All Astronautical Evolution posts in 2015:

Britain Takes the Wrong Approach to Manned Spaceflight (Dec.) (Comments)

“Drowning in Process” (Nov.)

Does Intergalactic SETI Make Any Sense? (Oct.)

SETI and Sanity (Oct.)

SpaceX, SpaceY, SpaceZ (Sept.)

A Letter to Britain’s New Space Minister (June)

Mars: 25 Years After Mars Direct – Discussion (May)

The Astronist Mars Strategy (May)

Mars: Still So Distant, 25 Years After Mars Direct (May)

The Mariner Anniversary Calendar for Mars (April)

Mars: An Awful or an Awesome Place? (April)

Should We Phone ET? (March)

More Pluto Controversy (Feb.)

The Pluto Controversy (Jan.)

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AE posts:

2022: What’s to do on Mars?…

2021: New space company Planetopolis…

2020: Cruising in Space…

2019: The Doomsday Fallacy, SpaceX successes…

2018: I, Starship, atheism versus religion, the Copernican principle…

2017: Mars, Supercivilisations, METI…

2016: Stragegic goal for manned spaceflight…

2015: The Pluto Controversy, Mars, SETI…

2014: Skylon, the Great Space Debate, exponential growth, the Fermi “paradox”…

2013: Manned spaceflight, sustainability, the Singularity, Voyager 1, philosophy, ET…

2012: Bulgakov vs. Clarke, starships, the Doomsday Argument…

2011: Manned spaceflight, evolution, worldships, battle for the future…

2010: Views on progress, the Great Sociology Dust-Up…

Chronological index

Subject index

General essays:

Index to essaysincluding:

Talk presented to students at the International Space University, May 2016

Basic concepts of Astronautical Evolution

Options for Growth and Sustainability

Mars on the Interstellar Roadmap (2015)

The Great Sociology Debate (2011)

Building Selenopolis (2008)


Issue 117, 1 October 2015 – 46th Apollo Anniversary Year

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SETI and Sanity

The alien as angel

What are the chances for Breakthrough Listen?

On 20 July 2015, Russian entrepreneur, venture capitalist and physicist Yuri Milner announced that he was putting $100 million over ten years into the search for extraterrestrial intelligence (SETI) in the form of two initiatives: Breakthrough Listen and Breakthrough Message.

For more details, I listened to Paul Carr’s “Wow! Signal Podcast” interview with Andrew Siemion of UC Berkeley, one of the astronomers involved.

According to Breakthrough Initiatives:

“In the last five years, we have discovered that planets in the habitable zone of stars are common. Based on the numbers discovered so far, there are estimated to be billions more in our galaxy alone. And there are hundreds of billions of galaxies in the visible Universe.
     Yet we are still in the dark about life. Are we really alone? Or are there others out there?
     It’s one of the biggest questions. And only science can answer it.”

With such a major injection of funding, SETI science will receive a tremendous boost. People the world over will be inspired to look up at the skies, and those elusive beacons announcing the presence of ET will surely soon be found. What’s not to like?

Doubts over SETI

Agreed: any project which spreads public awareness that humans are a very small part of an overwhelmingly vast universe is to be applauded. We need that perspective when addressing mundane problems on Earth, if those problems are not to overwhelm us.

The alien as devil

But what about the specific search for beacons or signals from alien civilisations which are aimed at attracting our attention? Is it in fact reasonable to expect any to exist?

Consider that any civilisation which develops technologies for interstellar signalling is also in possession of at least the theoretical foundations for interstellar travel. It must have mastered metal-working, electrical power, computers and therefore quantum physics, a substantial market economy that can support such non-productive activities, and a scientific culture. If society continues to grow, then these capabilities lead inevitably to spaceflight, and interplanetary travel leads by small stages to interstellar flight.

One of the most important theoretical advances in SETI was the publication in 1978 of the British Interplanetary Society’s Daedalus Report. This demonstrated that it is technically feasible to cross the vast interstellar distances between neighbouring stars, on the order of 5 to 10 light years, within a few decades to a few centuries, using nuclear physics which we – and any signalling species out there – already understand.

The same technologies which allow interstellar signalling also bind all the societies on one planet into a single global civilisation. This is vulnerable to natural or artificial disaster (asteroid impact, climate change, war, economic collapse, etc.). Therefore it is not reasonable to expect industrial civilisations to survive for long periods on their planet of origin alone.

A civilisation analogous to our own (which is what we are looking for in the SETI programme) will either collapse within at most, say, a million years, or it will spread into its local interplanetary space. The technologies for rapid interplanetary transport and sustained interplanetary living, notably nuclear fusion and life support systems independent of the home planet, lead inexorably to interstellar travel. The vast size of a planetary system in comparison with the surface of a single Earth-analogue planet guarantees that once a space-based civilisation comes into being, it cannot be killed off by a single disaster: a global war on Mars will not worry the inhabitants of space colonies in the Jupiter Trojans, a killer virus on Earth will have little effect on a civilisation among the satellites of Saturn.

This line of argument leads back to Michael Hart’s 1975 paper, which deduced that since aliens are not present in our own Solar System, no other technological civilisation in our Galaxy has yet arisen.

The alien as sex fantasy

Lost in time and space

Hart’s argument states a likelihood rather than a necessity: it might therefore be wrong in our specific case. It’s perfectly possible that the first two industrial societies to arise in the Galaxy – ourselves and an alien civilisation – might have evolved at roughly the same time, even though the probability of this is extremely low.

However, neither we nor they know this. They may have detected Earth from a distance of a few hundred to a few thousand light years, and decided to direct a signalling beacon at the Solar System in the hope of establishing contact with us.

Let’s assume that a coincidence has in fact occurred. Their evolution and our own are coordinated in time by chance. They started signalling us extremely recently. Let us suppose their beacon lit up when the Galaxy was already 99 per cent of its current age, making it a very close coincidence. So they started signalling us a mere 100 million years ago.

How long will their programme of beeping the Solar System continue? If they hear nothing after the first million years, will they have any appetite to continue for a second million years, or a third, or a hundredth? How long would such a programme (undertaken by creatures analogous to us, remember) last if managed by a terrestrial government or philanthropic organisation?

If they remain confined to their planet of origin, we must expect their civilisation to go into decline and lose its capability for interstellar signalling well within a million years. Alternatively, if it continues to grow, then we must expect it to master interstellar spaceflight and spread its scientific probes and its colonies throughout the Galaxy within several tens of millions of years (an estimate which I have discussed in more detail in a paper currently under peer review at a scientific journal).

The alien as machine

However one slices it, the time taken for human-analogue creatures to evolve on an Earth-analogue planet with an oxygenated atmosphere is in the hundreds of millions of years, but the time taken for them then to spread throughout the Galaxy should be about an order of magnitude less.

Furthermore, a beacon directed at the Solar System will only produce results if Homo sapiens evolves, and if it develops the culture of science, technology and industry. If these things do not happen in one or another system to which it is directed, then the beacon effort is completely wasted.

A physical spacecraft as an interstellar probe is of course vastly more expensive than a beacon. But to a civilisation growing into its interplanetary and interstellar environment, it should become affordable. The probe will produce results regardless of whether or not a human-analogue civilisation evolves. It will be able to report back on any biology that exists in the target system, from green pond scum up to handless and non-technological dolphin intelligences, giving a good overall picture of the place of biology in the Galaxy.

And even if the alien probe targets our own Solar System, it is likely in general to produce results much faster, within a few hundred to a few thousand years, depending on how far and how fast it has come, rather than having to wait periods of up to hundreds of millions of years for us to evolve and say hello, even granted a close coincidence between alien evolution and our own.

The alien as god

The “standard SETI assumptions”

The standard assumptions of SETI (after Brin) are:

“that the Others out there are at least benign, probably altruistic, not engaged in extensive colonization and interested in communicating with newcomer sapient species like us. Posit also that they are very long-lived and can take a patient attitude. Further, let’s suppose that such ancient ETCs have already used advanced instrumentalities to survey hundreds of thousands of solar systems in their galactic region, cataloguing those planets with oxygen atmospheres and other signs of life.”

In his wide-ranging paper, Brin does in fact go on to discuss the advantages of interstellar probes as opposed to radio messages, but does not draw the inference that radio beacons are therefore unlikely to be used.

The SETI project is therefore essentially a search for long-lived civilisations which have not reached the Solar System with either probes or colonisation ships. I would argue that this concept is self-contradictory. On the contrary, I assert:

Yes, there may be a beacon out there, and it may just take another round of SETI observations to pick it up and identify it as artificial. This could happen! But because of the vastness of the astronomical timescale it depends upon an unlikely chance coincidence, and is therefore not in itself worth a major search effort.

A better way to search

I don’t want to sound too negative. Radio astronomy is a major part of the process of scientific discovery and the enlightenment of our world-view. So let’s do more radio astronomy!

The alien as weird phenomenon

There are very likely new phenomena out there that can be detected by more careful search and analysis. We don’t yet know what they are. There could be clues as to the nature of the mysterious “dark matter” that astronomers have hypothesised as contributing to the gravitational dynamics of galaxies. There could be new types of stellar objects like the pulsars that were discovered in the 1960s. There could even be indications of the activities of one or more technological civilisations, up to and including the unlikely coincidence of a beacon signal intended to elicit a response from any radio astronomers on Earth.

I find it strange that, according to Andrew Siemion in the interview noted above, between 99 and 99.9 per cent of the raw data collected will be discarded after a single analysis. Yet in optical astronomy old photographic plates are not infrequently pulled out of the archives in a search for something whose significance was not realised at the time. This actually goes back to Galileo, who is now known to have made the first observation of Neptune, though he didn’t realise it himself.

The SETI programme is designed to look for just one specific thing – a signal beacon whose existence at this moment in time is highly improbable – and if it doesn’t find this thing very quickly it will trash the observations, maintaining only a relatively brief digest. This is surely bad scientific practice.

Furthermore, SETI can only detect an extraterrestrial civilisation if it happens to be transmitting to us at the present time (minus the distance in light years to the transmitter, obviously). It is a gamble on the propositions that extraterrestrial civilisations exist, that they are transmitting to us, and that they have not developed interstellar travel – a combination which I hope I have demonstrated is unlikely to occur.

If SETI fails to find that signal, then the question which excites everybody – “Are we really alone?” – is simply not answered either way. The radio search can only address the question as to whether we are receiving a signal at this moment, but the whole point of the signal is that it indicates intelligence at the other end, and the result “no signal” tells us neither that there is intelligence out in the stars, nor that there is no intelligence. An experiment which gambles upon a particular result is a badly designed experiment.

The alien as wise friend

SETI should therefore reorientate itself. Search the optical, infrared and radio spectra for new phenomena. Keep an open mind as to what they may be, and ensure that the raw data are available to researchers decades hence who may have found something unexpected and are asking whether it can be corroborated in the older data, which were not examined for that pattern at that time because it was then unknown.

But of course SETI will never do that now, because of its institutional inertia, and because of the glitz and glamour of invoking godlike aliens!

Yuri Milner is spending his own money, so who am I to complain? But if I had $100 million in spare change, I would not be putting it into SETI.


David Brin, “The Search for Extra-Terrestrial Intelligence (SETI) and Whether to Send “Messages” (METI): A Case for Conversation, Patience and Due Diligence”, JBIS, vol.67 no.1 (January 2014), p.8-16, section 2.1.

Please send in comments by e-mail.
Interesting and relevant comments will be added to this page.

Mike Garrett (Netherlands Institute for Radio Astronomy): “An experiment which gambles upon a particular result is a badly designed experiment.” – I don’t understand what that statement means.

There is a chance that other civilisations use radio to communicate. Some of these emissions might be “leakage”, some might be deliberate beacons. Either way, we should look to see if they are there. I do agree that if we don’t find them the conclusions we can draw are limited.

Cheers, Mike.

Stephen Ashworth (post author): Mike, thanks for your feedback. I am sorry if I didn’t express myself clearly enough in my blog post.

Consider the famous Michelson–Morley experiment of 1887. As you will recall, the objective was to measure the aether wind supposedly caused by the Earth’s motion through space. The fact that no such wind was measured did not mean the experiment was a failure. Rather it provided an essential observational foundation for what became the special theory of relativity. Thus the failure to find what was expected was itself a highly significant observation.


Now consider SETI. The objective is to find alien radio transmissions, in order to answer the question, “Are we alone in the universe?”, with all the implications that has for our place in the universe and our future. If artificial signals are received and can be confirmed as not of human origin, the existence of an extraterrestrial civilisation is demonstrated, and a major advance in our knowledge is achieved. But the experience so far is that no clear signs of extraterrestrial technological activity have yet been found.

Is this failure to find what was expected itself a significant fact? In the case of SETI, it is not, because it does not contribute towards answering our original question. It may be that no intelligent aliens exist, and none have ever existed, within the volume of search space. Or it may be that they once existed, maybe even signalled us, but have now died out. Or it may be that they do exist at the present time but have not industrialised. Or they may have industrialised but are just not signalling us at the present moment (minus light travel time). (This, I have argued, should be expected to be true for most of the lifetime of industrialised societies which are unaware that radio astronomers exist on Earth.) Or they may have industrialised and are signalling us using some technology (tachyons? neutrinos? gravitons? psychic waves?) which we have not yet invented.

Do you see my point? The failure to find what was expected is not significant in the SETI case, because it does not narrow down the range of possibilities very much. It does not tell us whether or not alien intelligence (or indeed alien life of any kind) exists at all, or whether or not, if it exists, it has ever signalled us in the multi-billion-year past or will ever do so in the future, or whether or not it is in possession of signalling technology beyond our current state of the art. Thus one possible outcome of the experiment is to provide no result at all, beyond the fact that there was no radio-capable civilisation actively signalling us from a particular direction at a particular moment in time. But that fact could have resulted from any one of a wide range of possible reasons, and therefore does not lead to any definite inferences about the fundamental questions we are addressing. In such a case the experiment has thus failed to return a worthwhile result.

This is why I described SETI as a gamble on a particular result.

I hope this now makes better sense.

Best wishes, Stephen Ashworth

Malcolm Smith: Radio SETI is not science. Why? It is not falsifiable. No signal detected? We need more powerful, more sensitive equipment. Still radio silence? We need more powerful, more sensitive equipment. Ad infinitum…

Stephen Ashworth (post author): I don't think I would go quite so far as to say that radio SETI is not science at all. But it certainly does veer in the direction of a stubbornly uncritical and unfounded belief in alien intelligence. Frank Drake has been quoted as saying: “I know that, at this very moment, there are radio signals from other civilizations passing through this room which we could detect and study if we but pointed our antennas in the right direction and tuned to the right frequency.” Not “I hypothesize”, not “There is a very small chance”, but “I know” – clearly in fact he knows nothing of the sort.

Drake’s quote is shown in the second image on a post of mine from last year; it originally came from the TeamSETI page, but they’ve removed the image now, presumably because of this kind of criticism.

SETI is a gamble that the subject of its investigations actually exists, and is actually transmitting identifiable signals in our direction. Its proponents think it’s a safe gamble; I think it’s an extremely long shot (a probability of about a million to one against, even if all conditions are in favour of our receiving a message). If they are right then SETI will certainly become legitimate science. But if they don’t find anything, they are under no obligation to amend their belief, because the lack of any signal today says nothing about the possibility of receiving a signal tomorrow. In this way, as you have pointed out, their hypothesis takes on the nature of an unfalsifiable belief.

Best wishes, Stephen

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