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SETI: Intermittency and Detection

My guess is that most people think of SETI as doing a ‘long stare’ at a given star, on the theory that it may take time to acquire a possible signal from an extraterrestrial civilization. But in reality observations take place over short time periods. The Mega-channel ExtraTerrestrial Assay, known by its acronym as META, led by Harvard’s Paul Horowitz and aided by The Planetary Society, could only devote a few minutes to any particular star.

The same was true of the follow-on BETA (Billion-channel Extraterrestrial Assay), while targeted searches like Phoenix, led by Jill Tarter and using facilities at Green Bank (West Virginia), the Parkes 64-meter dish in Australia and the 300 meter radio telescope at Arecibo, still observed targets for less than an hour. The problem with this is that there are numerous reasons why an extraterrestrial signal might be intermittent.

We’ve looked at this issue before, particularly in terms of ‘Benford beacons,’ as discussed by Greg and Jim Benford in these pages (see, for example, SETI: Figuring Out the Beacon Builders for an introduction to the discussion).

Robert Gray takes on the matter in a new paper in the International Journal of Astrobiology. Gray’s will be a familiar name to anyone tracking SETI closely, as the author of The Elusive Wow: Searching for Extraterrestrial Intelligence (Palmer Square Press, 2011) and the man most associated with the unusual reception at Ohio State’s ‘Big Ear’ observatory in 1977. The name comes from the ‘Wow!’ that radio astronomer Jerry Ehman inscribed on the computer printout of the event, which had characteristics of a genuine signal rather than noise..

Image: Independent SETI researcher and data analyst Robert Gray. Credit: Sharon Hoogstraten CC BY-SA 3.0.

Gray became fascinated with the signal when he learned about it several years after it was received. Since those days, he has led his own search for the signal, both with his own 12-foot dish and professional installations like the Harvard/Smithsonian META radio telescope at Harvard’s Oak Ridge Observatory as well as the Very Large Array in New Mexico. He would later extend the search to the Mount Pleasant Radio Observatory in Hobart, Tasmania. As you can see, Gray’s observations are the antithesis of the short dwell times that are the norm in SETI due to the desire to widen the search to as many stars as possible. The Wow! Signal has now had over 100 hours of follow-up, but no signals resembling the original one were ever detected.

What would happen if we could somehow extend SETI to long, fixed stares on high-interest stars? What Gray’s new paper points out is that signals that repeat at intervals of hours or more could be detected with such a capability, whereas current methods would be unlikely to find them. It’s interesting to speculate on why it might, in fact, be far more likely for signals to be intermittent than continuous. The Benfords have analyzed the issue in terms of cost, a thought Gray echoes in the paper by noting the power demanded by a continuous isotropic beacon.

Lower the duty cycle and the average power drain is sharply diminished, producing a possibly strong but intermittent signal. Thus a beacon might be operating at repetition rates that would be invisible to our current methods, as would directed transmissions, whether optical or radio, that targeted specific stars. We’ve wondered before in these pages about planetary radars like Arecibo, perhaps detectable at considerable distance, but appearing in an alien sky only momentarily as the signal swept by chance past the receiving apparatus. ETI’s astronomical community would be left with an interesting transient and no real hope of confirmation.

Image: The famous ‘Wow!” signal.

Here’s Gray on moving away from continuous isotropic broadcasting. I quote this passage because it places current SETI efforts in context:

…reducing the duty cycle to 1% could provide a 100-fold reduction in average power required, perhaps radiating for 1 s out of every 100 s. Searches observing targets for a matter of minutes might detect such signals, such as the Ohio State and META transit surveys which observed objects for 72 s and 120 s respectively, or Breakthrough Listen observing targets for three five minute periods…, or a targeted search such as Phoenix observing objects for 1,000 s in each of several spectral windows…, or the ATA observing for 30 minutes… Reducing duty cycle further yields further savings—for example a 10-4 duty cycle with a 104 reduction in average power might result in a 1 s signal every three hours, but most searches to date would be likely to miss such signals. Assuming longer signal duration does not help much; a 1-hour signal present every 100 or 10,000 hours would be very unlikely to be found by most current search strategies unless the population of such signals is large.

There are other ways of reducing transmission power that make sense, with repercussions for how SETI might detect them. And there are reasons for intermittency that go beyond broadcast strategies, all of which must be considered. Are there strategies that can help us here, given that our knowledge of signal duration — if indeed such signals exist — is nil? Gray suggests some possibilities that I want to look at tomorrow, as we continue to ponder intermittent signals and their possible reception.

The paper is Gray, “Intermittent Signals and Planetary Days in SETI,” International Journal of Astrobiology 4 April 2020 (abstract).

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{ 43 comments… add one }
  • Alex Tolley June 18, 2020, 15:33

    There may be a flaw in Gray’s thinking about targeted beams. An isotropic beam radiating in all directions assumes that ETI has no knowledge of who the recipients may be or where they are. This is then assumed for targeted beams as the number of possible targets rapidly becomes unmanageable.

    But let us assume an ETI that is perhaps just 100 years ahead of us technologically. Their telescopes will have characterized exoplanet planet conditions for all teh worlds within some radial bubble, let’s say 10,000 ly. Of those worlds, they may well have hints or even direct observations of technological civilization at some level of development. Early cities, cultivated fields, megacities, pollution, radio emissions, etc. The number of those worlds is likely very small, perhaps a handful at best, and most are either relatively early stage or very advanced. Therefore sending continuous beamed transmissions may be quite feasible. To make those signals be obviously artificial, they could be beamed in pulses with repeating short period Fibonacci sequences that would be sure to draw attention. Those signals could be radio or light waves. Light might be better because laser light would show up as a spike in a spectrogram of a star’s light.

    TLDR; ETI will have enough knowledge of other worlds to reduce communication energy requirements to a minimum by targeting just the low number of targets that might be able to receive them, with a signal that should be obvious to any technological species within a short time of development.

  • Gregory Benford June 18, 2020, 18:11

    Good idea. Latest Breakthrough paper
    https://arxiv.org/search/?query=A+3.95%E2%80%938.00+GHz+Search+for+Radio+Technosignatures+in+the+Restricted+Earth+Transit+Zone&searchtype=title&source=header

    says “This rETZ observing campaign was allotted twelve hours of Breakthrough Listen time on the GBT, with a 20% overhead time
    set aside for calibration and slewing of the telescope. We implemented a flux-limited method such that every target received an
    equal amount of observing time (28.8 minutes).”
    So still not much.

  • Gary Wilson June 18, 2020, 20:25

    A transmitting civilization might be very similar to us, having found no nearby targets which they think have advanced life. They would therefore probably adopt a wide transmission beam approach wouldn’t they? Even though we have only a small amount of data so far it seems quite possible that advanced civilizations are few and far between. Didn’t a recent study using a new algorithm (not the Drake equation) come up with a potential for about 30 civilizations in our galaxy (and a higher number with slightly adjusted parameters). They calculated about 17,000 light years on average between civilizations. It’s called the Astrobiological CopernicanLimit I believe.

  • DCM June 19, 2020, 4:40

    Listen but cultivate our own solar backyard.

    • ljk June 19, 2020, 8:49

      Would you clarify what you mean by this? We have no solid interstellar mission plans despite the hype from Breakthrough Starshot, if devoting resources and energies to a star probe over any other space activities is your concern.

      • DCM June 19, 2020, 12:33

        Don’t try to communicate. Just find out what you can.
        Devote most of available funds to using the Moon, Mars, asteroids.

        • ljk June 22, 2020, 10:36

          Setting aside for the moment the non-monetary issues involved with METI, you realize that SETI still gets relatively little funding even after the $100 million infusion of cash from Breakthrough SETI back in 2015 (has more funding been implemented since?).

          That funding was private. It did not come from NASA or any space agency. Therefore not funding SETI or METI has nothing to do and causes no interference with interplanetary exploration. So why go after SETI/METI funding?

          We are all working towards the same goals. SETI and METI should be pursued and at far higher rates and resources than have existed for most of their history.

          • DCM June 22, 2020, 17:13

            If aliens exist they are to be heard and not spoken to.

            • ljk June 23, 2020, 9:37

              Humanity has already been “speaking” to the galaxy for over a century now. There is an electromagnetic bubble around our Sol system about 200 light years across and growing.

              Also, advanced ETI would be able to detect that Earth has abundant life forms even if we never transmitted a single signal. That has been going on for a long while now.

              • DCM June 24, 2020, 12:56

                All the more reason not to try communicating.
                Nobody likely thought of this in 1900 but maybe there’s a corrective — cables or something we haven’t thought of yet.

                • ljk June 30, 2020, 12:04

                  People have and will continue to communicate with ETI. It is going to happen no matter how many more dictators and their minions try to control everything.

                  We should be preparing for the eventuality of contact rather than trying to stop something that cannot be stopped except in the most extreme circumstances – and then we will no longer have a society worth preserving.

  • ljk June 19, 2020, 9:24

    https://www.nme.com/en_au/news/music/the-avalanches-are-teasing-music-converted-from-a-1974-space-broadcast-2690646

    The Avalanches are teasing music converted from a 1974 space broadcast

    They were contacted by Frank Drake, the astrophysicist who created the Arecibo message

    By Josh Martin

    18th June 2020

    The Avalanches have teased new music converted from the 1974 Arecibo message broadcast into space in the hopes of contacting intelligent life.

    On Instagram today (June 18), the Australian plunderphonics group detailed how they were contacted by Frank Drake, the 90-year-old astronomer and astrophysicist responsible for the creation of the Arecibo message in 1974.

    According to the SETI Institute, the Arecibo message carried information about humanity to the distant galaxy M13, and was broadcast using two different radio frequencies from the Arecibo radio telescope in Puerto Rico on November 16, 1974. It remains the most powerful broadcast ever deliberately beamed into space.

    [Messier 13 is a globular star cluster located in our Milky Way galaxy, FYI.]

    “Frank found [the message] in his archives and was kind enough to share with us. Over the last few weeks [Nelly Ben Hayoun] and Franck Marchis at the [SETI Institute] have helped us digitalise the message using AI-based software to convert the original file provided by Frank,” The Avalanches wrote.

    “It’s now a string of 0’s and 1’s, ready for conversion into a MIDI sequence, and perhaps, shortly, for your listening pleasure. Stay tuned!”

    Alongside their note, The Avalanches posted an image of the “never before seen” code which, as promised, is a binary assortment of zeros and ones. See it here:

    https://www.instagram.com/p/CBjfN3PJ6M7/?utm_source=ig_embed

    • ljk June 19, 2020, 9:59

      By the way, it is completely inaccurate that the binary coding of Arecibo Message of 1974 has never been seen before. I have seen it plenty of times going back to just shortly after the METI project was announced to the general public.

      Here it is in various forms in this nice piece from 2014:

      https://writescience.wordpress.com/tag/arecibo-message/

  • ljk June 19, 2020, 12:47

    https://www.cfa.harvard.edu/news/2020-12

    CfA Scientists Collaborate on New Study to Search the Universe for Signs of Technological Civilizations

    Release No.: 2020-12

    For Release: Friday, June 19, 2020 – 8:00 am

    Cambridge, MA –

    Scientists at the Center for Astrophysics | Harvard & Smithsonian and the University of Rochester are collaborating on a project to search the universe for signs of life via technosignatures, after receiving the first NASA non-radio technosignatures grant ever awarded, and the first SETI-specific NASA grant in over three decades.

    Researchers believe that although life appears in many forms, the scientific principles remain the same, and that the technosignatures identifiable on Earth will also be identifiable in some fashion outside of the solar system. “Technosignatures relate to signatures of advanced alien technologies similar to, or perhaps more sophisticated than, what we possess,” said Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard. “Such signatures might include industrial pollution of atmospheres, city lights, photovoltaic cells (solar panels), megastructures, or swarms of satellites.”

    Knowing where to look for technosignatures hasn’t always been easy, making it difficult for researchers to obtain grants and a footing in mainstream astronomy. The surge of results in exoplanetary research—including planets in habitable zones and the presence of atmospheric water vapor—over the past five years has revitalized the search for intelligent life.

    “The Search for Extraterrestrial Intelligence (SETI) has always faced the challenge of figuring out where to look. Which stars do you point your telescope at and look for signals?” said Adam Frank, a professor of physics and astronomy at the University of Rochester, and the primary recipient of the grant. “Now we know where to look. We have thousands of exoplanets including planets in the habitable zone where life can form. The game has changed.”

    The study, “Characterizing Atmospheric Technosignatures,” will initially focus on searching for two particular signatures that may indicate the presence of technological activities on extrasolar planetary bodies: solar panels and pollutants.

    Solar panels are rapidly gaining in popularity as a means for harnessing the energy of Earth’s sun, and researchers believe other civilizations will do the same with their own stars as they seek new means to produce energy. “The nearest star to Earth, Proxima Centauri, hosts a habitable planet, Proxima b. The planet is thought to be tidally locked with permanent day and night sides,” said Loeb. “If a civilization wants to illuminate or warm up the night side, they would place photovoltaic cells on the day side and transfer the electric power gained to the night side.” Frank added, “Our job is to say, ‘this wavelength band’ is where you would see sunlight reflected off solar panels. This way astronomers observing a distant exoplanet will know where and what to look for if they’re searching for technosignatures.”

    In the search for life outside of the solar system, scientists also often turn to biosignatures detected as chemicals in planetary atmospheres. Jason Wright, Penn State University, said, “We have come a long way toward understanding how we might detect life on other worlds from the gases present in those worlds’ atmospheres.” While scientists can search for those chemicals produced naturally by life, like methane, they are now also searching for artificial chemicals and gases.

    “We pollute Earth’s atmosphere with our industrial activity,” said Loeb. “If another civilization had been doing it for much longer than we have, then their planet’s atmosphere might show detectable signs of artificially produced molecules that nature is very unlikely to produce spontaneously, such as chlorofluorocarbons (CFCs).” The presence of CFCs—or refrigerant—therefore, could indicate the presence of industrial activity.

    Loeb, Frank, and Wright are joined by Mansavi Lingam of the Florida Institute of Technology, and Jacob Haqq-Misra of Blue Marble Space. The study aims to eventually produce the first entries for an online technosignatures library.

    “My hope is that, using this grant, we will quantify new ways to probe signs of alien technological civilizations that are similar to or much more advanced than our own,” said Loeb. “The fundamental question we are trying to address is: are we alone? But I would add to that: even if we are alone right now, were we alone in the past?”

    About Center for Astrophysics | Harvard & Smithsonian

    Headquartered in Cambridge, Mass., the Center for Astrophysics | Harvard & Smithsonian (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

    For more information, contact:

    Amy Oliver
    Public Affairs
    Center for Astrophysics | Harvard & Smithsonian
    Fred Lawrence Whipple Observatory
    520-879-4406
    amy.oliver@cfa.harvard.edu

    • AlexT June 20, 2020, 2:01

      … The nearest star to Earth, Proxima Centauri, hosts a habitable planet, Proxima b…

      It is pure speculation, wishful thinking, but not scientific fact.
      Sorry (me too wish to find habitable planet close to the Earth) , but there is significantly higher probability, that Red dwarfs environment is not compatible with earth type life, so there is no any habitable zone at all around Proxima Centauri.

  • AlexT June 20, 2020, 1:51

    It is good to know that there are scientists, who understand that probability to detect any artificial signal from the space is very low down to impossible.
    Should governments spend funds for SETI projects? I am sure – not, leave this area for amateurs and romantic angel investors.
    SETI – it is dead tree that will never bring any fruits.

    • DCM June 20, 2020, 13:46

      You are likely right. If there are aliens with any degree of technological development they are probably very far away from us.
      Alas, much of the search seems based on the belief that more advanced creatures will be able to give us moral guidance. Yet they are probably going to prove more different from us than any Earth creatures and we wouldn’t seek advice from spiders.
      This is why I say we should make use of nearby planets that seem fortunately bare of life and build off-Earth habitat worlds. Don’t spend our resources on a wild goose chase.

      • AlexT June 21, 2020, 3:03

        …and we wouldn’t seek advice from spiders…

        As well as we all know, homo sapiens do not seek advice even from another homo sapience if it has different religious, ideological, political beliefs.
        The hope to find more advanced ETI who will teach us “good things”, it is type of God seeking, no more.
        So meanwhile independently of SETI efforts we do not have other real choice, but Solar System colonization and invention of more advanced propulsion engines.

        • DCM June 21, 2020, 13:00

          It is a type of God seeking but we shouldn’t assume that will make sense to any aliens. And you admit that can lead to all manner of strife.
          A good thing would be to drop the negativity toward humans that has infected us, especially the West, since WWII. It alienates people from science as well as inspires destructive self-hate; the alternative isn’t hubris but objectivity.
          Be glad there’s likely nobody nearby to falsely worship or rub the wrong way as we do develop our region.

          • Gary Wilson June 21, 2020, 18:10

            I don’t think we’re looking for a type of God who will teach us anything. It’s strictly a matter of curiosity for me and probably many others. The real point is to look for life in all its forms as far out as we can. Communication may be impossible with whatever we find despite clear signs of intelligence. And if we are to survive (and yes thrive) in the long term, that has to come from within us, not from without. We are making progress over time in our behaviour and attitudes, but will it be fast enough? I’m not sure. We’re within a hair of pushing the Earth’s ecosystems into collapse as well as permanently (in the sense of thousands of years at least) altering the climate away from the present mild conditions. All very dangerous indeed and eventually not fixable by humans.

            • AlexT June 22, 2020, 1:14

              The real point is to look for life in all its forms

              Sorry, but methods used today by SETI (electromagnetic waves detection). Does not allow to detect “life in all its form“, it is unable to detect even civilization located on Proxima Centauri b, if it has same level as “Western civilization “ in the period of WW I ( probably WW II ).
              So SETI methods are directed to search of civilization more advanced than we are. When detection directed to more distant worlds – difference (ETI civilization advance) will grows significantly with distance, it is direct consequence of speed of light communication. (With assumption that ETI civilization will not stop development or die).
              So , let imagine, if right now , some Proxima’s Albert Einstein is sitting in proxima’s patent bureau and discovering special theory of relativity , we do not have any chance to find his civilization using SETI instruments.
              So when we talking about SETI – it is not all types of life, but very specific one.

              • ljk June 22, 2020, 10:37

                If we do not look for alien life, we will likely never find it. Plus, it isn’t your money or time, so why keep complaining?

                • AlexTru June 23, 2020, 2:33

                  There are still tested by time good search methods:
                  – traditional astronomy
                  – direct exploration
                  SETI is only one (fruitless) branch of radio astronomy. Stop of SETI does not mean in any way stop of alien life searches.

                  • ljk June 30, 2020, 12:06

                    If only we could trust the traditional professional astronomers not to ignore or suppress any discoveries of ETI they might make.

                    I want to think Tabby’s Star is the sign that the times are a-changing, but many still want the status quo, and aliens are just too messy for them. Maybe as the old guard continues to die off things will get better.

            • DCM June 22, 2020, 4:11

              As long as we don’t worship creatures because of their advanced technology I suppose there’s no harm in “seeking God”. In fact, we’ll need that concept since of course we’re not likely intelligent enough to know or understand everything. We’re limited by physiology just as we realize that chimpanzee brains or dog brains are, for example. But let’s not get dogmatic or we’ll never improve.
              I seriously doubt we’re destroying the Earth. The last Ice Age peak ended about 12,000 years ago after people had existed at least 100,000 years and lived through such fluctuations. Are we to assume a few thousand campfires and the incessant sound of flint chipping caused this? No, the causes are geological and astronomical so let’s not throw any virgins into the volcano to make the weather colder, or indulge in some institutionalized self-hate.
              I’m interested in space travel and its uses simply to expand life, not to escape climate changes we’ve lived through a dozen times with simpler technologies.

              • Gary Wilson June 23, 2020, 11:18

                There is an overwhelming canon of knowledge suggesting you are wrong DCM. We have at least 50 years of data from tens of thousands of climate scientists (including many brilliant Americans) that show what is happening. And it is not happening on geological time scales. We are adding an unprecedented amount of CO2 to the atmosphere incredibly rapidly (the equivalent of burning a trillion barrels of oil at least). That in turn is destabilizing the climate. Next to come is methane being released from the thawing of vast quantities of permafrost. Methane is 25 times more powerful as a greenhouse gas than CO2 although it has a much shorter residence time in the atmosphere. This is not make believe. You have been subjected to enormous amounts of anti climate change propaganda in the US, especially in the time of Trump. Please read the literature as anyone believing in the scientific method should.

        • NS June 22, 2020, 3:39

          “As well as we all know, homo sapiens do not seek advice even from another homo sapience if it has different religious, ideological, political beliefs.”

          This explains why the Babylonians learned nothing from the Sumerians, why the Greeks were completely unaware of the Babylonians and Egyptians, the Romans never borrowed anything from the Greeks, Islamic cultures didn’t preserve Greek and Roman manuscripts, Europe never read translated Arab texts…

          In short, completely wrong.

          • DCM June 22, 2020, 17:20

            Exactly right. Modern humans probably learned from other human types as well. After all, we had children with them, especially neanderthals.
            The statement quoted is a fine example of the self-hatred that has permeated at least Western thinking and customs since around WWII. Time to leave it behind.
            Pride and confidence aren’t hubris.

          • AlexT June 23, 2020, 1:45

            Dear NS,
            You have very selective approach to human history, somehow forget non-stop wars between human being , genocides, death, slavery etc. when human kills and cell human due to difference in culture, religions, ideological, race.
            Most of ancient civilization you describe here vanished leaving very few scientific facts about them, so our knowledge about (fir example) Babylon is very limited.
            There is also separate history about American natives, who’s civilization was wiped away almost absolutely by “western” inviders.

            • DCM June 24, 2020, 13:09

              We have mapped Babylon and its neighbors and we can read such documents of their as survive. There are also accounts of them in Herodotus, the Bible, and other works.
              Part of the reason “Native Americans” — Indians — fell into that situation was neither their fault nor ours. They didn’t have much resistance to diseases that didn’t exist over here. That has also kept Western empires from totally occupying and colonizing Africa because Europeans had no resistance to that continent’s tropical diseases.
              Why don’t you rage against the Mongols, who systematically killed millions in the 1100s – 1400s? An estimate is that under Hulagu (mid 1200s) they killed 27 million in what’s now Iran and Iraq simply by beheading them, stacking gunpowder in buildings, then setting cities on fire. Yes, they had gunpowder and rockets. Why ignore this?
              We have, incidentally discovered how to read Mayan writing, recovering parts of their history.

              • AlexTru June 25, 2020, 1:56

                I see our conversation going to wrong direction (human history et .), but this short communication experience perfectly still illustrating the idea I try to explain :
                Homo sapience has serious problem to communicate even other homo sapience, so it is not clear how SETI optimists are planning to decipher absolutely alien message, when we will not have with ETI “common Babylonian roots” :-)
                There is nothing common with “self-hatered”, personally me accept Homo Sapience as it is, do not try to hide or ignore facts, that are not compatible with idealistic fantasy.
                To be more clear – in connection to climate changes, I am sure it has no connection to homo sapience, but some natural , periodic fluctuation, that was exiting long time before first primates appeared on the Earth,
                why should this natural fluctuation stop right now none of “climate alarmists“ can explain.

  • Gary Wilson June 20, 2020, 12:52

    You never know if you don’t try AlexT my friend. At least listening for incoming signals makes sense to me. We as a species spend money and resources on far more useless and destructive things (wars for example). Keep sending in those comments :).

    • AlexT June 21, 2020, 3:36

      Agree, Yes we spend lot of money on different stupid things, SETI one among of multiple bad choices.
      In connection to your sentence: “You never know if you don’t try”, it is problematic point, I will try to explain my position.
      1. Electromagnetic waves has natural limitation – speed of light, so if we take in account dual side information exchange we can suppose that there should be natural distance limit that makes impossible for homo sapiens to hold provide dual side communication.
      2. Suppose that more advanced civilizations should know about limitations of speed-of-light on cosmic distances.
      3. Meanwhile, We do not know ant fastest communication method.
      4. Let imagine native people the lived on isolated island in the middle of Pacific Ocean, if they decide to search for extra-islend-intelegence, shouting loudly and very carefully listening , despite their efforts – they do not have any chance to get any sound from more advanced Earth habitants… (and none will get their call too).
      “If you will not try”, SETI has background more than 50 Years of fruitless ETI listening , suppose there should be careful analyze what is going wrong with this approach, only requirement to spend more.
      I also cannot also understand what exactly scientific discoveries are standing after multiple professors and Ph.D degree in different SETI affiliated institutes… I can suppose that modern SETI it is something similar to theology…

      • ljk June 22, 2020, 11:34

        Your knowledge of SETI is outdated, limited, and incredibly biased, but you never bother to update or correct yourself for obvious reasons.

        If others want to search for alien life with their own funds and resources, that is their right and business, not yours to decide.

        As an example…

        I do not care for sports except in a certain historical context. I happen to think it is a huge waste of time and money, with the professional versions making only a relatively few very wealthy while distracting the masses and picking their pockets.

        But you know what? That’s just my opinion. I also know that sports bring a lot of joy as well as purpose and goals to many people. I am not going to take that away from them because they have the right to pursue these things that do not harm others. I believe in freedom of thought, speech, and action so long as it does not harm others.

        • AlexTru June 23, 2020, 2:40

          In almost every my comment related to SETI:
          SETI should be left to Radio Amateurs and angel investors, i.e. funded by private money only.
          If SETI organizations can exists on private funds only, well done!

          And yes, it is my own opinion only, no more.

  • Gary Wilson June 21, 2020, 15:31

    As long as it maintains a scientific approach with proper rigor I would think continuing the SETI project is worthwhile AlexT. The percentage of world GDP spent on SETI is infinitesimally small. I understand your point about the speed limit of light compared with the distances involved and the time required to receive an answer, but it is still possible that another technological civilization lives within a hundred light year bubble from us. I choose the hundred light year mark arbitrarily because it seems surmountable as a waiting period (200 years to receive a signal and send an answer which is received at most). We still have the problem of the low possibility of coincident (in time) civilizations being able to communicate as well. The odds are against us but the probability is definitely not zero.

  • AlexT June 22, 2020, 3:55

    The percentage of world GDP spent on SETI is infinitesimally small
    I am sure if we compare money spent to SETI with other astronomic projects, the difference will not be so significant. I prefer every cent better for real science, i.e. astronomy, that really gives us new knowledge.
    But if are talking about private funding – why not? But no any state organization funded by people taxes should be involved in “philosophic stone” searching.
    I very bothered by most SETI activists inability to make serious analysis of ~50 years fruitless efforts.
    Simplest question: are SETI right supposing that advanced intelligence civilization will spend energy and efforts for so problematic (if applied to astronomical distances) communication method like Radio?

  • Mike Serfas June 22, 2020, 13:14

    If signals are intermittent and sent at specific destinations (even if in a sector scheme) there should be some logic to the timing with which they are repeated. The “Big Ear” isn’t a uniquely human solution to the problem of trying to listen to the whole sky. I can think of two fairly-obvious ways to repeat the signal: the broadcast frequency, and the Planck time.

    If the Wow! signal was broadcast on August 15, 1977 at 02:16 UTC, then we should expect a rebroadcast at 2^n times either (1 / 1420.4058 MHz) (the hydrogen line assuming a blue-shifted source, per Wikipedia logic) or 5.391247(60)E-44 seconds (the Planck time). The same time next August 15 will be 43 years = 365*43 + 10 days = 1 356 912 000 seconds later. So we pick the next highest power of 2 higher than either 1.9273657E+18 or 2.516879E+52, getting 2^61 = 2.3058430E+18 and 2^175 = 4.789048565E+52, respectively. Now if the aliens rebroadcast on a more frequent schedule, hopefully that is another power of 2 and these intervals will work just as well!

    So in the first case, we simply listen at 2.3058430E+18/(1420.4058 MHz) = 1623369200 – 1356912000 seconds = 8 y 161 d 23 h 53 m later, so I think 2:09 UTC on February 13, 2029, give or take about two minutes. If you are not that patient you can redo the math hoping they rebroadcast our way every 2^53 cycles of the hydrogen line frequency or less.

    Now I haven’t corrected for the blueshift noted in the transmission frequency, which implies the signal will arrive slightly sooner, and I didn’t do the Planck time example. I should thank https://www.mathsisfun.com/calculator-precision.html . But note that in the right hands a first-principles system of intermittent broadcasts allows for very precise predictions, and should allow detection by brief, intensely targeted measurements long after the first signal is detected.

  • DCM June 24, 2020, 13:20

    No doubt the climate is changing. Modern people seem to have existed about 200,000 years. During this time there was severe glaciation for tens of thousands of years interspersed with warmer periods than the present for similar durations. There is no evidence of the type of industrial activity we have among humans or closely related species during this time. The causes were and are natural.
    And how do you propose to keep the Earth in a steady state climate?

  • ljk June 24, 2020, 20:48

    http://astrobiology.com/2020/06/risks-for-life-on-proxima-b-from-sterilizing-asteroid-impacts.html

    Risks For Life On Proxima b From Sterilizing Asteroid Impacts

    Press Release -Posted June 23, 2020 11:23 PM

    We consider the implications that a debris belt located between Proxima b and Proxima c would pose for the rate of large asteroid impacts that could sterilize Proxima b from life.

    Future observations by ALMA or JWST could constrain the existence of an asteroid belt in the life-threatening regime. We generalize our rate calculation of sterilizing impacts for habitable planets in systems with an asteroid belt and an outer planet.

    Amir Siraj, Abraham Loeb

    Comments: 4 pages, 5 figures; submitted for publication in ApJL

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    Cite as: arXiv:2006.12503 [astro-ph.EP] (or arXiv:2006.12503v1 [astro-ph.EP] for this version)

    Submission history

    From: Amir Siraj

    [v1] Mon, 22 Jun 2020 18:00:00 UTC (4,287 KB)

    https://arxiv.org/abs/2006.12503

    Astrobiology, Astrochemistry

  • Thomas R Mazanec June 29, 2020, 15:07

    In Carl Sagan’s “Pale Blue Dot” he mentions (Chapter “Darkness”, page 294) that Project Meta had detected 11 brief signals that seemed to be in the Milky Way, but had never repeated.

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