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

[Eugen Leitl]

On Sat, Dec 24, 2011 at 01:35:51AM -0700, 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?

There would be a spectrum and luminosity mismatch (see standard
candle in https://en.wikipedia.org/wiki/Cosmic_distance_ladder ). Plus the
dimming kinetics is quick enough so that it's impossible to miss.

But of course if you can see it, then they would be here already.
And you would be dead, so no observing of dimming for you.
 
> Kepler measures dimming, but with and without a planet, so it must be
> a different approach than that, assuming we have one.
> 
> Is there something about the spectrum of a star that tells us how
> bright it should be?

Indeedy.