Re: the end of fermi's paradox?

From: Philip Goetz (
Date: Fri Jan 05 2007 - 13:13:32 MST

On 1/5/07, John K Clark <> wrote:

> Be honest now, does this excuses put forward to explain away the lack of
> large scale engineering really strike you as credible? If you knew ET
> existed but had never seen the night sky is this really what you would
> predict the sky would look like?

Hmm... I would suppose that ET would use the energy of stars in some way.

ET might build big Dyson spheres around stars. But the problem is
that usable energy is the difference between something's energy, and
the background energy. If the Dyson sphere doesn't radiate energy as
rapidly as the sun inside it does, it will build up heat, and thus the
energy will be less usable. Someone made a similar point about
computation; that the energy needed to perform computation is an
increasing function of the background energy.

So ET needs to let heat radiate away from the star. So it's still
going to look, to the naked eye, pretty much the same.

ET's sun/Dyson sphere might radiate in different wavelengths than we
expect from a "wild" sun. The sphere would be composed of some
different substance, maybe a metal, that would emit different
wavelengths, perhaps.

I'm not aware of any stars that emit radiation at unexpected wavelengths.
However, if ET wants to make most efficient use of its star's energy,
I suspect that it will radiate heat like a black body. And that is
exactly what stars do. The spectra we receive from different stars
differ, AFAIK, only in ways caused by the stars' different
temperatures, their different velocities with respect to us, and by
absorbtion of some wavelengths by gas around the star and by
interstellar dust. So the radiation we see coming from stars is
exactly what we would predict to come from a star computer.

ET might modulate the radiation to use it as a form of communication.
The light coming from a star or sphere could be modulated so that it
would be a broadcast station. But the data being broadcast would be
compressed, and the more efficient compression is, the more data looks
like the highest-entropy distribution. So this modulation probably
would not make the radiation look any different to us. It would
probably be modulated at frequencies or resolutions too fine for us to
detect, in ways that would appear random if we detected them.

We could ask whether ET's local energy usage would vary over time. If
so, the star's emission would vary over time. I suspect that this
would not happen; that so much computation would be going on, and
that, since the cost of computation (in their currency) would likely
go down if demand went down, that the local energy usage (in their
star system) would stay pretty constant over time.

They might choose to release their star's energy at a different rate
than a "wild" star. So an ET-colonized system might appear to have
stars of a different type than that predicted in the wild. (White
dwarfs would be star computers running very slowly, for instance.)
This would be a useful thing to look for. I don't know if anyone has.
 The predominant SETI approach, which is to assume that ET has exactly
our level of technological development, give or take a century, is
dubious IMHO.

So, the short answer to your question, John, is "yes". The night sky
looks pretty much as I would predict it would, knowing ET existed.

- Phil

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