The Search for
Extraterrestrial Intelligence (SETI) is in the news. The biggest
recent effort to search for extraterrestrial civilizations is a
project called Breakthrough Listen. The project is a ten-year
project that began in 2015 with 100 million dollars in funding from a
Russian billionaire. A few days ago, the project announced what it had found so far.
A
few web sites made it sound as if something very interesting had been
found. The Daily Star site had a headline: “Alien
shock as scientists reveal 11 mysterious ‘signals’ hailing Earth
are probed for UFOs.” The web site sputniknews.com had a headline,
“SETI's Largest Project Reveals That 11 Signals From Space May
Point to Aliens."
But when you actually read
the release, you will hear about nothing indicating success. The 11
signals are simply the “highest ranked” in terms of strangeness.
The press release concedes that “the search has not yet detected a
convincing signal from extraterrestrial intelligence.” The press
release gives us no details of any one of these “highest ranked”
signals, which suggests that none of them is particularly
interesting. They are probably just emissions from natural phenomena
or from earthly sources.
This recent paper reports on a
search of 5600 nearby stars looking for signs of laser signals that
might show up in the spectra of the stars. The scientists reported
this:
We
found no such laser emission coming from the planetary region around any
of the 5600 stars. As they contain roughly 2000 lukewarm, Earth-size
planets, we rule out models of the Milky Way in which over 0.1% of
warm, Earth-size planets harbor technological civilizations that,
intentionally or not, are beaming optical lasers toward us.
A previous scientific
paper reported on a search for optical signals coming from sun-like
stars. 10,000 such stars were searched over the course of two years,
but no such signal was found. Extensive searches looking for radio
signals from extraterrestrials have also come up negative. This paper
describes a negative search for alien radio signals coming from 9293 stars,
consisting of 19,000 hours of observations carried out between May
2009 and December 2015.
Another search for
extraterrestrials looked for signs of large-scale engineering in
distant galaxies. Since the universe is about 13 billion years old,
if an extraterrestrial civilizations had appeared on a distant
planet, it would be more likely to have appeared billions or millions
of years ago. Such a civilization might have evolved into some state
of godlike power, allowing it to re-engineer entire solar systems or
entire galaxies. But a search of 100,000 nearby galaxies looking for
signs of extraterrestrial engineering came up empty.
These findings all cast
doubt on the vision of the universe advanced by the late astronomer
Carl Sagan. In books and a television show (the original version of
the Cosmos series), Sagan advanced rather dogmatically a set
of ideas that were widely influential. His ideas are summarized in
the visual below:
When I was a young man in
my early twenties, Carl Sagan was at the height of his influence,
and I bought quite a few of these ideas. But now quite a few of these
ideas seem dubious or untenable. As a whole, the Sagan Creed lacks
coherence, and parts of it seem to contradict other parts of it. For
example, if it were true that the galaxy was teeming with so many
extraterrestrial civilizations, why should we not expect that some of
them are visiting us now, or have visited us in the past? Oddly,
Sagan himself wrote a book briefly hinting that some archaeological
evidence suggested extraterrestrial visits in the past, but then
began denouncing that idea when it was vigorously advanced by Erich
von Daniken. Was he jealous that von Daniken's books advancing the
idea made many times more money than Sagan's own book briefly suggesting the same
idea?
Another inconsistent part
of the Sagan Creed is its insistence that extraterrestrial
intelligence is very common, but that mere blind chance is all that
is at work to produce extraterrestrial life and extraterrestrial
intelligence. Given all the great difficulties in life appearing by
chance (discussed here), and the equally great difficulties of intelligence appearing
by chance, we should not expect that extraterrestrial intelligence
should be common if nothing special is at work in the galaxy, and
that just blind chance is at work. But one has a consistent position
if you maintain either (1) that some great force of cosmic teleology
is at work, and that intelligent life has commonly appeared, or (2)
that nothing but blind chance is involved, and that intelligent life
is incredibly rare, requiring extremely improbable accidents.
Another inconsistent part
of the Sagan Creed was its assumption that extraterrestrial
civilizations would be using radio for communication, matched with
the claim that such civilizations are probably millions of years
older than ours. If such civilizations were so advanced, should we
not assume that eons ago they switched to something far more advanced
than radio communications?
Another inconsistent part
of the Sagan Creed was his repeated insistence on both the claim that
extraterrestrial life is very common, and that extraterrestrials
would never look anything like humans. He justified the idea that
extraterrestrials would never look like humans on the grounds that
there are trillions of possible paths evolution might make. But the
same reasoning can be used to argue that extraterrestrial
intelligence should be very rare, on the grounds that there are a
billion ways for life to become successful without becoming
intelligent (all far easier to do than for life to become
intelligent).
In this essay, Sagan said,
“When we do the arithmetic, the number that my colleagues and I
come up with is around a million technical civilizations in our
Galaxy alone.” The statement is nonsensical. First, it implies a
consensus on the topic, when no such consensus ever existed, with
estimates of the number of extraterrestrial civilizations in our galaxy ranging
from 0 to a billion. Second, there was never a sound basis for drawing such a conclusion. Suppose we calculate the odds based on the
difficulties of a chance appearance of the most simple type of life (requiring cells, DNA, a genetic code, and many types of proteins,
which are each exceedingly unlikely to appear by chance), without
assuming some special cosmic teleology that might improve the odds.
Then the answer you get is that we should expect no other life form
to have arisen anywhere else in the galaxy. That's not even considering
the difficulties of intelligence appearing after life has appeared.
A very strong argument can
actually be made that when estimating the number of extraterrestrial
civilizations in our galaxy, it makes no sense to make intermediate
estimates such as Sagan's (by intermediate estimates I mean those
which estimate a number of civilizations in our galaxy greater than
100 but less than a billion). The argument has to do with
interstellar colonization. Suppose there were, say, 100,000
extraterrestrial civilizations that independently arose on other
planets in our galaxy. Even assuming very slow interstellar travel,
there would have been abundant time (more than a billion years) for
interstellar colonization, in which many times a civilization spreads
out to colonize nearby solar systems. So within 100 million years or
a billion years, an original population of 100,000 civilizations on
100,000 planets should inevitably expand out to inhabit billions of
planets. The same thing should happen even if there were only 1000
extraterrestrial civilizations. So based on interstellar
colonization considerations, it seems that it makes no sense to
estimate that there exist something like a million civilizations in
the galaxy. But such a consideration does not rule out a much higher
estimate, that there might be billions of planets inhabited in
our galaxy.
The previously discussed
results of the Search for Extraterrestrial Intelligence (SETI)
suggest that Sagan's estimates about the number of extraterrestrial
civilizations in our galaxy were way off the mark. They suggest that
our galaxy does not seem to be teeming with a million or so
extraterrestrial civilizations as Sagan imagined. The very strong
evidence for psychic phenomena (such as I discussed here, here, here, and
here) suggest that Sagan was also dead wrong about paranormal
phenomena, which he attacked in his book The Demon Haunted World.
Carl Sagan was a pleasant,
sincere fellow who did lots of good work, but it seems that we don't
live in a Carl Sagan universe.
One of the more dubious
things Sagan did was to get NASA to put information disks in the two
Voyager spacecraft. Sagan chaired a committee that took almost a year
to select the contents of the disks. The idea was that the disks
would be a record of human activities that might be picked up in the
distant future by some extraterrestrial civilization when the Voyager
spacecraft left the solar system after exploring Jupiter and Saturn.
If our sun were the size of a grapefruit, the nearest star would be
2500 miles away. Given the incredible vastness of interstellar space,
the chance that either Voyager spacecraft will be picked up by an
extraterrestrial civilization is basically zero. So spending lots of
time preparing such a disk for the Voyager spacecraft was a silly
idea (conversely, putting such a disk on one of the Apollo lunar
landing vehicles would have made sense, for there would have been a
reasonable chance of discovery by extraterrestrial visitors in the
distant future). But NASA went along with the Voyager disks idea,
because Carl Sagan was pitching it. When you're a celebrity
scientist, it's almost like you are some Svengali or Pied Piper who
can get people to believe in something you sell, even if it makes no sense.
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