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Drake (2020)

last updated: 20 Jul 2020

The Astrobiological Copernican principle (ACP)

(*Drake equation 2020 update)

The Drake equation (1961) - is an equation which tries to estimate the number of alien species who live in our galaxy Milky Way
For 2020 there is an updated version of this equation (the ACP) with a more accurate estimate of the number of planets that could support life.
The study: The Astrobiological Copernican principle →
A review of the study in Forbes magazine →

The Astrobiological Copernican principle

(Drake equation 2020)
Modelling scenario

Number of stars (N*)

Total number of stars in our galaxy - the Milky Way

250 billion

Mature stars (fL)

The percentage of stars in our galaxy, which are older than 5 billion years

1.5%

Habitable zone (fHZ)

The percentage of stars in our galaxy, which have a planet that is old enough in the habitable zone

19%

Metallicity (fM)

The percentage of stars in our galaxy, which have a high enough metal content for life and technology to exist

49.83%

Available time (τ′)

The average amount of time available for life to evolve on a planet

1 bn yrs

Lifetime of signals (L)

How long has the advanced civilisation being transmitting into space

100 yrs
Results:

Number of Alien civilizations (N)

Estimated number of advanced civilisations in the Milky Way
- who are emitting radio signals now - so they are at the same technological level as us
- all alien civilisations who might have emitted radio signals more than 100 years are assumed dead by the scientists.

36
N = N* * fL * fHZ * fM * (L/τ')
Estimated number of Earth-like planets in Milky Way
355 million
Odds of intelligent life / planet
1: 10 million

Applying the latest Drake equation (2020) to the whole Universe

How do we apply the revisited Drake equation (2020) to the whole Universe?
We multiply the results from our galaxy Milky Way to 2 trillion galaxies (our latest estimate for the number of galaxies in the Universe as of 2020).
Even if this approach might seem simplistic, we are just trying to make an estimation of scale.
To apply the Drake equation to the whole Universe, could be a much more complicated affair with many other variables and estimations - and it is definitely something we hope scientists will look into someday.

Drake Model Optimistic Drake Model Moderate Drake Model Pessimistic
Aliens in Our Galaxy 928 60 36
Aliens in Universe

1.8 quadrillion ⌄

928 * 2 trillion galaxies

120 trillion ⌄

60 * 2 trillion galaxies

72 trillion ⌄

30 * 2 trillion galaxies

* The results represent only the number of alien civilizations who are at the same technological level as us!


Various chances for Intelligent Life in Universe ⌄

1.8 quadrillion alien civilizations in Universe?
Isn't that a bit too much?
Those huge numbers could be because the scientists in the study assumed that life always appears on Earth-like planets within a few billion years as a natural part of evolution (mathematically, chances are assumed to be 1:1 - life always appears).

What if life is rarer than they believe?
Another study → that is using bayesian statistics found that chances of life appearing could be 9:1 for primordial life and 3:2 for intelligent life.

Chances for Intelligent Life Drake Model Optimistic Drake Model Moderate Drake Model Pessimistic
1:1 (Drake 2020) 1.8 quadrillion 120 trillion 72 trillion
3:2 (bayesian study *) 1 quadrillion 64 trillion 38 trillion
1:million 1.8 billion 120 millions 72 millions
1:billion 1.8 million 120 thousands 72 thousand
* The results represent only the number of alien civilizations who are at the same technological level as us!
* bayesian study says ods for intelligent life are 3:2 →



All aliens who ever appeared in Universe ⌄

However, what if we assume some aliens actually did not die as assumed in the latest 2020 Drake equation?
After all, why assume they died after 100 years? Maybe they just evolved away from using the radio.

How do we calculate how many aliens ever appeared?
For the 1:1 chances - that means that life always appears on a planet like Earth. So basically we only need to find the number of planets in the Universe. To find this, we have the stars in Universe (1×1024) and then use the latest Drake equation (ACP) and take the worst scenario from there which gives us:
1×1024 (stars in Universe)
* 0.19 (% Stars with Earth-like planets - this is constant in ACP)
* 0.015 (Matured stars at least 5bn y old - this is the fL from the pessimistic scenario from ACP)
* 0.4983 (Metalicity - fM from the pessimistic scenario from ACP)

= 1.4E21 (1.4 sextillion Earth-like planets in Universe which could support life according with the most pessimistic scenario of the latest Drake equation)

Chances for Intelligent Life Aliens who now have the same technological level as us Some Survived (1%) All aliens who ever appeared
1:1 (Drake 2020) 72 trillion 14 quintillion (1.4E19) 1.4 sextillion (1.4E21)
3:2 (bayesian study *) 38 trillion 75 quadrillion (756E16) 756 quintillion (756E18)
1:million 72 millions 14 trillions 1.4 quadrillion (1.4E15)
1:billion 72 thousands 14 billion 1.4 trillion (1.4E12)
1:trillion 72 14 million 1.4 billion (1.4E9)

What are the chances that we are not alone in the Universe?

We have the Fermi's paradox ⌄

The Fermi paradox, is the apparent contradiction between the lack of evidence for extraterrestrial civilizations and the high estimates for their probability
There are a lot of explanations for this apparent paradox among which:
Civilizations broadcast detectable radio signals only for a brief period of time or Earth is deliberately not contacted, which look reasonable.

For example:
In a 2006 Sky & Telescope article, Seth Shostak wrote, "Moreover, radio leakage from a planet is only likely to get weaker as a civilization advances and its communications technology gets better. Earth itself is increasingly switching from broadcasts to leakage-free cables and fiber optics, and from primitive but obvious carrier-wave broadcasts to subtler, hard-to-recognize spread-spectrum transmissions."

Life could evolve on a planet (abiogenesis), it could come from the Universe (panspermia) or it could be created by God.
Our current scientific theories are:
- The Astrobiological Copernican principle (Drake equation updated 2020) which says life always appears on Earth-like planets where conditions are met and enough time passes.
- A bayesian study which says that the odds for life to appear on an Earth-like planet (in 5bn years) are 9:1 for primordial life and 3:2 for intelligent life.
- A study by By Leonor Sierra, University of Rochester which finds:
"By applying the new exoplanet data to the universe’s 2 x 10 to the 22nd power stars, Frank and Sullivan find that human civilization is likely to be unique in the cosmos only if the odds of a civilization developing on a habitable planet are less than about one in 10 billion trillions."

So - what are the chances that we are not alone in the Universe?

To be alone, the chances have to be less than 10 billion trillions.
We currently know of 2 trillion galaxies in Universe, each with billions of stars (250 bn in Milky Way), each star with its solar system and planets.
There are so many stars - more stars than all the grains of sand on planet Earth and so many planets and so much time - 14 billion years.
If life happens by an evolutionary process - a combination of chemicals, those chances have to follow the probabilistic theories.
According to our latest scientific theories, chances are astronomically high that we are not alone!




* Galaxy and stars numbers (2020 estimates)

Our galaxy - 250 billion stars

Universe - 2 trillion galaxies (2×1012)

Universe stars - 1×1024 - more stars than all the grains of sand on planet Earth

wikipedia

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