ARE WE ALONE?

We consider two topics:

• Probability for Other Intelligent Lifeforms in the Milky Way
• Detection and Communication with Other Lifeforms in the Milky Way

Probability for Other Intelligent Lifeforms

To get a handle on this number, consider something referred to as the Drake Equation,
N = (RxT) x F(p) x N(p) x f(E) x F(life) x F(int) x F(tech)

Terms in Drake Equation
• R = Star Formation Rate ~ 1 - 10 stars per year
• F(p) x N(p) x f(E) = fraction of stars with planetary systems with earth-like planets ~ 1/100,000,000,000 to 1/2 (all nonbinaries). Perhaps a more reasonable estimate is based on the probability for systems with planets:
  ===> 1/2 (x 1/4, observed systems)?
• F(life) = probability life develops = Habitable planets x Life forming ~ 1/2 (Mars and Earth) x 1/2 (Earth out of Mars and Earth)
• F(int) = probability intelligent life then develops ~ 1 (natural selection)
• F(tech) = probability intelligent life develops technology ~ 1 (based on ?)
• T = Length of time intelligent civilization lasts ~ 100 y ===> 10 billion y

For these probabilities, wind up with

N = (1-10)xTx(1/2-1/8)x(1/2x1/2)x1x1xTx1===>(1/32-5/4)xT

The lifetime of a technological civilization is the key. If we imagine that 1 out of 1,000 technological civilizations can last for around 5 billion years (roughly the nice part of the Sun's lifetime) ===> T ~ 5 million years ===> N ~ 160,000 to 6 million.

Comment if T ~ 100 years ===> N < 125.

Detection and Communication with other Lifeforms

The number of intelligent civilizations in the Galaxy is N.

Question: What does this tell us about the possibility of detecting and communicating with other lifeforms? If the average distance between civilizations is ~100 light years then direct (and/or two-way) communication by travel and radio to distant civilizations is difficult. For example,

• if we traveled at 100,000 miles per hour, then a round-trip would take:
  Time = 200 l.y. x 6,000,000,000,000 miles / 100,000 miles per hour ===> more than 1 million years!

• if we sent a radio message out, then a reply could reply only after > 200 years

This means:

• we must use other methods (or learn to travel faster or not care if we are around when we get there) in order to communicate with other lifeforms by direct visitation.

• if we try to communicate with other civilizations we should not expect answers in our lifetimes. Note--we have, in fact, off and on, tried to communicate with other civilizations. Sometimes on purpose and sometimes by accident.

The easiest way to communicate is through passive communication (listening). We try to pick up signals from extra-terrestrial sources. As noted earlier, this is a tricky business, because we have to know the frequency (channel) to which to tune our radios and we have to be able to figure out when we have received a signal from an intelligent civilization.