[UnderseaLcpl]

Originally Posted by Gargamel

The problem with that statement is that Xenobiology is an unknown sciece. Without ever studying anything, there is no way to ever say that is true or not.

True enough, but I still think the probability of finding anything worthwhile is small enough that there is no need to actively invest in xenobiology or much beyond localized space exploration, not including orbital observatories.

There are almost an infinite number of frequencies that could be broadcast on, and we have to directionally focus our receivers to listen for these signals. Now multiply that by the number of stars to listen to.... You get the idea why it's taking so long. And then you have to process each glump of data to figure out whats out there.

I used to think the same thing myself. However, once I began studying as a radio operator and took the time to get into the nuances of advanced elements like antennae theory and waveform propagation, I am no longer so sure.

The means by which SETI attempts to detect transmissions through ground-based directional receivers is actually kind of silly. Any type of long-range communications, such as those that would be used to communicate between planets or between a planet and a long-range probe, rely upon powerful transmitters that must operate on relatively long wavelengths to overcome interference.

Think of it this way: a large electromagnetic wave is a lot like a large wave of water, or a very loud sound. It may hit obstacles and suffer some loss of integrity as a result, but the wave is still mostly intact unless it runs into something bigger than it is. Even then, it retains enough energy to bounce off of whatever it hits and then bounce again multiple times and can still be received by the intended recipient. However, it will also be recieved by anyone else within "earshot".

In the void of space, there is virtually nothing that can block a large wave, so it is very likely that we would have detected such transmissions by now if they emanated from a reachable source.

Now, it is possible that an advanced civilization might employ some kind of advanced directional transmission technology that had enough raw power to overcome EMI and enough accuracy to reach a cosmically distant receiver, but such a method of transmission would generate enough "bleed-off" radiation that it would be detectable from a tremendous distance. There is no such thing as a truly "directional" transmitter aside from a physical connection. All antennae are sources omni-directional radiation to some degree, and when you consider the amount of power that it takes to transmit a short-wave signal or a microwave signal reliably over a long distance, those power requirements would be very high.

Hence, we would detect the "spilled" radiation from either source quite easily, assuming we employed an omni-directional reciever in very high orbit, away from the tremendous destructive interference of the earth's atmosphere and magnetospher. Beyond that, it's just a matter of looking for recurring instances of patterned EMF, which a computer can do easily, and interpreting the data.

This is why I say SETI's approach is kind of silly. If they really wanted to find evidence of extraterrestrial intelligence, they'd abandon this ridiculous approach of using ground-based dish receivers tuned to look for specific frequencies from specific sources, a few at a time. An orbital omni-directional receiver, which essentially amounts to a large, lightweight EM tuning-fork in space would serve the same purpose and do it much better.

(Coincedentally, if you want to help with that, you can join me help filter the data while your computer is not doing anything functional by joining BOINC and installing the SETI@Home project.

Thanks for the info and the links I'll take a look and consider joining the effort, provided it doesn't add any unreasonable strain to my already somewhat-taxed system resources. I really need to invest in a newer computer.

As much as I complain about SETI, the organization is there already, and if they have a way for me to help I might as well try it.

Your saying we should be able to see the exhaust from a single ship within 30 years travel, when we are having difficulty detecting asteroids the size of small towns that are a few days/weeks away?

Yes, that's what I'm saying. You're thinking in terms of active detection. Asteroids are small, cold rocks in space. To detect them, we have to actively paint them with a signal of sufficient power to generate a return, but without so large a wavelength as to miss the object entirely or bounce in a direction not aimed at our receivers. Think of it as looking for a periscope that is millions of miles away with decimetric radar.

A spacegoing vessel that is capable of interstellar or even interplanetary travel at practicable speeds, on the other hand, would generate a tremendous amount of heat radiation by virtue of the energy needed to accelerate its mass, and then slow it down on approach. Even for a very lightweight vessel, we're talking about trillions of kilojoules of energy. That kind of energy would show up on our radio telescopes.

Probably true, but nothing ventured nothing gained. Kennedy's to the moon speech is coming to mind.

And what did we ever get from the moon? It cost us the equivalent of $150 billion or so in today's currency just to land there once and get a some rock samples. Then we went there repeatedly. A lot of scientific data was gleaned in the process, but how much of it do we ever use? How much of that money would have been better-directed at developing something practical, like satellite technology or economic priorities?