A New Scale for SETI interest

I spent way too much time today trying my hand at another version of the Rio scale, one that does not assume that you understand the signal you see or know where it comes from, exactly.  I think it’s a little more useful down at the bottom (unlikely to be aliens signals) and a bit compressed at the top (very little discrimination among truly interesting signals). I also don’t think I have the weighting quite right yet.

Anyway, here it is.  It applies only to astrophysical anomalies for which the ETI hypothesis has some explanatory power.

It’s a 10-point scale (anything scoring below 1 is uninteresting). I conceived it as a log scale, so it roughly tracks as the product of three probabilities calculated as the sum of three numbers: A+B+C.

The idea is that you find where a given “detection” is in each category (maybe interpolating a bit). I give characteristic examples in brackets for each category, citing some famous (non-) examples of signals (n.b. “first pulsars” means the state of the field when the first pulsars were discovered, and there was not yet any theoretical explanation for their existence).

Note that these three categories are not orthogonal: the routine-ness of detection can influence likelihood of instrumental effects and astrophysical nature of anomaly.

A: Is the detection confirmed?

0: Unclear if detection is real [Poor metadata, possible transcription error, corrupted data]

1: One off: one event, one site [Wow! signal]

2: Verified: simultaneous observations at multiple sites OR multiple events at a single site [FRBs when they were still only seen at Parkes; something that survives strict coincidence detection]

3: Repeated: (multi-site AND multiple events) OR absolutely-no-doubt multiple events at single site [Tabby’s Star, especially with dimming]

4: Routine: Phenomenon regularly detected at different sites by independent groups [long-delayed echoes; FRBs today]

B: Could it be instrumental?

-7. Looks like a known instrumental effect

0. Does not look like a known instrumental effect, but too little metadata or understanding of data to assess signal reality; instrument builders / users not consulted [RATAN-600, SDSS lasers]

1. Data not likely to be instrumental, but instrumental or non-astrophysical cause cannot be ruled out [perytons, cosmic rays that look like lasers, early days of FRBs]

2. Data vetted by instrument builders/users; probably a real signal [Wow! signal]

3. Data thoroughly vetted with control; unambiguously astrophysical [FRBs today, Tabby’s Star’s dips]

C: Could the anomaly detection be natural or terrestrial?

-7: Obvious natural explanations exist [pulsars today, quasars today, RFI]

-4: Rare or somewhat ad-hoc natural explanations exist [J1407 rings, evaporating planets, GHAT III galaxies, FRBs today]

-1: Lack of study makes it unclear if any natural explanations could exist [Przybylski’s Star,SDSS lasers]

0. Only the rarest or most unlikely natural explanations make sense [Tabby’s Star]

1. No known natural cause, but new natural phenomena could be at play [first pulsars, first FRBs]

2. Not obviously intelligent communication or manufacture, but no natural explanations make sense [successful artifact SETI: complete Dyson sphere in the field, short-lived actinides in a spectrum]

3. ETI hypothesis is only plausible explanation [monolith on the Moon; communication: narrow band radio signals, pulsed optical, prime numbers, etc.]

Here’s how I interpret the outcome of a calculation:

Below 1: No interest warranted
1–5: SETI interest potentially warranted; no press interest warranted
6–8: SETI interest definitely warranted; technical popular press interest warranted; fun, off-beat news item for general press, with appropriate caveats. If not aliens, still very interesting.
9: Significant mainstream press interest warranted. Could be aliens
10: Aliens

OK, so how do our favorite candidates compare?

SDSS lasers: 2 + 0 – 1 = 1
GHAT III galaxies: 4 + 3 – 4 = 3
RATAN-600: 1 + 0 + 3 = 4
Przybylski’s Star: 4 + 3 – 1 = 6
FRBs before they were understood or seen at other telescopes: 2 + 3 + 1 = 6
Wow! signal: 1 + 2 + 3 = 6
Tabby’s Star: 3 + 4 + 0 = 7
First quasars (before understanding of their nature): 4 + 3 + 1 = 8
First Pulsars (before understanding of their nature): 4 + 3 + 1 = 8

This roughly (but imperfectly) tracks my impression of the SETI consensus on these “detections”: some signals are really interesting and only explicable as new phenomena (FRB’s, pulsars, quasars, maaayyybe Tabby’s Star, and Wow! signal, if it’s real) and they rightly rank high.

Some anomalies, like Przybylski’s Star are less compelling, but still intriguing and maybe deserve more attention than they get.  Then there’s a gap to things that will almost certainly not pan out on closer inspection.

Anyway, I’m not entirely sure it works well enough to be useful, but that’s my day’s-work contribution to the conversation about improving the Rio scale. Let me know what you think.

9 thoughts on “A New Scale for SETI interest

  1. jtw13 Post author


    Indeed, fixed.


    The purpose of the Rio scale is not to be comprehensive of anything. Like the Richter or Torino scales, it selves as a rough and simple guide to give the public a qualitative appreciation for a nuanced topic. Ideally, it will be something almost trivial to calculate from objective data involving a small number of dimensions and produce an easy to interpret score. Its two goals—to describe both level of media interest warranted in and the importance of the sorts of claims we anticipate encountering—are in some tension, but folks are reworking it now to better do what it is designed to do.

    Your work is impressively comprehensive, and anticipates a much broader range of potential discoveries and claims than the Rio scale, but I think serves a different purpose.

  2. Pete M

    I really like this rule of thumb because it is simple. There are cases, mentioned above, that will get through, but for creating a rule that someone as uneducated and lacking in critical thinking skills as some journalists have appeared to be, this is good.

    People prefer a single scale value. However, this is a two dimensional issue. A similar example is communications in which a receiver will report volume and clarity on a 5×5 scale. Scientific confidence depends upon other observers and other methods to confirm a phenomenon. It’s hard when the only way to make the observation requires heavy duty, rare or singular, expensive equipment, but that’s not the a fault of science. So think of it as clarity by confidence.

    However, this rating can probably stand for most main stream media purposes.

  3. Derek Fox

    Hmm, not sure we want to leave it there. The second pulsar excluded ETI for pulsars. The second FRB, from a position different than the first FRB (i.e. not a repeater), excluded ETI for FRBs (my opinion, since we still don’t have a good natural explanation here).

    If you wish, you may think in terms of Occam’s Razor: A single pulsar, FRB, or WOW! signal can be produced by a single alien civilization inhabiting a single habitable planet / system within our galaxy. Multiple causally-disconnected signals require a galaxy-spanning civilization with coordinated signaling protocols, enduring over the eons, which seems… substantially less likely.


  4. jtw13 Post author

    That’s a good point! As things currently stand in my scale, that would have to sneak into the third category, as part of a subjective assessment of how likely the signal is to be natural. As you say, if you see a second one somewhere else, that may convince you that there *must* be a natural explanation, and move things down the scale.

    I’m not sure that this principle is sufficiently well defined so as to be its own category: if we get a second “Wow! signal” from a different part of the sky at a different frequency at a different strength, does that change our assessment of the Wow! signal’s non-naturalness? Or could it be another node on the Galactic network? As you say, in the case of pulsars there was a good reason that the second one made things more likely to be natural, so perhaps it’s best kept as a component in the third category. One virtue of these scales is that they are simple, at the expense of being perhaps too reductionist for precise rankings.

  5. Derek Fox

    Your criteria ignore one important factor that was used by Jocelyn Bell to exclude ETI as explaining pulsars, and is high on Eric Korpela’s list of caveats as well. Namely: Is the source / phenomenology sufficiently unique, or rather multiplied in non-causal fashion within or beyond the galaxy / cosmos?

    Dame Bell Burnell has stated that after the *second* discovery she & Hewish felt confident pulsars would yield to a natural explanation (at that point, either rotating neutron stars or pulsating white dwarfs). That was because the idea that you could have two alien civilizations broadcasting with similar technology, at similar frequencies, from causally disconnected regions of the galaxy strained credulity past the breaking point.

    Similarly, and as argued by Korpela, the fact that the 234 “SDSS laser stars” have the self-same spectroscopic periodicity is the death knell for this claim – in this case, pointing to systematic effects arising in the analysis or calibration, rather than a natural phenomenon. Basically, they have too many candidates!

    It echoes a “rule of thumb” I have used for years with good results in searches for gamma-ray burst afterglows (and other interesting/rare source counterparts). This rule of thumb asks “How many candidates do you have?” and only allows you to get excited if you have one. Zero is obviously no good. But two or more is also not good! In the case of GRBs the reason is obvious, we know there will only be one (modulo strong lensing and some really fantastic data). However, I propose adoption of this rule of thumb within the “Rio scale” as well, as (I submit) it is far more likely that *when* we first identify the signatures of alien civilization it will be a “one of a kind” event distinguished robustly, in some way, from all known natural phenomena and instrumental artifacts, and interesting primarily for that reason.


  6. jtw13 Post author

    “verified” and “repeated” and “routine” are just labels for different levels of repeatability. The ranking is sort of:
    – Wow! Signal
    – FRBs (rare, only 2 sites have seen them)
    – Supernovae (you can’t study them whenever you want, but they’re common)
    – pulsars, quasars (always there)
    as a combination of their duty cycle and the number of sites that observe them.

    As I said, the 3 categories are not orthogonal: multisite measurements really help rule out instrumentals, as you say.

    As for naturalness, there’s a big difference between “I don’t think there’s a natural explanation” and “the entire community has thought about this and still has no good natural ideas”. There’s also a big difference between detecting an unnaturally shaped object orbiting another star and holding it in your hand — both might be obviously artificial, but the space left for natural explanations is much smaller in the latter case.

  7. Napier

    Under Is the detection confirmed:
    I don’t think multiple events at a single site should be considered as Verified. Only when observed from multiple sites should it be considered Verified. There was that case with a microwave oven causing a false detection at some observatory, for instance. There’s always the possibility of instrumentation, or some freak repeatable occurance that can be behind multiple detections.
    I don’t think Routine adds much after Repeated. Once it’s repeated and confirmed at different sites, that’s as good as it gets IMO.

    Under Could it be instrumental:
    There’s something on instrumentation that I can’t quite pin down. If it’s detected at various sites, then it make the instrumentation issue moot IMO. So autmatically a 3 if detected at various sites?

    Under Could the anamoly detection be natural…:
    What’s the difference between -1: Lack of study makes it unclear if any natural explanations could exist and 1: No known natural cause, but new natural phenomena could be at play?
    Also 2 seems similar to 1. A Dyson Sphere would obviously rule out natural explanations, right?

  8. Clément Vidal

    Dear Jason,

    Glad to see your variation on the Rio Scale. You might be interested in my recent paper about this topic, that includes a criticism of the Rio Scale (section 4.1):

    Vidal, C. 2015. “A Multidimensional Impact Model for the Discovery of Extraterrestrial Life.” In The Impact of Discovering Life Beyond Earth, edited by Steven J. Dick, 55–75. Cambridge: Cambridge University Press. http://homepages.vub.ac.be/~clvidal/writings/Vidal_2015-Multidimensional-Impact-ETL.pdf.

    Keep up the good work!

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