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Detectable Civilizations in our Galaxy 2

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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.

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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 dont have a clue of some of these
assumptions. We dont know what
fraction of planets capable of sustaining life
actually do generate life. We dont know of all of
the planets that have life what fraction of those
planets go on to have intelligent life and what
fraction 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 have 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 that
it can kinda 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?
Then what does it mean for things to eventually get
to the point that you have intelligent life?
You know, in all fairness to this, is
that probably two hundred years ago there
would have been no way to even have
a decent estimate of the number of
stars in the galaxy. Now we are starting to
do an okay job on that. 20 to 30 years ago
it would have been viewed impossible to say
the fraction of stars that have planets, but
now we are finding exoplanets. We are seeing
stars wobble. We are finding we are getting
more and more accurate instruments.
So we can start to think about planets that are
closer to the size of earth so we are even making
headway there. There are other indirect
methods to think about: You know, 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 are getting that maybe they are
capable of sustaining life.
So as time goes on and as technology
improves we might get better and better at
this. With that said, it's not going to happen
any time soon and the real value of all this
is really to structure our thoughts
about really a 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 a hundred thousand years,
but it's not releasing any type of thing that
we can detect. That's not what we care about.
We care about 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 will 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 a hundred years ago because
frankly, they would have to be no more than
a hundred 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 signal
for another tens of thousands of years.
So when I talk about now, I am saying that the
signals are getting to us. Signals getting
Signals recieved. The signals are being received
right now. So you could have a civilization
that developed radio seventy thousand
years ago, but they are seventy thousand light
years away and maybe they collapsed
ten thousand years later, but we are just
receiving their first radio signal.
So that would be a civilization that I would count
in this equation that we are setting up.
So just to make sure that we understand
it and then we can play with some numbers, let's
remind ourselves. This is the number of
our estimate of the number of stars
in 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 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, you 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 occured 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
their radio signatures are recieving us now.
And that's why we have this little term right
over here. So 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 criteria. whats 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?
So that's the detectable lifespan of that
civilization divided by the life of that solar
system or that planet because frankly,
the star and the solar system and
the planet are all going to essentially have
give or take, a few hundreds of thousands
of years or even a few millions of years
because we are thinking in the billions here.
They're going to have roughly the same life span.
And so if you have let's say, and
just to make this a little bit more
tangible, lets say the sun has a lifespan and
lets say that with the Earth and our solar system
has a lifespan of approximately ten billion years.
Ten 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. So we
have our best days ahead of us.
So 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 over 10 thousand.
So even though we might be around
sending out detactable signals for a million
years, the odds relative to the entire span
of the history of the planet and our sun,
if someone is just randomly sampling our
solar system at a random time in its history and a
random part of this ten billion years, there is only
a one in ten thousand chance that
they will be sampling us at a time that we are
releasing signals. Assuming that there weren't
any other civilizations on Mars or Venus or
that there weren't any other civilizations on Earth
hundreds of thousands of years ago
that were doing this, they would definitely
only have a one in ten thousand chance of
detecting us assuming that they are sampling
There could have been a civilization that
was around three million years ago and they
did this whole search for extraterrestrial life and
maybe they are twenty or a hundred or a thousand
light years away and they pointed their telescopes
at us, but a million or two million years ago they
would have pointed it at the direction of our sun
and they would have not gotten any radio
signals and they are like "Man, when is this
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.

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Detectable Civilizations in our Galaxy 2

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.