When listening for signals from aliens, it isn’t enough to just point an antenna at the sky. One must also choose details like directions, angles, frequencies, bandwidths, pulse widths, and pulse intervals. Apparently most SETI searches assume that for a given signal power density, aliens would pick details to make it as easy as possible for us to detect their signals. So standard SETI searches are optimized for such easily-seen signals. Two
This is why I think SETI is a waste of time and resources at present. We're a decade or two away from being able to directly search for life bearing planets. At that time any search for signals could be made vastly more efficient and precise.
The range of possibilities is far too broad right now to have much hope of detecting anything.
Not that different from a game where someone is trapped in rubble say, and others are searching for them. How loud should you yell and how frequently to maximize the probability you are found.
Looking at our own economically constrained system, I see a galaxy of civilizations all solving that game by adopting a strategy of listening, while rarely (potentially randomly) sending deliberate beacons. The primary emissions in that case would be from aliens communicating with themselves or their long range probes, potentially with analogs of the Deep Space Network (including repeater stations for longer distances, so highest directivity would be towards nearest/nearest habitable/nearest useful stars).
In that case, they are likely sending large amounts of information at high bit rates, and economic constraints would lead you to actually minimize energy density at fixed range (i.e. just enough to meet requirements).
The fundamental theoretical constraint for detection is the amount of energy required to erase one bit of randomness (I'm here!) = k T log 2 at a given range, which leads you to maximize energy density at fixed range in optimal directions. Although I think a more detailed analysis with the Shannon limit is called for. Optimal communication through a noisy channel should minimize false alarms. Since signals are presumably rare, you don't want the one you find to turn out to be a fluctuation.
It also looks like a coordination problem. If some alien species had found another one, then they might be more likely to "cooperate" and maximize the probability of communication with a new species.
Robin, I'm not an astronomer or SETI participant, but I invent, design. and analyze antennas (especially high power microwave antennas) for a living. You know where to reach me. :)
This is why I think SETI is a waste of time and resources at present. We're a decade or two away from being able to directly search for life bearing planets. At that time any search for signals could be made vastly more efficient and precise.
The range of possibilities is far too broad right now to have much hope of detecting anything.
Good analogy!
Not that different from a game where someone is trapped in rubble say, and others are searching for them. How loud should you yell and how frequently to maximize the probability you are found.
Looking at our own economically constrained system, I see a galaxy of civilizations all solving that game by adopting a strategy of listening, while rarely (potentially randomly) sending deliberate beacons. The primary emissions in that case would be from aliens communicating with themselves or their long range probes, potentially with analogs of the Deep Space Network (including repeater stations for longer distances, so highest directivity would be towards nearest/nearest habitable/nearest useful stars).
In that case, they are likely sending large amounts of information at high bit rates, and economic constraints would lead you to actually minimize energy density at fixed range (i.e. just enough to meet requirements).
The fundamental theoretical constraint for detection is the amount of energy required to erase one bit of randomness (I'm here!) = k T log 2 at a given range, which leads you to maximize energy density at fixed range in optimal directions. Although I think a more detailed analysis with the Shannon limit is called for. Optimal communication through a noisy channel should minimize false alarms. Since signals are presumably rare, you don't want the one you find to turn out to be a fluctuation.
It also looks like a coordination problem. If some alien species had found another one, then they might be more likely to "cooperate" and maximize the probability of communication with a new species.
Robin, I'm not an astronomer or SETI participant, but I invent, design. and analyze antennas (especially high power microwave antennas) for a living. You know where to reach me. :)