ETI and dark matter

A very wild though came to me, so please to kill me if I'm talking nonsense.

What if ETIs found a way to use the energy of a star for their own benefit,
and that is why we don't see a good portion of the matter in the Galaxy ?

For example, they could have formed Dyson spheres (solved the instability
problem) around stars and thus absorb all the star light. The only evidence
of the star would be in deep infrared (radiation of the Dyson sphere's
temperature).

If done on truely gallactic scale, then intelligent life could be
responsible for the missing 40% of matter in the Galaxy, which we currently
address to (so far theoretical) "dark matter"....

OK. Shoot me.

Rob

I just noticed that Pete Lynn had the exact same though and posted it in a
side-thread half an hour before me.

If two people have the same thought in such a short time span, then it is
likely that this idea came up before.

So did we already discuss this at some point in time, and is there any
observational data in favor or against this idea (ETI responsible for dark
matter), as far as anyone knows ?

Rob

Wasn't it Rob Dekker who wrote:
A very wild though came to me, so please to kill me if I'm talking nonsense.

What if ETIs found a way to use the energy of a star for their own benefit,
and that is why we don't see a good portion of the matter in the Galaxy ?

For example, they could have formed Dyson spheres (solved the instability
problem) around stars and thus absorb all the star light. The only evidence
of the star would be in deep infrared (radiation of the Dyson sphere's
temperature).

If done on truely gallactic scale, then intelligent life could be
responsible for the missing 40% of matter in the Galaxy, which we currently
address to (so far theoretical) "dark matter"....

OK. Shoot me.

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.

--
Mike Williams
Gentleman of Leisure

In message , Mike Williams
writes
Wasn't it Rob Dekker who wrote:
A very wild though came to me, so please to kill me if I'm talking nonsense.

What if ETIs found a way to use the energy of a star for their own benefit,
and that is why we don't see a good portion of the matter in the Galaxy ?

For example, they could have formed Dyson spheres (solved the instability
problem) around stars and thus absorb all the star light. The only evidence
of the star would be in deep infrared (radiation of the Dyson sphere's
temperature).

If done on truely gallactic scale, then intelligent life could be
responsible for the missing 40% of matter in the Galaxy, which we currently
address to (so far theoretical) "dark matter"....

OK. Shoot me.

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.

FWIW, my favourite fictional version of this idea is in Fritz Leiber's
"The Wanderer", where
'the planets are so thick around each sun they shroud its light... It
is the boast of our engineers "Wherever a sunbeam escapes, we place a
planet"... You haven't heard this news, simply because of the snaily
slowness with which light travels. If you could wait a billion years,
you'd see the galaxies grow dim, not by the death of stars, but by the
masking and miserly hoarding of their light by the stars' owners".
--
What have they got to hide? Release the ESA Beagle 2 report.
Remove spam and invalid from address to reply.

Rob Dekker wrote:
A very wild though came to me, so please to kill me if I'm talking nonsense.

CUT

I think it's a problem when you need "wild" ideas to explain where ETI's
are.
Occam's razor comes to mind.

Instead I believe we should focus on SETI's next project, the Allen
Telescope Array, which
will be completed next year. Until now we have only scanned a few
thousand stars in our
Galaxy. That's really nothing, just some stars in our neighbourhood.
With the new telecope
array, one million stars will eventually be scanned. That's a nice
sample of Galaxy stars, and
for the first time in our history, a large enough sample to make some
real constraints to how
common ETI's are.

Martin.

"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

Wasn't it Rob Dekker who wrote:

"Mike Williams" wrote in message news:MUxgKBA5NDwBFw
...
[....]
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 ?

Good point.

I've now looked into this and it seems like you'd get a fairly normal
looking microlensing effect as long as the radius of the Dyson sphere is
significantly smaller than its Einstein Ring Radius. I think you get a
fairly normal looking occultation if the radius of the Dyson sphere is
significantly larger than its Einstein Ring Radius. I suppose that if
the radii are fairly similar in size then you get some sort of hybrid
effect.

The Einstein Ring Radius depends on the mass of the lensing object and
the distances to the lens and to the lensed star. For example, if the
lensing object has the same mass as our Sun at a distance of 2
kiloparsecs from here and the light source is very distant, then the
Einstein Ring Radius is about 4 AU.

E = 4.03 * sqrt(M * D/2) AU

Where "E" is the Einstein Ring Radius
"M" is the mass of the lens in Solar Masses
"D" is the "reduced distance" the lens in kiloparsecs

The "reduced distance" is given by
D = Dlens * (1 - Dlens/Dsource)
If the source is very remote (as it typically was in the MACHO searches)
then the reduced distance becomes close to the actual distance.


Note also that the MACHO observations didn't throw away the data that
came from "variable stars". They passed information about thousands of
such observations on to astronomers who happen to be interested in
studying variable stars. If there were lots of Dyson Sphere occultations
in that data then someone should have spotted an interesting pattern.

--
Mike Williams
Gentleman of Leisure

Jonathan Silverlight wrote:
If you could wait a billion years,
you'd see the galaxies grow dim, not by the death of stars, but by
the
masking and miserly hoarding of their light by the stars' owners".

Yeah, and Larry Niven's "ringworld" or Dyson spheres can also blot out
light in similar way.

Mike
Thanks for checking the physics of micro lensing on this !
Where did you find the formula's ?

Any way, I guess you are right in that if half the Galaxy is filled with
Dyson spheres, that someone would have found some consistent pattern. Not
just in the MACHO search, but also in infrared I guess.

I also realized that if Dyson speres (or other ETI influence) is responsible
for missing matter, than at least we should see wild variations in missing
matter in other Galaxies...

So, it seems that intelligent life never makes it to the ultimate stage of
absorbing all energy in a Galaxy for its own benefit (unless we have
overlooked some 'dark' galaxies that only radiate in balmy infrared).

In our Galaxy, life did not make it to using (==transforming) a substantial
part of energy.

Finally one more 'quick' question : it seems that MACHO search is
concentrated on the 'halo' of the Galaxy. Why is that ? Can the 'missing'
matter in the Galaxy only be explained in the halo ? What if it is uniformly
distributed among the stars (thus, in a disk) ?
Or are we looking mainly in the halo because it is so nice and dark there ?

Rob

"Martin Andersen" wrote in message
. ..
[....]
With the new telecope
array, one million stars will eventually be scanned. That's a nice
sample of Galaxy stars, and
for the first time in our history, a large enough sample to make some
real constraints to how
common ETI's are.


I wish I could share your opinion about this conclusion.
Even though I am a big fan and supporter of the ATA, I do not believe that
an analysis of one million stars around us would give us much 'constraints'
on how common ETI's are.
The best thing that the ATA can prove would be that none (or some of these
star systems harbor a
civilization which deliberately sends a signal to us.
There would be no proof of an ETI NOT being there.
For that (proof of absense) we would need a much larger antenna, since we
would need to show that ETIs around these star systems do NOT use EM
transmitters of any form.

Rob