Duncan Forgan, University of St Andrews
We can probably detect places in the galaxy that might harbour life, and we might be able to tell whether itís intelligent or not, but what are the odds that theyíre there at all?
50 years ago astrobiologist Frank Drake proposed an equation that now bears his name to estimate of the likelihood of discovering intelligent extraterrestrial life in the galaxy. Astrophysicist Duncan Forgan has been using computer modelling together with recent astronomical discoveries, to build upon Frank Drakeís work to get a more accurate idea of whether thereís anybody out there, as he explained to Graihagh Jackson...
Duncan - Well, the Drake equation is a series of seven or eight terms, depending on who you speak to. These terms get multiplied together and when those terms are multiplied together, you get a number, and that number tells you, if you look up at the night sky, thatís how many communicating intelligent species there are.
Graihagh - Okay, so in this Drake equation, you start with how many stars are forming every year in our galaxy and then you subtract out all the stars that donít have any planets around them, right? Because you canít have life there, and then you subtract out all the planets that are too far or too close to the sun to support life, and so on and so on. You get the idea. Until finally, you come up with the number of planets, with intelligent life, that could transmit radio signals and be alive right now. So when you slot all the numbers into this equation, whatíd you get?
Duncan - Typically, when I try and write down numbers in this equation I get the total number of intelligent civilizations to come out in quite small numbers, letís say ten civilizations in the milky at this point in time.
Graihagh - Ten. Does that include us or exclude us?
Duncan - Strictly speaking, that includes us, so you should take one off. It should be nine.
Graihagh - Nine? Thatís even worse!
Duncan - Yes. Itís quite a tough challenge. Before we get into this, I should just point out that SETI scientists and astrobiologists donít use Drakeís equation as a predictive tool. Itís quite clear that itís very simple and kind of cuts out a lot of the nuance and the sophistication required to make an answer to that kind of question.
Graihagh - Iím wondering 50 years on, is there not a better way to make a more informed guess?
Duncan - Other ways you can look at this question would be to say, okay, we have statistical information on how stars form, we can say things in a similar vein about the masses of planets, we can say things about the likelihood of them existing a certain distance from the star, so you can build up a statistical picture of what the Milky Way looks like in terms of its star and planet population. And once you have that, then you can essentially build a model in which you can test different scenarios.
Graihagh - So what predictions have you been able to make?
Duncan - So when I first started doing this, I ran several different scenarios. Some were quite optimistic and some were quite pessimistic. And over the course of the Milky Wayís existence, I showed that there would be somewhere between, you know, 300 and 30,000.
Graihagh - Not so many given how many stars and planets there are out there then.
Duncan - Thatís right. Of course, these are very speculative numbers though, because weíre still stuck with the same problem that we just donít know how life forms on other worlds and we donít know really how that life becomes intelligent. So youíre still saddled with these uncertainties but you can say given our uncertainties and making some sensible educated guesses, here are some nice sensible looking bounds in which we can put those numbers.
Even when you take a fairly optimistic view of the equation and you put in some quite generous values for some of the terms and if you get a number thatís say tens of thousands, which sounds like a much bigger number. The Milky Way is very big, itís very big in space, itís about a hundred thousand light-years across and it is also very big in time, itís billions of years old. So we have this kind of dual quandary of how you get two civilizations to be close to each other in space and close to each other in time to appear about the same time. If one sends a radio signal, the other can see it before the other civilization goes defunct for whatever reason that might be.
Graihagh - And by Duncanís calculations, intelligent life that can transmit radio signals across the galaxy are likely to be alive for just one thousand years. A thousand years in a galaxy that is 13.2 billion years old with 300 billion stars and many, many more planets. When you take all of this into account, it seems pretty improbable that if there is anyone up there that will ever get the chance to talk.
Duncan - The probability might be low but that doesnít mean itís impossible, it just means that itís improbable. So even if we carry out a search knowing that weíre likely to fail, actually failing in the search is quite important because again, Iím just a theorist with a computer making some assumptions. At the end of the day, if you want to do it scientifically, you have to go out there and test it. So, youíve to make sure that youíve got observations to back up your theories and if we made a null detection after a significant and deep search, that has a lot of information in it as well as the opposite case where did detect something. It will still tell us something quite fundamental and important about what it means to be human.
Graihagh - I was gonnaí say what would that mean if we were the only sentient beings out there.
Duncan - It means that our existence is quite lonely and quite unique, and that human life in itself is even more precious than we might have thought originally.
Graihagh - And in some senses I guess then that would also mean that intelligent life of the whole galaxy rests on our shoulders.
Duncan - Well, in that sense, the stewardship of the Earth is not the only thing we are stewards of. We become stewards of a much larger volume of the universe and we have to be very careful and look after it if that is the case. So again, that has very strong implications for how we should behave as a civilization.
I think that intelligent life must exist but the distance would be so great that no interchange of communication would be possible considering the speed of light and the size of the universe syhprum, Tue, 30th Sep 2014
I can do no better than copy my response to a related question:
I have found intelligent life that is not human..
Communication with intelligent aliens could actually be easy, apart from dealing with long time delays if they don't come a lot closer. It would be easy enough for intelligent computers to show each other images and videos, naming things and actions that take place so that they can learn each other's language. In the old days when Captain Cook was exploring the world, they could stop off in places that had never been contacted before and hold competent conversations with the natives within as little as three days - they had experts with them who could learn the basics of languages fast just by working with a native and getting them to name everything around them and name actions and the like. Intelligent computers (which we will soon have and which any visiting alien would certainly have) would be able to cut this process down from three days to three seconds, and then there would be no communication barrier between us. David Cooper, Wed, 1st Oct 2014
Language of physics is mathematics.
Yes, it can be, and should be, if it has to be universal for deep cosmos alien species.
I think that we need a second reference point to tell how rare life is in the universe.
IMHO that's the wrong question, and the right question is this:
Gross left and right aren't particularly important to most species, though the chirality of some molecules determines their biological function. Faced with a coronal plane image of a human or a spider, I could probably work out that it was vaguely bilaterally symmetric and had a preferred orientation with respect to gravity. Given three projections and a scale (the hydrogen 21 cm line is likely to be a universal standard of length and time) I could make a fullsize model of it. So it's entirely possible for any life form that can control an electromagnetic technology, to initiate meaningful conversations with another. alancalverd, Fri, 3rd Oct 2014
I think that we need to find some aliens before we can learn how to effectively communicate with them. Which would mean hopping in a space craft to start scouring far off solar systems for signs of life.
Intelligence seems to be the realization of not knowing enough, then start asking questions. If the universe works by emergences, meaning 'jumps' that you don't really can back track to their constituents behavior before this 'emergence', then intelligence should be able to pop up everywhere I think. yor_on, Sun, 5th Oct 2014
We recognise intelligence in another animal by its ability to surprise us. It is the antonym of mechanism. So we should be looking for the mechanistically improbable- like the "WOW signal". The difficulty is recognising the difference between a surprising signal and random noise. alancalverd, Sun, 5th Oct 2014