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Detectable civilizations in our galaxy 2

Why do we even care about the Drake Equation. Thinking about the fraction of a planet's life when a civilization might be detectable. Created by Sal Khan.

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  • mr pants teal style avatar for user wolfpoulet
    Have we recieved any signals of unknown civilizations yet?
    (12 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      In 1977, a signal was detected in the Sagittarius constellation that appeared artificial. The person who printed the paper wrote wow on it and thus it became known as the wow signal. To this day, no explanation has been able to prove where it came from. Wiki it for more information.
      (32 votes)
  • piceratops ultimate style avatar for user davisswearingen
    Are there explanations for UFO sightings? Could they be extraterrestrial visitors?
    (0 votes)
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    • leafers sapling style avatar for user rcolling
      actually UFOs have Mystery around them because they are Unidentified Flying Objects UFO is just an abbreviation for this but people mainly connect UFOs with aliens like the "green skinned" kind but aliens are other life forms that live on other planets they actually have a alien fossil from mars that is a fossil of bacteria back to UFOs lots of them are actually weather balloons or meteorites or hoaxes of aliens but the prospect of them maybe being aliens keeps the subject interesting :)
      (5 votes)
  • starky ultimate style avatar for user Arik Schneider
    If a civilization was on the other side of the galaxy, how could its radio waves get through all the electromagnetic waves form the mass of stars in the center?
    (19 votes)
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    • orange juice squid orange style avatar for user Pranav Pillai
      That is the exact problems that our scientists have been facing, there is a miniscule chance that the signal would be able to get through the center, much less actually get to us due to the large size of the milky way. So the real question is, is humankind even going to still be there when the signal reaches us, if it does anyway.
      (3 votes)
  • old spice man green style avatar for user Brian
    what if creatures on other planets don't require water or the things humans need?
    (6 votes)
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    • leafers ultimate style avatar for user Caitlin Fischer
      That's an excellent point, and the answer is that we don't know. We generally assume that life would require water because it is so ubiquitously needed by life on Earth, and because its properties make it an ideal ingredient conducive to life, but ultimately, we're extrapolating from a sample size of 1.
      Alien planets and alien life could look vastly different from Earth life. But looking for Earth-like symptoms on other planets gives us a starting place to search from.
      (12 votes)
  • blobby green style avatar for user mageewl
    Wouldn't using oxygen or ozone for chemical signature be an indicator of life? Their spectroscopy are easily indicative.
    (4 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      Some life my be chemicly diferent from us. They may exhale something else. Some theorize that life may be on Titan and that they breath in hydrogen instead of oxygen or carbon dioxide, bind it with acetaline instead of glucose, and exhale hydrocarbons insted of carbon dioxide or oxygen.
      (8 votes)
  • male robot hal style avatar for user Giles
    In the event that we did detect a radio signal, how do we go about determining exactly when/where it came from? No alien signal is going to be using our calendar, and I get that we can hone in on the general direction using our radio telescopes, can we detect how old radio signals are? Don't they deteriorate over time / distance? Because otherwise wouldn't I be able to get radio from China?
    (6 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      You are right, we can't tell where it came from, but, it would most likely have come from a nearby star or else we would not have been able to detect it. By determining which direction it came from, we can make pretty good guesses on which star it came from.

      About radio from China, it is entirely possible. AM radio wave tends to bounce of the ionosphere and the ground which allow it to travel pretty far by bouncing in between the sky and ground. I had a teacher who was a HAM radio operator who was able to communicate with someone in an island nation in the Indian Ocean.
      (5 votes)
  • piceratops tree style avatar for user SpeedySanic
    What about life that doesn't require water? For instance, in 2007 scientists sent two species of tardigrade into orbit. They were exposed to the vacuum of space and to a sufficient amount of radiation. (enough to incinerate a human) When they were brought back into Earth, 1/3 of the tardigrade survived. Couldn't there be instances of life such as this?
    (5 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      1. The tardigrades were entirely dormant during that time and did not reproduce. They would eventually die and not really do anything like what life would do.

      2. We assume that life needs to have been able to develop on the planet as well, not just live. We can only image life being created in an ocean and have not found a conceivable way this could happen otherwise. This of course does not mean that it could not happen but we are not sure.
      (3 votes)
  • leaf blue style avatar for user Kenji
    Is it possible that the Oort cloud is distorting our signatures of life from others civilizations that are trying to locate other life?
    (2 votes)
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  • leaf red style avatar for user Michelle Tolfrey
    This could explain the 1977 "wow" signal that was never found again. Maybe the civilisation that sent it out died out before we could receive it fully?
    (1 vote)
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    • piceratops ultimate style avatar for user Scottyboy1
      That is certainly possible. We send all sorts of signals out into space.........but i doubt we will be here in 2.5 million years. Our light and sound will remain, you could be running into this same situation with the Wow! Signal.

      However, this was not background noise. The signal was strong, of long duration (up to 2.5 minutes), at one frequency, and the frequency was by design (it would seem) at 1420.0446 MZh. This frequency is forbidden on earth since it is the frequency at which hydrogen resonates.

      This signal, is the signal you would be likely to see if it came from extraterrestrials. It would be prudent for a civilization to send out a structured signal that any reasonably advanced civilization could identify as not natural to the background noise.

      Hydrogen is the most abundant molecule in the universe. Astronomers on other planets would likely be looking for civilizations that would be able to recognize the signal. If a civilization is advanced enough to recognize the signal then they are advanced enough to recognize the resonance frequency of Hydrogen. And we did recognize it and that's why it confuses us.
      The astronomer that found this, was anxious to dismiss it when he first saw the signal as earthbound or some collection of space debris reacting with sound in some odd way. He has since backed off of that position now very much leaning towards the signal being extraterrestrial in nature.
      (7 votes)
  • starky ultimate style avatar for user Alex Miller
    what if we already are receiving signals from extra terrestrials but we don't know that they are signals because we don't interpret them the same way for example what we here as stars may be them trying to talk to some one out there
    (3 votes)
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Video transcript

Some of you might be wondering, why are we even worried about this Drake equation, or why are we even tempted to go through this thought experiment of the number of detectable civilizations in the galaxy when we don't have a clue of some of these assumptions? We don't know what fraction of planets capable of sustaining life actually do generate life. We don't know of all of the planets that have life, what fraction of those planets go on to have intelligent life, and what fractions of those civilizations go on to using electromagnetic radiation as a form of communication. We don't know these answers. In fact, we probably won't know some of these answers for some time. So what's the point of going through this exercise? And that is a valid point of view. The Drake equation, or even this little equation that we've set up here, it's not an equation in the traditional sense, where we can immediately apply it to some engineering problem, or some physical problem, or anything like that. I view it more as a bit of a thought experiment. And what's interesting about it is it kind of can structure our thought around the problem, and I think that's where it has the most value. We'll probably not get a solid number on this any time soon, but it does lead us to thinking about these interesting problems of what does it mean, or what do we think has to happen for a planet to start getting life, even if it has all the right ingredients? And then what does it mean for things to eventually get to the point that you have intelligent life? And in all fairness to this is that probably 200 years ago, there would have been no way to even have a decent estimate of the number of stars in the galaxy. Now we're starting to do an OK job on that. 20 or 30 years ago, it would have been viewed impossible to say the fraction of stars that have planets, but now we're finding exoplanets. We're seeing stars wobble. We're getting more and more accurate instruments. So we can start to think about planets that are closer to the size of Earth's. We're making headway there. There's other indirect methods to think about, well, some of these exoplanets look like they're in the right zone, and they look like they have the right chemical signature based on other information that we're getting, and that maybe they are capable of sustaining life. So as time goes on, and as technology improves, we might be able to get better and better and better at this. But with that said, it's not going to happen any time soon, and the real value of all of this is really to structure our thoughts about really, a super, super interesting topic. Now, the other thing I want to talk about is a slight clarification of what I talked about in the last video. In the last video for this l, I said it's the civilization's lifespan, but what's actually relevant is the lifespan of the civilization while it is detectable. So, detectable. So it doesn't matter if the civilization is around 100,000 years, but it's not releasing any type of thing that we can detect. That's not what we care about. We care about that the 5,000 years, or the 10,000 years, or the 100,000 years when they are actually using some type of communications, or some type of electromagnetic radiation that we can eventually detect once those things reach us. Now, the other thing I want to make clear is we're talking about the number of detectable civilizations in the galaxy right now. And I'll write now in quotation marks, because we're not talking about a civilization that is maybe even a peer civilization with us that developed radio communication on the order of 100 years ago, because frankly, they would have to be no more than 100 light years away for us to be able to detect those signals now. If they were on the other side of the galaxy, we wouldn't be able to detect their for tens of thousands of years. So when I talk about now, I'm saying that the signals are getting to us. Signals getting, signals received. The signals are being received right now. So you could have a civilization that developed radio 70,000 years ago, but they're 70,000 light years away, and maybe they collapsed 10,000 years later, but we're just receiving their first radio signal. So that would be as a civilization that I would count in this equation we're setting up. And so just to make sure we understand it, and then we can play with some numbers, let's remind ourselves. This is the number of stars, our estimate of the number of stars of the galaxy. Multiplied by this, you now know the number of stars in the galaxy that have planets. You multiply by this n sub p, the average number of planets capable of sustaining life, and these first three terms will give you the average number of planets-- or I should say the number, the total number of planets in the galaxy that have been capable of sustaining life at some point in their history. Multiply it by this. This is the number of planets in the galaxy that have sustained actual life, not just capability of it. They actually had life on them at some point in their history. Multiply it by this, this is the fraction that have developed intelligent life on these planets. The number of planets with intelligent life at some point in their history. Multiply it by this fraction. All of these terms. We have the number of planets in the galaxy that have had intelligent life that became detectable, that started emitting some type of radio signature. We don't know, some type of thing like that at some point in their history. So over here, all of these first six terms tell us the number of detectable civilizations that occurred at some point in the history of the stars, the solar systems, the planets that are out there right now. But we care about the ones that are detectable now. We don't care about the ones that came and went, and their radio signature went past us while we were still living in caves, or we were hunter gatherers. We care about the ones that the radio signatures are receiving us now. And that's why we have this little term right over here. So this is the civilization of-- or I guess you could say this is the length of the detectable civilization. So while they were actually releasing a radio signature divided by the life of that planet, or that solar system, or that star. So for any given star or planet that meets all of these criterion, what's the probability that it's releasing its-- so at some point in the history, there was a detectable civilization or more that was releasing some type of a radio signature. But what's the probability that it's doing it right now? And so that's the detectable life span of that civilization divided by the life of that solar system, or of that planet. Because frankly, the star and the solar system and the planet, they're all going to essentially have, give or take, a few hundreds of thousands of years, or even a few millions of years, because we're thinking in the billions here, they're going to have roughly the same life span. And so let's say, and just to make this a little bit more tangible, let's say that the sun has a lifespan, and let's say that with the Earth and our solar system, has a lifespan of approximately 10 billion years. 10 billion years. And let's say that us as humans, let me be pretty optimistic about it, let's say that we are detectable as a civilization for one million years. Our best days are ahead of us. We are detectable for one million years. So this term right over here will be 1 million over 10 billion. So this will be 1/10,000. So even though we might be around sending out detectable signals for a million years, the odds relative to the entire span of the history of-- And I'm making some simplifying assumptions here, but relative to the entire span of the history of our planet and our sun, if someone is just randomly sampling our solar system at a random time in its history, in a random part of this 10 billion years, there's only a 1 in 10,000 chance that they'll be sampling us at a time that we are releasing signals. Assuming that there weren't any other civilizations on Mars or Venus, or whatever else, that there weren't any other civilizations on Earth hundreds of thousands of years ago that were doing this, they'll definitely only have a 1 in 10,000 chance of detecting us, assuming that they're sampling. There could have been a civilization that was around three million years ago, and they did this whole search for extraterrestrial life. Maybe they're 20, or 100, or 1,000 light years away, and they pointed their radio telescopes at us. But a million or two million years ago, they would have pointed at the direction of our sun, and they would have not gotten any radio signals, and they're like, man, when is extraterrestrial life going to show up? Even though the sun and Earth does eventually develop us, they weren't able to observe us because when they sampled was outside of that 1 in 10,000 window.