Detectable Civilizations in our Galaxy 1 A framework for thinking about how many detectable civilizations are out there.
Detectable Civilizations in our Galaxy 1
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- It's estimated that our galaxy, the Milky Way, has 100 to 400 billion stars,
- and when you hear a number like that the obvious question is:
- Are there civilizations on planets that are orbiting any of these stars
- and maybe even more interesting question is can we detect any of those civilizations?
- Have they gotten to the level of technological progress like us,
- that they are emitting electromagnetic waves into space
- and other civilization like ours can detect and say,
- "Hey, there is someone else out there watching television or using radio or whatever else they might be doing."
- So, what I want to do with this video is not answer that question.
- That's a big open question, we don't know the answer.
- We don't have anywhere near enough information to definitively answer that question,
- but I want to do is come up with a framework for at least thinking about that question,
- a way of actually estimating
- how many detectable civilizations there are in just our galaxy,
- and there is a formula, that you may or may not have heard of,
- called the Drake Equation.
- and what we are going to do is independently
- derive our own version of the Drake Equation.
- It's going to be slightly different,
- but it is the same thought process
- and in the future video, I'm going to maybe reconcile
- what we come up with, with the Drake Equation,
- and just so you know Drake equation is named for Frank Drake,
- who is a Professor at University of California Santa Cruz.
- He first, kind of put some structure around this problem,
- that's why the formula or the equation has his name,
- but the equation is not an equation you can apply
- on a daily basis and get results that you can use to build things,
- but what it's, it's the structures of our thinking around this question of
- How many detectable civilizations are there in our galaxy?
- And to answer this question, I am going to start little bit differently than Frank Drake did
- He starts with the number of new stars that're born each year,
- we will see that our definitions are actually pretty close to each other
- what I want to do, is start with the total number of stars,
- So, we are trying to come up with is,
- I will call it 'N' and this is number of detectable civilizations,
- number of detectable civilizations in the Milky Way, in our galaxy.
- and once again, there could be civilizations, looking back in the star field right over here
- this star right over here, maybe it has a planet that is in the right place
- that has liquid water and maybe there is intelligent life on that planet,
- but they might not be detectable,
- because, they aren't technologically advanced enough that they are using electromagnetic radiation
- or maybe they just figured out some other way to communicate
- or maybe they are beyond using electromagnetic radiation, you know, radio waves and all the rest to communicate
- so we will never be able to detect them.
- We are talking about civilizations like ours that are, to some degree,
- using technology not too different than our own.
- That's what we mean by 'detectable',
- so let's think about that little bit.
- I like to start with just the total number of stars in our solar system.
- So let's just start with, I will call it, N*,
- so this is the number of stars in our galaxy, and our best guess, I said is this's going to be 100-400 billion stars.
- We don't even know how many there are, some of them are undetectable,
- and the center of our galaxy is just a big blur to us
- we don't even know what's on the other side of that,
- e can't even see all the stars that are packed into the center,
- so this is our best guess, 100-400 billion stars.
- Now obviously, there is going to be subset of those stars that even have planets.
- So, let's multiply the times that subset; so lets multiply
- times the frequency of having a planet.
- If you are a star, this is the percent chance or the frequency or
- of the fraction of these stars that have planets (f sub p)
- so, I'll write this way "fractions that have planets",
- So, if this is a hundred billion, let's say I am making a guess here
- and we are learning more about this everyday,
- there are all these discoveries of 'exoplanets'- planets outside our solar systems,
- maybe this is one fourth.
- Then you could say, well that means there are 100 billion times one fourth,
- that means there are 25 billion stars that have planets around them.
- But that's still not enough to go to civilizations.
- We also need to think about planets, there could be a planet like Jupiter,
- and we don't know how life as we know it can survive on a planet like Jupiter or Neptune or Mercury.
- It has to have planets that are good for sustaining life.
- Preferably have a rocky core, liquid water on the outside,
- that's what we think are the ingredients we need for life,
- maybe we are just not being creative enough, that's what we know as life is being.
- So, let's multiply this times the average number of life sustaining or planets that could sustain life on them.
- So we don't necessarily know that they are going to have life,
- but they seem like they are just the right distance from the star,
- not too hot, not too cold. They have the right amount of gravity, water, all the other stuff,
- and we still don't know what this means,
- but this means average number, so given a number of solar systems with planets, what's the average number of planets capable of sustaining life,
- and once again, you don't know this answer.
- maybe it is 0.1, it's probably less than 1.
- Therefore any given solar system that has planets,
- the average number capable of sustaining life maybe its 0.1 maybe it's more than 1, I don't know.
- We don't know the exact answer here, but I will throw an answer in,
- I 'll throw out a guess, maybe it is 0.1.
- And here the fraction that has planets (f sub p), i don't know, i will throw that out as,
- and once again I am making up these numbers, we really don't know the right answers, this is one-fourth.
- But if we were to multiply this out we would have
- the average number of planets in our solar system that are capable of sustaining life
- that are around stars that have planets and these planets are capable of sustaining life.
- Now, n sub p will give us the total number of planets in our galaxy capable of sustaining life.
- Now, just because you have liquid water and right temperature and all the other rest of the ingredients
- doesn't mean that you will actually have life happening on your planet.
- So let's multiply that times the fraction that actually generate life (f sub l)
- So f sub p is the fraction that actually have life
- and this is actually a very , we dont know this answer, so this is the fraction
- that have life on them
- And this is a really big open question
- maybe if you have the ingredients, maybe every planet has life
- maybe it is a frequent thing that's happening in our galaxy and frankly our universe
- or maybe it's a very infrequent thing
- maybe it's just the right kind of freak set of circumstances that just have to happen
- i will throw out a number, just for the sake of having a number
- maybe it is one out of every ten planets
- that have all the right ingredients for life actually do generate life.
- My personal guess is probably higher than that given that
- life seems life seems such a robust and flexible thing we have seen in all sort of weird circumstances.
- Actually let me make it higher number than that so let me make it one half (0.5)
- assuming that we have all of the ingredients.
- So this should tell us essentially
- how many planets in our galaxy have had life on them at some point
- in those planets' lives.
- The life might have come and gone
- maybe destroyed itself through nuclear war.
- But this would tell us the number of planets in our galaxy
- that had life at at least one point in their history.
- Now we care about civilizations, about intelligent life..
- So maybe if the asteroid never hit earth...
- the dinosaurs would have never evolved to the point of generating
- radios and tvs and telephones and all the rest..
- and so it is kind of a freak circumstance
- that because they were destroyed these gaps in the ecosystem developed
- so we could emerge and and be intelligent and
- do all these crazy things
- like make YouTube videos and all the rest.
- So, let's multiply this times the fraction
- if you get all of this, the fraction
- that actually end up having intelligent life
- and maybe this fraction is,
- to a number of 1/10, then probably
- in the next video I'll calculate it all.
- Now this is very important to realise
- because once again, you could have life
- these are all examples of life right over here
- This is actually life on Earth, on our planet
- even though this looks quite alien
- this is a weeble, kind of looked at from very close-up,
- but there is all sorts of forms of life
- many of which we probably can't even begin to imagine
- but what we care is that if intelligent life
- starts to emerge on the planet
- because only intelligent life has a chance,
- we believe of being able to eventually communicate in ways
- that are detectable by us.
- Now I said intelligent life, but
- maybe not all intelligent life will eventually
- get to the technological sophistication, where
- they will be using radio waves, electro-magnetic radiation to communicate with each other
- maybe we might have stagnated at this stage
- if nothing of the right things didn't happen..
- So what we need to do now, is multiply this
- so right here, we would have the number of planets
- in our galaxy that have had intelligent life on them at some point in their history
- maybe not at a time that coincides with ours,
- but what we wanna do is bring it down even more to the percentage that get to the point
- that they can develop technology that allows us to detect them.
- So, let me multiply times the fraction that are, I'll put a 'C' here,
- 'C' for, maybe they're using communication; 'C' for communications
- that allow us to detect them.
- So this is detectable, the fraction that are detectable.
- Now you might think that we're done, this will give you the Total Number of Civilizations, or life-forms
- in our Galaxies or the planets that have life forms that developed detectable technologies at some point
- in their history.. Now it would be nice if civilizations be not born and die
- but the reality is, they do die. They might destroy themselves or whatever,
- and they might exist for only a small period of time for the history of that planet
- or the history of that Solar System.
- So in order to make it the number of civilizations that are in existance now
- and I'll clarify what "now" means in the next video because really if we are
- detecting something from a star that's 10,000 lightyears away
- our "now" means we are just receiving their signals
- so, they released the signals 10,000 years ago.
- But what I want to do is get to know what is the fraction of these whose signals
- are reaching us right now.
- and here, I'll say what's the average lifespan of a civilization
- I'll put that "L", who knows what is, maybe 10,000 years
- so civilization lifespan as going to be that over the life of the star
- So, I'll put a 'T' here, for the average lifespan for the star,
- and I could say the average lifespan for the planet,
- or whatever, but we're assuming once our star
- supernovas, you're not going to have a chance for
- life on Earth to develop anymore.
- So, maybe this thing appears ten thousand years
- and this down here is maybe 10 billion years.
- and if you were to multilply this out, you should get
- the number of detectable civilizations in our galaxy right now.
- I'll leave you there, and next we'll discuss it a little bit
- more, and reconcile it with the more famous version of Drake's equation,
- and I'll also try and talk about this little piece of bit,
- because I think it might be a little confusing, and
- I'll try to diagram that out a little bit more..
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