Gravity, as we know today, has the ability to twist space and time. As Einstein argued in the General Theory of Relativity (GTO), time goes slower as we approach the Earth. This is because gravity of a large mass, such as our planet, curves space and time around it.
This effect is called the “time slowing down effect” and it manifests itself even on small levels. Outside the physical laws, however, we perceive time differently, more precisely, distortedly. So, if you place one clock on the top of a mountain and leave the other on the beach, you will eventually see that all clocks show different times!
For the first time, the scientists observed the effect of time slowing down on a cosmic scale, when the star was passing near a black hole. Then, the same effect was recorded on a smaller scale – the researchers used a pair of extremely precise atomic clock mechanisms, and some watches were located 33 centimeters higher than others. The results showed that time slowed down again on a watch closer to Earth.
Time is heterogeneous: it flows at different speeds depending on where you are and at what speed you are moving.
The atomic clock is a device for measuring time. As a periodic process, it uses its own vibrations associated with processes occurring at the level of atoms or molecules.
The effect of time slowing down
Time deceleration goes back to Einstein’s Special Relativity Theory (STO), according to which movement in space actually creates changes over time. The faster you move through the three dimensions that define physical space, the slower you move through the fourth dimension, time, at least in relation to another object. So the clock in motion will be ticking slower than the clock on the ground. If you move at a speed close to the speed of light, the effect will be much more pronounced.
It is important to understand that time slowing down is not a mental experiment or a hypothetical concept, but a reality. This was proved by the Hafel Kitting experiments carried out in 1971, when two atomic clock mechanisms were mounted on aircraft flying in opposite directions. The relative movement actually had a measurable effect and created a time difference between two hours. This was also confirmed in other physical experiments.
Why do we remember the past and not the future?
But there is another remarkable detail: the slowdown of time due to gravity effects. You may have seen Christopher Nolan’s film Interstellar, where the proximity of a black hole makes time on another planet extremely slow (one hour on this planet equals seven Earth years). This form of time slowing down is also real. It is all about Einstein’s General Theory of Relativity, as described at the beginning of this article – gravity can curvature space-time, and therefore time itself. This means that absolute time does not exist.
The closer the clock is to the source of gravity, the slower time passes; the farther the clock is from the source of gravity, the faster time will pass.
So, for all the watches in the world and for each of us, time flows slightly differently. But even if time flows at constantly changing speeds across the universe, time still flows in some objective sense, right? Or does it not?
Physics without time
In his book “The Order of Time”, Italian theoretical physicist Carlo Rovelli suggested that our perception of time – our feeling that time flows forever – can be a highly subjective projection. After all, when you look at reality on the smallest scale (using quantum gravity equations, for example), time disappears.
So, why do we perceive time as moving forward? Rovelli notes that although time disappears on an extremely small scale, we observe entropy: order becomes disorder; an egg breaks down and becomes an egg. Rowelli writes that key aspects of time are described in a second law of thermodynamics, which states that heat always goes from hot to cold, like a one-way street. For example, an ice cube melts in a cup of hot tea, not vice versa. Rovelli suggests that such a phenomenon can explain why we are able to perceive only the past and not the future.
“Every time the future definitely differs from the past, some kind of warmth appears,” Rovelli wrote in an article for the Financial Times.
Thermodynamics traces the direction of time towards something called the “low entropy of the past,” still a mysterious phenomenon that is being debated. “The growth of entropy orients time and allows traces of the past to exist, and they allow the possibility of memories that reinforce our sense of identity. I suspect that what we call the “flow” of time should be understood by studying the structure of our brain rather than by studying physics: evolution has turned our brain into a machine that feeds on memory to anticipate the future. This is what we listen to when we listen to the flow of time. Thus, understanding the “flow” of time may have more to do with neurobiology than with fundamental physics. Finding an explanation for the sense of flow in physics may be a mistake.
Scientists still have a lot to learn about how we perceive time and why it works differently depending on the scale. But there is no doubt that beyond physics, our individual perception of time is also surprisingly elastic.
The strange subjectivity of time
On top of the mountain, time moves differently than on the beach. But to experience a distortion of perception of time, you do not need to go to the mountains or to the sea. Thus, in moments of intense fear, the brain releases a lot of adrenaline, which accelerates the internal clock, forcing the perception of the outside world as moving very slowly.
Rovelli notes that to work in the field of quantum gravity will have to face questions about the nature of time.
Another common distortion occurs when we focus our attention in a certain way. As Aaron Sackett, Associate Professor of Marketing at the University of St. Thomas, notes in an interview with Gizmodo, if you think about how time is currently passing, the most important factor affecting your perception of time is attention.
The more attention you pay to the flow of time, the slower it flows
When you distract yourself from the flow of time – perhaps from something interesting that is happening nearby – you are more likely to lose track of time. There is a strong feeling that it slips away faster than before. A well-known saying goes: “Time flies when you’re having fun,” but reality is more like “time flies when you think about other things.
In turn, Rovelli believes that what we call time is a rich, stratified concept with many layers. Some layers of time are only applicable to a limited extent in limited areas, but this does not make them illusions. The illusion is that time flows at absolute speed. The river of time may flow forever, but it moves at different speeds, between people and even within your own mind.