Lecture Notes
Updated Wednesday, 21-Jan-2004 10:19:37 EST

Life in the Universe

Note that both of these principles implicitly assume that ETIS would have certain similarities to us. Removing that assumption complicates these arguments somewhat.

N = R× P× E× L× I× C× T

[numbers in brackets below indicate permitted values to use in the equation]

N = number of ETIS in our galaxy

R = rate of star formation [number/year]

Our galaxy (Milky Way) is about 10 billion yrs old and contains about 100 billion stars, so R = 10 stars/yr is the standard assumption

P = fraction of stars with planets [0-1]

E = environmental factor = number of planets in a solar system that are ecologically suitable for life [0-?]

L = fraction of planets with suitable environment where life actually did develop [0-1]

I = fraction of inhabited planets where intelligent life-form evolves [0-1]

C = fraction of planets with intelligent life that has developed radio communications [0-1]

T = time [years] that a technically developed civilization survives

R = 10, P = 1, E = 5, L = 1, I = 0.1, C = 1, T = 5000 yrs

N = 25000 ETIS

R = 10, P = 1, E = 1, L = 0.1, I = 0.1, C = 0.2, T = 100 yrs

N = 2 ETIS

Copyright © 1998, Robert G. Melton

Updated Wednesday, 21-Jan-2004 10:19:37 EST