I think the 'There's no one out there!' thread has been full of interesting comments and counter comments. But, for a moment, let me look at the other side of the coin, so to speak.
Although I do not think there exists in the galaxy today, any other intelligent civilisations, there is one signal that even I find totally interesting yet enigmatic and, could possibly make me challenge that concept.
SETI@Home is clearly failling in its search to find any signal from ETI's. We need to go back over 30 years to consider an event that could or maybe should have virtually rendered SETI@Home obsolete.
This is known as the WOW! signal because the finder, Dr Jerry Ehman, on going through the previous day's data output from the Big Ear telescope couldnt believe what he was seeing. That was in August 1977.
Many people think the WOW! signal is some kind of coded message. But it isnt. Represented as 6EQUJ5, it is, put simply, merely the rise and fall in signal carrier wave strength over a 72 second period compared to the background noise. It is not clear whether WOW! is modulated or un modulated.
The Big Ear telescope which is no more, was a fixed antenna roughly the size of a football pitch. It had effectively 2 receivers or collection horns. Since the telescope was fixed to the ground, Big Ear used the earth's rotation to scan the sky. The rotation of the Earth means that each horn would collect data in, effectively, a period over 72 seconds.
Big Ear could not be pointed anywhere specific. It was converted in 1973 to search for narrow band radio source ie radio signals from other intelligent civilisations.
Ehman contends it was almost 4 days (probably 19 August 77) after the signal had been received that he was reviewing the previous days printouts. It was then thaat he noticed the remarkable data which he circled and wrote WOW! next to it, giving it its now famous name.
Without going into any technical detail, the WOW! signal can be imagined as the light from a lighthouse viewed from a distance. The light beam can be seen growing in brightness as it swings towards us. It is at its brightest when we are directly in line with the light. It starts to dim as it moves away from us before finally disappearing from sight.
Now imagine the light from the lighthouse is the WOW! signal and we are the Big Ear. As the signal starts to be received by the equipment, its strength is low but increases as the Earth's rotation starts to align Big Ear with it. The signal reaches a peak as the Earth's rotation is directly aligned with it then starts to fall away.
The signal lasts for 72 seconds, what one would expect due to the fixed position of Big Ear and the Earth's rotation. It was received in the 1420Mhz frequency range which is where a SETI signal could be expected to be found. Subsequent investigations have shown the signal co ordinates suggest it originated from the constellation of Sagittarius. Although Big Ear and other telescopes have tried many times to find the WOW! signal again, all have failed.
Subsequent investigation has been able to show what the WOW! signal wasnt.
The WOW! signal was a narrow band transmission of less than 10Khz meaning it is not 'natural' interference or phenomenon.
The positions of all solar planets was examined and none were even close to the location of the signal source \ direction. Some narrowish band transmission from Jupiter have been recorded but even these did not match WOW!
Positions of asteroids large enough to possibly emit a signal were checked and none were close to the source \ location or direction.
Satellites were discounted for a couple of reasons. WOW! was recieved around the 1420Mhz frequency. This is a 'forbidden' frequency for any Earth based station or satellites. An investigation of all known satellites locations were made but none corresponded to the direct WOW! came from. Even if a secret American or Russian satellite had been put into orbit, it wouldnt be transmitting on the 1420Mhz frequency. Even if it had, it would soon have been noticed and picked up by other telescopes.
Aircraft can similarly be excluded, again because no aircraft transmitters operate on 1420Mhz and, aircraft move rapidly compared to the stars. Wow! came from a fixed position.
Spacecraft can also be discounted for similar reasons, none transmit of 1420Mhz and would be moving rapidly compared to the stars.
A ground based transmission can be discounted again due to the 1420Mhz embargo. Also, since an earth bound transmitter and Big Ear are both fixed to the ground, there would be no way the WOW! signal would show up as gradually increasing to a peak and falling away again and more so in the 72 second period.
Some people have suggested WOW! was an earth based transmission bounced of a piece of space junk or small asteroid. This too was considered but can be discounted. First, it would require the transmission from Earth was on 1420Mhz and as such would break the embargo. Second, the object the signal was bounced off would have to be metal so would rule out a small asteroid. If it was metal, the object would have to be rotating very slowly (1 rotation in an hour or more) which would be unlikely. It would also need to be moving very slowly against the cosmic background which if it was a piece of space junk is highly unlikely.
The signal received by Big Ear can also be discounted to be a harmonic of a lower frequency than 1420Mhz ie 710Mhz or 473Mhz, since, filters on the original broadcasting equipment would significantly reduce the harmonic strength. However, that harmonic signal strength cannot be reduced completely to zero. Big Ear was sensitive enough to detect those harmonics. In any event, frequncies such as 710 or 473Mhz ie tv or radio, have a wider bandwidth than the 10Khz of WOW!.
Gravitational lensing was also considered but can be discounted for another reason.
Interstellar scintillation can best be described as when looking at stars they twinkle. Put simply this is because our atmosphere affects the light from those stars to make them appear to be shimmering. The same thing can happen to radio waves. It is possible for a signal to be enhanced this way and, if the signal was so affected, this indicates the origin is many light years away and tends to support the idea that WOW! is of extra terrestrial origin.
The scientific community will not recognise WOW! due to the fact it was only detected once. Since Big Ear had two recievers, WOW! was only detected in one of them. One would expect the signal would have been received by both receivers some 5 minutes apart ie the time taken for Earth's rotation to bring both of them to bear on the same point in the sky. This, as far as I can tell, is the only problem with WOW!
It is argued to be unlikely a civilisation would have turned off the signal or away from earth in the 5 or so minutes it should have taken the second of Big Ear's receivers to have detected the signal. It is also for this reason that gravitational lensing can probably be discounted.
This assumption however, does not take into account that the signal could have been transmitted our way for nearly 24 hours ie since the last completion of the Earth's rotation. It is not clear from the available information which of Big Ear's two receivers picked up the signal ie the leading receiver or the trailing one.
WOW! remains the most enigmatic signal ever received and repeated attempts to find it again have been unable to do so.
