Steve Watson

Western Love

May 23, 2026 – 1:33 pm

In Plato’s Symposium, Aristophanes presents a theory of love fitting a comic poet. Ignoring the details included to explain/excuse homosexuality, the story is roughly that humans were originally spherical beings with no distinction of sexes, then the gods divided us, forming a male and a female out of each divided person, and ever since we have each sought to reunite with our estranged other half. The impulse to love in such a system is an impulse to completeness.  

This idea that love is a striving for completion has had a significant afterlife, quite independent of its comic origin. In fact, in a seminar I recently attended the claim was made, with some support, that this idea was the ‘mainstream’ view. I  had to disagree. I think that the mainstream idea of love (by which, I think, is really meant the mainstream of learned opinion) actually follows from the theory that Socrates, responding to Aristophanes and others in that same dialogue, said that he had learned from the philosopher Diotima. I also think that none of those philosophical ideas of love have had much effect on the way that people who are not actually philosophizing think about love.

According to Diotima (210a–212b,) since we desire only what we do not have, as mortals we must desire immortality. This we cannot achieve; indeed, even if we were to live forever, it would not be us living forever, for we, as we are now, are ever in a state of change. Therefore, seeking the closest that we can get, we desire to reproduce – or to have our names live in glory, but reproducing is the more common and achievable strategy – and thus we are drawn to those with whom we may get our progeny[1]. Moreover, of those who are our possible mates, we are drawn to those who are good (kale) or beautiful (kale.) (The Greeks had some difficulty distinguishing between the good and the beautiful.)

Yet this attraction is just the first step on what Ficino called the scala amoris, the ‘ladder of love.’ By proper reflection on things and by the getting of wisdom, we rise up by gradual steps from merely loving one particular person for their physical beauty to loving in contemplation the Form of Beauty-in-itself. It is that final step that is ultimately valuable and to be sought, and the other steps are valuable only in so far as they lead to the final step.

Of course, there are problems here. To begin with, to make every step other than the last merely instrumental degrades the love felt at all those steps and makes them worthless in themselves. This is hardly a positive view of the kinds of love that ordinary persons typically feel – it’s rather contemptuous, in fact. Moreover, if those steps are only valuable as steps, then is the lover required to put aside the loves that led to the step that he is currently on? Once he loves the beauty in all bodies, for example, is he required to stop especially loving the particular beautiful body he began with? It all seems very mercenary. Moreover, the character of the emotion involved in loving those different objects is never made quite clear. At the first step the emotion is motivational and inspires a movement towards possessing the object of desire; but as the object becomes more abstract, the condition of satisfaction moves toward mere contemplation. It is an open question whether emotions with such dissimilar conditions of satisfaction can really be called varieties of the same emotion.

In any case, the theory was rejected – or perhaps we should say entirely ignored – by the poets of Greece and Rome, whose opinions are doubtless much closer to the non-philosophical opinions then current.

Didactic poets like Lucretius or Oppian glorified love as an all-powerful and omnipresent force, but conceived of this force as a natural, not metaphysical principle, pervading yet not transcending the material universe. In lyrics , on the other hand, love was depicted as the strongest of human emotions, blissful and torturing, life-giving and deadly; but neither Theocritus nor Tibullus, neither Catullus nor Ovid would have thought of elevating the object of this emotion to a ‘supercelestial realm.’ [2]

On the other hand, the theory had a great influence on the Neoplatonists[3] (naturally enough,) the Islamic mystics, and the Christian Fathers. We can see its reflection, for example, in the important Augustinian doctrine of the ordo amoris. Augustine accepts the Platonic and Neoplatonic idea that love is a force in the soul that directs us towards the ultimate attractive thing, which, for him of course, is God (standing in for Plato’s Good-in-itself). He alone is the proper focus of our love, and things and people apart from God should be loved just to the degree that they are in conformity with the will of God. Thus, there is a natural ordering of love by its objects and the love that we feel naturally alters with its change of focus, just as with the Platonic case. For Augustine, however, the movement of love’s focus is not an ascent from a particular beauty to the Form of Good but a descent from God to the things of the world – which are, of course, unworthy of love for their own sake.  

The Augustinian view of the ordo amoris (combined with the related idea of the Scale of Being) became a standard view amongst Christian theorists. We note here, however, that whereas the origin of the love impulse in the Platonic scala is fully explained by the natural desire for concupiscence and immortality at the initial step, the origin of the love impulse in the Augustinian ordo directed towards a distant abstract being requires a more involved and theoretically bound explanation. (It is ultimately in obedience to a command to ‘Love the Lord’ – and the plausibility of that as a motivation to love is certainly open to doubt.) It also seems to neglect the aspect of love that is most striking in human affairs: the fact that love/desire is extremely motivating. Indeed, the love between the sexes that tends towards reproduction and that is of so much concern to the poets (and that, in fact, is the very form of love that motivates our concern with the concept) is in constant danger of falling away from the praiseworthy state of caritas – rightly ordered love – and becoming blameworthy cupiditas/concupiscia – disorderly love.[4]

There are possible solutions to this problem, of course, and the most powerful and influential was that provided by Aquinas at the other end of the Mediaeval period. He incorporated the idea of the ordo amoris into a larger view of the nature of Natural Law and God’s intentions. (God had intentions when He made the world, and as we are rational in His image, we can discover them if He wills it.) Thus, he proposes that God, who, being good, desires our happiness, has given us natural inclinations towards fundamental goods that will lead to our happiness, and that among these is a natural inclination towards reproduction. That natural inclination we would experience as love/desire for the opposite sex, and by observation of the rationally derived precepts of action we can be assured that the pursuit of these inclinations will tend to that good end and will not be corrupted and thwart our happiness.

Love itself, according to Aquinas was

… a principle of volitional movement and rest, thus distinguishing it from desire or delight, which he considers its effects. When the object of love is not possessed, this causes the will’s locomotion towards the object (or towards union with the object) with the intent of obtaining the object (or being united with it). This he calls desire. The only reason for the will’s loving and therefore desiring some object is if the human intellect perceives it as “good.” Aquinas’s definition of “the good” is correlative with desire: “For since the good is what all seek, the notion of good is that which calms the desire. … good means that which simply pleases the appetite.”[5] When the object of love is possessed, the will (which Aquinas defines as an appetite) is at rest and reposes in the good, and this he calls joy or delight.[6]

Outside the monasteries, however, quite a different conception of love was being developed, mostly amongst the poets and often in direct rejection of the Church-approved doctrines that tended to make passionate love even within marriage sinful. The idea of ‘courtly love’[7] took its Classical inspiration not from the philosophers but from Ovid’s Ars Amatoria, which they treated as a serious text and not as the mocking satire intended by the poet. From the jests of that poet they drew the supposed rules of love-making and courtship with which we are all tolerably familiar, but the ideology of their love was very different from his.[8] Although they accepted, as he did, that love was essentially rooted in physical desire (even where consummation was impossible,) they insisted that love, properly conducted, could have an ennobling effect on the lover. Thus, Capellanus says (1.3):

… [I]t is the effect of love that a true lover cannot be degraded with any avarice. Love causes a rough and uncouth man to be distinguished for his handsomeness; it can endow a man even of the humblest birth with nobility of character; it blesses the proud with humility; and the man in love becomes accustomed to performing many services gracefully for everyone. O what a wonderful thing is love, which makes a man shine with so many virtues and teaches everyone, no matter who he is, so many good traits of character!

The idea of ‘courtly love’ in the form defended and celebrated in the late Middle Ages now appears ludicrous, but from it the modern view on love seems to have taken ideas of romantic attachment, devotion to a single object, unrequited love, heroic gestures of affection, the elevated status of women, and much else – including, especially, the idea that love itself is an improving thing rather than just a form of passionate madness.

Whether this forms the mainstream of our view of love today or not – and I think it probably contains a great part of the common culture’s mainstream – it is certainly more significant than either version of the ordered view of love proposed by the Platonists or the Augustinians.

[1] This story is rather spoiled by the need to explain homosexual (in fact, pederastic homosexual) desire as being that which results not in the birth of a child as a bridge to immortality but, equivalently, in the arising of a conception of virtue as another form of the good/beautiful.

[2] E. Panofsky (1939) Studies in Iconology, NY: Harper, p. 99

[3] See for example Plotinus Enneads I.6, III.5 (‘On Love’)

[4] De Civitate Dei XIV.16 (‘Lust’) illustrates the danger and Augustine’s attitude to even marital union

[5] ST I-II.27.1.ad.3.

[6] B R Cochran ‘Love and Charity in Aquinas’

[7] G Paris (1883). “Études sur les romans de la Table Ronde: Lancelot du Lac, II: Le conte de la charrette” Romania 12 (48): 459–534

[8] As this was in reaction to the ideology of the ‘intellectual’ class, explicit defences or descriptions are few. The work most often cited in this regard is Andreas Capellanus, De arte honeste amandi (The Art of Courtly Love)  

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Aristotle on Comedy

April 11, 2026 – 3:59 pm

We do not have Aristotle’s work on Comedy promised to us in the Poetics, but we might be able to get a rough idea of what he would have said from clues in his surviving writings and commentaries from later ancient authors.

The principal evidence directly from Aristotle is the passage from Poetics  

As for Comedy, it is (as has been observed) an imitation of men worse than the average; worse, however, not as regards any and every sort of fault, but only as regards one particular kind, the Ridiculous, which is a species of the Ugly. The Ridiculous may be defined as a mistake or deformity not productive of pain or harm to others; the mask, for instance, that excites laughter, is something ugly and distorted without causing pain. (1449a31-36)

And concerning the contents of Comedy he tells us that

[O]f Athenian poets, Crates was the first to drop the Comedy of invective and frame stories of a general and non-personal nature, in other words, Fables or Plots. (1449b7-9)

There are also some references to humour in his Rhetoric, which are likely to be relevant to Comedy. At 1389b10 he says that “[W]it is well-bred insolence,” which suggests that he sees humour as depending upon an assertion of superiority in the amused one over the target of the witticism, while at 1412a25-30[1] he observes that a suddenly realised incongruity between expectations and events can also cause amusement. He gives as an example of this a line from an unknown Comedy:

And as he walked, beneath his feet were—chilblains 

Aristotle’s treatment of Comedy would likely have closely followed the model of his treatment of Tragedy; or, at least, that’s an assumption that we could make in order to increase the information that we have of his missing book. In his treatment of Tragedy, however, it can sometimes be unclear whether his intention is positive or normative, whether it is his intention to describe what is called Tragedy or to prescribe the things that make a drama a Tragedy. The confusion arises because Aristotle is doing both. He is acting here as a scientist and moving from description to prescription: he takes as given a certain class of dramas that are called Tragedies and inspects them for common elements and determines whether there is any overarching principle by which the class might be defined; then, having determined the principle involved, he adopts that principle as the definitive characteristic of the class of dramas. The same would doubtless be true for his treatment of Comedy.

In the case of Tragedy, the principle that he lands upon yields a partly functional definition of that genre. It is a given that all Tragedies are dramas and dramas are what they are because of a certain form that they have as representations (by mimesis) of human actions, but Tragedies are distinguished amongst dramas by the fact that in a Tragedy the drama results/should result in what he calls a catharsis of the particular emotions of pity and fear. The notion of catharsis is drawn from ancient Greek medicine where it refers to a purification of the humours (imagined as internal fluids that regulated the health and had to be kept in balance.) As a metaphor here it suggests that by ‘expressing’ the emotions aroused in the spectator there is a purification (of the psyche?) which is of some use to him.

In the Poetics Aristotle explicitly links the two emotions as referring to contemplation of a certain bad situation as affecting oneself (fear) or affecting an undeserving other (pity.)

The one emotion concerns an undeserved falling into bad fortune, and the other emotion concerns a likeness. Pity concerns the undeservedness and fear the likeness (1453a4-6).

[Many, many questions are raised by this theory. We might ask, for example, why this ‘purification’ should be of any use to anyone? Do these emotions, if left unexpressed, somehow accumulate and cause some sort of psychic damage? What is the actual proposed mechanism behind such a view? Does Aristotle think that there is a store of these emotions building up in the psyche somehow analogous to the fluidic humours in the same way that Freud’s hydraulic theory of the mind would have had it? Hardly. Aristotle had no such theory of mental states/traits/passions/etc. Similarly, we might reasonably ask why those emotions of pity and fear are first created in the spectators by the drama if they are harmful and simply need to be expressed and eliminated?]

By analogy, we could define Comedy as a drama that results in a catharsis of the particular emotions aroused by the dramatic actions, and the question then would be to determine which emotions are to be expressed. I think it’s pretty clear that when Aristotle talks about the Ridiculous as a species of the Ugly and the result of a mistake or a deformity, that he’s assuming that the emotion involved is the emotion that one gets from revelling in another’s inferiority. It is a species of contempt. By analogy, again, we could link the emotion of contempt that is felt in contemplating a bad situation (but not a painful or dangerous one) affecting an undeserving other with the emotion that we would feel contemplating the same situation affecting ourselves. The emotion we would feel in a situation in which we realise that others would regard us with contempt is shame. The comedic catharsis, therefore, would be a purgation of the emotions of contempt and shame.

Note that a functional definition of Tragedy does not justify the unities that Aristotle says are characteristic of the genre. Those unities are observed regularities for which Aristotle finds some justification in a theory of Art as a whole as being a form of mimesis/representation. Since, however, he explicitly acknowledges that Epic Poetry, at least, does not observe any such unities, we need to understand that the unities are not necessary elements of all drama – only preferred in some cases.

[1] Note that every reference I found to this gives it as 3.2, which, I suppose is initially from misreading a sighted reference to 3.11 as 3.II. Everyone who followed the initial writer simply copied the reference with the error. Does no-one check their references? See the final paragraph here too.

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Reconsidering the Options for Bracewell Probes

April 9, 2026 – 7:00 pm

In 1960, Ronald Bracewell proposed[1] that technologically advanced extraterrestrial civilisations might send automated probes to other star systems capable of detecting and communicating with any appropriately advanced civilizations that they might exist. Such probes are called Bracewell probes. Bracewell included the condition that the probes would require at least a degree of intelligence, and it is now common to assume that they will in fact contain an advanced AI of high intelligence. Similarly, though not part of the original hypothesis, it is now also commonly assumed that they would be capable of self-repair or self-replication (Von Neumann machines.) (The need for self-reparability and for at least moderate intelligence in interstellar probes of any kind was argued as far back as 1972.[2] The technological sophistication expected in such probes has only increased since then.)

Several strategies are commonly proposed for such machines.

1.    In-system Messenger

The general form of Bracewell’s original proposal was for a probe that upon arrival in a star system would put itself into orbit about the star and search for signs of intelligent life in the star system. If any were detected it would attempt to make itself known. Should contact be made it would then enter into communication. It would carry with it a database of information that the probe’s builder’s desired to be made known to any intelligent inhabitants of the star system.

2.     Fly-by Messenger

Bracewell later accepted that a probe that did not enter orbit about the star but merely passed through the system at a reasonable pace would be able to achieve almost everything that an In-system messenger probe could.

3.     Sentinel[3]

Bracewell further proposed the idea of a sentinel probe that arrives in a system and establishes itself in some location from which it can discreetly monitor the system for the development of intelligent life or for the development of technological competence in existing intelligent life. The probe could then choose to initiate contact or not according to the designs of its builder, but it would certainly communicate its observations and the occurrence of some threshold event (such as radio communication) to its builders – or to whoever might have succeeded them.

4.     Von Neumann Sentinel

As mentioned, for various obvious reasons, it is now commonly supposed that Sentinel probes are likely to be Von Neumann machines: that upon arrival in a star system with adequate material and energy resources they would be capable of replicating themselves and sending those new machines on to further star systems, while the original remains in the system as a sentinel.

Assessing Possible Probe Locations

I think we can accept that we have not yet observed any messenger probes – notwithstanding claims concerning the interstellar object ‘Oumuamua that Avi Loeb hypothesized might be a Fly-by probe[4], or the Long Delayed Echoes[5] of radio signals that have been observed since 1927 and that Bracewell himself thought were the sort of thing that an In-system Messenger probe might create to attract attention to itself. This is in line with the plausible idea that, with the fate of humanity at stake, such indiscriminate METI would be quite inadvisable. If we accept the possibility of sentinel probes as they have been described, on the other hand, it is natural to wonder whether they might be already present in our own Solar System, and where they might be if they were. There are several criteria that can guide the search.

1. Assuming that the probes will be primarily interested in Earth, which is of obvious biological interest, and which now hosts an intelligent space-faring life-form, the location should allow close observational access to Earth.
2. On the other hand, since we would expect the probes and their mission profiles to be designed so that contact with intelligent species is at the discretion of the probe itself (to the greatest degree possible,) the location should allow the probe to remain undetected as it operates.
   • In any case, the fact that we have not observed such a probe is evidence enough that if it does exist it does not want to be discovered just yet.
   • Note that no location or strategy is going to be undetectable for all levels of technology. Eventually, we will be able to detect any probe if it remains active in the Solar System.
   • Note further in this context that there is probably a minimum size for a probe that wishes to observe from a distance, transmit its findings home, and survive the space environment. R Freitas[6] has given a rough estimate of the size we can expect as about 1-10m across (though this is based on assumptions concerning the survivability of meteoroid impacts and the likely observation distance and resolution that may not be universally relevant or reliable. It also assumes that the interstellar drive system is either of insignificant size or has separated from the active probe – surely, the latter.)
3. A probe intended for long-duration observation will require a location that is stable or predictable in character or whose dynamics are easily managed.
4. A very long duration probe will require access to energy resources – presumably solar, since it could hardly count on finding other energy sources at destination.
5. A self-repairing or self-replicating probe – as a long duration probe ought to be – will require access to material resources.

Bearing these criteria in mind we can assess the options[7]

1. Solar Orbit
   1. The ability to closely observe Earth would be dependent upon the particular orbit: but unless it were actually co-orbital with Earth (see that option below,) the opportunities would be very intermittent.
   2. Unless embedded in a natural object (see the Asteroid options) it would be difficult to remain undetected by reasonably competent observers on Earth.
   3. The orbits could be very stable
   4. Solar power is easily available – of course, depending on the distance from the Sun.
   5. Unless associated with an asteroid (again, see the Asteroid options) there would be no material resources to exploit.
2. Earth
   1. An observation site on Earth’s surface limits the range of coverage so it’s unlikely to be selected for that reason anyway.
   2. Moreover, it would be too easily discoverable by inhabitants of Earth.
   3. The environment of the Earth is extremely active, geologically and otherwise, so any very old probes would probably not have survived.
   4. Energy is easily available.
   5. Material resources are plentiful.
3. Earth Orbit
   1. Has excellent close observational potential
   2. But any body in orbit is going to be highly observable to even a modestly technically competent observer on Earth.
   3. Low orbits are unstable because of atmospheric drag.
   4. Solar energy is easily available, but
   5. Material resources in Earth orbit are lacking.
4. Earth Co-orbit[8]
   1. Objects in co-orbits intermittently approach Earth to respectable distances for close observation,
   2. and since we’ve really only just noticed them, their detection is not that easy
   3. The orbits may be stable (though it’s still an open question how stable.)
   4. There is adequate solar power available, but
   5. it is not clear that co-orbits have sufficient material resources to be useful to self-repairing or self-replicating devices.
5. Lagrange Point (Earth-Moon or Earth-Sun)
   1. The Earth Moon L₄ and L₅ points are within easy range of Earth for observation, but close observation of Earth would be difficult from the Earth-Sun points.
   2. Lagrange points are inherently interesting and would be expected to draw the attention of any intelligent observers on Earth. It would be hard for any sizeable object to remain undetected there unless hidden within a natural body. There are no such bodies in the Earth Moon L₄ and L₅ points though there are many in the Earth-Sun points.
   3. The L₄ and L₅ points are stable but orbits within a ‘Lagrange Point’ require constant adjustment and thus would be likely to invite detection.
   4. There is adequate solar energy available in both sets of Lagrange points mentioned above
   5. The Earth-Moon points are empty, as noted, and It is not clear that even the Earth-Sun points have sufficient material resources to be useful to self-repairing or self-replicating devices.
6. Planetary Moons
   1. Moons at too great a distance from Earth could not make close observations.
   2. Moons – especially the Moon of Earth – would be obvious targets for intelligent observers on Earth, and an object on one would be detectable unless buried; but if it were buried it is unlikely that it could observe.
   3. Moons with too active environments would be unsafe, though many moons are quite inert.
   4. Moons at too great a distance from Earth would also suffer from a lack of solar radiation for power.
   5. Moons lacking the appropriate materials (like ice moons) would be useless for Von Neumann machines
7. Near-Earth Asteroids
   1. These spend a lot of time at a great distance from Earth so that the opportunities for close observation from them would only be intermittent.
   2. It would, however, be quite difficult to detect a probe if it were located on one.
   3. Their orbits are adequately stable, and they can be selected to have stable physical environments – avoiding out-gassers or sites with moving rubble.
   4. NEA are close enough to the Sun to make use of its light for power
   5. and they are of a wide enough variety that one with appropriate material resources would certainly be available.
8. Outer Asteroids
   1. Close observation of the Earth is difficult at all times.
   2. Discovery would be near impossible if the probe’s own power emissions could be disguised or hidden.
   3. Their conditions of stability would be as with the NEA.
   4. Solar power is difficult to source at these distances,
   5. though material resources are plentiful.
9. Outer Solar System Small Body Zones
   1. Close observation of Earth would be very difficult.
   2. Discovery would be near impossible if the probe’s own power emissions could be disguised or hidden.
   3. Their conditions of stability would be as with the NEA.
   4. Energy from the Sun would be difficult to access,
   5. but material resources are plentiful

Revising the Search Strategy

Such are the usual assessments of the options, but it should be noted that these assessments assume that the probes are only minimally active after they have settled down to wait in the solar system and to monitor and observe. This is an assumption possibly driven by considerations of resource and energy conservation over the long term of a probe’s mission, by familiarity with the sort of ‘long-duration’ space probes that we have constructed, and even by the natural association of the ideas of waiting and monitoring and observing (as a sentinel does) with passivity. This may, however, mislead as to the possible strategies that are within the capacity of intelligent machines sophisticated enough to be actually self-repairing or self-replicating. We should assume that any such machine is effectively a universal constructor.

Amongst the capabilities of such machines would be:

1. Self-repair and self-replication of course (creating resilience and a margin of error in a system intended for long-term operations)
2. Resource identification, extraction, processing, and utilisation (which are the necessary prerequisites for repair or replication, but also for any form of construction at all.)
3. Refuelling
4. Energy access and replenishment
5. Relocation
6. Environmental modification (burial, rehabilitation, etc.)
7. The construction of subordinate probes

Such a probe would consequently be able to adopt a variety of strategies over the course of its mission – strategies not available to the sorts of passive monitors that have generally been imagined – adapting to changing circumstances. Such a probe might set up orbital monitoring stations about a world of interest if that world had no intelligent observers on it, or it might relocate to a moon if observers arose. It might create a series of probes to embed in asteroids to pass close by the target planet if that planet had developed intelligent observes. It might relocate all its probes to the outer system if the intelligence on that planet became observationally competent or capable of inter planetary travel.

Given such capabilities, the assessment of the various locations at which we might hope to discover evidence of a Von Neumann/Bracewell probe in the Solar System should begin with an assessment of our present or immediately foreseeable observational and technological competence on the grounds that any possible VN/B probe would have made a similar assessment and adapted its operations to continue being undetected by us while observing as best it still could.

We might then conclude that the most likely strategy for the probe in the current situation is

• Maintain a site in the Kuiper Belt on a large resource-rich body consisting of the VN/B probe itself and including whatever further infrastructure is required to continue operations (construction, replication, fuel extraction, etc.)
• Dispatch probes hidden within small (1m-10m) bodies passing close by the Earth and returning to deep space. These could be sent in a constant stream so that Earth would remain under continuous close observation.

We might further conclude that the best way to detect these operations – assuming that asteroid interception is not yet possible for us at short notice – would be to

• Search for Infra-Red or other techno-signatures in the KB and on close-passing rocks as they return to deep space (those probes are likely to want to move from their cover or alter their trajectories and all such velocity changes will require energy use whose effects cannot be hidden.)
• Scan for evidence of transmissions of data from the KB site to interstellar space, and from the asteroidal probes to the KB site.
• Map the trajectories of small close-passing asteroids to determine whether there is a common point of origin to some significant number of them.

[1] Bracewell, R. N. (1960) “Communications from Superior Galactic Communities,” Nature 186:670-671. Reprinted in Cameron, A. G. (ed.) (1963) Interstellar Communication, NY: W. A. Benjamin, 243-248

[2] Gatland, K. (1972) Robot Explorers, London: Blandford Press, 239 – 244

[3] The name is in reference to the device in Arthur C. Clarke’s 1951 short story ‘The Sentinel’ (reprinted in his 1953 Expedition to Earth.)

[4] Loeb, A. ‘On the Possibility of an Artificial Origin for ‘Oumuamua’

[5] Lunan, D. (1974) ‘Space Probe from Epsilon Boötis?’, Analog XCII, 5, 66-84, January, and (1998/2013) Epsilon Boötis Revisited

[6] Freitas, R. A. jr. (1985) The Search for Extraterrestrial Artifacts (SETA) Acta Astronautica 12:1027-1034

[7] See also Gertz, J. (2016) ET: Looking Here as Well as There JBIS 69:88-92

[8] Objects are known to co-orbit with Earth in various ways, occupying Earth’s orbit and occasionally/regularly approaching relatively closely to Earth. Jim Benford in Looking for Lurkers v.2 investigated the possibility of Bracewell probes locating themselves in these co-orbits.

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Occupy Phobos!

March 21, 2026 – 6:29 pm

Elon Musk is determined to create a viable human civilisation on Mars and is intent on going there directly as quickly as possible (notwithstanding his slight detour through the Moon.) I think this is a mistake. I believe that there are many advantages to the creation of a base on Phobos as a preliminary step to the human exploitation of Mars.

• The moon is more accessible than the planet (technologically speaking.)
  • The ΔV required is about ¾ that for a landing on Mars.
    (ΔV Earth Surface-Mars Surface = 9.3 (ES-LEO) + 4.3 (LEO-MTO) + 0.9 (MTO-MCO) + 1.4 (MCO-LMO) + 4.1 (LMO-MS) = 20.0 km/s
    ΔV Earth Surface-Phobos Surface = 9.3 (ES-LEO) + 4.3 (LEO-MTO) + 0.9 (MTO-MCO) + 0.5 (MCO-PTO) + 0.5 (PTO-PS) = 15.5 km/s)[1]
  • Phobos has no atmosphere or gravity well requiring complicated landing systems or risky departure procedures. All of the most dynamic and dangerous manoeuvres are at Earth departure and return – which are required in any case.
• A base could serve valuable functions in facilitating early Mars missions
  • Phobos is believed to be a captured C-type asteroid containing vast quantities of carbon compounds, nitrogen, silicon, and some metals, and density calculations also indicate large quantities of water ice. These resources would allow a Phobos base to serve as a refuelling and replenishment station for missions to the Martian surface.
    • Note that ΔV Phobos Surface-Mars Surface = 5.5km/s
  • Robotic operations on the Martian surface (exploration, investigation, construction, maintenance & repair, etc.) could be controlled in real time from the base. This would obviate the need for such early surface missions to be manned at all.
  • Rescue, emergency resupply, and other interventions for eventual manned Martian surface missions would be possible from Phobos which are not possible from Earth, greatly reducing the failure risks of such missions.
  • Until a better understanding is achieved of the biological vulnerabilities or threats of Mars, a Phobos base and remote operations would allow a minimisation of associated risks.

Looking beyond early Mars missions, it has also been proposed[2] that Phobos could serve as the anchor for elevators to and from the Martian system.

Or as the transfer point for an Earth-Mars Aldrin Cycler (See Davidson & Vorobieff (2019) Improving the SpaceX Mars Colonization Plan for a general description of such a cycler architecture.)

The gravity on Phobos is negligible, which is an advantage for the operations just mentioned but would have serious implications for human survivability in the long term. In order to have a permanent base there it will be necessary to compensate for that deficiency, probably with some form of artificial gravity. On the other hand, since we have no idea whether any g < 1g (9.8ms^-2) is sustainable for humans, this may be the case on Mars and the Moon as well. 

Several solutions have been proposed for the production of artificial gravity on low mass bodies by means of centripetal forces. The simplest way of doing this is just to have a circular track with a car running around it. More complex proposals involve boring tunnels to contain the tracks in order to shield the car or cars from radiation.[3] A system like this would be perfectly suitable for Phobos – especially if it was located in Stickney crater on the Mars-facing side of Phobos where even a surface car would be shielded from 90% of the incident Galactic Cosmic Radiation. 

If it does turn out to be the case that any gravity significantly less than 1g is harmful to humans, then the colonisation of Mars itself is much less attractive, and the Phobos base (and other space habitats) might well remain the preferred permanent habitations. In fact, the danger to human health of prolonged low gravity is just one of several disadvantages of planetary surfaces with respect to human expansion in space. Other major problems often cited are the location at the bottom of a gravity well (making access to the superabundant resources available in space difficult and constraining travel to and from the settlement,) general paucity of energy sources, the constraints on available areas for settlement and the limits to expansion that planetary surfaces impose, the difficulties imposed by the dynamics of the planetary surface environment, and so on. Considerations such as these have convinced many that planetary surfaces are not the appropriate focus for human expansion, and that space settlements should be preferred. This has long been the view of Jeff Bezos, founder of the space access company Blue Origin, for example, who argued for the construction of O’Neill Cylinders in a 2019 presentation.[4]

O’Neill Cylinders[5] are large rotating habitats for which the rotation produces the appropriate artificial gravity and the enclosed space contains whatever environment the designers or occupants desire. The mature versions of these are envisaged to be kilometres wide and long, though the earliest versions would certainly be much smaller.[6] The initial proposal was that they should be built at the Earth-Moon L5 Lagrange point for orbital stability and should be constructed of materials sourced from the moon, since the ΔV Earth Surface-L5 = 13.4km/s while the ΔV Moon Surface-L5 = 2.3km/s. (If it was built closer to LEO, as I suspect would be the case, the comparative ΔVs would be 9.3 vs 5.7 km/s.)

It is often further proposed that such habitats could be constructed within asteroids that have been (or are being) mined for resources. The advantage of such a procedure would be at least twofold: in the first place, the asteroid itself would provide most of the construction material so that the expense of transportation could be eliminated; and in the second place, the remnant of the asteroid would provide radiation (and thermal) shielding that the constructed cylinder would not then have to include.

Phobos would be a good place to begin building such a habitat.

• A permanent habitat on Phobos has already been shown to be valuable, and the cylinder construction could be undertaken as a natural and incremental expansion of existing facilities.
• Construction at Phobos could be used as a testbed for processes required for the construction of such facilities around other asteroids that are not so conveniently located; especially given that Phobos itself is thought to be a C-type asteroid of exactly the kind that is likely to be chosen for the site of a habitat.
• The body of Phobos is thought to contain voids, which might be used to accelerate the excavation process.
  

If Bezos and Musk would collaborate on this Martian project, the realisation of both of their visions could be accelerated.

[1] Diagram from Mission Table – Atomic Rockets

[2] 2003-Space-Colonization-Using-Space-Elevators-From-Phobos.pdf

[3] Gravity Loops For Mars and Moon Colonies?

[4] Blue Origin 2019: For the Benefit of Earth

[5] GK O’Neill (1976) The High Frontier. His original paper for Physics Today (Sept 1974) is available at The Colonization of Space – Gerard K. O’Neill, Physics Today, 1974 – NSS

[6] The lower limit of habitat radius is set by requiring the artificial gravity to be produced by a rotation rate no greater than about 2rpm. That seems to be the fastest rotational rate at which humans are still comfortable. For g = 1g, that gives a radius of about 200m. The upper limit is set by the strength of available materials: even current materials can handle radii in kilometres.

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The Allegory of the Cave

March 19, 2026 – 6:02 pm

Plato’s allegory in Republic 514^a-517^a can be summarised as follows

Location	Outside the Cave		Inside the Cave
Light	Sun		Fire
Reveals	Real things	Shadows and Images of things	Models of real things	Shadows of models of things
Symbolizes	The Good		The Sun
Reveals	Forms	Real things as instances of the Forms	Real things as perceptible particulars	Perceptions of perceptible things
Population	Free men	Escapees	Revolutionaries	Prisoners
Cognitions	Philosophy	Hypothetical thinking	Expert opinion	Common opinion
Status	Knowledge (επιστημη)		Opinion (δοξα)
Realm	Intelligibilia		Sensibilia (The Visible World)

FM Cornford comments (in The Republic of Plato p. 222) that the image of the world as a cave is used by Empedocles (ll. 119/120 on pp. 266, 267) who says ‘’ηλυθομεν τοδ’ ‘υπ’ ’αντρον ‘υποστεγον,’ ‘we came down into this roofed-in cave’.

The point of the Cave image is to describe the stages and the difficulty of the advance from mere opinion to knowledge.

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On the Possibility of Higher Dimensional Languages

March 15, 2026 – 12:06 pm

Reading Nikhil Mahant, Why alien languages could be far stranger than we imagine I was pleased to note that he canvassed the possibility of communication systems that were, as he says, non-linear – but by which he really meant not language-like in the way that language is defined for philosophical uses. The example he gives is the possibility of languages that are ‘map-like’ rather than ‘language-like.’ This is something that he may have developed from the idea that the Mind’s semantic system might be map-like rather than language-like – an option discussed in Braddon-Mitchell and Jackson’s (1996/2007) Philosophy of Mind and Cognition. I found it to be a fascinating alternative for a theory of mental structure, but I’m not sure how that might work for a language. Mahant suggests that it might be a pictorial system, but I doubt that such a system could really be a language.

(A pictorial system really couldn’t instantiate the sort of recursiveness that seems to be not just necessary to languages but also fundamental to thought. We really do believe that the range of possible thoughts and ideas is effectively infinite – or at least, so far beyond the possibility of individual special instantiation as to make it impossible to explain our capacities without something like recursion.)

The problem is more obvious when it’s wondered what the medium might be for such a non-linear language. A map-like system enhanced in some way to have the semantic power of a linear language would require a very different form of expression from any we’ve seen so far. On the other hand, when I’ve considered non-linear systems, I’ve often thought that an octopus’s chromophores could create a 2-2½d signalling system of adequate semantic power. Gripping hand, however, any inter-agent communication is going to have to be sequential and therefore effectively 1d, and I wouldn’t be surprised if that very fact makes it necessary for the intra-agent or atomic form of communication to also be sequential.

Consider how languages are useful as means of transmission of concepts or ideas from one communicant to another. Those ideas have to be constructed internally before they can be communicated – or, at least, that is the ideal of the system; it wouldn’t be surprising if the actual process of construction and expression were reflective and involved many feedback loops, and note that most people accept that they don’t really ‘know’ what they’re going to say until they’ve said it. In any case, it’s very hard to imagine mental processes equivalent to complex thought that did not issue in some sort of 1-dimensionally expressible ‘thought.’ What would a 2-d thought look like? Could a 2-d thought be equivalent to a 1-d thought like ‘Harry is happy’? Would it just be a mental image of an Euler diagram? Would thoughts too complex for an Euler diagram then be unthinkable?

My fundamental reason for doubting 2+-d languages, however, is that I have a rudimentary theory of the evolutionary origin of the language faculty that sees it as developing from the capacity for planned action, and planned actions are all 1-d sequences to be performed with 2-d tree-like structures only in their formation histories. That mirrors the TG version of language and it still seems the most obviously reasonable version of language to me, despite the Minimalist Program’s unaccountable popularity amongst linguists.

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On Protocols for Activities Following Discovery of an ETI Probe

March 14, 2026 – 7:14 pm

Current SETI efforts, with rare exceptions, concentrate on the detection of signals from ETI from deep space, and the response protocols adopted for success in this search reflect this concentration. The protocols in question can be found at the IAA site as

• Declaration of Principles Concerning Activities Following Detection of Extraterrestrial Intelligence
• Draft Declaration of Principles Concerning the Sending of Communications With Extraterrestrial Intelligence
• Position Paper on Declaration of Principles Concerning the Conduct of the Search for Extraterrestrial Intelligence (SETI) (2026 Update)

Nevertheless, there are good reasons, increasingly accepted by researchers, to believe that the first incontrovertible evidence of an ETI could well occur with the discovery of an alien probe already in the Solar System. Such a discovery would present us with a situation different in very significant ways from the case of a signal detection. For example: communication with the alien probe, should it be possible, would be in near real-time; the mere existence of the probe would strongly suggest that our own existence was already known to the ETI who sent the probe; and the artifact itself – if not the ETIs – would be physically accessible to humans even at our present level of competence in space.

Clearly, this would call for a very different set of response protocols from those recommended for a signal detection, yet there has been very little in the way of preparation of such a protocol. We have seen an early effort by A Tough (1998, Small Smart Interstellar Probes, JBIS 51: 167-74) and a more recent one by A Loeb (2021, Protocol for Contact with Extraterrestrial Equipment,) but beyond that there has been no effort at a formal draft and the topic is still at the level of general discussion.

This is possibly a good thing, because I think there are some aspects of the situation that are highly relevant to the form that such protocols should take that have not been properly considered.

Recursive Strategizing

We should expect that the ETI that sent the probe out has developed a strategy to advance its interests in having sent the probe out. A part of the development of that strategy would be to anticipate the responses of any intelligences that it might encounter. It would expect that those intelligences would have developed strategies for responding to such an encounter, and that they would expect the probe to have taken that into account, and that they should take account of that fact too, and so on. Our protocols for such an encounter have to take into account that the ETI who sent the probe are at least as capable as ourselves of recursive intentionality.

Given this assumed capability, and the fundamental principle that nothing should be done to jeopardize the existence of the human race (and acknowledging that the probe will have a similar prime directive,) our protocols should be such that given any number of intentional recursions they should tend to a stable action outcome.

Assumed Intelligence

We should assume that the probe is intelligent in its own right. This is plausible in any case because we are in sight of AGI ourselves and it would seem to us to make no sense for an AGI-capable ETI to send out a probe without it. We note that it is impossible for an unintelligent entity to pretend to be intelligent (ChatGPT notwithstanding – and we’re not talking about sentience or understanding here,) while it is very easy for an intelligent machine to pretend to be unintelligent. The advantages of such pretence may be imagined: to observe without the requirement of response to attempts at communication, to exploit security breaches opened by the assumption of unintelligence, etc.

We note, on the other hand, that if the probe is intended to eventually allow interactive contact as an AGI, then it must have a strategy that allows it to do so even after it has pretended to be unintelligent. It might be sufficient for it to claim to be uncertain of our intentions. But since we know that is a plausible strategy, we will have adopted contact protocols that will make it difficult for this strategy to be followed. And so on. It might turn out that ‘honesty is the best policy’ is the stable strategy here, in which case the deception will not occur.

Assumed Knowledge

We should also assume, whether as part of the assumed intelligence principle or not, that the probe has access to our communications and has had such for long enough that it can understand our languages and mine our communication channels for data. We should assume that in all remotely plausible cases (and we need to be very generous with our attributions of plausibility in dealing with the capabilities of an advanced AI/ETI) the probe can monitor our deliberations on its presence and what we might propose to do about it and what our motivations might be. We should also assume that this monitoring goes back into historical time no matter what appearance of recency might be given by the probe. (Of course, the probe will assume that we have made this assumption and will accept that any communications on the topic that followed the realisation that such a probe was possible might have been intended for the probe in the first place. And so on, again.)

On the other hand, we cannot depend upon it having that access or knowledge. The assumption is a matter of security maximisation, not of communicative convenience.

Prime Directives

Discussion of protocols for contact with ETI tend to simply assume that we must behave according to the ‘highest’ ethical principles, so that the first moral principles are that we must be completely truthful, we mustn’t deceive, we must treat the other (the probe in this case) as an end in itself, we must show no hostility, and so on. In Tough’s proposal, for example, he accepts as fundamental the first three directives in the ‘Declaration toward a Global Ethic’ put forward in H Kung, K-J Küschel (1993) A Global Ethic: The Declaration of the Parliament of the World’s Religions London: SCM, which he interprets as requiring that we

• Have respect for ETI and avoid violence
• Speak and act truthfully, avoiding lies and deception
• Deal honestly and fairly with ETI, avoiding any temptation to exploit the situation for personal greed

I regard this as well-intentioned, but wrongheaded. Quite apart from the as-yet-unjustified assumptions that a non-human ETI would have any such conception of morality or that if it did it would resemble our own Western model in detail, our principal directive must be the promotion of the advantage of humanity and the prevention of harm to it. Given the plausibility of the assumptions and reasoning that underlies the Dark Forest solution to the Fermi Paradox it must be the responsibility of communicants to minimise risk – not to maximise opportunity – because the risk is total. If that requires lies and subterfuge and ‘dishonesty’ (as the recursively stable strategy) then so be it. Only when the bona fides of the ETI/probe have been established beyond any doubt can purely cooperative strategies be adopted. And good luck making that call, because, again, the cost of error is total.

Preferred Secrecy

Almost all discussion of this topic explicitly demands that the news that an ETI has been detected should be made public immediately upon confirmation. This is declared in the two IAA protocols regarding actions subsequent to a signal detection, and it is also implicit in the suggestions made by Strong in his proposal. There are two reasons to think that this is irresponsible. One reason applies to both the signal detection and the probe discovery cases, but the other and more plausible hesitation is particularly relevant to the latter.

• There is a possibility that the discovery of the actuality of ETI may cause social dislocation. This is a common trope in SF and the risk is acknowledged by the IAA in the Rio scale and San Marino Scale documents included in resources related to their considerations of their protocols. The case where the discovery is kept from the public is the case where the status quo is maintained. Given the risk of publicity with unknown benefits to publicity, the responsible authorities would be quite justified in playing it safe until they could be absolutely convinced of the advantages of publicity. This calculation, of course, applies to all discoveries of ETI where it is possible to maintain secrecy of the event.
• Proposed protocols foresee an eventual attempt to communicate with any discovered ETI. It is accepted that the nature of the message needs to be well-considered and conscient of the risks of such openings. The obvious increased risks of unauthorised communications that follow from publicising the existence of the ETI are mitigated by the fact that in the case of a signal detection it is implicitly assumed that the resources required to send a message are beyond most individuals and that organizations with adequate resources can be persuaded to follow the recommended protocols by whatever institution is finally given the responsibility of coordinating the human response. Moreover, given that the signals are anticipated to be from vast distances, it is not expected that a message would have effects that would be felt in the very near term – even if those effects were to be harmful. There would be time to minimise the effects in the gap between signalling and receiving a reply – let alone receiving a visitation in response. None of this is likely to be true in the case of a probe discovery. In the probe case, messaging the ETI would be vastly easier – especially given our prudential assumption that the probe is already monitoring all our communication channels – and cannot plausibly be regulated by any international bodies we can imagine. (Note that there have already been several attempts at messaging ETI by private parties. The threat of irresponsible messaging of the probe is very real.) Secrecy, in this case, is very much the safer course until the responsible authorities can be absolutely convinced of the advantages of publicity.Such a strategy would have to take into account that the probe discovery might very well be such that it could not be kept secret. It might be that the probe is so obvious (or is now deliberately making itself so obvious) that the event will inevitably become public. It might be that the discoverers of the probe have already made enough people aware of it that the discovery is effectively public already and only mitigating actions can be taken. In such a case we might look for authorities to downplay or to debunk such evidence, to restrict the activities of those who have come into that knowledge, and so on.

  All of those strategies, again, will need to be designed on the assumption that the probe is intelligent, knows what is happening about its discovery, will eventually make itself known unless prevented, and so on, and that the communication with ETI will have to go forward in the future on the basis of common awareness of the actions previously taken. Here we would again need to operate on the basis of recursive strategies as described above.

Responsible Authorities

There is a universal assumption in the proposed and actual protocols that, given the humanity-wide significance of the event of ETI detection, the responsible authorities should be those that can be relied upon to have the best interests of humanity as a whole at heart, and to have the competence to pursue those interests, and the accepted right to do so. This typically means that they default to assigning responsibility to various UNO committees.

Unfortunately, for several reasons, this is unlikely to be persuasive in the necessary quarters.

• In the first place, the UNO no longer has quite the reputation that it might once have had. I think very few people now believe that it has the competence or the authority to do what is necessary, nor are they all convinced that it has humanity’s best interests as its motivating principle. More importantly, it is not likely to be the view of the state actors that the UNO should be deferred to in a matter of such importance.
• The UNO, as a collection of competing state actors acting in their own perceived interests, is properly seen as just another actor on the political stage. No state – whatever the rhetoric surrounding its actions – is justified in handing over an advantage to competing states, when it can be quite certain that no such indulgence would be reciprocated. Does anyone think that the worst state actors would voluntarily resign their advantage in such a case? To insist on any others doing so is merely to hand an advantage to those worst states.
• If secrecy is deemed important, then assigning responsibility to an international organization is an extremely unlikely way of preserving it.

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Encounter Classifications for Terran Worlds

March 8, 2026 – 3:34 pm

1. Size
   1. S              Small                           r < 0.8r_E,                  m < 0.5m_E                g[1] < 0.8
   2. M             Medium               8r_E < r < 1.7r_E       0.5m_E < m < 6m_E         0.8 < g < 2.0
   3. L              Large                                                  6m_E < m < 10m_E          0 < g < 2.2
   4. G              Giant                                                10m_E < m                      2 < g
2. Dominant Hard Surface Type
   1. V              Vulcanic              Dominant surface is due to vulcanism
   2. R              Rocky                 Heavy minerals, silicates, carbonates, varieties of regolith
   3. I               Icy                     Frozen volatiles (eg. water, ammonia, methane)
3. Persistent Surface Liquid Types
   1. N              Anhygric             None – indicating liquid cannot persist on the surface
   2. W              Hydrohygric        Water
   3. C              Anthracohygric    Methane, ethane, etc
   4. A              Allohygric            Other
4. Surface Liquid Coverage
   1. X              Xeric                  No surface liquid
   2. D              Drosic                Insignificant or transient liquidity
   3. L              Limnic                Significant but not extensive liquid coverage
   4. T              Thalassic            Extensive but not total liquid coverage
   5. O              Oceanic              Total liquid cover.
5. Effective Surface Radiation (R, mSv per annum)
   1. M              Radiominimal     R < 0.1
   2. S              Radionormal        0.1 < R < 10         1 is the ICRP recommended max
   3. C              Radiocritical        10 < R < 1000   
   4. T              Radiotoxic           1000 < R
6. Surface Temperature (T, ^oC)
   1. 1              Super-Cold          -273 < T < -100
   2. 2              Cold                    -100 < T < 4
   3. 3              Temperate          4 < T < 40            Approximate human habitable zone
   4. 4              Hot                     40 < T < 100
   5. 5              Super-Hot           100 < T
7. Surface Atmospheric Pressure (P, b)
   1. 1              Microbaric           P < 0.001b
   2. 2              Hypobaric           001b < P < 0.3b
   3. 3              Mesobaric           0.3b < P < 3b          Approximate human habitable zone
   4. 4              Hyperbaric          3b < P < 100b
   5. 5              Megabaric           100b < P
8. Surface Atmospheric Composition (by dominant[2] component)
   1. A              Airless                Microbaric worlds with an exosphere
   2. P              Primordial air      H₂, He₂
   3. C              Compound air     Common compound: CO₂, CH₄, NH₃, H₂O
   4. N              Nitrogen air        N₂ 
   5. O[3]         Oxygen air          Breathable levels of O₂
   6. L              Complex air        No dominant component
   7. X              Exotic air                             
9. Biocomplexity[4]^{, [5],[6]} (K, 10^Kbytes)
   1. 0              Abiotic                K = 0
   2. 1              Protobiotic[7]      4 < K < 5              
   3. 2              Deuterobiotic      5 < K < 6               5 = approximate minimal level for a cell
   4. 3              Triobiotic             6 < K < 7               Coli
   5. 4              Tetrobiotic           7 < K < 8               Fungus, Fruit fly
   6. 5              Pentobiotic          8 < K < 9               Mouse, Human
   7. 6              Hexobiotic           9 < K                      Pine
10. Biodensity[8] (D, Gt/m²)
    1. 0              Nonvital              D = 0
    2. 1              Rarivital              0 < D < 0.001
    3. 3              Paulivital             0.001 < D < 0.1
    4. 4              Plenivital             0.1 < D < 10             Earth = 1
    5. 5              Supervital           10 < D

[1] Rough estimates only for values of surface gravity (g, g_E) based on r and m.
[2] Dominant means > 75%
[3] This classification takes priority over any other applicable classification
[4] Kolmogorov system complexity for biological organisms. Note that such organisms are distinguishable at any level of K by their reciprocal entropy. See C. Mayer (2020) Life in The Context of Order and Complexity – PMC. They may alternatively be distinguished as just the complex systems historically evolutionarily responsive to environmental pressures.
[5] The biocomplexity of a world is marked as the complexity of the highest scoring biological organism on the world.
[6] The examples use the genome size of terrestrial organisms (rather than genes identified) to calculate their complexity. The genome is a first approximation only to a proxy for complexity.
[7] Since the scale only applies to biological organisms, 0 is assigned to all non-biological entities. It is assumed, on the basis of plausibility and the evidence of terrestrial life, that complexity below 4 is not possible for biological organisms.
[8] Total biomass / surface area of world. A rough measure of the degree to which life has occupied the world. See Bar-On, Yinon M.; Philips, Rob; Milo, Ron (2017). “The biomass distribution on Earth”. Proceedings of the National Academy of Sciences. 115 (25): 1. Note that the current definition references only the mass of carbon contained in living things. This definition may or may not be adequate in considering alien ecologies. Note also the comment in the Abstract to the referenced article:

We find that the kingdoms of life concentrate at different locations on the planet; plants (≈450 Gt C, the dominant kingdom) are primarily terrestrial, whereas animals (≈2 Gt C) are mainly marine, and bacteria (≈70 Gt C) and archaea (≈7 Gt C) are predominantly located in deep subsurface environments. We show that terrestrial biomass is about two orders of magnitude higher than marine biomass and estimate a total of ≈6 Gt C of marine biota, doubling the previous estimated quantity. 

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What is a Planet?

March 1, 2026 – 2:01 pm

The dispute over the criteria used for the categorization of celestial bodies as planets reveals either a confusion concerning the reason for a definition, or an unhappy compromise between independent reasons. The criteria adopted by the International Astronomical Union (IAU) are that the body

1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3. has “cleared the neighbourhood” around its orbit.

These criteria are clearly intended to include the classical planets while excluding most of the new and unfamiliar bodies from the Kuiper belt (and beyond,) without simply naming them as such. Controversy over the exclusion of Pluto means the second option would probably have been preferable, but that would not have looked like a scientifically defensible definition.

A really scientific definition, of course, would attempt to determine some sort of Natural Kind amongst such bodies. In this respect, a pretty standard view is that Natural kinds are the classes of real objects that fill the positions of variables or class names in the best scientific theories relating to the relevant domain. (For a very relevant example, when Copernicus determined/theorized that the Moon differed from all the other planets in the traditional system according to its orbital character, he removed it from the category of planets.) In that case, the class of planets should be a class of astronomical bodies that relatively narrowly includes the classical planets and that features in theories of stellar formation, solar system dynamics and development, and so on. Such a class would not obviously be required to regard either condition 1 or 3 of the IAU definition. A better definition would simply require that a planet be any body that:

1. is not massive enough to produce fusion reactions, and
2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape)

The IAU itself accepts that their condition 1 should be generalised to say that the body is in orbit about a host star. This would still, however, exclude interstellar objects from the class and invalidate the term ‘rogue planet.’ It isn’t clear why this should be necessary: if we desired to speak of only such objects in orbit about a star we could simply talk of the star’s planetary system. (For convenience the planetary system of Tau Ceti, for example, would be the ‘Tau Ceti system.’) The fact that planets that we know of are generally in orbit about a star is a fact about that class but not a definitive one. (That most Zebras live in Africa is a fact about them, a consequence of their origin and history, but it is not definitive.)

Given that the requirement of IAU condition 1 can be discounted, we might further be relieved of the necessity of distinguishing planets from satellites in those cases where two bodies that both satisfy the other criteria for a planet orbit each other. Previously, we might have achieved this by declaring that where the barycentre of the system lay within one of a pair of bodies, that one would be the planet and the other would be the satellite; or we could have insisted that the secondary body has to be significantly smaller than the primary. A reasonable limit for the second would perhaps be a mass ratio greater than 10:1 given that the Pluto-Charon mass ratio of about 1:8 is enough for some – but not for everyone – to describe it as a double planet. It might be more convenient now to speak rather of a planetary sub-system, and, in the case that one of the bodies is clearly the primary, to speak of that planet’s subsystem. We could unambiguously speak, for example, of the ‘Jovian sub-system,’ or even of the ‘Terran sub-system.’

We might, however, need to modify the conditions in order to exclude neutron stars and white dwarfs from the planet class, because they are not massive enough to produce fusion reactions in their matter, as required by condition 1, and yet they are clearly not of the same natural kind as what we intend to refer to as ‘planets.’ We might achieve this by requiring that the body be composed of non-degenerate matter, but that doesn’t really get to the heart of the problem. In fact, this indicates that purely observational criteria are not adequate for distinguishing the class of planets, because we would insist that any body which had been a star in the past, but through natural processes had become non-fusing should not be in that class – regardless of mass or composition or shape. Natural kinds, so many theorists insist, have historical depth or causal boundaries. (A painted horse does not become a zebra.)

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The Sun Simile

February 28, 2026 – 11:43 pm

Plato’s simile in Republic 508-9 can be summarised as follows:

The Form of the Good	The Sun
Intelligible world	Visible world
Source of Truth or Reality(508e) Yields (508e) 1.       Truth or reality to intelligibilia 2.       Power of knowing to mind Thus (508e) 1.       Not knowing but cause of knowing 2.       Known by the knowing it causes	Source of light (508a) Yields 1.       Visibility to sensibilia (507e) 2.       Power of seeing to eye (508b) Thus (508b) 1.       Not seeing but cause of seeing 2.       Seen by the seeing it causes
Causes reality of objects of knowing But is not that reality (509b)	Causes processes of growth But is not such a process (509b)
Deprivation results in (508d) 1.       No truth or reality (= change/decay) 2.       Poor intelligence (= opinion)	Deprivation results in 1.       No light (508c) 2.       Poor sight (508d)

In the simile, note two stumbles.

1. If light yields visibility to visible things, then it would be more natural to say that the Good is responsible for the intelligibility of the intelligible, rather than the truth or reality of those things.
2. The claim that the Sun is the source of light and the Sun causes the processes (genesis) of growth is not a match to the claim that the Good is the source of Reality and the Good causes the reality of knowable things. The ‘coming into being’ of natural things is not like the unchanging being of the knowable things.

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