Time

Physicist Mahdi Godazgar on the axis of time, Einstein's theory of relativity and the perception of time in quantum mechanics

Time is what we deal with every day and characterize as past, present and future. The progression of time is embodied in our experience, and the future becomes the present and the present the past. In fact, it is impossible to talk about movement and dynamics without the concept of time and its progression. This is similar to our perception of space. Speaking of an event, it is quite realistic to ask where it happened and when. Time, as well as spatial coordinates, is a marker for determining events. However, it is quite clear that time differs from space in the way we perceive it in everyday life. If we can walk freely in any direction along spatial coordinates, then in the case of time we are forced to move forward and all the time at the same pace. No matter how hard we try, the clock will always tick at the same pace. The future will replace the present, which in turn will become the past. This perception of time as following one direction is strangely not supported by the fundamental description of nature, and this question remains one of the most difficult mysteries of theoretical physics.

Time in classical physics and quantum mechanics

In classical physics, time is absolute and unchanging. All clocks tick at the same rate, and all people perceive time in the same way. The concept of time is very similar to our daily perception of it. However, it is important that classical physics does not choose the time axis. The flow of time in the opposite direction is a phenomenon in physics, completely equivalent to its usual flow. According to classical physics, walking forward down the street is the same as walking backwards down the street.

As far as the concept of time is concerned, quantum mechanics agrees with classical physics. Time ticks at a constant rate and is used to indicate event markers. Along with the central equation of quantum mechanics, the Schrödinger equation, which is T-symmetric, comes the concept of wave function collapse. It is the idea that the state of a system is determined only when an external observer begins to observe it that distinguishes quantum mechanics from classical. Thus, the collapse of the wave function is the process by which quantum uncertainty is resolved. This seems to be a T-symmetrical process. However, since the mechanism of wave function collapse is poorly understood, it is difficult to argue that this is the mechanism that determines the time axis. In particular, there are convincing arguments for suggesting that this is a T-symmetric process.

Time and Relativity

Einstein's theory of relativity completely changes our paradigm of understanding time. She argues that the progression of time is not universal and depends on who changes it. According to this picture of reality, the clock ticks at different speeds depending on who wears it.

By accepting a large acceleration or being near strong gravitational forces (for example, near black holes), you can change the speed of the flow of time or even stop it, turn it back. That's what the theory says. For example, for a person who is inside a black hole, space and time seem to be interchangeable, so the descent into the black hole becomes inevitable, as well as the subsequent passage of time outside the black hole. On the other hand, time becomes just another direction, like right or left. Relativity puts time on an equal footing with the spatial references we are accustomed to. Subsequently, time can be "curved", as well as spatial landmarks, which are not universal. The measure of this curvature is the speed at which time passes. Nevertheless, in the theory of relativity, the equations are also T-symmetric.

Axis of time

One of the common features of classical, quantum and relativistic mechanics regarding time is that none of the theories defines the time axis. Of course, solutions to these equations can break T-symmetry, but the theories themselves are T-symmetric. So where did T-symmetry come from? Much of the T-symmetry is the result of thermodynamics. In particular, the second law of thermodynamics states that the entropy of a system increases with time. As a result of this law, for example, you will never see how a puddle of water melting in the sun forms a piece of ice and heats the area. It should be emphasized that this law is more of a statistical statement than a rigorous mathematical result derived from the equation of fundamental physics. Why should such a statistical law be true, and how does it relate to the fundamental laws of physics? This question is now the "problem of the time axis".

Physicist Mahdi Godazgar on the axis of time, Einstein's theory of relativity and the perception of time in quantum mechanics

Time is what we deal with every day and characterize as past, present and future. The progression of time is embodied in our experience, and the future becomes the present and the present the past. In fact, it is impossible to talk about movement and dynamics without the concept of time and its progression. This is similar to our perception of space. Speaking of an event, it is quite realistic to ask where it happened and when. Time, as well as spatial coordinates, is a marker for determining events. However, it is quite clear that time differs from space in the way we perceive it in everyday life. If we can walk freely in any direction along spatial coordinates, then in the case of time we are forced to move forward and all the time at the same pace. No matter how hard we try, the clock will always tick at the same pace. The future will replace the present, which in turn will become the past. This perception of time as following one direction is strangely not supported by the fundamental description of nature, and this question remains one of the most difficult mysteries of theoretical physics.

Time in classical physics and quantum mechanics

In classical physics, time is absolute and unchanging. All clocks tick at the same rate, and all people perceive time in the same way. The concept of time is very similar to our daily perception of it. However, it is important that classical physics does not choose the time axis. The flow of time in the opposite direction is a phenomenon in physics, completely equivalent to its usual flow. According to classical physics, walking forward down the street is the same as walking backwards down the street.

As far as the concept of time is concerned, quantum mechanics agrees with classical physics. Time ticks at a constant rate and is used to indicate event markers. Along with the central equation of quantum mechanics, the Schrödinger equation, which is T-symmetric, comes the concept of wave function collapse. It is the idea that the state of a system is determined only when an external observer begins to observe it that distinguishes quantum mechanics from classical. Thus, the collapse of the wave function is the process by which quantum uncertainty is resolved. This seems to be a T-symmetrical process. However, since the mechanism of wave function collapse is poorly understood, it is difficult to argue that this is the mechanism that determines the time axis. In particular, there are convincing arguments for suggesting that this is a T-symmetric process.

Time and Relativity

Einstein's theory of relativity completely changes our paradigm of understanding time. She argues that the progression of time is not universal and depends on who changes it. According to this picture of reality, the clock ticks at different speeds depending on who wears it.

By accepting a large acceleration or being near strong gravitational forces (for example, near black holes), you can change the speed of the flow of time or even stop it, turn it back. That's what the theory says. For example, for a person who is inside a black hole, space and time seem to be interchangeable, so the descent into the black hole becomes inevitable, as well as the subsequent passage of time outside the black hole. On the other hand, time becomes just another direction, like right or left. Relativity puts time on an equal footing with the spatial references we are accustomed to. Subsequently, time can be "curved", as well as spatial landmarks, which are not universal. The measure of this curvature is the speed at which time passes. Nevertheless, in the theory of relativity, the equations are also T-symmetric.

Axis of time

One of the common features of classical, quantum and relativistic mechanics regarding time is that none of the theories defines the time axis. Of course, solutions to these equations can break T-symmetry, but the theories themselves are T-symmetric. So where did T-symmetry come from? Much of the T-symmetry is the result of thermodynamics. In particular, the second law of thermodynamics states that the entropy of a system increases with time. As a result of this law, for example, you will never see how a puddle of water melting in the sun forms a piece of ice and heats the area. It should be emphasized that this law is more of a statistical statement than a rigorous mathematical result derived from the equation of fundamental physics. Why should such a statistical law be true, and how does it relate to the fundamental laws of physics? This question is now the "problem of the time axis".