I’m surprised how often the Drake Equation is still mentioned when people discuss such things as the search for extra terrestrial intelligence (SETI), astrobiology and problems like the Fermi Paradox.
Fairly recent insights in such fields as cosmology, astrobiology and various future studies have changed our perception of the cosmos and the ways in which advanced life might develop.
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Posted by
James Brown on 05/31 at 11:18 PM
George - I liked your article but disagree with your logic in the type of signal we should be looking for. I have my own SETI station running and had to go through a long thought process in its development.
I had to decide what the signal might look like and then design the system around those assumptions. The conclusion I came to is that I must look for the most obvious signal - and that is the signal that I would choose to send myself. What that means is that:
I must look for myself
Any ETI that I might hope to detect must be more like myself than unlike me, in most basic ways. Not to put too fine a point on it, but, for example, I think this ET would think in the same time frame as we do. Not at the speed of a glacier or at the speed of bullet, but somewhere near our 'thinking speed'. This is necessary to make the signal recognizable to us when finally detected.
ET's physical makeup would have to be about the same as ours. Not as small as a bacterium or as large as one of the rolling hills I can see from my window, but somewhere in-between. This would give him the same type of control over his environment, and the same capability as I have to construct the needed transmitter, which could produce a signal which I can recognize. Not all ETI need be like me; only those who I have a realistic chance of detecting.
ET's transmitter must be an RF signal generator. Some other, more exotic form of communication may well be in use, but since I can't construct a receiver to detect exotica, it's not worth considering. This leaves open optical SETI - but not for me. I know nothing about the optics required on that scale. As an RF guy, I'll stick to the area where I have a shot at SETI success.
The signal must be a deliberate beacon. That's the only type I and most other SETI stations would have a ghost of a chance of hearing. Leakage detection seems less likely, if only because of the transmit power requirements needed to show up on my system. Detecting planetary Radar also seems unlikely, because it seems that it would only be sent for short periods. Once a radar echo was recovered, the transmitter would most likely be turned off or pointed somewhere else. The modulation scheme needed for an effective Planetary Radar might also make it difficult to recognize on this end.
If I were ET I would set my beacon up in the waterhole to maximize its chances of discovery. I would want to be heard, and that is the most obvious place to start. The hydrogen line is at 1420 MHz and the hydroxyl line at 1662 MHZ. I would transmit at exactly 1/2 way between the two at 1541 MHz. I would expect ET to similarly transmit somewhere near the middle of the waterhole, if he wants me to detect him.
An ideal interstellar beacon should be narrow band to concentrate the transmit power, and to make it distinguishable from natural sources. It must be directed at our star. This is necessary to conserve power, and to make possible reception over huge distances. So a directed beacon is what I am looking for. I can see ET pointing such a beacon at each candidate star, one at a time, sending the beacon for some length of time, and then moving to the next star.
My ET’s interstellar beacon would be locked onto each star for about a year at a time. We may have missed ET's signal already, and may have to wait another 300 million years for it to show up again. Or, it may be starting tomorrow. Since we just don't know, we may as well assume that it starts tomorrow.
If I concentrate on looking for myself, I may well miss signals sent by those not like me. But I know that creatures who think like me exist (if only by Earth's own example.) Designing our search around those not like us involves pure speculation, and will reduce our chances for SETI success.
Regards……… Jim
www.SETI.Net
Posted by
Athena Andreadis on 06/01 at 12:40 PM
The Drake equation was never a formal equation, nor meant to be. It was a string of factors that the astrophysicists deemed relevant at that time. I think that the reason for its continued use is that it is widely known, partly from Sagan's legacy. If those of us interested in these questions want to make the Drake expression evolve, nothing is stopping us.
Regarding the tautology of the arguments employed in Rare Earth, here is my review: www.setileague.org/reviews/rarearth.htm (the concluding sentences are quoted in David Darling's Life Everywhere: The Maverick Science of Astrobiology). Finally, it is too early for astrosociobiology, given that we are still dealing with a single sample.
Athena
IEET Blog