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Cosmology and astronomy
Course: Cosmology and astronomy > Unit 4
Lesson 4: Life in the universeDetectable civilizations in our galaxy 4
Taking a shot at estimating the number of detectable civilizations. Created by Sal Khan.
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What if a non-intelligent for of life develops some form of detectable technology? Could we eliminate one variable from the drake equation?(3 votes)
Well, that would be rather strange since anything that develops detectable technology would have to be intelligent by our definition.
However, we need to be open minded about one thing. Maybe there is a form of life out there that naturally communicates using radio waves, but that didn't necessarily developed any technology. It could be that such communication is innate to the biology of such life forms. But what would make such a form of communication travel interstellar distances? That would require a pretty powerful transmitter that's unlikely to come about through natural selection. So I find it very hard to imagine any form of life that has technology that's detectable to us on earth that isn't intelligent.
It's same to assume that any life that has developed technology would have to be intelligent.(12 votes)
Is it safe to assume that these other hypothetical civilizations are equally distributed through out the galaxy or are there areas that would have a higher probability of harboring intelligent life?(5 votes)
Well, the center of the galaxy is filled with deadly radiation because of the large amount of massive stars. The outer reaches of the galaxy don't have as much heavy elements as other areas and planets are less likely to form. Life is unlikely to form within 5 light years of a massive star as its radiation would sterilize planets even in other solar systems. The sun happens to sit in the area that we would predict life to come from. If you are looking for life, look for stars midway from the center and far away from massive stars.(8 votes)
So is it possible for another planet be searching for other planets as well but not using electromagnetic waves?(5 votes)
The only other force that acts at a significant distance, that we are aware of, is gravity. It is possible they could use that, but unlikely as gravity is a much weaker force than the electromagnetic force and therefore would require much more effort to utilize for communication.
There is another property of the quantum world, which we are currently exploring, called quantum entanglement in which entangled particles can 'communicate' their properties instantly at even great distances instantly, which would even be faster than the speed of light. We still don't fully understand this though and if it is possible to even use this property for communication. But it is possible a more advanced civilization has figured this out.(5 votes)
There are some other factors that influence this calculation that have not been taken into account, or at least lower the probability of some of the factors that are used. For example: the tides caused the moon contributed to the birth of life. Without it, evolution might have been slower. Also Jupiter saves the inner planets from bombardments. It's almost likely that a similar solar configuration is required for life to sustain for longer periods of time to be able to become intelligent.(6 votes)- There are things that should be lowered, but there are also be things that should be raised, like N*, F(p) and F(l). Ultimately I agree the number would probably be less than 12.5, maybe more like 7 or 8 (in my eyes anyway)(1 vote)
- How likely would intelligent life develop underwater? Could there be intelligent beings as intelligent or more intelligent than humans that would only live under water? Would their communications, electromagnetic or otherwise, be detectable?(4 votes)
A major problem with a purely underwater civilization is this: water and electricity do not mix, therefore an underwater civilization would have no means of using the electricity so central to our lives. So, although it is possible, I think it would be less likely for an intelligent species that lives underwater to create advanced technology with which they could broadcast into space and communicate than it would be for a terrestrial species.(1 vote)
What are the odds of two species on a single planet simultaneously developing intelligence to the point of detecting/transmitting signals from/to another planet? Here on earth, we speculate about the intelligence of other species, but our dominance of the planet has very likely prevented any other species from evolving intelligence to the same degree. Is it fair to assume that each planet that harbors life will have only a single "intelligent" species?(3 votes)- This really depends on the size and geography of the planet - it could be possible, and without any other planets with life to reference we can't really say . Something perhaps to consider when using the Drake Equation!(4 votes)
It seems to me that Sal's statement that f-sub-l (the 4th term) must be fairly large because life is "robust" and adaptable to all kinds of rugged environments is logically flawed.
Our assumption is that life evolved only once. So it is irrelevant how good life - once evolved - is at filling niches. Even if it fills every available square foot of earth... life still only evolved once... in one place. And the question is not whether a planet is able to SUPPORT life (which we can guess is fairly easy), but whether it is able to EVOLVE life from not-life (which... we have no way to guess).
But here is an example of the logical flaw. Sal's sweeping statement is like saying that any given place on any road on earth's surface is fairly likely to be a car factory, based on the observation that on almost every place in every road on earth (from the highest to the lowest, from the longest to the shortest, from the smoothest to the bumpiest) we find cars.
The fact that something can easily occupy a space is in no way correlated (I think) with whether that space can spawn such an object. Spawning being a radically different activity from "being found there".(5 votes)
what makes life considered intelligent?(3 votes)
I wonder if they will ever get to detecting non-intelligent life! that would be interesting! don't you think!? but I should be patient, people haven't even found intelligent life yet.(1 vote)
At1:46Sal says that dinosaurs may have been smarter than us, but they couldn't of been smarter than us because if they were, they could stopped the asteroid... Right? Or, they were smart enough, but they didn't have what they needed to stop it? What do you think, because that's confusing me. (We'll probably never know)(1 vote)- They were never aware of an asteroid.
Even if they had tech, it would have struck unexpectedly.
Like today, last year we almost got hit with an asteroid 50 feet across.
We didnt know until it got close.(2 votes)
- Would the 1936 Olympics be the first thing that aliens could detect?(1 vote)
- Possibly, it was one of the first broadcasts that had enough power to break out of our atmosphere.(2 votes)
1:46Video transcript
I've talked a bunch
about the Drake equation, or our own version
of the Drake equation that starts with the number
of stars in the galaxy, but I haven't given
it a shot yet. I haven't tried my own
attempt at thinking about how many detectable
civilizations there are. So let's actually do that here. So let's just assume that
there are 100 billion stars. 100 billion stars. So that's my first
term right over there. Let's say that 1/4
will develop planets. And let's say of the solar
systems that develop planets, on average let's say
that they develop an average of 0.1 planets
capable of sustaining life. Or really, that you'll have
one planet for every 10 of these solar
systems with planets. That's just my assumption there. I don't know if that's right. Now let's multiply
that times the fraction of these planets
capable of sustaining life that actually
will get life. And I don't know what that is,
but I hinted in previous videos that life is one of
those things that it seems like if you have
all the right ingredients, it's so robust. And you have life it these
underwater volcanoes, you have bacteria
that can process all sorts of weird things. So let's say that
probability is pretty high. Let's say that is 50%,
or half of the plans that are capable of getting
life actually do have life. I would guess that that
might even be higher. But once again, just a guess. Now we have to think
about of the life, what fraction becomes intelligent? What becomes intelligent over
some point in the history? Well, I'll say it's a tenth. A tenth of all--
maybe if the asteroids didn't kill the
dinosaurs, it wouldn't have happened on Earth. Who knows? Or maybe we'd just have some
very intelligent dinosaurs around. We don't know. And maybe there's other
forms of intelligent life even on our own planet that
we haven't fully appreciated. Dolphins are a good candidate. Some people believe
that octopuses, because they have
such flexible arms, there's a theory that they
could develop eventually the ability to kind one
day, if their brains mature, and all of the rest, make tools
the same way primitive primates eventually were able to
have larger brain sizes and actually manipulate
things to make tools. So who knows? I don't want to get
into all of that. So there's a 1 in 10 chance
that you get intelligent life, and then assuming that
intelligent life shows up, what fraction is going
to become detectable? I don't know. I don't know whether dolphins
will ever communicate via radio or not. So let's just say that
is-- I don't know. Let's say that is another 1
in 10 chance, or I'll say 0.1. And then we have to multiply
it times the detectable life of the civilization on average. Once again, huge
assumptions being here, but the detectable
life of a civilization, let me just put it
at 10,000 years. Either they destroy
themselves, or they get beyond that type of
radio type communication, electromagnetic
type communication. Maybe they start doing all
sorts of weird, wacky things. Probably it won't
take you 10,000 years to even progress it. That might take you less time. But let's just do this
just for the sake of fun. And then the lifespan
of your average star, that's probably
one of the things that we have the best sense of. So on average, let's put
it at 10 billion years, 10 billion years. So let's calculate all of this. Let's get my handy TI-85 out. And so we're going
to have 100 billion. That's 1 times 10 to the 9th. Sorry, that's 100
times 10 to the ninth. So let me clear it. Or you could have 1
times 10 to the 11th. That is 100 billion times
0.25 times 0.1 times .05 times 0.1 again, times 0.1
again, times 10,000 divided by 10 billion. So times 10,000, 1, 2,
3, divided by 10 billion. So that's one 1e10. 1 times 10 to the 10th power. 1 with 10 zeroes. So let's see what we get. We get 12.5, which is
kind of a neat number, but these are heavily
dependent on this. So we're saying if
given these assumptions, there should be 12.5
detectable civilizations in our galaxy right now. So the question is, why
aren't we detecting it? Maybe their radio signals, maybe
their electromagnetic waves are getting to us, but we can't
differentiate it from noise right now. And that's what the whole
SETI project's all about, of trying to keep track
of all this information, all of these radio waves, and
electromagnetic waves that are coming from outer
space towards Earth, and seeing if any of them
actually have any non noise signal, that actually look
like they're being generated by some type of
intelligent civilization. So maybe we're getting them, and
we're just not detecting them, or maybe something
else is at play. Maybe we've overestimated
one of these. Maybe there is a lot a
life, but maybe they're not using electromagnetic
waves to communicate. Maybe that's some type of
primitive way of communicating. Maybe they start doing
telepathy, or something crazy, or they start using some
type of quantum thing that allows them to communicate
more directly without having to wait for the speed of light. That is a very slow
way to communicate. And it is a slow way,
frankly, if you're trying to communicate
across solar systems, and stars, and planets,
or even across galaxies, one could imagine. So maybe we're just kind
of at a transition state of communication, that
electromagnetic waves, radio and all the rest is
just a transition state. Maybe in 100 years
we'll figure out another, better way
that's not detectable in our traditional ways. Maybe we're being bombarded with
another type of communication mechanism that we're just
not ready to perceive yet. Who knows, but it's just
a fun thought experiment to say that hey, given
these assumptions, there should be at least
a couple of civilizations, or a handful of
civilizations that we might be able to detect.