國家地理:New Search For ET 尋找外星人（下）
Is anyone out there? For over 40 years scientists have been searching for extraterrestrial intelligence, but they’ve found nothing. Now the new Allen Telescope Array, a string of 350 radio telescopes, is being built 300 miles north of San Francisco and is breathing new life into the search. Find out why SETI scientists now say we might be hearing from ET sooner than you think.
Senior SETI astronomer Seth Shostak tells us how this new telescope will work.
“And clearly, we are trying to find evidence of ET, and we are trying to do that by looking for a signal, in what’s called the electromagnetic spectrum, which is a fancy way of saying the radio dial, at least for us. Let me turn on my radio here, okay, now you hear that static, all right. That's just all natural noise. Galaxies and hot gas between the galaxies, and pulsars and quasars, they all make radio noise. And it’s everywhere on the dial. But if I tune more far over here, get that squeal and then, right there, intelligent life, okay. And that’s the difference between nature and some deliberate signal, because it’s at one spot on the dial. Nature does not make signals that are restricted to one spot on the dial in general. It just doesn’t do that. ”
Since the cosmos just don’t make Nero focus signals like this, finding one would be an almost certain sign of an alien culture. So what is it about this new array that makes it more likely to succeed? ''The Allen Telescope Array, basically, is all about speed. We can look at more than one star at once. And so whereas in the last decade, we looked at about a thousand stars, in the next decade, we’ll look at a million.''
That’s because the Allen Array's field of view, the area of sky it sees at one time is much larger than any other telescope. And it can capture millions of frequencies from multiple star systems simultaneously. Basically, the Allen Telescope Array is a SETI hot rod with SETI astronomers at the controls 24/7.
“So, if you look inside here, you kind of see where the robot meets the rod in terms of these antennas. I mean, the operation is actually in principle very very simple. The radio waves come in from the sky and then they come down to this Buck Rogers-looking thing here. This is called the feed. But really all it does is to take sorts of incoming radio waves and amplifies them and turns them into electrical signals, the things go down to a fiber rob cable back underground to the control room. Now, this thing looks so funny, because it’s got to be able to pick up radio waves at various wavelengths from the, you know, from relatively long to relatively short. So that’s why it has this taper-looking backgear here for the longer wavelengths and front-line for the shorter.”
“The antennas send everything they collect from the cosmos into this room, there comes in like I hear. If you think of what Frank did in 1960, he had one channel of radio noise, he was modeling one; here we’ve got a hundred million channels coming in and then we move up the dial to take in another hundred million and another hundred million.''
The sheer scale of the search is almost impossible to imagine. Remember, in our galaxy alone, there are over three hundred billion other suns, many with orbiting planets. And beyond that, lie a hundred billion other galaxies, just like our own. Even in its current configuration, the arrays virtual dish gathers nine times more information than present-day processor technology can decode. That means, ninety percent of what the telescope observes is simply thrown away. So for the next decade or two, the technology in this little room will be playing catch-up with the dishes outside.
“We know that technology is gonna continue to advance in an exponential rate, and so all this stuff will be replaced in another five years by yet faster machines which allow us to look at more star systems, more channels, in other words, to speed up the SETI search.”
And as that search accelerates, Tarter and other SETI scientists are thinking about the consequences of success.
“If we detect a signal, we’ll do everything that we can at the sight to make sure that it isn’t our own technology that’s fooling us, or that it isn’t a deliberate hoax. If we get an independent confirmation, then, we will in fact tell the world, because a signal isn’t being sent to the Allen Telescope Array, it’s being sent to the planet earth, and the planet earth deserves to know about it.”
But once the world has been notified, then what? Let’s just say, an official response plan, probably won’t be necessary. “If you ever announce that you’ve detected a signal, and give the description of what it is and where it’s coming from. Anybody with a transmitter is gonna get on the horn and shout whatever they want. And wouldn’t that be just about the best characterization of 21st century earth in an unorganized cacophony?” That’s exactly the kind of thing SETI scientists are seeking. Even the accidental noise of an alien culture would answer one of the most ancient questions of all--Are we alone?
''Humans have been asking it forever. The probability of success is difficult to estimate, but if we never search, the chance of success is zero.''
pulsar: 脈沖星
rotating neutron stars that are observable as sources of electromagnetic radiation.
quasar：類星體
an astronomical object that looks like a star in optical telescopes (i.e. it is a point source), and has a very high redshift.
exponential：
exponential growth, increase etc becomes faster as the amount of the thing that is growing increases
cacophony：
sound that is harsh and unpleasant-sounding.
Senior SETI astronomer Seth Shostak tells us how this new telescope will work.
“And clearly, we are trying to find evidence of ET, and we are trying to do that by looking for a signal, in what’s called the electromagnetic spectrum, which is a fancy way of saying the radio dial, at least for us. Let me turn on my radio here, okay, now you hear that static, all right. That's just all natural noise. Galaxies and hot gas between the galaxies, and pulsars and quasars, they all make radio noise. And it’s everywhere on the dial. But if I tune more far over here, get that squeal and then, right there, intelligent life, okay. And that’s the difference between nature and some deliberate signal, because it’s at one spot on the dial. Nature does not make signals that are restricted to one spot on the dial in general. It just doesn’t do that. ”
Since the cosmos just don’t make Nero focus signals like this, finding one would be an almost certain sign of an alien culture. So what is it about this new array that makes it more likely to succeed? ''The Allen Telescope Array, basically, is all about speed. We can look at more than one star at once. And so whereas in the last decade, we looked at about a thousand stars, in the next decade, we’ll look at a million.''
That’s because the Allen Array's field of view, the area of sky it sees at one time is much larger than any other telescope. And it can capture millions of frequencies from multiple star systems simultaneously. Basically, the Allen Telescope Array is a SETI hot rod with SETI astronomers at the controls 24/7.
“So, if you look inside here, you kind of see where the robot meets the rod in terms of these antennas. I mean, the operation is actually in principle very very simple. The radio waves come in from the sky and then they come down to this Buck Rogers-looking thing here. This is called the feed. But really all it does is to take sorts of incoming radio waves and amplifies them and turns them into electrical signals, the things go down to a fiber rob cable back underground to the control room. Now, this thing looks so funny, because it’s got to be able to pick up radio waves at various wavelengths from the, you know, from relatively long to relatively short. So that’s why it has this taper-looking backgear here for the longer wavelengths and front-line for the shorter.”
“The antennas send everything they collect from the cosmos into this room, there comes in like I hear. If you think of what Frank did in 1960, he had one channel of radio noise, he was modeling one; here we’ve got a hundred million channels coming in and then we move up the dial to take in another hundred million and another hundred million.''
The sheer scale of the search is almost impossible to imagine. Remember, in our galaxy alone, there are over three hundred billion other suns, many with orbiting planets. And beyond that, lie a hundred billion other galaxies, just like our own. Even in its current configuration, the arrays virtual dish gathers nine times more information than present-day processor technology can decode. That means, ninety percent of what the telescope observes is simply thrown away. So for the next decade or two, the technology in this little room will be playing catch-up with the dishes outside.
“We know that technology is gonna continue to advance in an exponential rate, and so all this stuff will be replaced in another five years by yet faster machines which allow us to look at more star systems, more channels, in other words, to speed up the SETI search.”
And as that search accelerates, Tarter and other SETI scientists are thinking about the consequences of success.
“If we detect a signal, we’ll do everything that we can at the sight to make sure that it isn’t our own technology that’s fooling us, or that it isn’t a deliberate hoax. If we get an independent confirmation, then, we will in fact tell the world, because a signal isn’t being sent to the Allen Telescope Array, it’s being sent to the planet earth, and the planet earth deserves to know about it.”
But once the world has been notified, then what? Let’s just say, an official response plan, probably won’t be necessary. “If you ever announce that you’ve detected a signal, and give the description of what it is and where it’s coming from. Anybody with a transmitter is gonna get on the horn and shout whatever they want. And wouldn’t that be just about the best characterization of 21st century earth in an unorganized cacophony?” That’s exactly the kind of thing SETI scientists are seeking. Even the accidental noise of an alien culture would answer one of the most ancient questions of all--Are we alone?
''Humans have been asking it forever. The probability of success is difficult to estimate, but if we never search, the chance of success is zero.''
pulsar: 脈沖星
rotating neutron stars that are observable as sources of electromagnetic radiation.
quasar：類星體
an astronomical object that looks like a star in optical telescopes (i.e. it is a point source), and has a very high redshift.
exponential：
exponential growth, increase etc becomes faster as the amount of the thing that is growing increases
cacophony：
sound that is harsh and unpleasant-sounding.
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