We do improve our energy efficiency. For example, combined cycle gas generators are 60% efficient, about twice a good as nuclear reactors. So, in the absence of cogen, 40% of the heat is discarded. But, so it the other 60%. Turning on a light heat the wall the light shines on..... So, it is 100% waste heat eventually. It is the 100% stuff (after use) that must be emitted to space and that is what the paper proposes to search for.

That is covered with their parameter nu. From their table 1: "Power of other waste disposal (e.g. neutrino radiation, non-thermal emission, kinetic energy, energy-to-mass conversion)" so yes, there may be ways to reduce the signature.

suggests that the aliens might not abandon these stars just as the energy get is getting good. He may have a point there.

Energy used efficiently is still energy used. There is always waste heat. The paper addresses what would be an o[optimal waste heat temperature. http://arxiv.org/pdf/1408.1134... If you want your waste heat half as warm, your Dyson Sphere has to have four time the radius so you material use becomes excessive.

That is covered with their parameter nu. From their table 1: "Power of other waste disposal (e.g. neutrino radiation, non-thermal emission, kinetic energy, energy-to-mass conversion)" so yes, there may be ways to reduce the signature.

Not really. The luminosity of a Dyson Sphere will be the same as the luminosity of the star it surrounds. The color temperature of the radiation will be lower by a factor of the square root of the ratio of the radius of the star to the radius of the sphere.

They are usually putting gamma equal to alpha in the paper so Dyson spheres, cubes or pyramids is pretty much what they have in mind. http://arxiv.org/pdf/1408.1134...

I suppose if you condensed the material in an AGN jet you get chunk of mass going that fast and reaching another galaxy. There are high velocity stars (not that high though) that might be three body interaction ejections from Andromeda http://www.technology.org/2013...

I was thinking them. Other galaxies are pretty far away.

They can be assimilated?

This is not a search for plants but rather Dyson Spheres. http://en.wikipedia.org/wiki/D...

Would we want to? They sound like locusts.

This method has a difficulty. Most of the starlight from a galaxy comes from stars that will soon be gone. These are the luminous giant stars. But a big investment in a Dyson sphere would probably be made around a star more like our Sun which will stick around for a while. But even if most of the mass in stars is involved in this, it still won't get most of the light so long as it is the low luminosity stars that get the tech investment.

It comes down to fig. 3 in their paper. http://arxiv.org/pdf/1408.1134... Natural source don't have the expected colors for waste heat from a solid surface. But that is the case when perhaps half the starlight in a galaxy is being used for power (their gamma=0.5). So, the civilization has to be pretty much like locusts for it the be easy to discern. There may be some civilization lifetime issues to worry about in that case.

These are infrared array cameras mounted of space telescopes. How high tech do you want? http://wise.ssl.berkeley.edu/