[ExI] fermi question alive and well

[John Clark]

On Thu, Mar 28, 2019 at 11:56 AM Stuart LaForge <avant at sollegro.com> wrote:

> *Looking for waste heat in the sky might be like trying to find needles
> in a haystack.*


Not if it's a type 2 civilization, and a type 3 would be obvious from
anywhere in the universe.

> *So how precisely do we distinguish between brown dwarfs and Dyson
> swarms? *


A star needs at least 75 Jupiter masses (or 8% of the sun's mass) for it to
undergo nuclear fusion, a Brown Dwarf is less massive than that and thus
would be a lousy power source because it is not a star.  The smallest true
stars are M class stars but they can't be Dyson Spheres. If you plot the
total energy output of a star against its color (principle wavelength
outputted) you get a Hertzsprung Russell diagram. This plot has been made
for many millions of stars and the space on the diagram where Dyson Spheres
should be is a big blank, no star has the needed combination of luminosity
and color. For example a star that had the same luminosity as our sun but
radiated most of its energy in the infrared would be a very strong
candidate for being a Dyson Sphere, but nobody has ever seen such a thing;
there are infrared stars but all of them are either thousands of times less
luminous than the sun or thousands of times more luminous. In ever star so
far discovered the relationship between luminosity and color can be
explained with the standard theory of stellar evolution with no need to
resort to ET.

Hertzsprung Russell Diagram
<https://cdn-images-1.medium.com/max/1600/0*k1vaMquGoiOVBiOE.jpg>

>
> *When it comes to ET, I don't think we know precisely what we are  looking
> for or how to go about looking for it.*
>

We are looking for a civilization that makes use of high frequency light
and outputs low frequency light as a waste product, and we know exactly how
to look for it, with infrared and microwave telescopes, but we've never
seen even a hint of it.

John K Clark
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