 Greetings and welcome to the Introduction to Astronomy. In this video we are going to talk about the search for extraterrestrial intelligence or intelligent life outside of our own planet. So we want to look at a few different things here and we are going to start off looking at the possibilities of interstellar travel. How can we travel, possibly travel between the stars? It is not something easy to consider. Distances are tremendous beyond anything we can consider. And if we think about that, we've had the New Horizons spacecraft, the fastest craft yet launched from Earth, took 10 years to get out to Pluto. And that is only about 40 astronomical units away from us. And to try to go to the nearest stars, we are talking hundreds of thousands of astronomical units. If we think about even light travel, it takes light traveling at the speed of light four years to reach the nearest star. And if we look at some of the current craft, such as the Voyager spacecraft, which are the most distant ones away from the Earth now, it would take them 80,000 years to reach another star. And even by the time we did that, of course, it would still take years to get signals back from them, even if we could send something to another star. So it becomes very difficult to do, something that is very difficult unless we find some other form of travel that goes beyond what we know right now. If we look at just one trip, so what is the expense of traveling faster? If we could get up to 70% the speed of light, meaning that it would still take years to get to the nearest star and back, it would take hundreds of thousands of years of the electric consumption of the United States to be able to generate that amount of energy. So we need some new source of energy that would be able to allow us to travel with current technology it just is not feasible to be able to travel between the stars to look for other intelligent life. However, there are other methods that we can use to still try to communicate with life that may be out there. So we have sent some messages out and this is an example. This is the pioneer plaque, which contains information about our solar system and where we are. So our solar system shown down here, each of the sun and the planets, including Pluto at the time, when this was made, and then marking where the craft is and which planet it came from, so identifying where we are. We have the sizes of two human figures relative to the craft itself and the position of the sun relative to the center of our galaxy and a number of different pulsars. So this is all binary encoding of the various pulsar pulsar tines and that could be then used to triangulate the position. It also shows the little what looks like two little eyeballs up here is the spin flip transition of hydrogen relating to the 21 centimeter radio line. Very important for studying intergalactic material, interstellar material, and that would be something that we think another intelligent civilization would be interested in. So we've sent this out. Of course, this was on the pioneer craft and these are still ones that are just getting to the point of leaving the edges of our solar system. We also sent a record out on the Voyager spacecraft and in fact the golden record here containing the sounds of earth, containing greetings in 60 different languages, music samples from various cultures, natural and man-made sounds from the earth, and various diagrams and photographs that have been encoded in this. Now we have to remember that we talked about already it's going to take 80,000 years for a craft like this to reach another planet, to reach some place, to reach another star. So while we've encoded all of the information there, it's not something that an alien civilization is likely to detect in the near future. Space is just so vast and empty that the likelihood of them being found is very small, that these will ever be found is incredibly small, and will they be correctly interpreted? Have we specified general enough things that would actually catch the interest of an alien civilization that might happen to detect these? So that's another very slow method of communication. So let's look at how we could possibly communicate over these interstellar distances. How can we communicate those? Well one of the best waves is going to be radio waves. Radio waves do travel at the speed of light. They also penetrate through dust, so they're very easy to travel through large portions of the solar system. It is a quicker way to make contact than trying to send out spacecraft, but still is not fast. It is still a slow process, taking 8.6 years to receive a response from the nearest star. So if we look at an example, if we send a signal on January the first of 2020, we could expect a response probably sometime in July of 2028. That means it would take eight and a half years for it to get a signal back, and that's if the beings detecting it were able to decipher it and respond immediately. Otherwise it could take even longer to get that back. And that is for the nearest star. If the star were further away that we were trying to communicate with, it would take even longer. Now the question becomes do we broadcast or listen or do we do both? Certainly if everybody listens, we're never going to detect a signal, because everybody's sitting there listening for a sound and nobody is doing the talking. So we're looking like we need to do both because if everybody else is listening, then we're not going to be able to detect a signal. Will the signals be strong enough to detect? We send out signals all the time, radio and TV broadcasts. Those would not be detectable even at the nearest stars. Even though those signals are traveling out there, they're not being beamed in a specific direction. So just general signals like that would be unlikely to be able to be detected. If we were to send a specific signal beamed towards a star, then we need to discuss where we want to send that signal. What stars are going to be most likely to have some kind of life around them? And finally how do we determine if a signal is natural or is it artificial? Things like pulsars were discovered as very regular signals that occurred. And they were thought maybe to be an artificial signal at first, but eventually found to be something natural, a rapidly spinning neutron star. However, it may take some time to be able to determine whether any signal we're getting is a natural one or an artificial one. Now we can look at the radio spectrum and that is a big place to be able to look for signals. What part of it do we listen? What frequency, at what frequency do we want to look for signals when we're listening for them? At what frequency do we want to broadcast signals when we are selling them? Now here we see essentially the noise. So the higher the lines on this, the more the noise and the harder it would be to detect a signal. So the galactic noise here is very hard to detect. There's some other noise here that makes it very hard. So where this is the lowest right in here is probably the region we want to look. And we tend to look at this region between emission of two lines, one of hydrogen and one of the hydroxyl or OH molecule. And that is what we call the water hole because H and OH makes H2O or water. So we call that the water hole and this region is one of the areas where we most look for signals and where we try to broadcast signals. It is a region of low noise, but it also has some significance with water being very important for life. Now what kind of signals can we expect to detect? Leakage is very hard to detect. So just leakage, our television shows, our radio shows. Those have traveled out, well radio shows almost 100 light years away from us. However they are so weak that it would not be able to be detected easily because we're not beaming them towards a specific star. We are just sending them randomly out into space and they get weak very quickly. We would look for beacons or messages being beamed to us. So what is being sent straight towards us that we would then be able to detect? And that would be much easier. So let's look at sending some of these signals and what has been done. This is an example here of what stars. Do we look at sun-like stars? Do we do stars with known habitable planets that we begin to know about? And will we receive a response? One of the problems is what is the technology level of the civilization? It has to be comparable to ours to be able to receive that. So if we look at that, if a civilization is much as we are, we're back in the 1700s, even just a few hundred years ago, we're never going to receive a response for them. Even if they were as we were in 1900, we are not going to receive a response for them because we had not yet developed radio communications. Radio telescopes were not really developed until the 1930s and didn't pick up until the 1950s. So if someone had sent us a signal at this time, we never would have been able to detect it. So another civilization at this level of technology would still not be able to receive and detect our signals. Are they interested in communication? Do they not care? That's something again that we do not know. Now, we did send a message here that I'm showing on the right-hand side. This is the Aeroscebo message sent in 1974 towards a globular cluster known as M13. That cluster is 25,000 light-years away. So while it was sent in 1974, it'll take 25,000 years to get there. And who knows what we will be like by the time it gets there. And of course, if someone there does respond, it will take another 25,000 years for the signal to get back. Now, within it, there are a number of things encoded, including the DNA molecule, the Aeroscebo telescope itself. This is our solar system with the Earth kind of sticking out. There's a human figure in here, and the various amino acid encoded in here as well. There's a number of different pieces of information were encoded, but the problem is trying to be able to decipher this and to get it. And what is sent is what we call an anti-coded message. And that means it's set so that there's only two ways to decipher this message. For example, if you were to send a message with 24 pieces of information, 24 bits of information, well, you could look that as one string of 24. You could look at it at two strings of 12. You could look at it at three strings of eight. You could look at it at four strings of six. Or you could go six strings of four. If you get my message here, what there are, there are a lot of ways to be able to decipher this. If you send something that is with, like a, say, 35, then it can only be seven by five or five by seven. So there are only two ways to decipher the message. And that is what this has done. There are only two ways to put this together. One would give you gibberish and one would give you a message. So there are not a lot of ways to be able to do it, as there would be with certain types of messages. Now, one of the other things that I want to look at here is what is called the Drake equation. The Drake equation is a way to estimate the number of technological, communicative civilizations that are present in the galaxy right now. So that's kind of amazing. We can use this equation to calculate the number of civilizations that are there. It's based on estimates and probabilities. So some of the terms are better known than others. And all we have to do is multiply these seven terms together. And that tells us the number of civilizations present right now. The thing is, we know some of these numbers pretty well. And others are a great big question mark. So we don't actually know all of the values accurately going into it. But it still is a great discussion point for starting. Let's look at what those terms are. And the first one is the rate of star formation, how fast stars are forming in the galaxy. The second is the fraction of stars with planets. And the third is the number of Earth-like planets. These first three are the astronomical terms. So these come from astronomy. And they are relatively well known. They may not be known precisely, but we can get a pretty decent estimate on these. We're starting to find lots and lots of stars with planets, so we can get a pretty good estimate of things like the rate of star formation and the number of Earth-like planets that we're beginning to be able to detect. So we have a pretty good handle on these. The other ones are... The next three are sort of the biological and cultural... Let's do all four. Biological and cultural terms. These ones we do not know. What is the fraction of planets that develop life? We only know of one place this has ever happened. What is the fraction of those planets that develop intelligent life? Again, we only know of the Earth. We're life-formed and then intelligent life-formed. We could be optimistic and say it's one, that every planet that develops life will eventually develop intelligent life. Or we could be pessimistic and say it's one in a hundred, one in a million, or one in a billion, and that would make it much less likely. Do they develop communications? So do they develop a way of communicating? And the big question mark is the lifetime. How long is that civilization actively communicating? How long does a civilization last? So it could be a very small number, or it could be a very large number. Do civilizations last millions or billions of years? Do civilizations last only a few decades? And that's something that we have absolutely no clue of. So let's look up what's the answer to this equation. There is none. The answer is a great big question mark because we don't know. There's a wide range of values, especially when it comes to these last four. We really do not know. There could be one civilization, us. There could be thousands or millions, depending on the values that you pick for these different terms. It is really more of a discussion point than an equation that will ever have a definitive answer. So let's finish up here. We have that first, is there life out there? It's an open question. We can't honestly answer it. Yes or no? We do know that the building blocks of life, the amino acids are common in the universe, and that there are likely many planets with conditions that are similar to the Earth. The big question is how easily does life form? Does life form easily? Or is it a very difficult thing? We believe life form very quickly on the Earth, very early after its formation. That gives us some confidence that maybe it is easy for life to form elsewhere. But we do not know any of that for sure, and whether that life then evolves to intelligence within a regular basis. That took a long time on Earth. That took billions of years. So even though life forms easily, how common is intelligent life? And again, the biggest question, how long does that advanced civilization last? It may not, if it's only a few decades, then we're unlikely to communicate with anyone else. Even if it's millions of years, will they quickly become too advanced to even want to communicate with us? So let's finish up here, as we do with our summary. And we talked about really the possibility of life in the universe. It's a big question mark. We know of life here on Earth. We don't know of any place else where life has ever formed. We have sent messages to civilizations by a number of different methods. And we talked about the Drake equation, which allows us to consider the variables needed to determine if there are other civilizations out there. So that concludes our lecture on the search for extraterrestrial intelligence. We'll be back again next time for another topic in astronomy. So until then, have a great day, everyone. And I will see you in class.