[ExI] Fermi question, was is a FTL drive a dream

[Anders Sandberg]

On 2011-12-24 09:35, Kelly Anderson wrote:
> Uh, maybe dumb question here... but how would we tell a star was
> dimmer unless we measured the brightness before and after the
> civilization had created their Dyson swarm or whatever it was that
> dimmed the star? Is there a way to tell it's dimmer than it should be
> without having measured it's brightness before?

Yes. Stars shine with (roughly) a blackbody spectrum, telling us their 
temperature. Normal stars fall into certain curves on the 
Herzprung-Russell diagram,
http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram
which relates their absolute magnitude (total energy output) to their 
temperature. If you Dyson a star it will become dimmer (less magnitude) 
but the temperature will be unchanged (same color): it will move 
straight downwards. So if you see a star outside the big clusters, that 
could be an indication of a partial Dyson shell.

In addition, a Dyson shell will re-radiate the energy as deep infrared, 
so the next step is to check if there is a huge excess of cold blackbody 
radiation.

http://home.fnal.gov/~carrigan/infrared_astronomy/Other_searches.htm

-- 
Anders Sandberg
Future of Humanity Institute
Oxford University