If we wanted to design a communications system for communicating with a planet around Alfa-Centauri could we communicate directly? I highly doubt it. The radiation from the Sun would outshine the artificial radiation source by over ten orders of magnitude. At best the angular separation would still be less than one second of arc. I would imagine the only way to do it would be to place a relay station .1c out in the Oort Cloud and the same at the other end.

Why would we use uwave radiation which is where SETI is looking? We would not. Lasers are far more efficient. Any spillover radiation, like the in movie Contact, would be drowned out by the distant star. How can SETI expect to find anything?

Seti is not looking strictly for intentional communication, but errant signals that were basic communication. The signals radio/TV that are emitted from earth have a range of about 100 light years before the dissipate into the noise background. Since our signals have been traveling about 100 years, stars 100 light years away may just be getting our signals. likewise, stars 50 light years out could have received signals 50 years ago, and either attempted a reply, or jumped in their ship at light speed, and would just be reaching us. Now even that would be a 100 year round trip for an alien species, even if they just stayed a day or two before returning. Our sun is a G Type star, and there are only 63 G Type stars within a 100 light year radius.

the Astropulse signals we are trying to detect should have a range of 50,000 light years, but that data, as well as multibeam came from Arecibo. The new green bank data is actually targeted from newly discovered planetary systems. For an alien to detect a signal from earth, would be easy within 100 light years. We broadcast continuously. With us detecting an alien signal might me more difficult, depending on if they allowed continuous transmissions, or just directed transmissions. Finding a needle in a haystack would be easy compared to this search.

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

If the signals were coming from deep space you would be right, but that is highly unlikely. They would be coming from an Earth like planet orbiting a star. The star would completely jam the signals. In the satellite communications business this is called a Solar Transit Event which occurs two weeks a year for about ten minutes. This is when the Sun passes behind the satellite. Viewed from several light years away the event would be constant.

You are incorrect in that the Sun will outshine any attempt at communication.

Any transmission from us would be extremely narrow-band: perhaps at a single frequency of light. For instance, a detector for humans works on the frequency of our bodies emitting in the infra-red at 98.6 degrees even in broad daylight. The sun's radiation is splashed over a wide spectrum and we would choose frequencies that had less of the sun's energy than others.

Even 50 years ago we designed sensors for humans that would respond the instant that any person walked into our Lab. Sensors could be designed now that are vastly more sensitive.

But SETI does not search at light frequencies. Uwaves are not that selective. It would be an interesting calculation to see if a 10KW laser could outshine the Sun even in a width of 1nm. I doubt it. Considering the power output from the Sun even in a 1nm slice the 10KW laser would be jammed out by several orders of magnitude from the Sun. No signal has a hope of being received without angular separation from its star.

The problem with detecting a laser, is that it is a targeted signal. Unless an alien species first knew we were here, (100 light year distance our own radio waves have traveled to be discovered.) there would never be a reason to point a laser at us. Depending on a bunch of math, I'm not sure that if they pointed it at mars that we could detect it. (It depends on how distant the star was, and how much the beam spread out.) It is far easier to detect a omni-directional signal, than the minute chance of a directed signal. After all, no civilization outside of 100 light years would have any idea there was intelligent life here. They can do what we do, and detect a planet in the Goldilocks zone, but that's it.

Steve

Edit: A laser is also a short duration signal. The radio broadcast we are doing are constant, and easier to detect. We may get laser pulses for a few minutes, and unless we were looking directly at them when they hit us, we would never know.

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

I agree. Another reason why I dont think SETI will ever find anything.

Seti is just a search. We may detect something in a day, a week, a century, or a thousand centuries. Or we may never detect anything. To not search is to never try to discover what may be there. With Arecibo, there is a 3° band that we can see as the earth rotates, and goes around the sun. We are not selecting the data, but analyzing the data other scientists have taken. With the Green Bank data, we are actually targeting exo-planets. The chances of detection are still very small, but much greater than the random data we get from Arecibo. We would all love to actually discover an intelligent signal, and it would change things on this planet forever. We are a part of that search. At least we have identified places where signals are not found, whether they were sent or not. The earth would be easy to detect within the 100 light year distance, as we do broadcast 24/7. An alien species, even with technology, may or may not do the same thing. With some 40 trillion galaxies, each with hundreds of billions of stars, most of which have maybe a dozen planets, the chances of us being the only intelligent life are incredibly small. The problem is to detect and identify another civilization.

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

My point is that searching for uwave signals within one second of arc from a star is futile. The odds are zero. The star will jam any artificial signals. Am I wrong?

Yes, you are wrong. What is important is distance, and strength of signal. The signals we broadcast, not only have reached about a 100 light year distance, but beyond that fall into the background. If what you say is true, then the voyager would not have been able to hear the last commands we sent it. I believe the last command was this year, and it is in interstellar space.

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

Voyager is pretty close. Its antenna can differentiate between the Sun and the Earth. At stellar distances this is impossible. Even with Voyager I I would imagine that there are several weeks per year when outbound communications are impossible due the the Solar Transit Event. With Voyager II this might not be a factor since it is outside the ecliptical plane.

My point is that you cant point an antenna at a star and expect to get anything but solar noise.

Randy, an example that you are wrong is the fact that we can communicate with probes like the Voyagers that are very far out from the sun, even when the earth is immediately in front of the sun from the point of view of the probe.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

Bob's right. Think of constructive and destructive radiation. In order for the sun to cancel out a radio signal, it would have to be broadcasting at exactly the same frequency, but 180° out of phase. Yes, the suns radio emissions would be stronger than the earths, but the earths would not be cancelled out. In Seti, we are looking for signals that have frequencies most like that of hydrogen, which carry long distances through interstellar space. Even if we matched the suns frequency, the sun would not cancel out any modulation. Although the frequencies we listen to have greatly expanded since we first started looking, we are still looking at the frequencies most able to travel through space. We are thinking of what we would look for, if it was our intention to broadcast out from the earth. I think we have only sent signals out twice, and they were frequencies that would achieve distance.

Steve

Edit: Of course the radio signals we constantly transmit, are not near the suns frequency, but will still dissapate around the 100 light year distance.

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

Randy,

if what you say is correct then we are wasting our time here at SETI@Home. Perhaps you are thinking about the effect of solar flares on the ionosphere here on Earth which can disrupt communications that depend on bouncing off of this layer.

I suspect that searching for ET signals from near a star may well be a waste of time.

Constructive/destructive radiation is only a factor if the frequencies are identical. Unless they are synchronized this basically never happens. We are talking about noise here. Maybe some of you remember the '70s vacuum cleaners that made your TV turn to snow every time they were turned on. Same idea.

Forget Voyager, how about the Mars rovers. I suspect that JPL takes a vacation two days a year when the Earth passes in front and behind the Sun. In any event communication would be impossible on those days. Predictable losses of signal are trivial things. Think of spacecraft passing behind the Moon.

Someone else will know for sure but I would guess that as seen from Mars the earth would only take a few hours to pass in front of or behind the sun and I have never seen a reference to LOS for that reason.

You are not the only person that thinks that SETI is a waste of time and their reasons are varied.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

As I suspected the earth and Mars are not exactly on the same plane as they orbit the sun and therefore only on rare occasions would the sun mask a signal from Mars to the earth or visa versa.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

Radio astronomy is one of Eric's areas of expertise. I would be really cool if he were able to offer Randy some information that might tell him where he's misunderstood interstellar radio communication.

I've just got to wonder why people like Randy (and many others who have asked similar questions) are here to start with with such opinions in the first place where scientists think otherwise.

Randy, if you can work out how to intercept laser beams then let us know.

Cheers.

Simple, you point the HST at the laser, of course it only works if the laser is sufficiently far from the star (Oort Cloud) and is pointed at you. A tiny chance is better than no chance though. Like I hypothesized in my original post I cant think of another way of communicating between two solar systems.