What is time? And why does it seem to go faster as you get older?

Think back to those sun-drenched summer holidays in France from your childhood. Yellowed photos of equally yellowed cotton tents are the congealed snapshots of them, but try to recapture the feeling of the length of that vacation. It lasted forever, didn’t it? And at the same time the days flew by. Older people notice just the opposite: the days don’t end, but you don’t pay attention and another year has passed.

VolkskrantReaders are amazed at how we deal with time. ‘If you have to wait ten minutes for the train, it seems to take an hour. But if you only have ten minutes left to catch the train, it seems like five minutes’, writes Martha Hoek, for example. Others wonder if time even exists at all or if it is just an appointment that we humans have made.

They are in good company. ‘What is time?’, the church father and theologian Augustine wondered in the 4th century AD. ‘As long as no one asks me, I know; but if I want to explain it to someone who asks me, I don’t know’.

No man can step into the same river twice, for it is not the same river and he is not the same man, Presocrat Heraclitus remarked nearly a thousand years earlier. Everything is under the influence of time in a continuous state of change. Everything flows: panta rhei. It was an unsatisfactory starting point, it turned out later, because the philosophers after him were mainly looking for the unchanging. In fact, the time came very poorly: the true being is the eternal now. If only it were that simple. Of course there are special moments in which we have the idea of ​​being totally present and living in the now, but much more often we experience the scourge of time, which eats away the future like a pac-man at lightning speed.

Maybe it doesn’t have to be that complicated after all. For as a famous quote, alternately attributed to literary greats, philosophers, and physicists, states: time is what prevents everything from happening at once.

‘Quite a nice summary’, says theoretical physicist Carlo Beenakker of Leiden University. ‘We have known since Einstein: time is not absolute’, he says. Where everyone – including physicists – used to tacitly assume that the cosmos follows the compelling rhythm of a universal metronome, reality turns out to be more unruly. Move faster or get close to a heavy mass and time will flow differently, according to Einstein’s theory of relativity, like a river full of rapids and slowdowns. Panta rhei, but different.

Moreover, that is more than ‘just’ theory. ‘Our GPS satellites, for example, compensate for that effect every day,’ says Beenakker. And so, as is often the case, Einstein was right. That he came to his conclusions by calculating everything within a four-dimensional reality – space-time – which links the three known spatial dimensions (top/bottom, left/right, front/back) with one of time (earlier/later), also implies that it is something real. Time is not an illusion.

The arrow of time

Yet time behaves differently from space. Where you can easily travel to work or school in the morning and return home the same route at the end of the day, there is no such thing in time. It follows an arrow that forces us from earlier to later. The future irrevocably becomes the past, but the past never becomes the future.

Yes: there are some – highly theoretical – ideas about how you might one day make the clock tick back, but those are probably curiosities. ‘Can I completely rule out the possibility that you can, for example, ever send a particle back in time by a nanosecond? No,” says Beenakker. “But more than that I think is impossible.”

According to him, you see this especially when you look at how logically the universe works as soon as you forbid travel to the past. ‘If you don’t, our free will will be compromised, for example,’ he says. After all, anyone who can go back to the past can suddenly reverse the order of cause and effect.

But why does time really move forward? Most physicists look for the answer in physics, thermodynamics. Now take a movie of a bouncing ball. ‘When I play that backwards, everyone immediately sees that it’s not right: the ball will bounce higher and higher. That’s strange’, says Beenakker. The reason is that behind the scenes friction causes the ball to lose energy in the form of heat, for example. And that’s how it should always be: a cup of hot coffee always cools down on your desk and doesn’t get warmer spontaneously. This ‘second law’ of thermodynamics, many physicists suspect, gives time its direction.

grainy stuff

But do they also know ‘what’ that time is made of? We count it in daily life by the ticking of our clocks, dividing it into cubes of days, hours, or seconds. But is there also a smallest block? Is time a continuously flowing river or a granular substance?

‘Nobody has an answer to that yet,’ says Beenakker. You would first have to be able to capture time very precisely in the laws of quantum physics, which describe the state of physical reality on the smallest possible scale.

On that scale it is quite conceivable that time is indeed granular, consisting of ‘pieces’ as long as a so-called planck time, a time interval of 5.39 x 10⁻⁴⁴ seconds. That is so staggeringly short that any comparison to anything in the normal world falls short. But whether that is really the shortest possible time, nobody knows. ‘Maybe we’ll find an answer when we have an ultimate theory of everything,’ says Beenakker. One that mathematically combines Einstein’s theory of general relativity with quantum physics, a goal that has been just out of reach for decades.

Just like the answers to all the remaining physics riddles around time are hiding in almost inaccessible places. Inside black holes, for example, where time may stand still. Or shortly – a Planck time – after the Big Bang, when space and time came into being, a period completely beyond our perceptions.

Things are so far beyond our everyday world that new insights may reveal what the basic fabric of reality looks like, but at the same time have little to say about how we humans experience time.

Time illusions

Around 1900, the French philosopher Henri Bergson made a useful distinction between time as studied in physics and time of consciousness. So it’s high time to untangle the tangle a little further and travel by train to Groningen for a conversation with Douwe Draaisma, professor emeritus of psychology at the University of Groningen and author of the bestseller Why Life Speeds Up As You Get Older from 2001. Draaisma is fascinated by so-called time illusions: the moments when our experience of time deviates from the clock time. And of course also because of the question that logically follows. Namely: which factors influence this?

But before that, let’s just briefly explain how we estimate time, independent of external clocks. In general, and under normal circumstances, it works quite well. Ask someone to estimate how long a minute lasts, then the deviation is really not that big. In everyday language we speak of a biological clock, but this is not the case. Of what Draaisma calls a ‘subtle interplay’ of dozens of physiological clocks. For example, our heart rate, blood pressure, respiration, metabolism, cell division. All with their own cycle.

While seated in an establishment in a place in the center of Groningen where time seems to have stood still (the Prinsenhof), Draaisma points to one of his fingers. The top is hidden under two thick plasters. “It takes forever for this cut to heal these days. If my granddaughter had a similar wound, it would heal in no time.’

undisturbed

It is one of the explanations that Draaisma also gave twenty years ago in his book for the phenomenon that time seems to go faster and faster as we get older. Our internal clocks run slower, making the world around us faster. Following the example of the French microbiologist Alexis Carrel, in his book, Draaisma uses the analogy of a river that slides at a steady pace through lowlands.

During the first hours, man runs briskly along the bank, faster than the current. After that, around noon, the river and the man go together for a while. And eventually, at the end of the day, he gets tired and falls behind. “Finally he stops and lies down, beside a river that continues its course at the same imperturbable pace it has flowed all day.”

The irrevocable passing of time (ageing) therefore disrupts our perception of time, but there are many more factors that make time shrink or expand. Our body temperature, for example. With a fever, everything seems to take much longer. Another important factor is whether something is happening in your life. If you don’t experience much, the days will creep up. And, as we noted earlier, the years pass by.

Draaisma speaks of an inverse relationship between how fast time seems to pass during experience and how we look back on it. That works both ways: short days go hand in hand with long years and vice versa. But that’s not enough, the psychologist warns: ‘Time does not only expand with little activity, but also with extremely high activity.’ Think of the last seconds just before a collision, which seem to be stretched to the absurd.

Telescopy effect

Okay, one last time illusion then: the telescopic effect. ‘With major events you tend to underestimate how long ago that was.’ Take the murder of Peter R. de Vries, which took place a year ago, much to the surprise of many. “The fact that you have sharp memories makes you look through a telescope, so to speak, which makes you think that something happened much more recently.” Lots of detail? It must be a short while ago, we mistakenly think. ‘Ironic really. Then our memory works well for once and we can remember many details, but then we estimate the time completely wrong again.’ Draaisma can laugh about it.

The return journey from Groningen seems to take much shorter than the outward journey. A river flows in the distance.