37, 964 civilizations we'll never talk to

The Drake Equation is explored. [Link]

There’s a lot of complex maths in the paper, and author Duncan H. Forgan says that when it comes to biological parameters the figures are basically guesswork, given that there is only one known biosphere.

Forgan applies his methods to different theories concerning the likelihood of life, including Panspermia, the Rare Life Hypothesis (life is rare, but life is likely to become intelligent), and the Tortoise and Hare Hypothesis (we assume civilizations that develop rapidly are more likely to destroy themselves) with the following scores:

• Rare life: 361 advanced civilizations
• Tortoise and Hare: 31,573 advanced civilizations
• Panspermia: 37, 964 advanced civilizations

More on the Drake Equation:

The Drake equation states that:

where:

N is the number of civilizations in our galaxy with which communication might be possible;

and

R^* is the average rate of star formation in our galaxy

f_p is the fraction of those stars that have planets

n_e is the average number of planets that can potentially support life per star that has planets

f_ℓ is the fraction of the above that actually go on to develop life at some point

f_i is the fraction of the above that actually go on to develop intelligent life

f_c is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L is the length of time such civilizations release detectable signals into space.

The number of stars in the galaxy now, N^*, is related to the star formation rate R^* by

,

where T_g is the age of the galaxy. Assuming for simplicity that R^* is constant, then N^* = R^* T_g and the Drake equation can be rewritten into an alternate form phrased in terms of the more easily observable value, N^*.^[2]

Historical estimates of the parameters

Considerable disagreement on the values of most of these parameters exists, but the values used by Drake and his colleagues in 1961 were:

• R* = 10/year (10 stars formed per year, on the average over the life of the galaxy)
• f_p = 0.5 (half of all stars formed will have planets)
• n_e = 2 (stars with planets will have 2 planets capable of supporting life)
• f_l = 1 (100% of these planets will develop life)
• f_i = 0.01 (1% of which will be intelligent life)
• f_c = 0.01 (1% of which will be able to communicate)
• L = 10,000 years (which will last 10,000 years)

Drake's values give N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000 = 10.