Drake Equation: Explaining N Value

  • Thread starter Andrew Jacobson
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In summary, the Drake equation is used to estimate the number of currently detectable intelligent civilizations in the universe. The L term in the equation represents the length of time that these civilizations release detectable signals into space, and acts as a filter to account for civilizations that no longer exist. This is important because advanced species may face challenges that could lead to their downfall. AI is one such challenge and could potentially replace biological species, but it would not change the overall number of detectable civilizations. The Drake equation is not a law, but a way to rationally estimate the number of detectable civilizations, taking into account various assumptions and uncertainties.
  • #1
Andrew Jacobson
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Hi, I'm doing a presentation about the fermi paradox and I use the drake equation:
[itex] N = R_* \times f_p \times n_e \times f_I \times f_i \times f_c \times L [/itex]
Where the symbols have their usual meanings. I don't understand why this would give the number of civilisations whose EM emissions are detectable. Surely it would give the number of civilisations created in L years whose EM emissions are detectable? If somebody could explain why the L (length of time which such civilisations release detectable signals into space) would give the N value that would be much appreciated, thanks.
 
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  • #2
The motivation for thd L term in the Drake equation is to weed out civilizations that no longer exist. The objective is to approximate the number of currently detectable intelligent civilizations, not the total number that may ever have existed.
 
  • #3
It is assumed that advanced species will have several logistical hurdles that they have to get through to remain active. We've already past one of these hurdles: the development of nuclear weapons. If our species were just a little bit more aggressive, we may have used them and set our civilization back another thousand years. AI will likely end up being an existential threat that'll make nukes look like child's' play, and there are probably more hurdles ahead of us that we haven't even dreamed of yet. That's why L is an important (an unknown) factor.
 
  • #4
newjerseyrunner said:
AI will likely end up being an existential threat that'll make nukes look like child's' play, and there are probably more hurdles ahead of us that we haven't even dreamed of yet. That's why L is an important (an unknown) factor.

AI's would also be observable sentient species. This, replacement of a biological species by an AI species would not change the numbers.
 
  • #5
Perhaps it would help to reframe the equation in the following way. The key part that you are asking about is the R*L, so let us instead say R=N/t, where t is the lifetime of a star (since there are many types of stars, with their own lifetimes and formation rates, we just add up terms like this for each type), and N is the number of stars in the galaxy (or that particular type, if we are keeping track). Then say R*L = N*L/t, and notice the ratio L/t = P can be viewed as the probability P that any civilization that appeared at that star is actually there now (where we needn't worry about the time of flight of the light, just use a lookback time in place of "now", it's no big deal). So instead of R*L, we have N*P-- the number of stars N that have life on them now, where P is interpreted as a fraction of those stars.
 
  • #6
The Drake equation is not a law or observed relationship, but an attempt to rationally guess the number of detectable civilizations. It includes some assumptions, and the range of some of the terms are large, so the answers you get range from about zero to millions. Hopefully all the exoplanets we've found can narrow down some of the terms.
 

What is the Drake Equation?

The Drake Equation is a formula that attempts to estimate the number of technologically advanced civilizations that may exist in our galaxy. It was created by astronomer Frank Drake in 1961.

What does the "N" value represent in the Drake Equation?

The "N" value, also known as the "number of communicating civilizations," is the estimated number of civilizations in the Milky Way galaxy that have the ability and desire to communicate with other civilizations.

How is the N value calculated?

The N value is calculated by multiplying together a series of factors that are believed to influence the development of extraterrestrial civilizations. These factors include the rate of star formation in our galaxy, the fraction of stars that have planets, the fraction of planets that are habitable, and the fraction of habitable planets where life actually evolves.

Is the Drake Equation a reliable way to estimate the number of alien civilizations?

The Drake Equation is not intended to provide a definitive answer to the question of how many alien civilizations exist. It is simply a way to organize our current knowledge and assumptions about the factors that may influence the development of extraterrestrial life. As our understanding of these factors improves, the estimated value for N may change.

What is the significance of the Drake Equation?

The Drake Equation serves as a framework for discussing the probability of extraterrestrial life and stimulating scientific and philosophical discussions about our place in the universe. It also highlights the importance of ongoing research and exploration in the search for life beyond Earth.

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