Re: [GZG] A number of scientists respond to Hawking's concerns about Aliens

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http://mail.csua.berkeley.edu:8080/mailman/listinfo/gzg-lOn Mon, May 10,
2010 at 9:39 AM, Doug Evans <devans@nebraska.edu> wrote:

> TomB, John T, and Indy, respectively:
> [...]
> > Reading some of the points in this thread, it seemed to me that
> > maybe some people out there in the great black think SETI has a more
> > active role in detecting extraterrestrial civilizations than merely
> > listening?
>
> I believe I've heard of a bit of sending associated with SETI; very
> limited, though. Nothing in volume, either duration or
omnidirectionality
> (is that a word?), to compare to the drivel at the start of the
radio/TV
> era. However, I think it was somewhat more selective in frequency.
>

When I met Seth Stostak a few years ago he made it pretty clear they
(SETI)
were just listening, not transmitting.

Amending that slightly, in 1974 SETI used the Arecibo radio dish once to
send a brief message out toward the globular cluster M13 - some 25,000
light
years distant. As this was a beamed message to that location, any
civilizations elsewhere won't hear it. And anything that might pick it
up in
the cluster won't catch it for another 24,964 years. A response may take
another 25,000 years, give or take, depending on technology.*

This was more a demonstration that we _could_ send a message, rather
than a
real attempt at communicating with another species.

Further, three other transmissions were made from Earth (but not with
the
Arecibo dish), to a dozen selected star systems. Again, not wide-band.
The
group behind these transmission (1999, 2001, 2003) is called "Active
SETI"
or more directly, METI (Message to Extra-Terrestrial Intelligences). It
is
affiliated with SETI in that it is searching for aliens, and that some
members of METI are also SETI, but SETI in and of itself is a passive,
listening-only program.

Seth also went into detail on how transmissions from Earth had gone
'quiet'
in the 80s (as outlined in my previous post :) ), and that this is a
concern
for SETI in how other civilizations may have gone with their
communications.
If when SETI started listening they missed catching the blip of a wide
broadcast civilization before that race went quiet, SETI would not hear
them
now.

* - an interesting side topic to all this is is the subject of
interstellar,
FTL, travel. Being a romantic, I am in the camp that believes someday
we'll
figure it out and go. But there are strong cases against it ever being
possible (as we perceive things now). First, if you can go FTL, you can
send
a radio message to a destination, then beat the radio waves to the
target.
So in the case of Arecibo-1974, it will be ~25,000 years before M13
civilizations hear us, but in the meantime we might have FTL'd out there
in
our starships, found them hostile, and be engaged in an
interspecies/interstellar war.	Or discover they are vastly more
powerful
than us and we're trying to hide - but oops, radio signals are coming!

Another even more damning case against FTL travel is gravity. You
generate a
gravity field because you are composed of some mass. If you FTL to
another
star, say 10 light years away, an observer sitting at the midpoint
between
where you were and where you are will see you appear in two different
places
at once - AND (let's say they have the technology) detect your
gravitational
influence at the same time from two separate locales. This means you've
effectively doubled your mass in the universe, at least for the
particular
observer's location (and in the plane orthogonal to the FTL line you
flew).

I'm sure there are counter-arguments to this, but I haven't worked them
through yet.

Mk