Can you expand on your idea about the stars? I follow why gold coins aren't found in the street, but not how intelligent life would scoop up stars.

It is not my idea (I wish it was), but the basic idea is that any intelligent life a little more advanced than us would build Dyson spheres [1] around each star to capture the energy being released. This would shift the stars EM spectra heavily into the red. Combine these with von Neumann machines [2] and the stars soon cease to shine.

Interestingly while we are not really capable of searching for such stars right now we have found few possible candidates [3]. I personally think these are likely to all be false positives because any civilisation capable of building a Dyson sphere will be able to capture all the energy being emitted and so the black body temperature of the sphere will be only be a little above 2.73K. These we would not be able to detect.

1. http://en.wikipedia.org/wiki/Dyson_sphere

2. http://en.wikipedia.org/wiki/Self-replicating_machine

3. http://home.fnal.gov/~carrigan/infrared_astronomy/Other_sear...

Awesome, thanks for writing this up for me.

I wonder if there's reason to think that all or many stars would need capturing.

Also, is there perhaps an alternative situation, where, put simply, there power needs can be sufficiently met without capturing all that available? (Lower power tech, or some very efficient power capture / production?)

Once you have von Neumann machines spreading they will take over each new star system pretty much as soon as they reach it. Assuming the von Neumann machines are small and are being powered by an energy source (i.e lasers) from their origin star system they will spread through the galaxy at close to the speed of light. This spread method creates an interesting effect in that we would not see the stars go out until the von Neumann machines had almost reached us if the origin star was within our galaxy - basically the von Neumann machines would be traveling only a little behind the light front from the origin star system (this would make a good science fiction story).

If the origin star system was far enough a way, then the slightly slower speed that the von Neumann machines would travel at should allow us to see them progressing though a distance galaxy. Such a galaxy would look to us like part of the galaxy had a chunk taken out of it. It would be worth looking through the galaxy classification data set [1, 2] to see if there are any galaxies like that out there that look like this. My feeling is we won't find any as I think intellegent life is near unique within the visible universe, but it is at least a testable hypothesis.

1. http://www.galaxyzoo.org

2. http://en.wikipedia.org/wiki/Atlas_of_Peculiar_Galaxies