travelling to the nearest neighbouring stars would be fairly easy to accomplish.

When one thinks of the resources that have been poured into various defence projects by the Earth's nations, this could have been well under way already.
Then again, we probably have the defence industry to thank for most of the advanced technology we enjoy today.

Someday, maybe, those that make the decisions may see the light.
But while it is not financially advantageous to embrace this idea, it will not happen in the immediate future.

We have to assume that any signal from ET would be continuous over the course of a VERY long time, possibly millions of years or longer.
If the signal is not continuous over a very long time, then SETI will not work.

The first very weak radio broadcast on (from) Earth took place in 1906.

Thus an extraterrestrial civilization cannot have detected our signal from a distance of more than - at most - 102 light years.

For that reason it sems unlikely that an electromagnetic beam has been directed at us from a longer distance than this - and possibly outside the 3 to 30 cm frequency window, because our early broadcast were in the long wave spectrum.

More later.

Did you read this part of my post?

There's no reason not to believe that ET will have extensively analyzed and cataloged every single visible star in the galaxy; the technology and time required to do this isn't that great. In fact, the Kepler mission, launching in 2009, will extensively analyze the (potential) planets of over 100,000 stars within four years. Within a time-span of years, missions will be launched to not only detect Earth-size planets, but to analyze their atmospheres. The James Webb Telescope and ultimately the Terrestrial Planet Finder will be able to do this.

Considering that WE essentially possess the technical capability right now to not only detect the presence of an Earth, but to analyze its atmosphere, it's reasonable to conclude that an older civilization would also possess that capability.

Assuming such a civilization has observed and analyzed every visible star in the galaxy, it's reasonable to conclude that this civilization would be aware of the existence of Earth. It's also reasonable to conclude that this civilization would also be aware of the composition of Earth's atmosphere; since there is no natural mechanism other than biological processes to explain the level of oxygen in Earth's atmosphere, that civilization will also be aware that there is life on Earth.

All ET would have to be able to do is to analyze the chemical composition of our atmosphere via spectroscopy.

Let me make this clear:
*We* already possess this technology. Atmospheric analysis of exoplanets has already been done. Furthermore, the James Webb Space Telescope will be able to analyze the atmospheres of Earth-like planets.

If we were ever to detect a planet that contained the levels of Oxygen that are present in Earth's atmosphere, there would be no other feasible way to explain it; that planet would have life.


Earth's atmosphere has been sending out this biosignature to the universe for at least 1 billion years. That essentially means that any civilization in our galaxy (or indeed, the universe) that is able to see our planet (assuming we are not obscured by the galactic bulge), has had 1 billion years to detect the biosignature in our atmosphere.

If you don't believe me, here's an interesting article by Seth Shostak on this very subject:
http://www.seti.org/news/features/can-aliens-find-us.php

...and as far as our ability to detect the atmospheric composition of other worlds, listen to the Are We Alone radio show I linked to earlier.

Anyway, it seems certain that *if* older alien civilizations actually exist in the Milky Way Galaxy, then they are likely not only aware of the Earth but aware that it hosts life.

The question is, would an alien civilization predict that intelligence might one day evolve on Earth or exist already? Assuming they would, would they send a directed radio signal to Earth with the knowledge that an emerging civilization is likely to come to the conclusion that there are probably other civilizations in the galaxy (as they once did), and listen for potential communications from those civilizatons? If ET has any desire to communicate with potentially intelligent creatures on Earth, it would seem a simple matter to have a long-term project in which a radio signal is constantly directed toward Earth with the knowledge that some day, that signal will be detected. It may be possible that ET has some sort of "emerging civilization communicator" in orbit around their planet, constantly pinging a list of targeted planets on which life is known to exist.

The funny thing is, we may find ourselves in the role of ET some day.

We have to assume that any signal from ET would be continuous over the course of a VERY long time, possibly millions of years or longer.
If the signal is not continuous over a very long time, then SETI will not work.

The first very weak radio broadcast on (from) Earth took place in 1906.

Thus an extraterrestrial civilization cannot have detected our signal from a distance of more than - at most - 102 light years.

For that reason it sems unlikely that an electromagnetic beam has been directed at us from a longer distance than this - and possibly outside the 3 to 30 cm frequency window, because our early broadcast were in the long wave spectrum.

More later.

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Split personality - who, us?

As a further note:

It seems to me that anywhere an intelligent civilization evolves, they will inevitably possess the technical capability to avoid the effects of the death of their star.

The good news for us and any other intelligent civilization; these things happen slowly....VERY slowly.

Our Sun's temperatures will not be lethal to life on Earth for another 900 million years. That's a LONG time in which to plan.

Even if we had only 1 million years, that would also be a LONG time in which to plan.

Planets further away from the star can be colonized, migrations can be made to neighboring stars. These seem to me to be fairly straightforward, simple endeavors given the basic technical capability and powerful enough motivation (the death of your star should be a good enough motivator for any civilization).

Even if a civilization does not possess near-light-speed travel capability or worm hole technology or anything like that, traveling to the nearest neighboring stars would be fairly easy to accomplish. All you would need is stable, self-sustaining resources (like food) and enough room for however many individuals choose to travel. A journey of thousands of years might be a tough wait, but it would be guaranteed to escape the fate of the homeworld's star.

I actually think it's more likely than not that interstellar migration and colonization will occur long before the death of the homeworld's star anyway.

So the way I look at it, the average lifetime of stars is a useful variable with which to calculate the probability of the evolution of life or intelligence with regards to timescales, but I see it as inapplicable as a factor regarding civilizations that are already assumed to have arisen.

I agree to most of your posting. There are, however, the problem of energy expenditure for a signal in all direction with a flux sufficient to be detected at a reasonable distance.

But it wouldn't be a signal in all directions; it would be specifically sent to Earth.

I don't think anyone seriously believes that ET is wasting energy to blanket the cosmos in radio waves that will target every single star in the galaxy with the blind hope that one of those stars has an orbiting planet inhabited by extraterrestrials.

I think it's safe to assume that ET would possess the technology to detect exo-planets just as we do; arguably their ability to detect the planetary systems around stars would be significantly superior to ours considering that they would have to be older than us for SETI to work in the first place.

There's no reason not to believe that ET will have extensively analyzed and cataloged every single visible star in the galaxy; the technology and time required to do this isn't that great. In fact, the Kepler mission, launching in 2009, will extensively analyze the (potential) planets of over 100,000 stars within four years. Within a time-span of years, missions will be launched to not only detect Earth-size planets, but to analyze their atmospheres. The James Webb Telescope and ultimately the Terrestrial Planet Finder will be able to do this.

Considering that WE essentially possess the technical capability right now to not only detect the presence of an Earth, but to analyze its atmosphere, it's reasonable to conclude that an older civilization would also possess that capability.

Assuming such a civilization has observed and analyzed every visible star in the galaxy, it's reasonable to conclude that this civilization would be aware of the existence of Earth. It's also reasonable to conclude that this civilization would also be aware of the composition of Earth's atmosphere; since there is no natural mechanism other than biological processes to explain the level of oxygen in Earth's atmosphere, that civilization will also be aware that there is life on Earth.

Also, it does not address my main point: That we may have come into existence too late - perhaps even billions of years too late.

A good listen on that very topic:
"Are We Alone", the SETI radio show (episode on recent astrobiology conference)
http://radio.seti.org/past-shows.php#2008-05-05.php

Astrophysicist Charley Limeweaver discusses the fact that the occurrence of planets is a function of stellar metalicity, and since metals can only be created in post-Big Bang events like Supernove (only hydrogen and helium existed at the time of the Big Bang), the early universe did not have terrestrial, Earth-like planets since there were no metals from which they could form. According to Limeweaver's calculations regarding metalicity, terrestrial earth-like planets likely could not have formed in our region of the galaxy earlier than ~7.6 billion years ago.

Not only that, but *specifically addressing your issue*, Limeweaver further calculates that the "average 'Earth' in the universe, not just the galaxy, is about 1.8 billion years older than the Sun." (quoted verbatim)

Most stars in our galaxy (the vast majority) are M-Dwarfs/Red Dwarfs (not Sun-like stars); when you say that "most" stars in our galaxy are 7-9 billion years old, you're probably referring to these. They have extremely long, stable lifespans; estimated at 10s of billions, possibly trillions of years. Though Red Dwarfs have high metalicity, they were thought to be poor candidates to host life due to the fact that any planet in the theoretical habitable zone would be so close to the star that it would be tidally locked and its surface temperatures would be too extreme. These notions are now being thrown out as recent studies have proven the situation is far more complex than previously thought and stable atmospheres are plausible, perhaps even likely on such worlds.

As far as sun-like stars (G2-dwarfs), new ones are being born and old ones are dying all the time. I don't know of any reason to believe that we live in a time period beyond the capacity for most sun-like stars in our galaxy to develop and sustain life. Indeed, it seems the opposite is more likely to be true considering the time scales required for supernovae to bring about the build-up of metalicity beyond the galactic core.

Any electromagnetic signal, which has been transmitted from even the most remote point in our galaxy more than 100,000 years ago will now have left the galaxy forever.

... We have to assume that any signal from ET would be continuous over the course of a VERY long time, possibly millions of years or longer.
If the signal is not continuous over a very long time, then SETI will not work.

I agree to most of your posting. There are, however, the problem of energy expenditure for a signal in all direction with a flux sufficient to be detected at a reasonable distance.

Also, it does not address my main point: That we may have come into existence too late - perhaps even billions of years too late.

But: Never forget the saying "Faint of heart never wins fair lady" (Thomas Hardy), and let's keep trying. I hope that we are not alone in our galaxy - like someone said (sorry, can't give credit where due) "such a waste of space".
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Split personality - who, us?

Any electromagnetic signal, which has been transmitted from even the most remote point in our galaxy more than 100,000 years ago will now have left the galaxy forever.

Bill is right.

If ET only sent a signal once, for 1 minute or for 100 years, and then stopped signaling us, whether it was 100,000 years ago or 100 years ago, then all SETI efforts are doomed to failure.

The chances that we would be looking in the right spot at EXACTLY the right time at EXACTLY the right instant when the radio signal hits the Earth are pretty much zero.


But we assume ET would know that and we don't think ET would do that. ...After all, we have to assume they're smart enough to realize that we wouldn't have a decent chance of detecting any signal that wasn't continuous over a very long period of time. We also have to assume that they would be smart enough to carry out such an endeavor only if it had a reasonable chance of success. We have to assume that ET would be smart enough to realize the chance of success would be zero if they signaled us only briefly and then stopped forever, and since SETI acts on the assumption that the ones making the pro-active effort are the aliens (they're doing the signaling), we also have to assume they would only make that effort is they had a reasonable idea of how to do it successfully.

SETI assumes that any civilization we might receive a signal from would be more advanced than us and would know they're more advanced than us, and would therefore know that for their signaling effort to succeed, the signal would have to be continuous for a very long time.

Lighthouses don't turn their light on for 1 minute and then stop forever, hoping that some ship just happened to be within range to see that light and happened to be looking in that exact direction during that 60 seconds when the light was on.

People tapping out SOS messages to be rescued don't send out an SOS just once or just for a few minutes hoping that a plane or ship happened to be in the area during that 2 minutes and happened to be listening to that frequency at the exact time the SOS was sent.


We have to assume that any signal from ET would be continuous over the course of a VERY long time, possibly millions of years or longer.
If the signal is not continuous over a very long time, then SETI will not work.

It would help if our aliens broadcast a contemporaneously overlapping (allowing for travel time) and continuous signal.

A simple solution to the Fermi Paradox - why we haven't stumbled onto some alien broadcasts in space or have met ETs - may be that our Sun seems to be an "afterthought".

Any electromagnetic signal, which has been transmitted from even the most remote point in our galaxy more than 100,000 years ago will now have left the galaxy forever.

Most stars in our galaxy seem to have been created some 7E9 to 9E9 years ago. Our Sun is only about 4.6E9 years old.

According to the present star models, when our Sun reaches the age of about 6.5E9 years the market for long johns will be exhausted - the oceans will have evaporated and life as we know it will become extinct.

Assuming that an extraterrestrial civilization reached Earth a few E9 years back, even if they did build observation stations on Earth, plate tectonics may well have removed any trace of this incident.

Let's hope for the best, a 3-armed and 3-legged friend somewhere working on his emoh@ites project ::-))
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Split personality - who, us?