- 3128 - LIFE - on other planets? 99.9% of all the species evolved on Earth have gone extinct. Only 0.1% still exist of the 50,000,000,000 species that have lived on Earth. Of these only 1 species has become a communicating civilization of 6,500,000,000 people. Only 100,000,000,000 people have ever lived on the planet. 6.5% of them are alive today.
----------------------- 3128 - LIFE - on other planets?
- There are over 4,000 exoplanets that astronomers have discovered outside our solar system. Most of these are large Jupiter size planets orbiting stars that are among the billions of stars in our own milky Way Galaxy.
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- The Milky Way is 120,000 lightyears in diameter. To reach other galaxies we have to go much farther but there are 100,000,000,000 more galaxies in the Observable Universe. And, we could see only 4% of the Total Universe. The other 96% is the Un-observerable Universe because the light will never reach us.
- The early searches for life in our own solar system concentrated on the microbial life similar to what has existed on Earth for 4 billion years. The definition of life for this purpose is something made of cells, ingests energy, excretes waste energy, and passes on its genes in some form of reproduction. They can respond to their environment and can adapt and evolve.
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- When we go outside our solar system we change the strategy and search for intelligent life as well. Intelligent life on Earth has only been with us for a few million years. But, if we expand our search for intelligent life we may be able to find the signals that other intelligent beings use to communicate with each other.
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- A mathematical equation is an organized way of thinking as we develop a strategy to find other intelligent life. In 1961 Frank Drake first proposed this equation:
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- The number of civilizations capable of interstellar communications that are currently in the Milky Way Galaxy = R * f(p) * N * f(L) * f(I) * f (c) * L
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- The astronomical terms in this equation are: R * f(p) * N
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------------ R = the average rate of star formation in a galaxy.
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------------ f(p) = the percentage of stars with planets
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------------ N = the number of habitable planets per star.
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- The biological terms in the equation are: * f(L) * f(I)
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------------- f(L) = the percentage of habitable planets on which life actually arises.
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------------- f(I) = the percentage of life bearing planets with intelligent life.
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- The sociological terms in the equation are: * f c * L
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------------- f (c) = the percentage of intelligent civilizations that will communicate across the galaxy.
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------------- L = the average lifetime of communicating civilizations.
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------------ R = the average rate of star formation in our galaxy. There are 200 billion stars in the Milky Way Galaxy. The age of our galaxy is about 10 billion years. So, the average rate of star formation in our galaxy has been about 20 stars per year.
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------------ f(p) = the fraction of stars with planets. To get this fraction we estimate that abut 33% of the stars have heavy elements and need to be at least 5 billion years old. Because planets need heavy elements and they need at least that long to form. If 30% of the star are at least 5 billion years old then that gives us a fraction of 0.1. If half of these old stars have accretion disks that gives us the fraction of 0.05. Now, if half of those with accretion disks actually form planets, the fraction becomes f(p) = 0.025 with a range of 0.3 % to 20%.
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- ------------ N = the number of habitable planets per star. To get N we have to estimate how many stars are spectral type F, G, K, and M because the lifetime of more massive stars is too short for intelligent life to arise. We need to estimate the fraction of planets that are the right distance from the star to have liquid water and habitable temperatures. We need the fraction of planets that are the right size. The fraction that will have stable climates. The fraction that survive comet and asteroid bombardments. Multiple all these fractions together and get 1 chance out of 25, or 4%, with a range of 0.0000001 to 10%.
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- That is all the astronomy. For the biological and sociological fractions use you own guesses. Here are mine:
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------------- f(L) = the percentage of habitable planets on which life actually arises.(1)
My guess is 1% ranging from 10^-300 to 20%.
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------------- f(I) = the percentage of life bearing planets with intelligent life. My guess is 5% ranging from 1% to 10%.(2)
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------------- f(c) = the percentage of intelligent civilizations that will communicate across the galaxy. My guess is again 50% with a range from 1 % to 100%
------------- L = the average lifetime of communicating civilizations. My guess is 1 billion years ranging from 100 years to 10 billion years.
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- Ok, now multiple all these fractions together and what do you get?
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--------------The number of civilizations capable of interstellar communications that are currently in the Milky Way Galaxy = R * f(p) * N * f(L) * f(I) * f (c) * L
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------------ Intelligent Life in our Galaxy = 20 stars/year ( 0.025) (0.04) (0.01) (0.05) (0.5) (10^9 years) = 5,000 planets with intelligent life able to communicate with us. There are 20,000,000 habitable planets. Only 10,000 of those planets have intelligent life on them. But, if they have intelligent life 50%, or 5,000, will develop the technology for interstellar communication. That’s my guess.
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------------ If we take the most pessimistic view:
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------------ Intelligent Life in our Galaxy = 10 stars/year ( 0.003) (10^-7) (10^-300) (0.01) (0.01) (10^92years) = no chance of planets with intelligent life able to communicate with us. We are the only one and will end up talking to ourselves. Of course there are 100 billion other galaxies that we have not checked out yet. They just happen to be a lot further away. If we got a message a billion lightyears away it was sent a billion years ago and who knows what the civilization is doing now.
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- If we take the most optimistic view with the range of fractions we get:
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--------------The number of civilizations capable of interstellar communications that are currently in the Milky Way Galaxy = R * f(p) * N * f(L) * f(I) * f (c) * L
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------------ Intelligent Life in our Galaxy = 40 stars/year ( 0.2) (0.1) (0.2) (0.1) (1.0) (10^10 years) = 160,000 ,000 planets with intelligent life able to communicate with us.
There could be as many as 160 million civilizations trying to communicate in our own galaxy. Here is a summary for your quick review and a chance to make your own estimates:
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------------ R = 10 to 40 stars form each year in our galaxy.
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------------ f(p) = 3% to 20% of stars are with planets
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------------ N = 0.0000001 to 10% of planets are habitable per star.
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------------- f(L) = 10^-300 to 20% of the habitable planets where life actually arises.
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------------- f(I) = 1% to 10% of life bearing planets will get intelligent life
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------------- f (c) = 1% to 100% of the intelligent civilizations will actually communicate across the galaxy.
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------------- L = 100 years to 10 billion years lifetime of communicating civilizations.
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- Therefore, there are 1 to 160,000,000 communicating civilizations in our Milky Way Galaxy. We have been an interstellar communicating civilization for only 60 years out of the 12,000,000,000 years for our galaxy. That not quite 1 chance out of 200,000,000. So we would need that many communicating civilizations out there for an even chance of communicating with them. The optimistic view would get us there.
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- If you use my most optimistic estimate of 160,000,000 communicating civilizations the Milky Way is 100,000 lightyears in diameter. The area would be 7.8 billion square lightyears. The average distance between communicating civilizations would be 50 lightyears. So, with our 60 years of communicating this civilization would just now be receiving some of our communications. Hello, is anyone there?
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- 99.9% of all the species evolved on Earth have gone extinct. Only 0.1% still exist of the 50,000,000,000 species that have lived on Earth. Of these only 1 species has become a communicating civilization of 6,500,000,000 people. Only 100,000,000,000 people have ever lived on the planet. 6.5% of them are alive today.
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- April 19, 2021 LIFE - on other planets? 845 3125
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--------------------- --- Tuesday, April 20, 2021 ---------------------------
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