英語語言學(xué)習(xí)：地球人與外星人
Douglas Vakoch: For 50 years astronomers have been pointing radio telescopes at stars, looking for signals from other civilisations. It's a project called SETI, Search for Extra-Terrestrial Intelligence. But to date our focus has been passive. We have been waiting for signals from other civilisations. With Active SETI we reversed that process and take an active role in transmitting intentional, powerful, information-rich signals to other civilisations in the hope of getting a response.
Active SETI is a controversial activity. No one less than the cosmologist Stephen Hawking said, 'Whatever you do, do not transmit or we may have an alien invasion on our hands.' But the reality is that any civilisation that has the ability to travel between the stars can already pick up our accidental radio and TV leakage. A civilisation just 200, 300 years more advanced than we are could pick up our leakage radiation at a distance of several hundred light years. So there are no increased dangers of an alien invasion through Active SETI.
Active SETI is an enterprise that deserves a broad-based international discussion. I would be delighted if the Secretary-General of the United Nations said to the general assembly, 'I want Active SETI at the top of your agenda,' but I'm not holding my breath. A decade ago the International Academy of Astronautics SETI committee held a debate about whether transmissions de novo should be included in protocols to regulate transmissions from Earth, and on three separate occasions they voted no. So if an organisation like that will not take the leadership, who should?
I would argue that the organisations that are most interested in launching Active SETI programs have a special responsibility to engage in a broad-based discussion. The SETI Institute, we've done this in a number of ways. In 2009 we launched a web-based project called Earth Speaks to gather messages from people around the world about what they would want to say to extra-terrestrials. In November we held an international conference with scholars from over a dozen disciplines in the humanities, arts, social sciences, natural sciences, to grapple with the question; how do we say something intelligible to another civilisation? And we are going to have an extension of our AAAS Active SETI session at the SETI Institute to deal with the scientific, policy, legal, ethical issues. So those are good starts for the discussion.
The most critical thing we need to do is overcome this simplistic notion, sort of an either/or thinking; either we have international discussions, or we transmit. We should be doing both. Active SETI is a reflection of SETI growing up as a discipline. In the past we have focused on what we can gain in the short term by listening for signals. Active SETI asks what can we contribute that may benefit future generations of humans and extra-terrestrial civilisations.
Sometimes we talk about SETI as an attempt to join the galactic club. But no one ever talks about paying our dues or even submitting an application, and Active SETI is both, and it may just be the approach that lets us make contact with life beyond Earth.
Robyn Williams: Doug Vakoch from SETI.
Now a critic, David Brin, the author.
David Brin: Active SETI, or METI, Message to Extra-Terrestrial Intelligence, has not been handled well. We have, for instance, been characterised as being paranoid about expecting invasions of slathering Cardassian invaders and things like that. Yes, well…none of us have ever mentioned such things, ever.
Now, the context in which this has to be said is what's called the Fermi paradox, and that is the notion that for 70 years our friends such as the late Carl Sagan and of course the great Frank Drake who works with these fellows at the SETI Institute, they started out expecting that very soon by just swinging primitive early radio telescopes they would spot vast tutorial beacons because it seemed logical that altruistic and beneficent aliens would be broadcasting how-to manuals to help species like us who are stumbling along through the minefield of adolescence. And this underlies the hope, I believe…well, in a sense, salvation from omnipotent people above, and in a sense METI could be considered an analogue to prayer.
What I'm saying is that if you have people like Stephen Hawking, who is on our side of the issue, is afraid of slathering Cardassian invaders, the fact is that this is the only really important scientific field without any subject matter. Think about that. It's an area in which opinion rules. And everybody has a very fierce opinion. Those who want to proceed with METI have very strong opinions about the likelihood of altruism in advanced civilisations. Lately, however, they've added a flavour to it of contempt, that the aliens who are so advanced and naturally altruistic so they would never do anything bad to us nevertheless are cowards or too reticent, and it is the job of the youngest and least advanced technological species in the galaxy to initiate the conversation.
Well, if you catalogue all the possible explanations for the Fermi paradox…and this has been my task, instead of saying 'I know what it is', I've been cataloguing them for 30 years…of the 100 or so general categories of hypotheses, of these maybe a dozen project the possibility of a dire scenario. Maybe those who are out there are being quiet because they know something we don't know. That is the first parsimonious Ockham's razor hypothesis. None of them rank in the top 10 for explanations, in my opinion, of the Fermi paradox. We are talking about scenarios that have low probability.
But if you're going to transform several of the major characteristics of our planet, we've learned that small groups shouldn't do that peremptorily, or by setting up a few meetings that they control and calling that 'discussion'. This is something that should be discussed worldwide and it should involve our peers in many other specialties such as history. And the historians would tell us, well gee, we have some examples of first contact scenarios between advanced technological civilisations and not so advanced technological civilisations. Gee, how did all of those turn out? Even when they were handled with goodwill there was still pain.
I'm not saying that extra-terrestrials aren't going to be way advanced over Cortes and Pizarro. It is very likely that they will be. But this is an area in which discussion is called for. What are the motivations of species that they might carry with them into their advanced forms that might colour their cultures?
And if you take a close look at some of the assumptions that are made, Doug said of course…it's called the barn door excuse. You are trying to close the barn door because the horses are already out, they've already detected I Love Lucy…well, all of the top radio astronomers who've done this calculation have indicated that this is a myth and it is very difficult for advanced civilisations to have picked up…at our noisiest in the 1980s when we had all these military radars and big television antennas. Now we are much quieter. No, they want to send maser-like, laser-like coherent beams that are a million times the intensity at target or more than I Love Lucy. So do not take this barn door excuse. Besides, it's illogical. We should go ahead and send a million times intensity beams because they've already detected us. And yet what is their intent? To change the situation.
Copyright Australian Broadcasting Corporation
Seth Shostak: I'm not going to get into the controversy that David has just mentioned, except to note that the paradox means nothing in my view. If you had asked the Europeans in 1491, 'Do you think there are civilisations across that big ocean to your west there?' And they would have said, 'No evidence for that, they must not be there.' To begin with, the visibility of Earth…I want to come back to this because it's true that most of our radar, our TV, our FM radio, those are all high-frequency signals that go out into space willy-nilly, those are very hard to find. If we had the best of our SETI experiments at 100 light years, nominal distance, 100 light years, they would be too insensitive by somewhere between two and six orders of magnitude to pick that up. I've done these calculations for radars, those are the strongest signals we are sending into space. It's not reality television, that may be a relief to you.
[interview] Seth Shostak, I'm senior astronomer and director of the Centre for SETI Research at the SETI Institute.
Robyn Williams: At the session just now somebody accused your whole field of having no information, no data. What was your response to that?
Seth Shostak: I would say that there are data. For example, when we reckon the visibility of Earth to extra-terrestrials that might be out there, that's a calculation. To say that that's no data is to ignore the fact that we have some physics. So you can figure out, is there additional danger in terms of is there additional visibility to Earth if we were to, for example, broadcast to some nearby stars. So in that sense there is data. We don't know who is out there, but on the other hand if you don't look of course you still won't know that there is anybody out there.
Robyn Williams: Exactly, and the point is you've been looking for, what, 50 years or roughly half a lifetime, and not finding something is kind of what you'd expect. But if you do find something, extra-terrestrial intelligence, what would the impact be? Would it be huge?
Seth Shostak: Well, I think it would be a very huge new story. We have some idea of what it would be like because there are analogies in history. They are not very good analogies though. But in my experience whenever we get a signal that looks enticing, the first thing that happens is not that the government shows some interest, that would actually please me because maybe we could get some government funding if they are really that interested, but in fact what really happens is that the media are very interested.
So if we were to pick up a signal tomorrow night or next week or next year, in the next decade, the first thing that would happen is there'd be an enormous media blitz. Even before we were sure that this signal wasn't just interference or college prank, it would be a big story. But the long-term implications are much more interesting because that depends on whether you can understand anything or not and how many other societies you find. But it would become a big thing because we would know we are not the only kids on the block.
Robyn Williams: Indeed. Well, you are sending messages and you are hoping to receive messages. How can we understand them when they come in and how will the alien, whatever, be able to decode our stuff?
Seth Shostak: Well, in the case of us broadcasting to them, we can do a little bit of anti-cryptography, we can send them lots of pictures, maybe a picture dictionary so that they can eventually speak perfect English, as they always do in the movies I note. We might be able to make it easy for them. But they have not necessarily made it easy for us. If they are trying to get in touch, if they feel some obligation to educate the rest of the universe, maybe they will make it easy for us, but my assumption is that we accidentally pick up something that really wasn't intended for us. Whether we can figure that out or not, I don't know. I think it's unlikely. I don't think that the Neanderthals, for example, could have ever figured out a modern-day television signal, even though they are pretty smart.
Robyn Williams: Yes indeed, the information coming from, say, agent Egypt, Greece, even though it was written down for them, we've managed to decode, haven't we.
Seth Shostak: Yes, we have. It's true that we've been able to understand some of these ancient cultures, but I think that's because there's a big corpus of symbolism, whatever it is. In the case of ancient Greek, there's a lot of ancient Greek around so that you can figure it out. It's also a language that is not so distantly related to what we already speak, so there's also that. But consider the Mayan codices. We have a hard time understanding those. The Dead Sea scrolls. It's too limited. So that's why I think that if we were to broadcast you should send a lot of material because that gives you a better chance that they may in fact pick it up.
Robyn Williams: My final question, when it comes to the broadcast we've got 100,000 planets possibly out there, many of which we've already found, and so we've got places to send the messages. And in 300 years' time I think you mentioned the speed and the reach of our messages will be so much greater. How?
Seth Shostak: Well, to begin with there is sort of a ball of radio waves, if you will, sort of leaking off the Earth, moving out into space at the speed of light. So that ball…consider transmission since the Second World War, so that's 70 years ago, so those messages are 70 light-years out. But in 300 years the messages will be 370 light-years out, and within that distance there is on the order of a couple of hundred thousand star systems, of which at least half have planets. So I think that within 300 years a lot of societies or at least some societies will know that Homo sapiens is alive and kicking on this planet.
Robyn Williams: Good luck, thank you.
Seth Shostak: Thank you.
Robyn Williams: Seth Shostak from the SETI Institute at the AAAS in San Jose. And you're listening to The Science Show on RN, now reaching 20,000 planets and any number of LGMs and LGWs.
