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"Beyond Drake's Equation" --New Insights into the Search for Extraterrestrial Civilizations





The SETI project – Search for Extra-Terrestrial Intelligence – has been in existence in one form or another for several decades, dating back to American astronomer Frank Drake’s first SETI experiment named Project Ozma. SETI is basically the search for intelligence through listening for radio waves of another civilization. For Drake back in the 1960’s, this was the sign of a technologically prevalent society, and the smartest means to search for life.

In 1961 the Russian cosmonaut Yuri Gagarin became the first man to orbit Earth, while Frank Drake (image below) developed his now famous Drake Equation, which estimates the number of detectable extraterrestrial civilizations in our Milky Way galaxy, based on current electromagnetic detection methods.



The Drake equation states:

N = Ns x fp x ne x fl x fi x fc x fL N = number of alien civilizations in the Milky Way

Ns = estimated number of stars in the Milky Way;

fp = fraction or percentage of these stars with planets on its orbits; ne = average number of these planets with potential to host life as we know it;

fl = percentage of these planets that actually develop life; fi = percentage of these planets that actually develop intelligence on human level;

fc = percentage of these civilizations that actually develop electromagnetic radiation emitting technologies;

fL = percentage of these civilizations that keep emitting electromagnetic signals to space. This factor is extremely dependent on the lifetime a civilization remains electromagnetic communicative.

Looking at the Drake equation factors,  says, it is obvious that none can be precisely determined by modern science. More than that, as we move from the left to right in the equation, estimating each factor becomes more controversial. The later terms are highly speculative, and the values one may attribute to each of them might tell more about a person’s beliefs than about scientific facts.

But the Drake equation must not be evaluated only by the numerical values it produces. Some say the Drake equation is a way to organize our ignorance. By exposing the extraterrestrial intelligence hypothesis mathematically, we limit the real possibilities to each term and approach the final answer: how many alien civilizations are there?

The L term is considered the most important one in Drake equation. We have no idea how long a technological civilization can last. Even if only one extraterrestrial civilization lasts for billions of years, or becomes immortal, the L factor would be enough to reduce Drake’s equation to N = L. Actually, Frank Drake recognizes this in his license plate: “ NEQLSL ”

However, one can only look at the decision to search for intelligence through listening for radio waves of another civilization and see it as a mistake. At least, that is what some scientists and others connected to the field of extra-terrestrial search believe, such as George Dvorsky, who serves on the Board of Directors for the Institute for Ethics and Emerging Technologies. Recent insights in such fields as cosmology, astrobiology have changed our perception of the cosmos and the ways in which advanced life might develop.

In the early days of SETI its astronomers predicted a steady rise in radio traffic, as populations and technology advanced. But the reverse has happened. Point to pint communications have become dominated by low-powered satellites directing their signals Earthward while the bulk of telecommiunications shifted away from radio to buried fiber optics for cable TV and Internet traffic. In another hundred years there will be no substantial radio output from Earth.

Another key weakness is Fi -the fraction of those Earthlike planets (10,000 was Drakes estimate in the Milky Way) on which intelligence evolves. To date, there isero evidence that there is a "life principle" directing primal chemical soups towards the glory of a homo sapiens-like species. Until we find strong evidence for life on an exo-solar planet, Fi remains moot.

The Drake Equation does not take into consideration such factors as the age of the Galaxy, when intelligence first emerged, or the presence of physio-chemical variables such as the presence of metals necessary for the presence of life and the formation of planets. The equation, Dvorsky emphasizes, assumes "a sort of cosmological uniformity rather than a dynamic and ever changing universe."

The equation asks us to guess the number of Earth-like planets, but it does not ask us to estimate when Earth-like planets evolve advanced life forms. The Milky Way's extreme age and the potential for intelligence, which may have been present as long as 2 to 4.5 billion years ago, to have emerged at disparate points in time leaves an absurdly narrow window for detecting radio signals.

The Drake Equation, Dvorsky believes,  does not tell us about exponential civilizational growth on account of Von Neumann probe disbursement. "It does not tell us where advanced ETI’s may be dwelling or what they’re up to (are they outside the Galaxy? Do they live inside Jupiter Brains? Do they phase shift outside of what we regard as habitable space? ). 

This is a serious shortcoming because the answers to these questions should help us determine not just where we should be looking, but they can also provide us with insight as to the makeup of advanced intelligence life and our own potential trajectory."

In other words, Dvorsky concludes, post-Singularity machine-based intelligence may represent the most common mode of existence for late-stage civilizations. And that’s who we should be looking for rather than radio transmitting civilizations.

Since 1992 astronomers have been finding more and more exoplanets and as of today over to 2000 exoplanets are confirmed. The number of Sun-like stars with planets is believed to be around 40% or higher. Currently most of the planets found are massive and orbit very close to their stars (they’re called Hot Jupiters), but as detection techniques improve scientists think many more planets will be found of different sizes and orbits.

Research of the past two decades have shown that literally billions of planets in the Milky Way might have niches that would support at least a level of life represented by Earth's extremophiles. 

Yet, in 2012,  Drake Equation is of still of seminal importance because it orders our thinking. This one equation formed the backbone of astrobiology as a science. Carl Sagan was inspired that the Drake Equation showed the chances of intelligent alien life were high but he also added that extraordinary claims require extraordinary evidence.

In 2010, the Italian astronomer Claudio Maccone published in the journal Acta Astronautica the Statistical Drake Equation (SDE). It is mathematically more complex and robust than the Classical Drake Equation (CDE).

The SDE is based on the Central Limit Theorem, which states that given the enough number of independent random variables with finite mean and variance, those variables will be normally distributed as represented by a Gaussian or bell curve in a plot. In this way, each of the seven factors of the Drake Equation become independent positive random variables. In his paper, Maccone tested his SDE using values usually accepted by the SETI community, and the results may be good news for the “alien hunters”.

Although the numerical results were not his objective, Maccone estimated with his SDE that our galaxy may harbor 4,590 extraterrestrial civilizations. Assuming the same values for each term the Classical Drake Equation estimates only 3,500. So the SDE adds more than 1,000 civilizations to the previous estimate.

The image below is the Gaussian or bell curve showing the probability of finding the nearest extra terrestrial civilization from Earth.




Another SDE advantage is to incorporate the standard variation concept, which shows how much variation exists from the average value. In this case the standard variation concept is pretty high: 11,195. In other words, besides human society, zero to 15,785 advanced technological societies could exist in the Milky Way.

If those galactic societies were equally spaced, they could be at an average distance of 28,845 light-years apart. That’s too far to have a dialogue with them, even through electromagnetic radiation traveling in the speed of light. So, even with such a potentially high number of advanced civilizations, interstellar communication would still be a major technological challenge.

Still, according to SDE, reports, the average distance we should expect to find any alien intelligent life form may be 2,670 light-years from Earth. There is a 75% chance we could find ET between 1,361 and 3,979 light-years away.

Beyond 500 light-years away, the chance of detecting any signal from an advanced civilization approaches zero. And that is exactly the range in which our present technology is searching for extraterrestrial radio signals. So, the “Great Silence” detected by our radio telescopes is not discouraging at all. Our signals just need to travel a little farther – at least 900 light years more – before they have a high chance of coming across an advanced alien civilization.

The Daily Galaxy via, and

Image credit: With thanks to Maccone (2010) and



Aside from a couple of editing glitches (the only significant one being the paragraph beginning "The equation asks us to...") this is one of the best-written articles I've seen on this site, and one of the clearest treatises on the Drake Equation and (though it's never cited) the Fermi Paradox. Well done.

A well written article and to be fair the drake equation is just as much a guessing game as the fermi paradox (its a theory not a paradox). The one thing that makes perfect sense is that looking for intelligent life on other planets using nothing but radio technology is moronic. Its like looking for a needle in a haystack at the bottom of an ocean. There must be a way of communicating that bypasses the speed of light and makes instant or near instant interstellar communication possible. We simply do not possess the technology to communicate at these distances.

Alien robots are already on their way.

"15,785 advanced technological societies could exist in the Milky Way.If those galactic societies were equally spaced, they could be at an average distance of 28,845 light-years apart."

The Milky Way is only 100,000 light years across.

What formula are you using to arrive at an average distance of 28,845 light years with a galactic diameter of 100,000 light years?

I think I might be missing something but to me, the Drake equation was an attempt to put some sanity into the search. Not an end all, but a starting point for the discussion. As has been disucssed at other times, and based on our own violent history, any truly intelligent species will want to mask their radio waves to avoid detection.
SETI based only on 'radio' waves is most likely a waste of time.

The main problem of Drake Equation is the missing distance factor.
Since it is different for each star system, and even the closest of them is so far that the low frequency radio weaves will reach us with very low power after hundred thousands years after they firstly been emitted.
So - I think it's equation is close to the real count of been there, is there, and will be there count of civilisations, but unfortunately it does not provide the right tools for proving it's correctness.
Plus - another issue is the missing possibility of alien civilisation firstly developed something else than electromagnetic way of transmitting data, or even further - they might actually doesn't need to transmit data between them due a clear natural way of exchanging it.

So - The Drake Equation is just a number showing how many of such civilisations existed, exists, and will exist at some point in time, and we must accept it as more than 50% good chance of been true.

One more thing, I would say even that it's equation is a bit pessimistic, since it rarely fits in the possibility of 1 planet having 1 or more moons which could be suitable for life.
Just accepting this possibility the golden zone will expand for life friendly conditions more than twice.

The sign of a technologically prevalent society, and the smartest means to search for life.

good article but I think the problem remains with "fl" and "fi"

a more indepth undertanding of how life emerged on earth and how human evolution occurred results in a more humble estimate of the possibility of finding life elsewhere (esp. intelligent life)- the actual number of conditions, factors and events that need to occur are nearly as numerous as there are stars in the known Universe (sorry) - of course this assumes carbon based organic life (life as we known it). Still... intelligent life might be extremely rare.

reminder - there is still no proof that life existing anywhere else in the Universe - except here on Earth. And what's rare should be considered all the more precious.

(required reading = "rare earth" ward and brownlee, 2000)

We don't need radio signals to discover other civilizations. In fact this one of the most inefficient ways to do so. Using advanced hypertelescopes(which we already can design), it would be possible to take images of planets including their landmasses, city lights, possible mega-engineering projects, and other signs of not only life but technology.
In fact if there ever was a advanced civilization with technological ability to travel across the stars, it would also be able to map most of planets with life in the galaxy.

One of the more profound ideas I learnt in a History of Communications class, was that old mediums never completely vanish.

For example, we still have people today who carve information/messages on stone tablets (ie: grave/tombstone carvers, or masons who add messages to the sides of buildings).

We also still have people who convey entire stories and idea in stained glass windows!

Similarly, we still have many people today who utilize Ham Radios, and even morse code, despite the Internet! (In fact Ham Radios and CB radios are seeing a trendy blip in popularity.)

Many are also surprised to hear that Google, a company that holds unimaginably large amounts of data, still does a large/significant amount of data-backup on magnetic tapes!

(Magnetic tape can be less expensive and more efficient than hard-drives, although you lose the ability for random access and have to read the entire tape... but for long term emergency backup storage it's ideal).

1800's style punch cards (which used to feed instructions to mechanical systems, and automated pianos) are still used in some parking garages and work-clock sign out stations.

And so... all this is to say that even if aliens have evolved far beyond using radio communications, there still may be some place for good old fashioned radio in their hyper-advanced civilizations (if only with the hobbiest aliens!)

For example, radar is excellent for navigating/docking ships in space, and so a highly advanced civilization could still utilize radar-waves.

In short, just because a medium is old-fashioned, doesn't mean that it isn't still useful in some ways, and doesn't still have a place in advanced society.

Afterall, in the end the final message and communication that summarizes all of our lives will likely be carved upon stone (tombstones).

In 2008, I also submitted for comment here at DailyGalaxy my own statistical distribution model (Gaussian) that broadens the Drake Equation. My model estimated approximately 50,000 advanced space traveling civs in the visible universe (FTL capable). I felt also that sentient life’s technological progress follows an exponential development, and if a civ survives long enough along the curve the progress becomes ‘explosive’ and FTL (and perhaps dimensional, time travel, etc) will occur. But, the ‘kicker’ in any Drake modification is the ‘Reset’ function of supernovae which effectively creates a standard window for evolution of super civilizations, i.e., 4.5 billion years (following the posting here on DG of a summary of work on that subject). Essentially what that means for us here on earth is we are on the verge of entering the ‘explosively’ fast tech evolution to super civ which will see humans advance extremely soon into FTL and many other wonderful advancements, e.g. singularity, dimensional portals, time ‘travel’, etc.

A brief comment on the above comment: the supernova “reset” horizon of 4.5 Billion years or so (a layman’s incomplete research guestimate) , means once life ‘happens’ (a major part of the supernova cycle from the current human example) the follow-on advanced life forms face an ever shortening “up and out” deadline. Fortunately if technological advancement is exponential, some life forms might make it out in time. There are other cycles apparently operating such as the 2-3 million year comet/killer meteor belts earth happens to experience, but these are evidently survivable to life forms in general and evolution corrects for species die-offs. However, a supernova inundation would be a complete scouring, sanitizing experience for a cosmological region. No corrective mechanisms would survive presumably.

I had commented on the Drake equation once before. I see no reason to give it any credibility since it is only based on imagination and speculation that has very little actual factual data onhow many planets exist,stars that exist or habitable worlds that exist. Earth is the only example of a world with life. Listening for radio or TV signals from other worlds is like trying to read a smoke signal in Arizona from a camel in Saudi Arabia,the signals are too weak to go very for on a galactic scale.

we are alone, get used to it, we haven't even found as much as a f**king bit of bacteria outside Earth lol.

Stop watching Star Trek you muppets, and get used to the simple fact WE ARE ALONE.

Very pessimistic Stephen. I think that once even simple extraterrestrial life is confirmed to exist, or confirmed to have existed (e.g. fossil evidence),then that will be the game changer. And either of these may be confirmed in the not too distant future, just by looking around our own back yard - Mars, Europa etc. If life has begun in more than one place then, although not all will have progressed to civilisation and technology, we are the proof that the process does occur. Then the Drake Equation, or an improved version thereof, becomes more meaningful because we know there is an actual number that belongs out there on the left hand side of Mr. Drake's equation.

Exactly the information I was looking for. Another interesting stat, would be the probability of intercepting an E.T probe, here on earth (based off assumptions, including the drake equation).

When putting together the Drake equation, did Drake take into consideration the timing upon which planets are formed in the Goldilocks zone? Would it be wrong to imagine that if a Goldilocks zone planet (GZP) formed just a little bit later than our own earth did, then the surrounding planets would've grown more in mass and gravity, thereby pulling all, or most, of the ice meteors in? This would have left little or nothing left for the GZP to accumulate enough water to form and sustain life.

In just the opposite, if the GZP increased in gravity EARLIER than the other forming planets, it would have pulled in an enormous amount of ice meteors and flooded the entire planet, leaving no land for intelligent life to evolve on.

Also, the first living creatures to crawl onto land would have had no predators. With such freedom, and on any planet, all of these first creatures would probably grow to the size of dinosaurs. Without an extinction level event to kill them off, the smaller creatures with the potential for intelligence would remain in the trees and never evolve.

It seems that our earth formed at just the right time, and experienced just the right traumatic events (again, at the right time) to bring about intelligent life. The recipe for producing intelligent life sure seems pretty specific, with the possibility for creating it to be quite rare. To the point of being damn close to miraculous.

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