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Érudit est un consortium interuniversitaire sans but lucratif composé de l'Université de Montréal, l'Université Laval et l'Université du Québec à Montréal. Il a pour mission la promotion et la valorisation de la recherche. Érudit offre des services d'édition numérique de documents scientifiques depuis 1998. Pour communiquer avec les responsables d'Érudit : erudit@umontreal.ca Article Andrei Cornea Laval théologique et philosophique, vol. 63, n° 3, 2007, p. 459-472. Pour citer cet article, utiliser l'information suivante : URI: http://id.erudit.org/iderudit/018172ar DOI: 10.7202/018172ar Note : les règles d'écriture des références bibliographiques peuvent varier selon les différents domaines du savoir. Ce document est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y compris la reproduction) est assujettie à sa politique d'utilisation que vous pouvez consulter à l'URI http://www.erudit.org/apropos/utilisation.html Document téléchargé le 7 juin 2013 04:35 "“If There Were an Eye on the Back of the Heaven…” (Plotinus, Ennead 4.5,3 and 8)" Laval théologique et philosophique, 63, 3 (octobre 2007) : 459-472 459 “IF THERE WERE AN EYE ON THE BACK OF THE HEAVEN…” (PLOTINUS, ENNEAD 4.5,3 AND 8) Andrei Cornea University of Bucharest Romania RÉSUMÉ : Notre article analyse deux passages curieux du traité Sur les difficultés relatives à l’âme III. De la vision (Enn. IV.5,3 et 8), dans lesquels Plotin paraît concevoir la possibilité d’un autre univers, situé en dehors du nôtre. Or, cet autre univers doit rester inconnu pour nous à jamais, quand bien même il y aurait un « œil placé sur le dos du Ciel » qui voudrait le voir. En outre, nous ne saurons même pas décider si cet univers existe ou non. En effet, expli- que Plotin, plusieurs univers ne peuvent absolument pas communiquer entre eux, précisément parce qu’ils forment des univers différents. S’ils communiquaient, ils seraient autant de parties du même univers et non pas des univers séparés, parce que la communication (la sympathie dans les termes de Plotin) circule seulement à l’intérieur du même univers. Nous rapprochons cet intéressant argument de certaines idées astrophysiques modernes et de la philosophie « des mondes possible » de David Lewis, sans pour autant pratiquer une lecture « modernisante » de Plotin. ABSTRACT : Our paper discusses two curious passages of Plotinus’ treatise On some difficulties concerning the Soul III. On vision (Enn. 4.5,3 and 8), where the philosopher seems to contem- plate the possibility of another universe outside this one. Yet we could never know this other universe, nor could we even decide whether it exists or not, even if “there were an eye on the back of the Heaven” able to look at it at close range. In fact, Plotinus explains, different uni- verses cannot communicate at all among themselves. If they could, they would no longer be separate universes, but only parts of the same universe, because communication (or in Plotin- ian terms, sympathy) flows only within the same universe. We compare this interesting argu- ment to some modern astrophysical ideas, as well as to the “philosophy of possible worlds” of David Lewis, while trying to avoid any “modernizing” perspective on Plotinus. ______________________ I re there any other universes besides this one ? How can a plurality of universes be conceived of ? And, provided there are more than just one, how can we make sure that they are really universes on their own and not just remote regions of our universe ? One of the first principles of contemporary cosmology is that the uni- verse is a closed and completely interconnected system, which means that it does not A ANDREI CORNEA 460 present interior regions among which causal information cannot flow.1 The same idea has been advanced by some of the philosophers of “the possible worlds”, such as David Lewis : “There are no spatiotemporal relations at all between things that be- long to different worlds”, he writes.2 This entails that, even if other universes existed, we could receive no data from them, for otherwise they would be just parts of our universe.3 (And conversely, the objects from which we do receive data or which caus- ally influence us must be parts of the same universe as we.) But since we cannot re- ceive any data from other universes, we cannot decide whether or not they really ex- ist. Therefore, this proposition (P) “our universe is unique” is necessarily neither true, nor false : it is intrinsically non-decidable. Contemporary cosmology actually admits that there may be regions of our uni- verse that are completely disconnected from each other and thus unable to causally interfere with each other, at least at present and perhaps also in the future. Ex hy- pothesi they are considered “regions of our universe”, but if it is closure and interior connectedness which define a “universe”, nothing seems to conceptually distinguish between these disconnected regions of one single greater universe and a few “sepa- rated universes” on their own. The explanation of this phenomenon is the so-called “horizon problem” : we cannot receive any information from objects lying beyond the distance light could travel from the beginning of the cosmological expansion.4 This distance fixes the size of our “horizon” and is estimated around 14bn light years ; it is the reverse of the so-called “Hubble constant”. Hence, “if some region of the universe lies outside the horizon of some other region, at some time t after the Big Bang, then these two regions are causally disconnected at time t : they have not yet had time to communicate with each other via light signals.”5 And if there is enough distance between them (say, for instance, 100bn light years), they may never have time to communicate, because they may be both extinct until their respective horizons expand enough to overlap. Therefore, nothing forbids us to consider these so-called regions to be universes on their own. Consequently, propositions such as : “there are (or there are not) regions of our universe beyond our horizon”, or rather “there are (or there are not) other universes outside this one”, or “there are so many colors, umbrellas or cats in other universes”, etc., and especially “this universe is the only one” (P), as well as “P is true (or false)” are intrinsically non-decidable : although they refer to the present and to the past, they are simply neither true, nor false, insofar as some of their direct or indirect ref- erences are not part of the universe we live in. In other words, we can never tell whether or not an assertive proposition is true, unless both we who are uttering it 1. Luc BRISSON, F. Walter MEYERSTEIN, Inventing the Universe. Plato’s Timaeus, the Big Bang and the Problem of Scientific Knowledge, New York, State University of New York Press, 1995, p. 67, 77 ; Lee SMOLIN, Three Roads to Quantum Gravity, Orion Publishing Group, 2000, p. 28. 2. David LEWIS, On the Plurality of Worlds, Oxford, Basil Blackwell, 1987, p. 2. 3. Ibid. According to him if two objects are spatially and temporally related, they are necessarily worldmates. 4. BRISSON, MEYERSTEIN, Inventing the Universe, p. 116. 5. Ibid. “IF THERE WERE AN EYE ON THE BACK OF THE HEAVEN…” 461 and all its explicit and implicit references belong to the same universe. Obviously, the result seems to be an observer-dependent logic.6 In fact, if we define the “universe” as a closed, interconnected system, Aristotle’s logic, which concedes the infringement of the principle of the excluded third only to singular propositions referring to the future (the “contingent futures”), may not suf- fice7 : the propositions “x exists” and “x existed”, where x is an object beyond our ho- rizon, or (which amounts to the same) belonging to a different universe than ours, can be said to be neither true, nor false by us, although the former proposition refers to the present, and the latter to the past. The truth-value of these propositions varies ac- cording to the location of the person who is expressing them, whereas in Aristotelian logic it solely depends on the concordance between speech and facts, irrespective of the location of the speaker. Thus, in addition to the Aristotelian “contingent futures”, one has to accept cer- tain “contingent presents” and certain “contingent pasts” whose truth-values are non- decidable as well. Therefore, we either have to modify our standard logic by adopting a topical, observer-dependent viewpoint, or, if we prefer to keep our Aristotelian, standard logic, we have to stick to “God’s viewpoint” — and by this syntagm I mean the condition of someone who thinks he “knows” that all P-like propositions are nec- essarily true. II All these considerations are intended to serve as introductory remarks to a discus- sion about a rarely tackled passage from a treatise of Plotinus.8 There the philosopher surprisingly calls into question the uniqueness of our universe by inventing a thought experiment and examining whether and how different universes, provided there are more than just one, can interfere with each other. Why “surprisingly” ? Because since Plato’s Timaeus and Aristotle’s De Caelo and Metaphysics, the dogma of the uploads/Litterature/018172ar-plotinenn4-5-3-8-eyeonthebackofheaven-erudit-org-laval.pdf