Science Fiction and the Drake Equation


Science Fiction and the Drake Equation

I start­ed think­ing about one of the clas­sic authors of sci­ence fic­tion, and the set­ting he cre­at­ed for some of his sto­ries.  I often won­dered what the impli­ca­tions for the Drake equa­tion would be in that par­tic­u­lar set­ting. I’ve tak­en a sub­set of the sto­ries for this set­ting, since not all of the sto­ry set­tings are self-con­sis­tent.  Let me review the three con­di­tions from four books:

    1. Human­i­ty dis­cov­ers that there are ancient alien civ­i­liza­tions on both Mars and Venus.
    2. Life is found on Ganymede.
    3. The first two inter­stel­lar loca­tions vis­it­ed by human­i­ty have life, and one of them has an alien civilization.

This is a sig­nif­i­cant dif­fer­ence from our recent dis­cus­sions about the Drake equa­tion applied to the uni­verse as we know it.

Lets first look at the prob­a­bil­i­ty of life.

In the sto­ries, there is no indi­ca­tion of there being life on the Moon oth­er than the life in the domed colonies that human­i­ty put there. There is also no indi­ca­tion of life on any oth­er of Jupiter’s moons, nor any of Saturn’s.

Assum­ing we only count Io, Europa, and Cal­is­to from Jupiter, and Titan from Sat­urn, we have a total of 4 bod­ies with life and 5 bod­ies with­out. This gives a chance of a plan­et hav­ing life at 44.4%.

Next, we look at the prob­a­bil­i­ty of plan­ets hav­ing life also hav­ing intel­li­gent life.

With Venus, Earth, and Mars all hav­ing intel­li­gent life, it fol­lows that 0.75 of all life bear­ing plan­ets have life evolv­ing to intel­li­gence. If we include the oth­er two plan­ets from out­side the solar sys­tem, we find four out of five plan­ets, or 80%.

Extend­ing this to the galaxy, we move on to attempt find­ing the num­ber of civ­i­liza­tions that are present.

The ini­tial val­ue for the prob­a­bil­i­ty of a star hav­ing plan­ets at rough­ly the time these sto­ries was writ­ten is about 0.1; how­ev­er, we have the fact that at least two stars have plan­ets besides the Sun.  This can be except­ed as true since we don’t have enough evi­dence to set it at any oth­er val­ue. (Note: the author’s lat­er work intro­duced a mul­ti­tude of worlds but the all sup­port­ed life, but this real­ly did­n’t talk about all stars or all worlds with­in the solar systems).

The num­ber of plan­ets with­in such a sys­tem is an aver­age of nine, one, and one (I don’t recall see­ing addi­tion­al plan­ets men­tioned in these sys­tems).  We’ll set that aver­age to be 4.

The frac­tion­al num­ber of worlds hav­ing life is 0.44, and the frac­tion hav­ing intel­li­gent life is 0.8.

The frac­tion of those civ­i­liza­tions hav­ing the abil­i­ty for inter­stel­lar com­mu­ni­ca­tions will be assumed to be 0.5, only Earth and Mars.

This give  f*(0.1)*(4)*(0.44)*(0.8)*(0.5)*L, where f is the stel­lar for­ma­tion rate and L is the life­time of the tech­no­log­i­cal civ­i­liza­tion.  Thus the num­ber of civ­i­liza­tions in the galaxy is f*L*(0.07). Giv­en that the stars form approx­i­mate­ly 1 per year, and that we take the life­time of a civ­i­liza­tion to be a mil­lion years (using the fact that Mars was on the verge of col­lapse after a mil­lion years), we can now esti­mate that in this author’s milky way galaxy would con­tain 70 thou­sand civilizations.

For details of this cal­cu­la­tion see my arti­cle on the Drake Equation:

Mind you, it’s been a while since I read the four books men­tioned above.  For those want­i­ng to look for them­selves for some­thing I have missed, they are: Between Plan­ets, Farmer in the Sky, Uni­verse/­Com­mon-Sense, and Methuse­lah’s Chil­dren by  Robert A. Hein­lein.  Anoth­er Nov­el of his, that is in one way con­tra­dic­to­ry to the oth­ers, seems to nail the idea of the galaxy hav­ing thou­sands of civ­i­liza­tions: Have Space­suit Will Travel.