[ExI] Tabby's star

Rafal Smigrodzki rafal.smigrodzki at gmail.com
Sat Dec 10 11:56:41 UTC 2016

On Fri, Dec 9, 2016 at 7:36 PM, Keith Henson <hkeithhenson at gmail.com> wrote:

It's going to take more effort than I thought to make sense of the
> weird data we have from Tabby's star.  But here is a start.

### Have you tried calculating the density of Dyson-sphere building
civilizations from the Tabby's star data, assuming they are indicative of
an alien civilization?

Let's assume that the volume of space the has been searched by our
telescopes well enough to detect all Dyson sphere building efforts is a
cube 4000 ly on a side, centered at Earth, or 64 billion cubic light years.
If this is true, then the expected average density of such Dyson spheres is
1 per 64 billion ly, assuming lack of correlation between Earth and the
Tabby aliens.

The volume of the Galaxy is 8 trillion cubic light years. Therefore it
contains, per calculation above, 125 Dyson spheres in the process of being
built, at a speed of about 1/1000 years. The visible universe contains
about 100 billion galaxies, so there are roughly 10 trillion Dyson spheres
being built every 1000 years.

Now, how many Dyson spheres were built in the past 100 million years in our
galaxy? Assuming no great changes in the speed of building, the answer is
125 x 10e5, and about 100 000 in our immediate vicinity.

Do I make reasonable assumptions? Do we have automatic surveys of star
brightness in a cube of 4000 light years on edge centered on Earth? If not,
the expected Dyson sphere density would go up by the ratio of surveyed
stars to all stars in our neighborhood. Is it correct to assume that our
galactic neighborhood and our place in time are average, allowing simple
calculation of average Dyson sphere density from our local observation
point in time and space? I think yes, by and by.

If all of the above is correct, then taking aliens at Tabby's star
seriously would require believing that aliens, who built tens of millions
of Dyson spheres in our galaxy in the last couple of hundred million years,
have failed to manifest in other ways. We failed to notice 100 000 Dyson
spheres in our neighborhood? Did we fail to see the multiple Dyson spheres
in the surrounding 100 light years, at our doorstep? We found 28 planets
(!) in this area and failed to see the Dyson spheres?

This strains my credulity. I am willing to take a bet up to $1000 at 10:1
odds against me that in the next year there will be no peer reviewed
confirmation of alien activity at Tabby's star, or anywhere else in the

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