The Drake Equation

American astronomer and exobiologist, Frank Drake, proposed a simple (if, rather lengthy) algebraic equation, back in the early 1960s - for determining the potential number of communicating civilizations/societies/populations, in our Milky Way galaxy as represented by the variable, N. These would be civilizations that are both, capable of, and are communicating, at some wavelength via the Electromagnetic Spectrum (EMS). These parameters might be applied to any spiral, or barred-spiral galaxy in the universe, comparable in size and age to the Milky Way.

N = R* x Fp x Ne x Fl x Fi x Fc x L Graphic by Dale Alan Bryant.

Radio Astronomy is an area of research that uses,  giant, dish radio telescopes for monitoring the sky for potential EMS signals from extraterrestrial civilizations/societies/populations, emanating from planets in orbit around stars, other than the Sun. The SETI (Search for Extraterrestrial Intelligence) Institute is the largest organization devoted exclusively to this area of research. The EMS is the natural source of radio, television, visible light, infrared, ultraviolet, x-ray, gamma-ray, cosmic, and other radiations, which continuously surround us, and in fact, pervade the entire Cosmos. It is presumed that any intelligent beings that have reached a certain technological level of existence, will have discovered the potential for the EMS to be used in long-distance communication, particularly, interplanetary and interstellar communications.

Here is the equation, in its entirety:

N = R* × fp × ne × fl × fi × fc × L

Where: N = the Number of galactic civilizations releasing detectable Electromagnetic Spectrum (EMS) signals into space. R* = the average annual rate of solar-type star formation in the Milky Way galaxy. fp = the fraction of those stars, that formed planet. ne = the average number of those planets, that lie in the star's ecological, or, habitable zone. fl = the fraction of those planets, that actually go on to develop life, at some point. fi = the fraction of those, life-bearing planets, that go on to develop intelligent life. fc = the fraction of those planets, that harbor intelligent civilizations/societies/populations, that are capable of developing a technology that releases detectable signs of its existence, through EMS emissions into space. L = the length of time, for which, a given civilization/society/population releases detectable EMS signals into space (the species, Longevity).

In 1961, when the Drake Equation was introduced, it was thought that very few stars harbored planetary systems, and the conservative value of N, generally, was placed at around 36 million. But as of January 2017, it is known that - almost all stars - have at least one, orbiting exoplanet. (Planets orbiting stars other than the Sun are called, 'exoplanets') As many as 8 exoplanets have been detected orbiting one star - and, one planet - orbiting as many as four stars! More than 4,500 confirmed exoplanets are known, to date. Most of these planets lie within one tiny sector of the sky; the only sector analyzed by the Kepler Orbiting Space Telescope, during the first phase of its mission: an area about the size of a postage stamp held at arm’s length! It lies just east of the constellation Cygnus, the swan (also known as the Northern Cross).

The number of new exoplanets being discovered through data that is still being reviewed from Kepler - is rising dramatically - and, so is our expectation for life elsewhere in our universe. Moreover - if algebraic equations are just not your cup of tea - I think you will find that this one, just might be! - the only variables in the equation that are currently known, are, R*, and fp, so, you can modify the values of the other variables and play around with the equation, conservatively or radically, as I have, to your heart's content! I've obtained values for N, from, in the millions - all the way down to...3.

Here is a guide for plugging quantities into the variables in the Drake Equation. I say, "guide", but only roughly: some of the variables are confirmed; some of them are assumed - and, still others are entirely unknown, so, as we progress down the line we become more and more unsure of their exact values. But this is where you come in! - YOU get to decide: the number of planets, where life, or even intelligence, has evolved, or, how many planets might lie in a sun's Habitable Zone - and so on.

I've given you some figures - that I input - the last time I played with the equation, but the numbers can vary wildly, depending on your level of conservativeness, radicalism, or liberality, at any given time (please remember, we are using multiplication throughout).

The values of the first two variables are given with some surety: R* (annual rate (whole number, in 'billions') of star formation in Milky Way galaxy) = 400 billion (400,000,000,000). Fp (fraction of those stars, that form planets) = .99 Ne (average number of those planets, that lie in a star's ecological zone) = 2

And now, the fun part (your input - see, I told you!): Fl (fraction of those planets, that actually develop some form of life) =. 01 Fi (fraction of those life-bearing planets, that go on to develop intelligent life) = .05 Fc (fraction of those planets bearing intelligent life, whose populations advance to form civilizations that are capable of communication, via the Electromagnetic Spectrum (e.g., radio, visible light, etc. ) L (longevity, in years, of such civilization) = 800

My answer here, for the value of N - using extreme conservatism, throughout - was, of course - 95.04. That is 95 communicating civilizations, within the Milky Way galaxy, alone. That is a rather poor number, comparatively, but it is a bit more than just, "something". In other, less pessimistic moods, I've come up with hundreds of thousands of living civilizations in our galaxy (including ourselves). Give it a try!...

Dale Alan Bryant
Senior Contributing Science Writer

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ETI Signals Would Look Like This

Well, the answer to the age-old question, "Are We Alone?" - might, very well, soon be answered. And if the current, apparent, scenario is confirmed by two other teams of astronomers, that answer will be: "No. We Are Not." - for better or for worse.

Ermanno F. Borra and F. Trottier, two astronomers from Quebec's, Laval University have published a paper in the Astronomical Journal, announcing that they have received signals, from an area of space that contains 234 stars of near-Solar spectral type, that, after having ruled out all of the 3 other possible causes, exactly correspond to an ETI communications hypothesis published prior to their most recent submission.

Graph from the Astronomical Journal of December 2012.

Astronomers, generally, have an idea of what would likely be expected in an intentional beacon signal, broadcast by an extraterrestrial civilization to the stars. It might be a signal generated in the radio portion of the electromagnetic spectrum, or, the more recently favored optical window near to, or including, the visible light band. A signal generated from the latter would be visually detectable by humans, and interestingly, I think, by any ET species which had evolved on a planet of a star in the F-G-M spectral range. Our star, of course, is a type G2V yellow dwarf star, "Sol", or, the Sun. They would want to direct their signals at stars similar to their parent star, for this reason.

Borra and Trottier's paper shows signals, embedded in the SDSS (Sloan Digital Sky Survey), spectra that conform to these expectations, in the form of nano-bursts, or, pulses, which include varied and repeating time intervals in between, which were outlined in Borra's previous work and which are, "so unusual that it can only be artificial. A most unusual signal would be made of a spectral modulation of the spectrum that is so unusual that it warrants more observations, which will then reveal that it is artificial." Borra and Trottier make it clear that the signals confirm "exactly" as outlined in the paper of 16 OCT 2016 to the Astronomical Journal. Current technology allows humans, to send such signals out to at least 1,000 light-years, without any significant degradation, using a spectroscope and a 10-meter optical telescope, at an energetic 15,000 photons per 3 nanoseconds.

Any signal by an ETI located at a distance of 1,000 light-years from Earth, means that the signal had to have been sent at least 1,000 years ago. Considering the current level of human technology, ETI technology, which was the rough equivalent of humans 1,000 years ago must be wildly advanced by present-day standards.

The commonality here is the EMS. It's available to anyone, anywhere, and obeys the same physical laws bestowed upon Earthlings. It would be the universally agreed-upon method of trying to get the attention of any other sentient beings that may exist in the galaxy.

The ETI hypothesis as a source for the signals is the only hypothesis that was not ruled out by Borra and Trottier but it needs confirmation by at least two other teams, trying to find natural reasons for the signals.

So - the answer to that age-old question - is still ways off, for now.

Dale Alan Bryant
Senior Contributing Science Writer

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Time Troubles

I just calculated something out and the result, well, rather depressing... This is a photo of a portion of the Milky Way galaxy. Each dot in the photo is a star. More than 50% of all stars have planetary systems such as our Solar system. The nearest star to Earth, is Proxima Centauri, one of three stars in the Alpha Centauri system. Proxima is 4.2 light-years away. There are 5.8 trillion miles in one light-year (or 5.8 thousand billion, or, if you prefer, 5,800,000,000,000), so, we're dealing with about 25 trillion miles.

A view of the Milky Way toward the  constellation 
Sagittarius.  Source: Wikipedia.

OK, That's bad enough. But, let's say we decide to send an astronaut to Proxima Centauri, in the fastest rocket, at the fastest manned flight speed we've been able to attain (that would be the Saturn V, a 3-stage booster used for the Apollo program - a top speed of 26,000mph). Now, even if we could send that astronaut at the speed of light (exactly 186,282.3976 miles per second, in vacuo), it would take her (or him), 4.2 years to complete the trip as measured by an observer on Earth (because of the relativistic effects of time dilation, only a few days will have passed, as judged by the astronaut - but we're not going there! - not here - that's another story, for another time). But, now for the sad part...

At 26,000mph 0.000037% the speed of light, the trip would take 116,000 years. That's one-way. Our astronaut would be, long ago, fossilized. Time dilation is negligible here, so we don't need to factor it in at such low velocities. One of the nearest stars with a known planetary system is around 15 light-years. So, if we have cosmic relatives somewhere out there within that range, the chances of meeting up with them, are about, absolutely, nil. These distances and times involved are the reason most astronomers don't believe in UFOs, or, that we're being visited by extraterrestrials. YES, WE DO BELIEVE they exist but, not that we're being visited by them on any regular basis. The situation isn't much better with radio communications. Even though radio waves travel at the speed of light, transmission to any hypothetical beings in, say, the Fomalhaut planetary system, will take 15 years. That's one-way. Telepathy, should it prove to be viable, would be much more economical, assuming it to be instantaneous. Another plausible answer might be, to travel through wormholes, to beat the clock, but, for now, they're hypothetical. Other than that, due to the restrictions on speed, we may never meet anyone else; we might always be alone - surrounded, perhaps, by a myriad of Celestial Peoples - and yet alone, regardless.

Dale Alan Bryant
Senior Contributing Science Writer

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