“What then is time? If no one ask me, I know. If someone ask me to explain, I know not”.
(Augustine of Hippo)
In just a second, a bee can flap its wings up to three hundred times. During the same amount of time, our Solar System travels 200 km across its orbit around the centre of the galaxy, while Earth travels 20 km around the Sun.
A second is also the time you need to read this period, if you are very good readers; by the time you get to the fullstop, the heart of a hummingbird in love will have beaten between ten and twenty times, while yours just a couple. Our life, as well as the whole universe, is punctuated by a succession of an infinite series of instants, which we give meaning to, more or less consciously; but how long exactly does a second last?
Despite seeming intuitively trivial, answering this question might be more complicated than it looks: there are lots of factors that can alter time streaming (or its perception), from the physical state of the system we are in, which is an external variable to the observer, to our the temporary or chronic emotional state, which is an internal variable. This last type will surely be more familiar: it happens to anyone to lose track of time during a nice evening with friends and be surprised when looking at the clock. When we have fun, time flies; when we hurt, we are anxious or scared, every second seems to pass very slowly. On the other hand, this is just the generalization of Albert Einstein’s definition of his general theory of relativity:
“When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute—and it’s longer than any hour. That’s relativity.”
Through this useful semplification, Einstein introduced the idea that time is not absolute and unchangeable, but subjected to forces of the Universe it can’t avoid, such as gravity force. The higher this force is, the higher is the curved spacetime; in other words, astronomical objects exerting a stronger gravity force cause a bigger time distortion, which makes time significantly slower.
Think of spacetime as a sheet of paper: if you hold its ends, the sheet will be parallel to the ground. If you try to put a light object at the centre of the sheet, the paper will bend around it: this curve represents the timeline distortion. Now imagine to put in the same spot a heavy object: the sheet will bend so much that its ends will touch and assume a cylindrical shape; in this situation, the time flow would slow down so much that it would look completely still to an outside observer!
The areas of spacetime in which the developed gravitational field can cause a time flow collapse are well known, not only to astrophysicists; there are astronomical objects which gravity is so strong that even light can’t escape it: these are called black holes and can’t be observed in any way. On the edge of the event horizon (the surface beyond which events cannot affect or be affected by an outside observer), the black hole mass completely bends the spacetime on itself; two twins, one on the Earth and one on the boundary of the black hole, would grow old at different speeds: after more than fifty years, the former would look like a middle-aged man, while the latter would still be a baby. For the same principle, clocks put at different altitudes mark time asymmetrically: a clock at sea-surface height would be slower than a clock on top of Mount Everest, because of the gravity difference between these places.
However, the reference physical system isn’t the only variable that can alter our personal concept of time: although the external reality is fundamental in determining the compression and dilatation of time flow, an alteration of our time perception can also depend on our internal reality. How many times did we hear our parents or grandparents say that time seems to go faster as the years go by?
The American psychologist William James, partially referring to the philosopher Paul Janet’s proportional theory, says: “The apparent length of an interval at a given epoch of a person’s life is proportional to the total length of the person’s life itself”: when we grow old, every time interval becomes an increasingly smaller portion of our life and this unavoidably influences our perception. For a newborn, a week represents an incredibly large window of time and experience; coversely, a week isn’t that significant for us and it usually goes by fast and quietly.
On the contrary, the neuropsychologist Warren H. Meck found the cause of this gradual acceleration in the neurochemical modifications experience by our nervous system during old age: a physiological dopamine decrease seems to cause the alteration of time perception mechanisms.
Regardless of age, emotional state can influence time perception too: boredom, fun, pain, can all cause nonpathological alterations in the estimation of time intervals; but what happens when this alteration, which we experience almost every day, becomes pathological?
In the DSM (Diagnostic and Statistical Manual of mental disorders), American Psychological Association’s diagnostic manual, now at its fifth edition, we can’t find a clear classification of time perception disorders. Most specialists, however, seem to share the distintion between subjective (affecting only the internal experience) and objective time disorders (the chronological time, independent from the self): distorted time perception and age disorientation belong to the latter category and are similar to the alteration of spacetime caused by gravitational fields, so much that the line separating the outside world from the psychical world becomes hidden, at least for what it concerns time.
Distorted time perception is frequently found among those suffering from mood disorders, especially depressive disorder and manic disorder. Depressed patients usually experience an objective decrease in time flow estimation, which leads them to underestimate the duration of thirty seconds (by six seconds on average); for a depressed person, the world becomes fast and the mind becomes so quiet that it causes a compression in time perception.
On the contrary, the excessive restlessness of non-psychotic manic patients (which still have reality testing capabilities) makes them overestimate the same interval; the world slows down, compared to their cerebral hyperactivity, and thirty seconds can be perceived as forty or forty-five. Age disorientation is even more interesting. It can be found in those suffering from organic pathologies such as Korsakoff syndrome or in psychotic disorders, such as chronic schizophrenia. In these conditions, time is not distorted, but stopped: as on the event horizon, these people are unavoidably trapped in a single, interminable instant of their past, while the world world around them goes on inexorably. At first sight, these patients could be just considered nostalgic, but in reality they are confined in the cultural period during which they developed the illness: they dress, talk and behave accordingly to that period, as time had no meaning to them. It is like they began to live on the edge of a black hole.
For these people, a second, which is worth less of a breath to us, can have the value of a whole life.
Graduated in Psychological sciences and techniques at Firenze University
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Rovelli, C. (2014). Sette brevi lezioni di fisica. Milano: Adelphi.
Oyebode, F. (2008). Sims’ Symptoms in the Mind. pp. 103-118, 397-424., Sauders Elsevier.
Warren H. Meck. (1995). Neuropharmacology of timing and time perception. Cognitive Brain Research 3 (1996) 227-242.
Lennart Tysk (1984), Time Perception and affective disorders. Perceptual and Motor Skills: Volume 58, Issue , pp. 455-464.
O.W. Sacks, (2008)“L’uomo che scambiò sua moglie per un cappello”, Adelphi.
S.W.Hawking, ( 2015) “La grande storia del tempo”, Bur.