SkepticblogSkepticblog logo banner

top navigation:

Is SETI Science?

by Steven Novella, Apr 29 2013

I recently receive the following e-mail question:

Got a question for you: do you consider the Search for Extraterrestrial Intelligence to be science or pseudoscience? I recently got into an online debate and found myself in the minority because I maintained that the central thesis — that if intelligent life exists somewhere out there in the greater universe, we would be able to recognize it based upon patterns in radio waves — is not falsifiable.

It would seem to me that the only way to truly falsify SETI, we’d need to map quite literally every body in the universe and rule them out one by one and say that they don’t have anything there in terms of extraterrestrial intelligence.  Unlike other complex hypotheses that are limited by available technologies, I’m not convinced that the task of mapping the universe is even possible, even with a sufficiently advanced technology.

I have received some version of this question many times over the years, always by people who are trying to be skeptical and apply what they have learned about the differences between science and pseudoscience.  It therefore seems like an excellent opportunity to explore this important issue.

SETI is the search for extraterrestrial intelligence and refers to a number of programs over the years that have listened for intelligent radio signals from space. NASA for a time had a SETI program, but this was canceled in 1993. The SETI Institute now carries on this endeavor with private funding.

Whether or not you think SETI is a good idea, is it real science? The issue here is how do we define science. One major criterion for science is that a scientific hypothesis must be falsifiable. This, however, is not strictly true and is an oversimplification.

A hypothesis does not need to be falsifiable in the sense that it is possible to be proven 100% wrong. All that is necessary is that the hypothesis is testable – there is some observation or experiment that you can perform that will make the hypothesis more or less likely to be true.

Sometimes a hypothesis can be stated in such a way that a single counter-example will disprove it. The now classic example is that all swans are white. A single non-white swan will falsify this hypothesis. How thoroughly do you have to search, however, before we can conclude that all swans are white? Would you have to simultaneously survey every swan in the world? If it takes 10 years to conduct a thorough survey can you be sure that a black swan was not born in the last 10 years?

The problem here is in thinking in absolutes. Scientific theories, rather, often deal with probabilities and are not necessarily wrong when exceptions are found. In the case of swans, the more thoroughly we look for non-white swans without finding them the greater our confidence is that all swans are white, and we can certainly conclude that most swans are white and that any exceptions are rare.

Of course this is the classic example because black swans were discovered in Australia.

With regard to SETI the hypothesis is this – life arose spontaneously on Earth, there is nothing special about the Earth and therefore it is possible for life to arise elsewhere in the universe. It is possible that some of that life evolved intelligence, and some of that intelligence developed technology. One method for a technological civilization to communicate across stellar distances is through radio signals. Therefore, perhaps the Earth is being bathed at this moment with intelligent radio signals from other worlds.

Every link in that logical change is perfectly reasonable. The best way to test that hypothesis is to simply look. Looking is part of science. It is a valid way to test many hypotheses. It is not necessary to be able to prove that there are no intelligent radio sources anywhere in the universe in order for this endeavor to be properly scientific.

Like the search for non-white swans, a single example is all that is necessay, in this case to prove that the hypothesis is valid. The more we search without success the more information we will have about the density of radio-transmitting civilizations in the universe. This survey will never be complete, but that is irrelevant.

The broader issue here is the importance of understanding that science is not one method but a collection of various methods. It is important to a proper understanding of science not to have an artificially narrow view of what counts as science. As long as there are hypotheses that are testable with empirical evidence, you are doing science (whether or not you are doing rigorous high quality science is a separate issue).

Frequently the opponents of science try to limit what counts as science in order to deny legitimate science (it is a major tactic of denialism). To be clear, the e-mailer is not doing that here, and he states later in his e-mail that he supports SETI as an endeavor.

It is, however, a common ploy of creationists. They try to deny the legitimacy of all historical sciences because what has happened in the past was either not directly observed or cannot be run as an experiment in the lab. Historical sciences, however, can still make observations and generate hypotheses that can be tested with further observations. There is even a field of experimental archaeology that conducts experiments to test hypotheses about how things were done in the past.

So, yes, SETI is legitimate science. It is searching for evidence that directly tests a very interesting hypothesis. The fact that it can never prove a negative version of that hypothesis (there are no intelligence radio sources in the universe) is irrelevant.

Recommended Reading

32 Responses to “Is SETI Science?”

  1. Bob Blaskiewicz says:

    Massimo Pigliucci has an interesting passage on this question in Nonsense on Stilts.

  2. Trimegistus says:

    It’s really just a matter of framing the hypothesis properly. SETI isn’t asking the question “is there intelligent life elsewhere in the Universe?” but rather “will this method detect signals from intelligent life elsewhere in the Universe?” The first is not falsifiable, the second is.

  3. Old Rockin' Dave says:

    Not all of SETI is based around detecting radio signals; it’s only that to the best of our knowledge, it is the most likely to yield results, but there have been other searches as well. Gamma ray and neutrino searches have been held by some to have promise, in that there patterns that might be observed that are less likely to be natural, and more in line with those that we produce with our technology. Even optical searches have been proposed; I think at least one pilot project was carried out.

    • Old Rockin' Dave says:

      I was too cautious – an optical SETI program has been going on for a number of years.
      (Oh, and I meant “their patterns”, not “there patterns”.)

  4. Daniel says:

    Historical sciences (which, because you contrast it with creationism, I take to include evolution/natural selection) are falsifiable. If we were to discover the fossil remains of a hominid that predate the dinosaurs, it would disprove evolution, or at the very least call it into serious question.

    A more interesting question for anyone who understands it, and can speak in layman’s terms, is whether string theory is science or just a set of fancy mathematical formulas.

  5. Max says:

    Are you sure it’s testable? SETI discovered the exact signal they were looking for, the Wow! signal, and they never saw it again and to this day don’t know what it was. So even if they do detect a signal from an alien civilization, would they ever be able to identify it as such with any confidence, or just rule out any known explanations? How is it different from UFOlogy?

    • Daniel says:

      I believe the story is that SETI discovered what it thought was the Wow! signal, but then confirmed that it was something else. So in that sense it was falsifiable.

      • Max says:

        They thought it might be a reflection of a signal from Earth, but then ruled it out, so I think it remains a mystery.
        Sure, the hypothesis that the signal is extraterrestrial is falsifiable, but I’m asking whether it’s testable, i.e. whether scientists can ever say it’s from an alien civilization. Otherwise, it’s not a search for extraterrestrial intelligence, but a search for unidentified signals, analogous to the search for UFOs.

      • Max, you are assuming that any detected signal would be a one time or short duration thing. That is not was SETI is looking for. Their procedure requires that the signal be persistent for a long time, just to confirm it’s ET origin.

        Then, assuming it contains information, they might have to build special equipment to detect it with sufficient resolution to read the data it contains.

        They are not looking for a on-off short duration signal.

    • Daniel says:

      BTW, even if you are correct, it actually shows that SETI does follow the scientific method. A UFOlogist will take some unexplained light in the sky that appeared on some night and conclude that it’s aliens. SETI observed some kind of anomoly, and, after being unable to detect it again, concluded it was just that.

      • Max says:

        Take a skeptic who studies UFOs. He’ll observe some kind of anomaly, and, after being unable to detect it again, conclude it was just that.
        But at least when it comes to searching for alien visitors, there’s some hope of obtaining physical evidence. No hope of of that when searching for alien civilizations light years away.

  6. Pete says:

    I am surprised thay SETI is attracting this kind of attention. To me – SETI seems a very logical approach. Let’s look at why. If we consider the development of our own species as a example … at some point intelligent beings will find a way to generate radio waves and radio messages. They will begin to explore the electromagnetic spectrum. This causes signals to be sent out into space. Thse signals will have encoded information … for example AM or FM transmissions. That is what SETI is looking for. It doesn’t matter if SETI cannot decode the actuall message – it simply matters that an AM or FM signal came from somewhere in another part of the universe. So this approach to scanning the skies makes a lot of sense.

    I actually had a discussion with a SETI scientist several years ago. The bottom line is that their radio antennas are super-sensitive and so YES they really could detect a signal coming from a distant star i.e. a signal created by another group of intelligent lifeforms.

    In some ways I find it rather surprising that SETI has not succeeded in their quest. You would think that if various intelligent civilizations are out there – these signals should be detectable. It’s almost astonishing that SETI is not seeing something.

    My conclusion is that whoever is out there has “moved on” and now uses some other form of communication. Possibly by a method that bypasses the speed of light as a limitation on the transmission of information. Einstein’s theory applies to the part of the universe that we seem to be able to observe – but it is unlikely we understand the whole structure of the universe. The speed of light is really rather slow for sending signals between stars – something much faster is clearly needed! We simply don’t understand that technolgy yet, so we cannot look for it.

    Pete, Redondo Beach

    • Old Rockin' Dave says:

      There is no reason to think that an advanced civilization has to use radio for communication or for any other purpose. Why might they not use light? Why couldn’t they have gone to optical fiber for long range communication?
      We just don’t know what an alien civilization might do. As someone says in one of Joel Rosenberg’s novels, the thing about aliens is that they’re alien.

  7. Tom says:

    Why does it have to be ether science or pseudoscience? Can’t the answer be: Neither?

    Would you call Bob Ballard’s searches for the Titanic or Bismark science? I wouldn’t. SETI seems to be the same sort of pursuit on a galactic scale.

  8. BillG says:

    “Whether or not you think SETI is a good idea…”?? Instead of the semantics, perhaps this is the better question. Most funded endeavors have risks vs benefits.
    (Which competing pursuits have the better success/rewards to offer?)

    Spending billions, should we chase every Higggs boson out there that may or not provide a benefit? Regarding SETI and the exception to satisfy our curiosity, I believe it’s overblown romaticism that humanity will greatly benefit once we dial into ET.

    • Max says:

      I think the real benefit is in looking for any anomalies that science can’t explain, because that’s how you learn new things, but the “Search for Unexplained Signals” doesn’t sound as interesting.

  9. Phea says:

    The fact that the universe created something,(us), that can actually begin to recognize it’s pure majesty, mystery, and scope, is, (for me), difficult to put into words. In a strange way, I kind of feel honored. This feeling, this realization, goes way beyond any myth, miracle, or mystic, religion has ever offered up. That being said, to not at least try to discover other manifestations of intelligence, is just not part of our basic, curious nature.

    Of course SETI is science. A hundred, or thousand years from now, SETI might be proven to be totally wrong and looked on the way we look at astrology today… who knows? Back in the day, astrology was science, (or at least our best attempt at it). We were trying to figure out why all that stuff was up there, what it was, and how it affected us. We were wrong about a lot of it, but we learned plenty from it, and early astrologers/astronomers, were probably among the very first who could be called, “scientists”.

  10. Al Denelsbeck says:

    Sometimes, it’s simply a matter of what direction the question is approached from. “Is there other intelligent life in the universe?” is, as indicated in the e-mail that sparked the post, not falsifiable – we’d have to know what was in the entire universe. “Is there NO other intelligent life?” however, IS falsifiable, by simply finding another example.

    Moreover, that’s not really how falsifiability is applied. It refers to evidence, and the ability to eliminate other possibilities that contradict a hypothesis. String Theory is considered unfalsifiable because we have no way of collecting evidence for it (or against it.) In detecting a radio signal, one compares it against various things like known frequencies from human sources, regular patterns (oscillations from rotating stars,) solar activity, and so on. If we can find a non-intelligent way of producing the same signal, that increases the probability that it isn’t intelligent.

    The biggest issue with SETI is how limited it is, requiring a lot of assumptions – intelligent life is very much like us, possesses curiosity, wants to contact other forms, uses radio frequencies, is willing and able to throw lots of energy into space, et cetera. Being wrong on just one assumption can mean no signal to detect, so what’s testable is a very narrow set of conditions – which may have nothing whatsoever to do with intelligent life. Not bothering to look for such signals, however, drops the possibility of finding them down to zero.

  11. madscientist says:

    SETI is not pseudoscience but I have my doubts that SETI can ever be successful. Using our best available technology we cannot even transmit a signal a few light years to the next nearest star; we simply have no beacons which have a high enough output power and a narrow enough beam. Creating such a source on earth may be beyond the realm of the possible even though strong enough natural sources such as stars are plentiful.

  12. Mark says:

    When a field of scientific inquiry is too broad to have specific falsifiable claims, instead of experimentation we do EXPLORATION. SETI is an example of scientific exploration.

  13. Dave says:

    “As long as there are hypotheses that are testable with empirical evidence, you are doing science (whether or not you are doing rigorous high quality science is a separate issue).”

    This is a little off topic but the above quote immediately made me think of the Mythbusters. Lots of people like to criticize them as not being true scientists because their sample sizes are too small, etc. But according to this, they are, in fact, doing science, and are therefore scientists. Could their science be more rigorous and high quality? Yes, of course, but not for a popular, hour-long tv show.

  14. Pete says:

    I think the real issue with SETI is essentially the reverse of what has been discussed here. You can figure that from about the time of World War One (1914) planet Earth has been radiating quite a lot of radio waves out into space. Of course, Marconi showed radio transmissions could be effective in 1888. But I choose 1914 as about the time a lot of radio energy really started to get radiated from our world. So roughly in the time frame of the last 100 years this radio energy has been beaming outwards into space. And then over say the last 50-70 years, the amount of electromagnetic energy (radio, radar, microwave, extremely high frequency) energy has just exploded in volume. And also some bursts of gamma radiation from various nuclear explosions and tests starting in 1945.

    Therefore, signals “advertising” intelligent activity on Earth have radiated out through a sphere with a radius of about 100 light years. And there is a smaller sphere of about 50 light years with a much higher level of activity of all bands of the electromagnetic spectrum.

    Hence if there are alien astronomers out there (alien scientists who have their own SETI programs), they should pick up this energy. Pretty much if there is any intelligent life belonging to an advanced civilization within 100 light years of Earth – then they already KNOW about us. It is possible that such “people” have already sent some sort of reply. Or that they have prepared some other form of response – such as sending a spaceship of their own to investigate what is happening here. But we don’t know about that reply yet, because it has not reached us yet.

    Every year our radio signals from planet Earth travel one more light year out into the universe. So if there is someone looking out there for signs of life – they will notice us. Hence the situation is more likely to work in reverse as far as SETI is concerned.

    Pete, Redondo Beach

    • madscientist says:

      Not really; for the signal power we’re pumping out you’d need an antenna the size of our solar system to detect any signal. Think of it this way: the Voyager 2 can still receive a few unambiguous signals each second from some very large antennas on earth with moderately high power transmitters. Voyager 2 is roughly 1.6×10^-5 light years from earth. Each time that distance is doubled, you will need 4 times the power or twice the diameter of antenna to maintain the same signal level. So for 1 light year you need to up the power by a factor of about 4,000,000,000 (yup, 4 billion) and for 2 light years you have 4B*4B. You quickly run into incredibly large numbers. In principle you can go for simply detecting radiation rather than radiation which is encoded with information provided there is no natural source for that radiation and the radiation is not attenuated by the galactic medium. However, even in the best case the numbers are staggering.

      • madscientist says:

        Oops .. got the wrong numbers in my rush – I used the ly distance from the earth to the sun, not the sun to pluto. So instead of 4B, the factor is roughly 2.7M. I also got the scaling wrong; 2 ly will require 2.7M*4 and the next nearest star at about 4 ly requires a factor of 2.7M*16. So these numbers are more reasonable but still huge and very much set against anyone in another star system being able to find us.

  15. Pete says:

    Madsci – doesn’t that just mean that our “friends” the alien SETI astronomers just need to do two things … (1) build a super-sensitive receiver, and (2) Find a clever way to achieve a very large antenna. Both are quite possible. The antenna does not need to be literally the size of the distance from the Earth to the Sun. It could be a series of smaller antennas, but spaced across much larger distances. How about 20 large antennas spaced across 500 million miles? That is way beyond our technology, but maybe not beyond theirs. I will leave the technology of the low-noise super-sensitive receiver to the aliens themselves. If they are curious – they can look for us. My premise is simply that it’s easier for them to detect Earth than vice versa.

    • madscientist says:

      Unfortunately it’s not so simple. From what we know of physics the aliens will have just as hard a time. Some radio receivers have been cooled down to liquid helium temperature and going a bit further to push them to milliKelvin temperatures wouldn’t really gain anything. As for many small receivers rather than a single large one, that trick is used to increase resolution far more than it is used to improve the signal-to-noise figures. When you’re only receiving on average a photon or two per square kilometer every few seconds there’s little hope of finding anything. Come to think of it, there are a few such experiments being run on earth where observable events are extremely unlikely; it’s not surprising that quite a few years have gone by and those experiments have still shown no clear signal.

  16. Jordan says:

    Or the simple answer is that we are the only life in the universe and SETI will never find a signal because there isn’t one to be found.
    If the universe is a certain number of years old, and if there are a certain number of habitable planets, there would have arisen intelligent life billions of years before humans on earth. There should be all sorts of signals bombarding our planet by now.
    Since there are none (that we can tell with our technology, I’ll grant that much) we can conclude that it is more likely that we are alone.

    • madscientist says:

      I go for “no evidence either way”. On the one hand there is nothing preventing the development of intelligent creatures on another planet and it is incredibly likely that there are many planets currently out there which have the right conditions for life to start. However, just as there is nothing preventing the development of any sort of life on other planets, there is no guarantee that it would happen anywhere else either. The lack of a definitive ET signal is in no way any evidence that there is no intelligent life elsewhere, and certainly not any sort of evidence that there is or is not any life on another planet.

    • Phea says:

      If we are “alone”, if we are the ONLY thing in existence that is consciously aware of the universe… and beginning to unwrap it’s mysteries. To me, that would be much more mind boggling than the alternative, as instead of feeling insignificant, we would rightfully hold a type of, “god” status.

  17. Pete says:

    “Or the simple answer is that we are the only life in the universe and SETI will never find a signal because there isn’t one to be found.
    If the universe is a certain number of years old, and if there are a certain number of habitable planets, there would have arisen intelligent life billions of years before humans on earth. There should be all sorts of signals bombarding our planet by now.”

    It’s interesting to speculate about this. My comments here are also pure speculation. I tend to look at it this way. I don’t see any reason why planet Earth is a “special neighborhood”. In terms of our own galaxy, we are living “in the sticks”. We don’t have prime real estate :-) So if intelligent life could develop here, it can probably do so elsewhere. I think that probably in due time (many thousands of years from now) we will find that various forms of “life” are not uncommon in the universe. However, intelligent civilizations may be somewhat less common.

    The problem with radio and electromagnetic signals is that they are just not practical for sending messages between the stars. Distances are too big, travel times are too long, and as Mad Scientist pointed out above – the decay of energy in the signal is too great. Our race has only been using radio for about one-and-one-quarter centuries. It’s a very short time period in terms of the overall development of the human race. It’s really just a short window in time.

    Hence it seems unlikely – even if there are intelligent beings out there – that we would just happen to catch their technology when radio was a “big deal”. The advanced civilizations have probably moved on to something much better.

    Pete, Redondo Beach