We speak of a double when, within a single spatio-temporal context – that is, within a single possible world created by literary, digital or some other fiction – the identity of a character is duplicated: one becomes two; the character therefore has two incarnations: two bodies corresponding to the same identity and often to the same name.

This is a symbolic world that duplicates, and at times even replaces, the real one, with which it stands simultaneously in a relationship of similarity and difference. Similarity, because all these ancient forms of the double faithfully reproduce the appearance of the person who has been doubled. Difference, because they are not perceived as simple copies, but as effective presences, even if partial ones (and often tragically partial).

In Book V of the Iliad Apollo repeatedly intervenes to defend Aeneas from the destructive and impious fury of Diomedes; in the end he is forced to carry the Trojan hero safely out of the fray, into his own temple, and to set upon the battlefield his "double": "The god of the silver bow, Apollo, then fashioned a double, exactly like Aeneas, even in his armour."

In the Phaedrus, Plato tells of the poet Stesichorus who, struck blind by Helen for having spoken ill of her, immediately composes his Palinode and thereby regains his sight, imagining that the real Helen never went to Troy, but rather her double: "But I never went to Troy: that was only my double." Helen has always been the paradigm of seduction, adultery, and fatal, destructive eros: a negative image, the product of a patriarchal and sexophobic society, which can sometimes be transformed into a positive image, but only on condition that she is portrayed as the victim of superhuman forces. In Book VI of the Iliad, for instance, Helen herself, speaking with her brother-in-law Hector, describes herself as a "perverse and hateful bitch" who wishes she had died at birth, before she caused so much evil.

If, in art and literature, the "double" – often referred to by the German term Doppelgänger – is a metaphor for the dark side of man, in twentieth-century psychological thought the double represents the unconscious realm of the human being. It becomes functional for explaining the phenomena of alienation, dissonance and dysfunction. The theme of the "double" was studied with particular attention by Otto Rank, a pupil of Sigmund Freud, in his 1914 work Der Doppelgänger, in which he links the sudden appearance before us of our double to repressed fears. It is an invasion of the unconscious into the field of the conscious, the return of the repressed, which becomes, according to Freud’s definition, "uncanny". Put simply, for psychoanalysis the "double" is the "other" part of us, that which we are, but which we do not know rationally, of which we are not consciously aware.

In Michel Tournier’s novel The Golden Droplet, the young Saharan Idriss travels to Paris in search of a photograph taken of him by a French tourist, troubled by the idea that his "double" might be wandering the world and threatening his integrity as a person. The person of antiquity became aware of themselves through the gaze of others: it is no accident that in Greek the same word, prósopon, denotes both a mask and a face. This is, in fact, a culture of exteriority, devoid of the modern idea of inner consciousness, in which various external images are constitutive parts of identity.

In the era of the digital revolution we are living through, the so-called Digital Twin of artificial intelligence – where the theme of the double, the twin, the shadow, the mirror image, the alter ego is ever-present – opens up a path for humanity towards an indeterminate identity, whose I is in constant mutation and can take on different forms. A digital twin replicates the physical characteristics of an individual and transfers them into a virtual environment, including their functionality, characteristics and behaviour. Digital twins rely on available data to transfer information from a real-world object to a digital-world object, where it is essentially possible to see data updates in real time. Up to now we have essentially been speaking of objects, but artificial intelligence (AI) is a field of computer science devoted to solving cognitive problems normally associated with human intelligence, such as learning, problem-solving and pattern recognition. This means that digital twins are becoming firmly established not only in industry, but are also relentlessly striving to extend their dominance into the private sphere of users.

In the case of human beings, the emergence of digital copies has begun at both the micro and macro level. At the micro level, for instance, it is now common practice to digitise our medical examinations. These biological representations of parts of our body then enable the doctor to find solutions for the patient. At the macro level, we can regard Facebook (and numerous other social networks) as a kind of digital twin capable of recording aspects of our lives: what we do, who we are, what we like.

This information-saturated mirror image of our person often reveals more about us than we assume – starting with something as simple as listening to our favourite songs through a music app. You might say: we have created a kind of twin on the World Wide Web, a double, which is constantly being enriched with new information and which – as we know from numerous privacy scandals – we can now barely control. What exactly happens to our data? Where does it go? How long is it kept? We often find comfort in telling ourselves that it is all anonymous – and after all: "Just a few pieces of information won’t do any harm..." In reality, however, only a handful of data points (four are enough) are needed to de-anonymise anonymous profiles with 95 per cent certainty, that is, to connect all the details of our lives using only our name.

And the result is: we are no longer alone in everyday life (in a way, a "data shadow" always follows us) nor in private (hardly anything about us remains hidden from others). What is life like with this existence in which our twin also exists?

We are no longer alone: this is the great, utopian promise of data and technology companies. We are constantly watching ourselves. We are no longer alone, but at the same time there is also the dystopia of the digital twin, the data shadow, which almost always follows us. We live in a kind of divided existence. We are constantly being assessed and monitored, and we behave accordingly. Human autonomy is gradually turning into heteronomy. This has consequences. How free are we still?

And here awareness of good and evil begins to fade, because this means not only suggesting and steering individuals, but also predicting their choices and behaviour.  The distinction between true and false also begins to fade. Social networks allow us to be constantly online and to let our virtual alter ego live continuously and in parallel with our everyday life, and they allow anyone to create an alternative, virtual identity which, besides being configured as "public", helps filter all the information relating to a given topic and choose only what you want to present in the eyes of others. The virtual double can ultimately become a "sanitised" double that is shared with others, while whatever is less socially acceptable, or unacceptable, remains confined.

Moreover, there are cases in which an individual creates several virtual identities, each representing one or more aspects of their personality; failing to find cohesion among their different aspects, they present them practically speaking separately, depending on whom they are addressing, something which, in the digital world, extends exponentially in relation to the relationships possible in the real world. It is like an explosion,  like a scattering of our I, which is then reassembled and in this way intensifies the sense of our own I.

Ultimately, the trend is towards reuniting all these scattered pieces of data about a person into a single whole. The advantage of this model lies not only in creating an infallible memory encompassing our entire experience, but also in the possibility of accessing all relevant information and the individual’s entire accessible world. In this way we arrive at our "digital twin".

But digital transformation has given rise to another kind of unconscious, perhaps an even more powerful one, which in turn can shape our way of thinking and behaving. With the advent of big databases, and with access to social media data, the tendency to identify and catalogue each  one of us, especially for the delivery of commercial offers and administrative services, has been strongly accelerated. All our activities (and in the future this will potentially be the same for our thoughts too) are analysed and tracked, catalogued to serve the profit of companies and governments. For each of us, this complex system represents a kind of digital unconscious scattered across the world’s databases, which can present a great challenge and numerous dangers.

When it comes to stolen identity, the duplication is caused by an external force, marked by absolute otherness, which violently takes over the identity of the character.

In another situation of unusual resemblance, the two halves are instead on the same level (resemblance – as Augustine would say): these are two different characters, yet united by an extraordinary similarity, often marked by being born on the same day and having a similar present, which produces phenomena of identification and projection.

Finally, the doubling of the ego is based on a complete identification with a consciousness split into two parts, with no explanation of the (probably hallucinatory) cause of the split: a person may therefore become completely immersed in a fictional world, in two incarnations of the same character, closely bound up with social and cultural constructions. This leads to confusion, isolation and other difficulties encountered by people in the digital world.

When a person finds themselves in difficulties, they are driven to wish for a substitute, then to deny their own name and, finally, nonetheless to assert their own identity. And this is repeated using expressions typical of his condition as a slave, as in the Odyssey: « Yet you will never be able to make me change my views, so that I no longer belong to this house. There is no other slave among us named "the Double" except me ».

To the accusation that he is unwell, the Double reacts with a wavering over his own identity, expressed in a string of rhetorical questions: "You are the one who is unwell, not I! Did our ship, the one that brought me here, not arrive last night from a Persian port? Did my master not send me here? Am I not now standing at the door of our own house? Do I not have a lamp in my hand? Am I not speaking? Am I not awake? Did this man not just strike me? My teeth still ache, poor me! So why, then, am I assailed by doubts? Why do I not go into our house?"

These questions and the recognition of one’s own condition open the way, so that the duplication and disruption of identity can be brought to an end. In the work mentioned above, this comes through hearing a story, told by a servant, about the birth of twins and about Heracles’ first extraordinary feat, performed while still in his cradle, and so on. This leads to the establishment of real contact with others and involvement in real social life.

Very striking are the verses in which Helen speaks of her own appearance as of a colouring that ought to be wiped away: "Oh, if only I could wipe away my radiant appearance, the way colour is stripped from a statue, and take on the uglier one instead (my true self). The Greeks would forget the terrible fame that now surrounds me, and would keep a positive image of me, instead of the negative one they now hold!"

Menelaus, her husband, remarks: "What can I say? I am speechless! I have just heard of my new, terrible misfortunes: I brought my wife back, I am leading her from Troy, I arrive here and hide her safely in a cave, and then I discover that here in this very palace there lives another woman who bears the same name as my wife." Menelaus is unconvinced, for he sees all the laws of space and time set in contradiction: "How could you have been here and in Troy at the same time?" Helen answers him: "A name can be anywhere; a body cannot." He reads the event in a supernatural light, and thinks he is confronting a ghost: "But I am not the husband of two wives: I am one person, just one I!"

Our psychological condition presupposes a natural interiority, a "self", an I that becomes aware of the things around it and, more or less, freely governs its own life. In this sense, the principle of our being and acting begins within us (the head, the heart, sexuality), while everything else is regarded as other, different, foreign. Let us consider where our gestures, movements, decisions and thoughts come from. They are certainly born somewhere within us. Sometimes a decision may be influenced by some external force, a command, someone else’s influence, but ultimately the act always originates from ourselves, from our own body. Yet there are invisible influences that seem to be part of us and are taken for granted.