Re: Fermi paradox


dkomo wrote:
spintronic wrote:

dkomo wrote:

spintronic wrote:


Where are they?


See "Searching the Electromagnetic Spectrum" at

http://en.wikipedia.org/wiki/SETI

I find this to be interesting:

"Cosmic and receiver noise sources impose a threshold to power of
signals that we can detect. For us to detect an alien civilization 100
light years away that is broadcasting "omnidirectionally", that is, in
all directions, the aliens would have to be using a transmitter power
equivalent to several thousand times the entire current power-generating
capacity of the entire Earth.

It is much more effective in terms of communication to generate a
narrow-beam signal whose "effective radiated power" is very high along
the path of the beam, but negligible everywhere else. This places the
transmitter power within reasonable ranges, the problem being now of
having the good luck to coincide with the path of the beam, with the
possibility approaching to zero as distance increases."

Consider what the probability would be that a narrow beam of microwaves
or a laser beam sent from one hundred light years away would interesct
the orbit of the earth. Seen against the surface area of a sphere 100
light years in radius, our entire solar system would appear as a
microscopic dot. The beam would have to hit this dot, *then* fly across
the earth's orbit.


--dkomo@xxxxxxxx


Your way over simplifing this, If what you say was true, and the only
stars with life capable of being reached where within a 100Ly radius,
then there would "only" be 20,833 stars to search for. Im sure seti
would have scanned these stars long ago.


Where did you get this number, 20,833?

Obviously the funding comitees that invest their precious money into
seti, dont think seti has only 20,833 stars to search, or theyde be
locked up for throwing their money down the drain by now.

As for hitting a dot.

You assume that any such civalisation would have to aim such a beam
right at us. Thats just not true.

> Any such signal would more likely be sent out like a rotating
> light-house beakon, or a pulsar.

Why, right you are. You should edit that Wikipedia article and point
this out. I simply quoted it without pausing to reflect on the
narrow-beam signal.

But now that I think about it, an advanced alien civilzation could do
much better than an old fashioned rotating light-house beacon. They
could electronically steer the beam with a space-borne phased antenna
array. This way they could cover every point in the sky hundreds of
times a second -- all 360 degrees around, and all 180 degrees from nadir
to zenith.

But the pulsar idea is a bit much. A pulsar has billions of times more
energy than the aliens could control. I mean, how do you modulate the
emissions of a rotating neutron star?

Also pulsars and GMB's

What the heck is a "GMB"?

(even though
being much more powerful) are sent out in a highly focused rotating
beam. And weve picked up hundreds of these, picking up 300+ pulsars in
our own galaxy alone and thousands of GMB's to date. These events would
be far rarer than the supposed emergence of life on a given world. Yet
we detect them no prob.


--dkomo@xxxxxxxx

The figure is how many stars (max) could be packed in your 100ly
radius, spaced at average of 4 ly each.
I said like a pulsar, i didnt mean they could actually utilise a pulsar
to send a signal.
A GRB is a gamma ray burst, these are sent out in almost laser like
beams, And i was just illustrating that weve detected thousands of
GRB's even though they only emmitt for a short period.
Albeit, GMB's are much-much more powerful, yet most they have been
detected as far as hubble can see.

So im sure if someone was transmitting, we could pick it up.

.

Relevant Pages

  • Re: Fermi paradox
    ... signals that we can detect. ... the aliens would have to be using a transmitter power ... the path of the beam, ... then there would "only" be 20,833 stars to search for. ...
    (talk.origins)
  • Re: Fermi paradox
    ... signals that we can detect. ... the aliens would have to be using a transmitter power ... the path of the beam, ... then there would "only" be 20,833 stars to search for. ...
    (talk.origins)
  • Re: Fermi paradox
    ... signals that we can detect. ... the aliens would have to be using a transmitter power ... the path of the beam, ... then there would "only" be 20,833 stars to search for. ...
    (talk.origins)
  • Re: Fermi paradox
    ... "Cosmic and receiver noise sources impose a threshold to power of signals that we can detect. ... For us to detect an alien civilization 100 light years away that is broadcasting "omnidirectionally", that is, in all directions, the aliens would have to be using a transmitter power equivalent to several thousand times the entire current power-generating capacity of the entire Earth. ... It is much more effective in terms of communication to generate a narrow-beam signal whose "effective radiated power" is very high along the path of the beam, ... Seen against the surface area of a sphere 100 light years in radius, our entire solar system would appear as a microscopic dot. ...
    (talk.origins)
  • Re: Space Based Solar - was Re: useful analogy
    ... You are speaking of peak power ratings- ... household appliances the way people do now. ... A peak 1kW beam wont come anywhere near being adequate. ... just another cost you need to factor in. ...
    (sci.energy)