"Mike Williams" wrote in message ...
[....]
That scenario would be detectable by the observations that were used to
test for the MACHO theory of dark matter. If there were a significant
number of Dyson spheres in the galactic halo, then those observations
would have detected large numbers of gravitational lensing effects as
they passed in front of distant stars.


Interesting.
However, the MACHOs they are looking for are considered small (smaller than the stars behind them) and rather dense.
A Dyson shere will be large (range of 1AU radius), and thus much larger than the stars behind it. They are not so dense, since all
it's mass is concentrated in the center (the star that it encircles).
I don't know much about the physics of microlensing, but common sense tells me that a Dyson sphere might actually block the
starlight behind it more than 'microlense' it.
If that is so, stars behind it will fluctuate in strength, but will go down in intensity rather than get a microlense boost...
Stars behind a Dyson sphere would then show up more as 'variable' stars... And a lot of 'variable' stars have been detected.
Does this make sense ?

--
Mike Williams
Gentleman of Leisure