[ExI] Where are they? was Re: 2^57885161-1

spike spike66 at att.net
Wed Feb 20 02:53:35 UTC 2013



>. On Behalf Of Tomaz Kristan
Subject: Re: [ExI] Where are they? was Re: 2^57885161-1


>>. I am struck with this picture {NASA deep space image} of one tiny
patch of sky containing at least several hundred galaxies, each with
billions of stars.  I just can't get my head around the notion that
intelligence came together only once with all that out there.  There must be
something fundamental we are missing or still haven't discovered.

>.It is just not enough of galaxies that a coin could land 200 times head
up, if one was tossed every second on every plane.

>.Or just about once. The same holds for life.  Tomaz



Well now let's look at that Tomaz.  If coins are tossed 2^200 times then the
probability of 200 consecutive heads coming up at least once in that
sequence is about 63%.  2^200 is about 1^60, so let's take the generally
accepted estimate of the number of stars in the observable universe at about
100 billion galaxies times about 100 billion stars per galaxy, and ignore
for the moment that the estimate is generally higher in recent years.  Then
the number of stars is about E22, and we can imagine that a fairly typical
star has about between 1 and 10 orbiting objects on average, keeping in mind
that our sun has about 50 that meet this description because we include
larger satellites but not all those asteroids.  But assume about 10 per star
for conservative measure, so about 1E23 orbiting objects, and now using your
one coin per second, and accepting the estimated 14 billion year life of the
universe and leave some time for heavy elements to be cooked up in stars and
subsequently being supernova-ed into the cosmos to form accretion discs and
planets, so about 1E33 planet-years which is about 3E40 planet-seconds since
the observable universe was about 4 billion years along from the big bang.
So if we want to have that .63 probability, we need not one coin toss per
planet second, but rather about 3E19 coin tosses per planet-second.  


OK then, what if we get one coin toss per square meter of planet surface,
rather than one coin toss per planet second?  I see this as perfectly
reasonable; if you are a bit of goo trying to become a lifeform, you are
small, so a square meter is a lotta area.  The surface area of our typical
planet is about 4pi(6300000)^2 or about 5e14 m2, so we have about 1.5E55,
which still leaves us over 4 orders of magnitude short, so let us recognize
and press a little harder on the previous notion that to a bit of organic
goo, a square meter is a nice sized playground, and recognize that a square
millimeter is a pretty good sized backyard too.  If you do that, we get
about 1.5E61 square-cm-seconds in the post-big-bang observable universe,
which is about 15 times the original target of 2^200.  


So if we want to go with that perfectly arbitrary estimate of life
probability and perfectly arbitrary estimate of the reference area for an
orbiting object, we might reasonably estimate 15 tech-enabled civilizations,
out there somewhere, possibly in this small patch of sky:



Do stare at this photo for a while please, until it stares back, then remind
me, what were we talking about?








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