Celebrity endorsement impersonated

     

 

 

I hate the French! Give back our weirdo hillbilly television, you goddamn Frogs!
-- Tjames Madison

 

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

How to Outshine the Sun

"So that's kind of neat."

Splicer

Splicer looks into the Pattern, as
the Pattern looks back at him

TCS: Do you look at things other than the simple narrow-band signals? Do you look at the patterns that are created here on Earth, to see perhaps what you should be looking for?

Seth: Well, no, not so much, because keep in mind that in order—if there are radio signals washing over this room right now, as we expect that they are, then they're going to be weak. Because if they were really, really strong, probably we would have found them by now. There have been some surveys in the entire sky. And so if there were persistent, very powerful signals somewhere in the sky, those would have been found. So the expected ET signal is not going to be, you know, enough to cook birds at this distance or anything like that. They're going to be weak.

And in order to find weak signals one thing you can do is, as it were, make a time exposure. Just the way, with a camera, if you want to take pictures at night, you leave the shutter open for a long period of time and let the light build up. You can do that, and you can see very faint things that way. Astronomers do that all the time. But if for example you were making a photo of a pulsar, with a telescope that way, and you exposed the film for 20 minutes, then you wouldn't know that pulsar was flashing, would you? It would just be a bright spot on the film.

Well, we do exactly the same thing in the radio. We, as it were, integrate the signal over 300 seconds in order to build up the sensitivity. But that means if it's changing a hundred thousand times a second, or millions of times a second the way a TV signal does—all that's gone. It's all lost. So that's why finding the message is much harder than finding the signals; finding the signals you can integrate. What we do do is, we look at—we break up the data into one-second chunks, and we see if there are any pulses in there. Slow pulses. Beep. Beep. Things that are longer than a second in frequency. Then we would find those. We do look for those kinds of pulses. But nothing more complicated than that, because of the sensitivity.

Siduri: I think Steve was asking, though, if we were looking at what we're sending out there, just accidentally?

TCS: That's what I asked, although I think that Seth in his answer addressed that that was not...

Seth: I should have said...

TCS: ...that it wouldn't be very fruitful to figure out what we're sending out if we're not going to be able to hear it.

Seth: Right. What you're saying is that what we should be looking for is the kind of stuff that we send out?

TCS: Right, and you said that we wouldn't be able to hear the kind of things that we send out.

Seth: Yeah, what you could hear from Earth are powerful military radars—not very interesting to listen to, but powerful—or TV signals. You know, one-third of the power in the TV signal is from the carrier, which is this very narrow-band component of the TV signal. I don't know if you know this, but a TV signal is spread out over four or five megahertz—a big chunk of the dial. But there's a very sharp carrier component, which your TV set needs to tune in. So one-third of the power is going in there. And that's 10,000 times easier to find than the picture itself. So that's what you would hear from Earth, is carrier signals. Really big antennas could see I Love Lucy. You'd know that the TV transmitter is on, you just wouldn't know what show it is. If you want to know the show you'd need lots of antennas.

Mark: Is SETI looking at different kinds of modulation other than just amplitude?

Seth: Well, as I say, we don't look for really modulation at all, we just look for energy within a given band. The way it's changing...

Mark: Perhaps polarization changes, or...

Seth: Yeah, you could look for all that, those are ways to encode information on the message. But unless it's very, very slow—really slow—then we won't see it, because we just average everything. As I say, it's like taking time exposures. Take a picture of the city and you'll see that the stoplights have red, green, and yellow all lit up on the film. All the real information about how that's cycling is gone.

Siduri: Now, isn't there an optical SETI program starting up?

Seth: Yeah. There is. In fact, that's the Berkeley one; picture's over here. But there's one the Institute is involved with, and that's at Lick Observatory, down near San Jose. You ever been to San Jose?

Siduri: Uh-huh.

Mark: Nice drive up there. I wondered what those...

Seth: Mostly, they—actually, that's where a lot of these extrasolar planets have been found.

Siduri: Really?

Seth: Yeah. Geoff Marcy, who found probably more than anybody, works at San Francisco State, and Berkeley. But that's a telescope that he's been using. Now he's using the Keck telescope in Hawaii. But they still use this thing; they use it for a lot of stuff. Anyway, there's a telescope out there; I have a picture. There's a telescope up there with a one-meter mirror, and this young lady, Shelley Wright—she was an undergraduate, 23 years old I guess, or 22—she built a box to go in the back of this thing to look for flashing laser pulses. And so every night they use that telescope—not every night: those nights that it's available, which is about half the nights—they point it at nearby stars.

What they're looking for is flashing lights. And the reason this makes sense is because—I mean, you might think "Enh, that doesn't make sense, because the star itself is putting out a lot of light and that'll swamp any laser on a planet orbiting the star; you can't even see the planets, how could you possibly see somebody's laser?" Well, it turns out that if you take the most powerful lasers that we could make, the ones they have at Lawrence Livermore and places like that, that if you aim that laser into a mirror that's the size of this table or something, and then aim it at a nearby star, and put all the power from that laser into a billionth of a second flash, you see, concentrating the energy in time now, then for a billionth of a second that laser will outshine the star.

Siduri: Oh wow.

Seth: Yeah. So, what she does is, she just looks for a billionth of a second and looks for a bunch of photons coming in. It wasn't originally her idea, but that's the experiment we're involved in. And that's kind of neat, because nobody's really done that much before, so you could maybe find something. Maybe some alien civilization nearby has a big laser, and they've just got a little mirror assembly for the output of the laser, and it directs the light onto a big mirror [mutter mutter]. But, you know, they just ping each star that's near them for five seconds a day or ten seconds a day. They don't know which ones might have civilizations, but they just do this, automatically. And then all we have to do is get a lot of people looking at a lot of stars and we'll see some that are pinging our way. So that's kind of neat.

Siduri: How long has this been going on for?

Seth: It's been going on for about six months. I mean the idea of looking for flashing lights in the sky is not new, but actually doing it is new.

Next page: SETI@Home

 

Over.  End of Story.  Go home now.

vwbugger@pigdog.org


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