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Interview with Seth Shostak —Reported 2001-12-21 19:42 by Siduri

How the Hell That All Works

"And if you don't hear ET there? Well, tough toe-corns."

Mark: Now, I imagine there must be many, many false alarms. Things that are picked up and determined to be background noise, anomalies, perhaps galaxies emitting natural things that while they have patterns, they're not signs of intelligent life. How do you determine whether a pattern is background noise or a signal?

Seth Shostak

Seth indicates where the ay-leens come from

Seth: Yeah, well, this is a question we get asked a lot—"Do you have a cryptologist or a cryptographer sort of looking at these things to say, well, this looks natural, that looks artificial?" In a way we do, although we really don't. We don't have any cryptographer. We can barely afford to have someone just clean up the rooms. The way it's done is, the nature of the signal itself is the decryption. If it's a narrow-band signal, that's something that's really easy to build a transmitter to make, but that's extremely difficult for nature to make. Nature doesn't make narrow-band signals.

I mean, listen to quasar with a radio telescope and you hear "PSHHHHH." It almost doesn't matter where you turn your knob, you'll hear that blank noise 'cause it's all across the band. Even if you listen to a pulsar, pulsars go on and on, maybe a thousand times a second, faster in some cases. But what you hear is "PRRRRR" or "PSH-PSH-PSH-PSH-PSH." It's still white noise. It doesn't matter where you're tuning your radio. You'll hear the pulsar, you see. Tune across a wide, wide range of frequencies and you still hear "PSH-PSH-PSH." So that's clearly nature because nature doesn't care about wasting a lot of energy. No person who was designing a transmitter would build one that sent ten pulses a second all over the band. It's a total waste of energy; it's bad engineering.

So that's how you do it, you say, "Hey look, if they put all the energy into a small region of the dial, that's something nature never does but transmitters do all the time." So that's how you tell.

Mark: Now, have we scanned the entire spectrum?

Seth: No, not by any means. We have only looked at a tiny fraction of the radio spectrum. Our experiment, Project Phoenix, which is run by the Institute—[pointing to a photograph on the wall] that antenna, the one in the middle—looks at more of the spectrum than any other experiment ever has. It's looking over from 1,000 to 3,000 megahertz. Each channel is about 1 Hz wide so that's like 2 billion channels for each star that we look at. That's still not the whole spectrum.

Mark: This is actually a question that came from one of our contributors. I don't know if it was Paul or Zach. They were under the impression that the signals are scanned for 300 seconds, approximately?

Seth: Yeah, that's about right.

Mark: How do you determine which bands to target first?

Seth: Oh, well, we just start at the bottom of the band and work up. How are you gonna know. If you start at the bottom of the band you may miss ET's transmission at the top of the band, yeah, but maybe if you start at the top of the band you'll miss his transmission at the bottom of the band. You don't have any information about that so you just—it's a matter of being methodical. We always do it the same way. Start at the bottom of the band and work up. It takes, you know, about ten to twelve hours to go through all those frequencies for any given star.

Mark: Yeah, but how much information is captured in that five minute window?

Seth: Well, in a five minute window you're listening to 28 million channels. So you're getting information about 28 million, actually, it's 56 million channels. It's 28 million frequency channels, but the receiver has—there are two polarizations that you're actually sensing, so there are actually two receivers in one at the focus, so it's actually 56 million channels. So during that five minutes you're looking for signals that are within those 28 million frequencies. And if you don't hear ET there? Well, tough toe-corns, move up and do 300 seconds on the next batch of frequencies. No ET? Go up the dial a little bit and do more, and that's the way it's done. And actually, observing one star isn't done at once, it's done in pieces, over the course of a couple days.

Siduri: I believe Paul's exact question was, "Ask how the hell that all works."

Seth: How the hell that all works. Well, what didn't I answer?

Mark: Perhaps you could start by telling us, once the data is collected by the telescope, where does it go? The project has been going on longer than hard drives have been in common use to store this data.

Seth: Mm-hmm.

Mark: Does it get printed out onto paper reels?

Seth: In the old days it was printed out on paper, yeah, it was. Not anymore. Those were the good old days. You could come in and there was only one channel, or ten channels, or some small number of channels, a hundred channels. So it was possible to put all the data out on a, usually a line printer. In the very earliest experiments it was just a strip-chart report. You know, one pen on a piece of paper. Maybe two, if you had two pole positions. When Frank did the first experiment in 1960, that's the way it was done. He just had a little motor that essentially turned the knob on the receiver and turned it up and down the dial, very slowly, you see, so the frequency was changing. And you could just look at the output. And he had a loudspeaker connected to it. It was all very simple. And then ten years later you could look through a hundred channels at once, so then you needed a line printer.

That was what was being used in 1977 at Ohio State, when some guy came in in the morning looking through the stack of computer printout, and saw one big signal and said "wow!" Wrote WOW next to it. The Wow Signal.

Mark: Can you talk a little bit more about that?

Siduri: Yeah, whatever happened to that?

Seth: Yeah, the wow signal. Well, it's pretty wow-y. But it doesn't seem to have been ET. Lots of people have gone back and they even, they immediately had a following beam on the sky that swept through that same patch of the heavens, just shortly after they got that signal, and didn't see it. And people have gone back there looking, you know, with more sensitivity, more frequencies, and nobody's ever found it again. So it's not good enough. It's like seeing a ghost in your basement once. It's not enough to believe in ghosts. If you see them every time you look, now that's okay, you might believe then. So it was undoubtedly some sort of interference.

Siduri: Is that the closest you've ever come to finding...

Seth: Well, how do you know? That's like pregnancy, I mean, are you close? It's not a matter of close, it's yes, it's a one-bit experiment. It's not that you're close. There have been lots and lots of false alarms. Particularly in the early days, because in the early days you would usually report the data. As you said, it was before hard disks. But what would happen is that you would go the telescope and you had a hundred channels, and normally you would just write everything to computer tape. Back with these big tapes, and you would put them on computers wherever you were, and play 'em back, and then look at all the data.

And you'd always find signals. You've got these huge antennas, you know, with very sensitive receivers, and hundreds of channels, thousands of channels, and now millions of channels, so of course you found signals. But then what did you do? What do you do with them? You could call up the local papers and say, "By the way, I found all these signals," and that would work the first time. But, well, how do you know it's ET? And you say, "well, I don't know." Then the next time you went back to Tucson you'd try to look at those parts of the sky again. And that's very tedious.

But now, what we do, is we check out all the signals right away, in real time. All the data's processed real time. So you don't leave the telescope with a stack of mystery signals. You know each one of them because you tracked it down. So in the early days there were lots and lots of these sorts of false alarms. Not anymore.

Mark: Does that mean that the sensitivity to signals may be less now than it was before?

Seth: No, the sensitivity's clearly better now. The sensitivity's better but the processing's better. That's just because, you know, digital electronics is better than it was. So now you can conceivably process everything in real time. That's the way it's done. When you're sitting down there in Puerto Rico, you're sitting at the control room, and the signals are coming in about—you get hundreds of signals every night. Hundreds. And each one of them is checked out. So far each one of them has been us.

Next page: Hoaxes and False Alarms

 

Over.  End of Story.  Go home now.

vwbugger@pigdog.org


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