probability is between 0.1 and 1 is pretty good indeed.

And yet SETI can’t find ET.

With all due respect to the efforts of the SETI people, right now SETI is akin to a colony of relatively intelligent ants trying to discover the existence of humans by trying to sniff the pheromones in the cubic metre of air around their nest.

Bear in mind that for us to find a Jupiter-sized planet with a semi-major axis similar to Jupiter itself (one revolution every 11 years), we’d need up to 11 years of non-stop observation, not including duplication which would add another decade. Neptune takes over 160 years per revolution. Only two planets in our system could be discovered through current observation methods in reasonable time. Mercury and Mars are too small; everything else is too far out. Not complaining about the efforts, which are remarkable, but we gotta admit we’re still guessing here. If there’s one thing to be learned about Fomalhaut b, it’s that some planets orbit stars at over 100AU — more than twice Pluto’s distance from the Sun.

[I'm trying to catch up with all the news that's been released this week while I was off lecturing in Texas. This is Part 2 of a few articles just about exoplanets. Here's Part 1, and here's Part 2.]

This is part 2? I thought it was part 3!

(Sorry.)

Great news & fascinating field of astronomical inquiry. I love reading about this stuff. Thankyou BA.

Will we ever leave this beautiful island world and strike out across the the vacant ocean of space in search of new worlds to conquer? Probably, since as a species we seem to have an innate wanderlust. Long before technology made ocean travel safe and practical, humanity had spread almost over almost the entire Earth. We are more widespread, I believe, than any other single species. It seems unlikely that mere distance will stop us from spreading further, some day.

@36 Brian
The Dyson Sphere in ST:TNG was made of a carbon-neutronium alloy.

Although another big problem is where to get all the material. Assuming a sphere the size of the Earth’s orbit and 1 m thick, this would need a volume of material of 2.7 x 10^23 m^3. Now if you made it out of iron with a density of 7860 kg/m^3, you would need 2 x 10^27 kg of iron. The Earth weighs 6 x 10^24 kg so you’d need about 350 Earth masses of iron. Possible but way outside our current capabilities.

Also, one thing about the Dyson objects that has always bothered me. They are supposed to use planetary resources to create a thin, strong, stable shell. However metals are by far the most suitable material for such construction. AFAIK most of the material in most planets is rock. Rock is strong in compression but very weak in tension and entirely unsuitable for creating thin shell structured objects. What am I missing? Unobtanium?

@16. Ganzy,

There were numerous Star Trek Voyager episodes exploring these themes. The series adopted the use of a Temporal Non-Interference rule to explain why the time travellers were not normally seen/known.

http://www.lasalle.edu/~didio/courses/hon462/hon462_assets/sound_of_thunder.htm

Barring the theoretical space plus (or minus), ie star trek etc, realms used for communications, We humans have only the electromagnetic spectrum in which to draw from. This includes radio, light and then the higher freguencies of gamma and Xray. All of which we do scan to a degree and should someone be communicating in this band, I feel what we would notice something interfering with our own data in use.

Note that any advanced communications will be limited to certain frequencies as mimics by natural sources will swamp out or degrade the signal over long distances of travel. We try to focus our receiving equipment to be most sensitive over the bands where there is the least amount of interstellar noise generated. (of course SETI has giga band receivers being used to try to keep an open mind on the search.

I was thinking that with the increase of potential stars with planetary bodies, figuring out where to point becomes less of an issue, and distance and time of transmission is more relevant. (I think….)

If you really wanted to overcome the distance and possible amount of data “particles” reaching us, maybe we should look for AM or FM modulation in Tachyon particles….

Hmm. how to build a Tachyon generator without a lot of mass.

and while Dyson Spheres or stellar beacons are visible over interstellar distances, again we haven’t searched much for these. And there are likely more efficient means of energy production – black holes anyone?

In agreement with the last sentence here, I actually think Dyson Spheres are probably very unlikely. If you really think about what a Dyson Sphere entails, you realize that at the heart of the conception lies a glaring anachronism.

The energy generation/collection technology envisaged for it is decidedly 20th Century (passively collecting stellar radiation via surface area absorption) while the construction and engineering technology needed to actually build such a thing is well up in the 30th Century range.

In other words, if anyone out there has the capacity to build a Dyson Sphere, it is highly unlikely that they’re going to need to use anything so crude.

So unless they’re building it as an art project, or children’s toy….

All else is secondary, tantamount to party conversation, unless you don’t mind the human race being wiped out.

The human race is likely going to be wiped out no matter what, eventually. But we’ll have a longer run if we get off this rock. Possibly a MUCH longer run.