What’s the dope on the detection of this signal?
I recently watched a “Naked science” episode on NatGeoTV which one of the SETI scientists theorized that it could have been a communication signal between two alien ships. From reading the wikipedia entry, the idea that it could have been from a natural source is debatable. Anyone have any info on this?
There’s really not a lot of data here. You have this anomaly that came in once. Listening to the same part of the sky didnt produce anymore signals. Also the fact that its on a specific frequency that is calculated using a 10 base system and a 60 second system proves to me that its terrestrial:
I dont see how someone arguing for ET could possibly explain that it came in exactly at 14.2700000.
This is why I think SETI is a waste of money. They are trying to find signals that we would use on earth. Don’t radio waves become static after a few lightyears or so? It also assuming aliens use a base 10 system. Isn’t base 8 “better” when compared to base 10?
The article you linked to doesn’t say the Wow signal was exactly 14.2700000 MHz. It’s talking about ways to determine if a “Wow”-type signal is terrestrial interference or not.
It’s a hypothetical, not what actually happened.
I have no idea what you mean about radio waves becoming static, and I’ve never heard of any SETI project that assumed that aliens use base 10 (or any other particular base).
I don’t know anything about signaling, so can someone explain why 14.27 is an exact number in decimal? What if it was 14.29 or 14.255, would that be evidence of human agency?
The number quoted was 14.2700000 MHz, not 14.27.
14.2700000 MHz means exactly 14270000 Hz, plus or minus 0.5 Hz, while 14.27 MHz, with no other qualifier, is typically assumed to be an approximate value that could lie anywhere between 14265000 and 14275000 Hz. If I found a source emitting at such an exact multiple of 10 kHz, I’m going to assume a human transmitter until proven otherwise.
It’s not the decimal that’s important for this argument so much as the long line of zeroes afterwards. If we measure the frequency of a signal to end with several zeroes (within the limits of our precision), then it’s likely that the time unit involved is some simple fraction or multiple of the second. A true alien signal would come in on a frequency more like 14.2763425206 GHz (plus or minus 0.0000000002 GHz) rather than 14.2700000000 GHz (plus or minus 0.0000000002 GHz).
Some simple wiki’ing gives this: Wow! Signal
Neither of these values is 14.2700000 MHz, so that’s not right. But doesn’t the fact that they’re near the hydrogen line suggest that they didn’t originate from too far away? I’ve heard of multiples of this frequency being suggested for our own attempts at contacting hypothetical extraterrestrials, because they would be relatively conspicuous and therefore easy for an observer to find. But this frequency itself would be quickly interfered with by interstellar hydrogen, wouldn’t it? IANAAstrophysicist, of course.
The other reason you wouldn’t want to use the hydrogen hyperfine line itself for a communication is because then your recipient would have to worry about the possibility that it was natural. It’s not too hard to come up with a scenario of something in nature that would emit a big burst right at that frequency; it’s harder to come up with a scenario that would emit at exactly twice that, or pi times that, or whatever.
I’m sure that many of you Dopers have heard of the Wow! signal (for those who haven’t; some people think that it may have been our first message from ET). I know that the signal was sent from an unoccupied area of space, on a radio frequency which I believe cannot come from natural sources. What I don’t get is, what exactly was in the signal? Was it significant simply because the signal came at all?
FYI, here’s a previous thread on the same subject.
Not static as opposed to dynamic, but static in the broadcast-signal sense. The signal-to-noise ratio deteriorates (or is presumed to deteriorate) below intelligibility.
Cheers for the link, Dewey. I did read through it but must admit, I’m still not sure I get it. Is the fact that it came through on a particular frequency the reason it could be a big deal? Obviously it’s not a direct message saying “Is anyone else out there?”, but wouldn’t you expect some kind of observable information with any such broadcast?
The signal is significant because it is a very narrow band of energy, which makes it much less likely to be of natural origin. It’s also on a protected frequency, which people aren’t supposed to broadcast on.
Unfortunately, there just isn’t that much you can say about the WOW signal one way or another, because there just isn’t much data there. The antenna that picked it up as actually a double antenna that does not move relative to the earth, so it scans the sky based on the earth’s rotation. The way it is designed, you can’t tell if a signal is coming in one antenna horn or the other. What you would expect, if it picked up a constant signal, is that you would see the signal twice, once for 72 seconds (peaking about halfway through) as the first antenna horn swept past, then again three minutes later for another 72 seconds as it gets picked up by the second antenna horn. The WOW signal only got picked up once, though. Of course, the signal could have started or stopped in between the sweep of the two antenna horns, so that doesn’t necessarily say much.
And that’s it. That’s about all we know. Yes, it was a signal. Was it extraterrestrial? Who knows. If both horns had picked up the signal, this would have been better evidence that it was extraterrestrial, but being picked up by only one horn doesn’t necessarily mean that the signal was not extraterrestrial.
The signal is significant because it was strong relative to the background noise. There isn’t enough data to make any other conclusions about it. This isn’t like some sci-fi movie where the entire signal was captured and can be analyzed with some spiffy 3-D screen display resulting from it. All we have is a chart of signal strength. We know the frequency. We know the signal strength. We know the bandwidth (roughly) of the signal. We don’t know how long the signal lasted, all we know is how long one horn of the antenna picked it up. That’s all we got. It ain’t much to work with. There may have been all kinds of “observable information” in the broadcast, but we don’t have that data.
Dr. Jerry R. Ehman, who discovered the signal, has cautioned against “drawing vast conclusions from half-vast data.” I personally like that quote.
Hmm. Sounds like we’d better call the world’s radio astronomers and explain to them that their field can’t exist.
Merged the new thread into the existing thread.
I think what is being stated is that due to relatively weak signals we send out (radio, TV, etc), we would not be detectable to far-away ‘civilizations’. After some distance (forget approx how far), our signals get so weak that they are drowned out back-ground noises and/or natural frequencies. An inverse-square law thing regarding the strength of any signal as it travels outwards from the source… Using radio telescopes to see humongous powerful ‘sources’ (like things the size of stars) is a bit easier overall than to pick out a very faint signal from natural background noise.
It is perfectly possible to get intelligable signals way below the level of noise. However there is a hard rule about this. It comes down to Shannon. The information in a channel is the product of the bandwidth of the channel and the signal to noise ratio. Now if the signal is less than the noise this doesn’t mean that the information rate is zero, it means that it is very low. Basically this means you just need to listen for longer to get any information.
My favorite example is the GPS signals. The signal to noise ratio for signals from a GPS satellite is -30db. The signal is a thousand times less powerful than the background noise across the same bit of spectrum. But if you know what you are looking for and listen long enough, you can pull the needed signal out of the noise and get your position fix.
Radio astronomers may need to listen for rather a while. The problem with the Wow Signal seems to be partly that it simply didn’t last any useful length of time - so even if we had an approriate recording - there still may not have been enough of it to gain any traction.
An interesting point about the GPS signals, and indeed a great deal of modern transmissions. Compression or encryption both seek to limit the amount of observeable entropy in the signal. A touchstone of how good your encryption or compression algorithm is, is how hard it is to externally predict the next symbol in the stream. This is why you need to know what to look for with a GPS signal. The signals themselves look just like noise unless you know the key. This, along with a huge host of other issues, is why SETI is essentially a total waste of time. Unless the aliens specifically want to talk to us, no even vaguely advanced technology is going to be wasting energy sending around signals that look any different to noise to the uninvited observer. Ships talking to one another? Only in B grade SciFi movies. “SETI scientist” is getting close to an oxymoron here.
While a highly-efficient compression of data will leave it indistinguishable from random noise, nobody actually uses or even wants compression that efficient. All real compression schemes will put in a little extra information that’s completely predictable, in such a way that deterioration of the signal can be corrected or at least detected. This would actually make alien transmissions easier to recognize, not harder: We probably wouldn’t be able to figure out how to decompress the data, but that’s fine, because we would be able to recognize that it is compressed, and the most important message we could get from the data anyway is the mere fact that the aliens exist.