[Remembering Frank Drake, who transformed the search for alien
life and extraterrestrial intelligence into a full-fledged scientific
endeavor. ]
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ALIENS, SETI, AND THE LEGACY OF FRANK DRAKE: 1930–2022  
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Ethan Siegel
September 5, 2022
Big Think
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_ Remembering Frank Drake, who transformed the search for alien life
and extraterrestrial intelligence into a full-fledged scientific
endeavor. _

Frank Drake, rperrino (CC BY 2.0)

 

KEY TAKEAWAYS

* Perhaps the biggest question we've ever asked about existence is
whether we're alone or not: are there any other intelligent,
technologically advanced civilizations out there besides us? 
* Where might the aliens be? Are they just unwilling to contact us?
Do they even exist? The only way to truly find out is to
scientifically search for the true answer, whatever it may be. 
* The person who transformed the search for extraterrestrial life
and intelligence into a science was Frank Drake. He passed away on
September 2, 2022 at the age of 92. Here's what he left behind.

Throughout human history, each time we’ve looked upward toward the
night sky’s glittering canopy of planets, stars, the Milky Way, and
more, we haven’t been able to stop ourselves from wondering just
what might be out there. Were there other stars like the Sun, other
worlds like the Earth, and other living, intelligent, self-aware
beings, perhaps not so different from humans, in this vast Universe we
inhabit? As astronomy and astrophysics developed as sciences over the
centuries and millennia, our knowledge of what’s out there has
increased tremendously, but our wonder at the possibility of life
beyond Earth has never waned.

In 1950, famed physicist Enrico Fermi wondered aloud, “But where is
everybody?” In 2022, this question – now known as the Fermi
Paradox – still weighs on our collective minds without a definitive
answer. But less than a decade after Fermi posed his question,
scientist Frank Drake set about to transform this question from a
philosophical one into a scientific one. He became the first person to
begin searching for signals of technologically advanced alien life,
pioneered the Search for Extraterrestrial Intelligence (SETI),
designed the first message to be broadcast from humanity to any
curious aliens who might be listening, and put forth the first method
for estimating the number of intelligent alien civilizations that
might be out there, right now, for us to communicate with: the Drake
Equation.

On September 2nd, 2022, Frank Drake died at the age of 92, after a
glorious career that revolutionized his field, but with humanity still
yet to make our first discovery of life beyond Earth. His legacy will
remain with us for generations to come, and we’ll all have him to
thank when we first do discover extraterrestrial life – or even
extraterrestrial intelligence – for the very first time.

This image of the Very Large Array in the southwestern United States
highlights the importance of arrays of radio dishes in measuring many
different properties of our Universe, including searching for
potential extraterrestrial signals that were created by an intelligent
species.

(Credit [[link removed]]: Alex
Savello/NRAO)

Drake was the first to realize the power of radio astronomy for
interstellar communications between intelligent civilizations. Of all
the signals that propagate through the Universe, none travel faster
than photons: the massless particles that compose all the forms of
light in the Universe. Traveling at the speed of light in a vacuum –
and interstellar/intergalactic space is the best vacuum in the known
Universe – the only means of communication that are comparably fast
are gravitational waves and cosmic neutrinos: both of which are far
more difficult to detect.

Light comes in many different wavelengths; not just the visible light
our eyes are well-adapted to see. There are shorter wavelengths:
ultraviolet, X-ray, and gamma-ray light, all of which possess greater
amounts of energy-per-photon than visible light does. On the
longer-wavelength side, there’s infrared, microwave, and radio
waves, with longer wavelengths corresponding to lower
energies-per-photon. In the case of radio waves, you can create over
one million photons in that frequency range for the same amount of
energy it would cost you to create a single visible light photon.
It’s possible to encode a tremendous amount of information in radio
signals by expending very little energy relative to every other
option.

The size, wavelength and temperature/energy scales that correspond to
various parts of the electromagnetic spectrum. You have to go to
higher energies, and shorter wavelengths, to probe the smallest
scales. On the largest wavelength scales, only very small amounts of
energy are needed to encode a large amount of information. Even matter
particles have wavelengths dependent on their energy, as the quantum
nature of existence gives particles a de Broglie wavelength that
enables them to probe structure on a variety of scales.

(Credits
[[link removed]]:
NASA and Inductiveload/Wikimedia Commons)

Although natural radio signals are copious throughout the Universe,
Drake realized that a technologically advanced alien civilization
could deliberately create an unambiguous signal that announced, “We
are here, and we are not natural.” Things like mathematically
recognizable pulse patterns, video or audio signals, and other types
of encoded information could be teased out of any received radio
signal, limited only by the imaginations and technological limitations
of the alien species that chooses to make such a broadcast.

Drake became the first to recommend and conduct a systematic survey of
objects-of-interest in the sky, searching for such intelligent alien
signals. Although numerous candidates have emerged over time, none
remain that cannot be explained through natural, astrophysical
processes. Today, endeavors such as the Search for Extra-Terrestrial
Intelligence (SETI) continue Drake’s legacy, scouring the full suite
of radio data from the Milky Way galaxy and beyond for any signals
that might emerge as deliberate, intelligent creations.

[extraterrestrial]

Before its collapse in 2020, the Arecibo telescope was the first to
see multiple fast radio bursts from the same source. Although they are
not a signal of intelligent alien origin, the telescope has been used
to set many of the strictest limits on the existence of transmitting
alien civilizations, as well as having been used to transmit messages
from humanity out into the Universe.

(Credit
[[link removed]]:
Danielle Futselaar)

Drake also envisioned the possibility that perhaps, after thousands or
millions of years, or even longer periods of time spent announcing
their presence to the Universe, intelligent aliens within the Milky
Way had simply given up on the possibility that anyone was out there.
Perhaps it was even possible that our terrestrial civilization, here
on Earth, was the most advanced species at the moment. If so, he
realized, it would be up to us to be the first to announce our
presence to others: engaging in an effort known as either “active
SETI” or METI: Messaging Extra-Terrestrial Intelligence.

Drake realized that an incredible amount of power – at least,
relative to the power typically used for radio broadcasts on Earth –
would be needed to create a message that could be received by a
civilization lying across the vast interstellar expanse. When the
Arecibo telescope in Puerto Rico was completed, Drake designed
what’s now known as the Arecibo message: a simple signal containing
only a couple of hundreds of bytes of information, but one that was
unmistakably intelligent in nature. Filled with information about who,
what, and where we were, along with a mathematical “code of
instructions” for understanding this message, it was the first time
we ever deliberately broadcasted a message intended for an intelligent
extraterrestrial observer.

Even if it were decoded incorrectly, as illustrated here, the signal
of the Arecibo message in this format appears sufficiently organized
to enable an intelligent extraterrestrial receiver of this message to
conclude that it is not a random signal.

(Credit
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jarmokivekas at the Wikipedia project)

But arguably the most enduring contribution Drake ever made to the
field of science was through the equation that now bears his name: the
Drake equation. The question of Fermi, “But where is everybody?”
carries with it three assumptions.

* That aliens are not, and have never been, present on Earth.
* That if intelligent life is common throughout the galaxy, then it
should only be a matter of time before one civilization
technologically advances to the point where they’ve explored the
entire galaxy, and should have made “contact” with us by this
point.
* And therefore, something is wrong, or at least puzzling, about our
line of thinking and the conclusions we’re drawing.

Where was the flaw in this argument? Is intelligent life exceedingly
uncommon, perhaps? Could life be intelligent, but the challenges of
interstellar exploration are simply too great – regardless of
technology – given the constraints imposed by the laws of physics?
Are humans simply too primitive, too uninteresting, or too flawed for
anyone to _want_ to make contact with us? Both before and after
Drake, ideas such as this were floated as possible resolutions to the
Fermi Paradox.

[Drake equation]

The Drake equation is one way to arrive at an estimate of the number
of spacefaring, technologically advanced civilizations in the galaxy
or Universe today. However, it relies on a number of assumptions that
are not necessarily very good, and contains many unknowns that we lack
the necessary information to provide meaningful estimates for.

(Credit
[[link removed]]:
University of Rochester)

Drake’s approach was revolutionary. To simply ask, “Where are all
the aliens?” is too detached from something we can hope to measure
today, with current technology. Instead, Drake took the approach of
breaking such a complex question up into smaller, more digestible
components. Each one of those smaller questions could potentially be
answered in a scientific fashion, but each answer would inch us closer
to the overall goal of understanding what our expectations ought to be
for formulating an accurate estimate for the number of civilizations
that are out there, right now, for us to communicate with.

Drake’s breakdown stated that if you multiplied:

* the star-formation rate (number of new stars formed per year),
which he assumed was constant,
* by the fractions of stars, overall, that possessed planets,
* by the number of Earth-like (i.e., potentially habitable) planets
around each planet-possessing star,
* by the fraction of those planets where life actually does arise,
* by the fraction of living planets where intelligent life arises,
* by the fraction of intelligent-life-having planets which reach the
level of technology necessary to receive and send interstellar
communications, and which engage in that endeavor,
* by the amount of time that such a civilization exists, on average,
before going extinct,

you’d wind up with a number that reflected how many intelligent
civilizations were out there, right now, for humanity to communicate
with.

[first contact]

Intelligent aliens, if they exist in the galaxy or the Universe, might
be detectable from a variety of signals: electromagnetic, from planet
modification, or because they’re spacefaring. But we haven’t found
any evidence for an inhabited alien planet so far. We may truly be
alone in the Universe, but the honest answer is we don’t know enough
about the relevant probability to say so.

(Credit [[link removed]]: Ryan
Somma/flickr)

The remarkable advance of this approach is easy to see. Yes, it’s
true that, in the absence of knowledge of every single one of these
terms, it’s impossible to make a precise, accurate estimate for how
many intelligent extraterrestrial civilizations are out there. But by
breaking a large, complex problem into smaller, more digestible
components, the Drake equation gave us a systematic way to begin
investigating the various factors that influence how many
extraterrestrial civilizations are out there, as well as how many
“partial successes” there are out there for each such step along
the way.

There should, for example, be many planets out there around stars with
conditions that could have led them to be potentially Earth-like:
where the raw ingredients and plausible conditions for life to emerge
are present, something we could uncover through the endeavor of
astronomy alone. There should be many instances of inhabited planets
out there in the galaxy and the Universe – where life emerged from
non-life – irrespective of how complex, differentiated, or
intelligent that life ever became. And even if there are only a few
intelligent civilizations (maybe even as few as one) around in
today’s Milky Way, there may have been many others in the past, who
have simply gone extinct through either natural means or due to
self-destruction.

The Ivy Mike nuclear test was the world’s first thermonuclear
device: where fission and fusion reactions combine to create a more
energetic yield than a fission bomb alone can achieve. Unlike the
bombs dropped on Hiroshima and Nagasaki, where the yield was measured
in the tens of kilotons of TNT, thermonuclear devices can reach tens
or even hundreds of megatons of TNT-equivalent. There are enough such
devices on our planet to bring about a complete end to human
civilization on Earth.

(Credit: “Ivy Mike” atmospheric nuclear test – November 1952
[[link removed]] /Wikicommons)

Sure, it’s easy to point out numerous flaws and oversights in the
Drake equation given today’s understanding of the Universe. For
example, the star-formation rate changes over the Universe’s
history, as does the fraction of stars that form with planets around
them; this is inevitable in a Universe that began with a hot Big Bang
a finite amount of time ago, and came into existence without the heavy
elements needed to form rocky planets like Earth or the raw
ingredients for life.

But Drake had no way of knowing this; when he first formulated his
equation, the critical evidence supporting the hot Big Bang as the
preferred idea for our cosmic origins – the Cosmic Microwave
Background – had not yet been discovered. Today, we can make much
better estimates of the number of potentially Earth-like planets that
are out there, and we can be more granular about it: how many of them
are around stars of each of the various sizes, masses, lifetimes, and
metallicities (i.e., with specific fractions of heavy elements
relative to the amount we have in our own Solar System) that stars and
stellar systems come in? Today, these numbers are calculable.

[5000 exoplanets]

The more than 5,000 exoplanets confirmed in our galaxy so far include
a variety of types – some that are similar to planets in our Solar
System, others vastly different. Among these are a variety we lack in
our Solar System that are largely mis-named “super-Earths” because
they are larger than our world. However, all but the hottest planets
that are more than about ~130% of Earth’s radius will likely be
mini-Neptunes, not super-Earths, and potential habitability remains an
open question.

(Credit
[[link removed]]:
NASA/JPL-Caltech)

The idea and the approach recommended by Drake, however, have endured,
even if some of the specifics that he put forth have since evolved.
Today, scientists are taking a three-pronged approach in their
attempts to reach the one milestone Drake always dreamed we would
someday attain but never lived to see: the discovery of alien life
beyond Earth.

* EXPLORATION OF THE WORLDS IN OUR SOLAR SYSTEM. Is there dormant or
fossilized life on a once-wet Mars? Does life exist high in the
Earth-like conditions found in Venus’s cloud-decks? Could there be
life around the hydrothermal vents at the bottoms of sub-surface
oceans on moons like Europa or Enceladus? If life is common in the
Universe, “interplanetary paleontology” might lead to its
discovery. 
* SEARCHES FOR BIOSIGNATURES ON EXOPLANETS. Visible signatures exist
that Earth is inhabited. The continents green-and-brown with the
seasons; CO2 levels rise-and-fall annually; our oxygen-rich atmosphere
was created by life; the presence of chlorofluorocarbons reveal
humanity’s presence. With advances occurring in the astronomical
fields of transit spectroscopy and direct planetary imaging, this is
perhaps our best hope for finding alien life in the coming
decades.   
* CONTINUED SEARCHING FOR EXTRATERRESTRIAL INTELLIGENCE. And yet,
SETI could still succeed. If signals from intelligent aliens are out
there – either via radio signals or from any other method of
communication – we remain open to the possibility of finding
something spectacular so long as we continue pushing the frontiers of
how and where and when we monitor the Universe.

Although it hasn’t happened yet, the possibilities for success are
continuously increasing with each and every scientific and
technological advance we make on every one of these fronts.

When an exoplanet passes in front of its parent star, a portion of
that starlight will filter through the exoplanet’s atmosphere,
allowing us to break up that light into its constituent wavelengths
and to characterize the atomic and molecular composition of the
atmosphere. If the planet is inhabited, we may reveal unique
biosignatures.

(Credit
[[link removed]]:
NASA Ames/JPL-Caltech)

Today, thousands of scientists worldwide are active in the hunt for
extraterrestrial life and extraterrestrial intelligence. Although we
cannot know how or when it will happen, the day will no doubt come in
the not-too-distant future where we discover the presence of life
beyond planet Earth for the very first time. Perhaps it will be
primitive and rare, found on a world or a fragment of a world here in
our own Solar System. Perhaps there will be overwhelming indirect
evidence arriving from an exoplanet orbiting a star many light-years
from our own. Or perhaps we’ll detect it because we looked at or
listened to or put a message out into the Universe in just the right
way, and discovered that we weren’t “alone” as intelligent,
technologically advanced life forms, after all.

One thing, however, is certain: we’re no longer reliant on aliens
coming to Earth and announcing their presence to us if we hope to
discover them. Instead, the search for life beyond our planet –
including intelligent life – is now firmly a scientific endeavor,
and Frank Drake was the person who brought that transformative leap to
our civilization. May we honor his legacy by bringing his ultimate
dream to fruition, and continue to search for the answer to perhaps
the biggest existential question of all: who else is out there in the
Universe?

_Ethan Siegel is a Ph.D. astrophysicist and author of "Starts with a
Bang!" He is a science communicator, who professes physics and
astronomy at various colleges. He has won numerous awards for science
writing since 2008 for his blog, including the award for best science
blog by the Institute of Physics. His two books "Treknology: The
Science of Star Trek from Tricorders to Warp Drive"
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the Galaxy: How humanity looked beyond our Milky Way and discovered
the entire Universe"
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available for purchase at Amazon. Follow him on
Twitter @startswithabang [[link removed]]. _

_Join the Big Think community of more than 10 million lifelong
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