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I was listening to Jeff Kuhn's talk on SETI's Colossus telescope project.


He explains his theory that a civilization living somewhere the galaxy would want to hide, and thus would shortly learn to avoid broadcasting radio signals all over the galaxy, so as to avoid attracting attention (presumably to avoid inter-stellar predators).

Then he comes up with a great idea; due to the second law of thermodynamics, they would have to dissipate heat-energy, and thus, one can detect them anyway, because they have no way to hide this heat-energy. This, particularly when they are a Type I civilization, and nearing Type II; in this case, to avoid global warming, they would capture and use almost all solar energy, and emit an equivalent amount heat-energy.

Thus he proposes a telescope to focus on single stars, which would be capable of detecting this heat-energy (by the distinctive infrared light emmited).

My question:

If a civilization was smart enough to hide all of its radio signals, wouldn't they know that they cannot avoid emitting heat-energy? Thus their predators would be able to find them anyway, and thus, it is pointless to hide the radio signals?

Therefore, we should already be seeing their radio signals, and this telescope is being built for a theory with some holes.

Note: I am not suggesting that the telescope shouldn't be built; I think it could have other very valuable uses, and it would also be interesting to eliminate the theory if it is indeed incorrect (or prove it correct ... somehow). I am just asking if there might be justifications for the theory, in light of my point-in-question, which I am missing.

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The real reasoning has nothing to do with some civilization "deliberately" hiding its radio emissions. Rather, the problem is that we can not expect some other civilization to do something we would not do ourselves.

It makes no sense whatsoever to radiate large amounts of energy into space when there exist other, more economical alternatives. Radio transmitters circa 1911 required whole dedicated dynamo machines to run at abysmally low efficiency - these days we are using tiny battery powered devices with directed radio beam steering and adaptive power minimization as to not transmit a single joule more than absolutely necessary to get the data through to intended destination.

Another problem arises from the fact that most of the "radio SETI" effort to date was concentrated around the "cosmic waterhole" (the frequency of interstellar hydrogen emission). This is a reserved frequency here on Earth, so nobody broadcasts on it. Common sense suggests that aliens would probably do the same - after all, we expect them to have developed radio astronomy as well. Unfortunately, listening on any other frequency will probably pick up locally generated broadcasts first and completely mask the weak alien signal.

Given the above, what choices are we left with? One would be to construct a large radio telescope somewhere Earth radio emissions can not reach - the far side of the moon or even a trans-solar location on the Earth orbit come to mind. Unfortunately, such project, while doable, is hugely expensive.

The other approach is to develop "distributed" telescopes which can be built gradually on low budget and to develop techniques to cancel the local noise. For low frequency radio telescopy such project is already ongoing:

For infrared, we've got this "Collosus" proposal, but place our hopes on JWST (

And we don't expect to see much in visible light for all the obvious reasons.

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