Time Perception: Where Does Time Go?

Where does time go physically?

Time, by itself, isn’t a physical object. It is a product of human perception; there are no literal “time particles” that push time along, at least not any outside of speculative theories. However, science has linked time with physics through the notion of spacetime (or space-time). Spacetime considers how time and physical reality intersect, and popular “fourth dimension” models of time emerge from the concept of spacetime. 

Four-dimensionalism asserts that any physical object has different “temporal parts” for every instance in time in which it is located. Think of temporal parts as frames on a film strip. Each frame represents a snapshot in time, or a temporal part, of whatever is pictured within it. Much as a film strip creates the illusion of motion when it runs through a projector, the movement from one temporal part to another creates the illusion of time passing in space. 

What happens to time when it is passed?

Despite phrases like “Where does the time go,” time is not a physical object and does not experience the effects of the physical universe in ways most humans intuitively understand. Time does not physically “pass” any point in space. Referring to time passing is a product of human perception, a part of the human experience that we can use to understand the world around us. 

Time is relative, which in this case means that time exists relative to a physical object or object but is not a property of it. For humans, time tends to be kept by natural rhythms, like the rising and setting of the sun. The body’s master clock helps synchronize biological systems, but it, too, is relative. Like most uses of time, the master clock serves a synchronous function, meaning it helps bodily functions stay in rhythm with one another, much like people use clocks to stay in sync with one another. 

Which way does time go?

On human scales, time’s arrow is always moving toward the future; it is not possible to move backward through time. However, a concept known as thermodynamic asymmetry may indicate that time is not so unidirectional at smaller scales. The laws of thermodynamics illustrate a concept known as entropy. In the physical world, any thermodynamic system can move from a high-order (or high-energy) state to a low-order state using the energy in the system but cannot move from a low-order state to a high-order state unless energy is added. The system will eventually reach equilibrium or maximum entropy if energy isn't introduced. 

For example, consider a thermodynamic system consisting of an iron bar and a bucket filled with water. Before being introduced to the system, the iron bar is heated until bright red. Predicting the effects of such a simple system can be done intuitively; when the iron bar is dropped into the bucket, it will immediately heat and boil the water within (assume steam is trapped and condenses back into the bucket). The iron has a high-energy state, and the water has a low-energy state. The iron rod will continue to transfer heat until it is at the same temperature as the water around it. Once that point is reached, the system is at equilibrium, and no change will occur unless additional energy is added. 

Humans intuitively understand energy can only move from high to low states. A ball won’t roll up a hill by itself, but placing it on top of a hill imparts it with potential energy from gravity, meaning the system has energy and is not in equilibrium. It is easy to see the energy asymmetry in a thermodynamic system; it can only move in one direction. 

While the arrow of time in thermodynamic asymmetry is intuitive at human scales, mathematical models pose a problem. Consider the water bucket and iron bar system described above; if you were to zoom in on the water so much that you could see individual water molecules, you would notice that the arrow of time disappears. If you could record a video of two water molecules colliding, upon rewinding it, you wouldn’t be able to tell which way was forward and which way was backward. At the molecular level, the phenomenon that produces heat (molecules colliding) is time-symmetric, and is not necessarily bound by the laws of thermodynamics. 

Is 1 hour in space 7 years on Earth?

It is a myth that one hour in space equals seven years on Earth, for the most part. The misconception is attributed to the movie Interstellar, and the “one hour, seven years” description refers to a fictional planet called “MIller’s Planet.” Miller’s Planet orbits a supermassive black hole named Gargantua, significantly slowing down time on the planet’s surface. Although Interstellar is fictional, the concept they refer to, time dilation, is real. 

The concept of time dilation is defined by Albert Einstein’s theories of general and special relativity. Special relativity defines the relationship between an object’s mass, its velocity, and time. It states that as an object approaches lightspeed, its mass becomes near infinite, and time slows proportionately. Theoretically, a person moving at or near lightspeed would experience a stoppage of time around them. 

General relativity incorporates gravity into Einstein’s theory and is where Interstellar derives its inspiration for the passage of time on Miller’s Planet. It states that the closer an object is to a source of gravity, the slower time moves relative to areas with lower gravity. In Interstellar, the gravity of the black hole is strong enough to slow time sufficiently such that one hour on Miller’s Planet equates to seven years on Earth. 

Is time a dimension?

Time is often referred to as a proper dimension, although physicists aren’t satisfied with that description. The concept of describing time as the fourth dimension arises from the problems encountered when trying to describe the positions of objects in spacetime. Consider a standard X-Y plane. Y is the vertical axis, and X is the horizontal axis. One can use coordinates (X, Y) to plot the position of an object on the plane. 

Now, imagine that the plane is transformed into a cube with equal sides. While the plane was two-dimensional, the cube is three-dimensional and thus has another axis to represent the third dimension, Z. As before, coordinates can be used to plot an object's position within the cube, this time with the points (X, Y, Z). To mark exactly where something is in the cube, one merely needs to know where it falls on each of the three axes. 

While three dimensions work fine for navigating a three-dimensional physical world where nothing changes, problems emerge when considering an object’s position in time, also called its temporal position. In our original cube model, an object cannot occupy the same space that another object occupies. Once an object is located at certain coordinates, nothing else can occupy that space. 

Of course, spacetime - and real life - consider time and change. Our original cube model doesn’t consider movement; objects are fixed in place, and time does not progress. By adding a fourth dimension to the cube, time, it is possible for two objects to occupy the same physical space, so long as they do it at different times. This creates a four-coordinate system, commonly represented as (X, Y, Z, W). An object’s position in time is now factored into its location in spacetime. As with the 2nd and 3rd dimensions, two objects can't simultaneously occupy the same coordinates.  

Is it possible to travel time?

Physical time travel between the past, future, and present, like that portrayed in movies and TV shows like Dr. Who, is impossible. While fringe theories exist, often based around wormholes, black holes, and string theory, they are all speculative and based only on educated guesses of scientists. A person can only travel toward the future, even if where it takes them is not the future they wanted in the first place. 

While physically traveling time is likely the stuff of science fiction, at least for the foreseeable future, it is possible to modulate your perception of time. Humans don’t always feel the motion of time the same way. For example, many people report “time blindness” - a failure to notice that time has passed, often for hours - when highly engaged in an interesting task. While human perception may be malleable, the laws of physics are more rigid, and until science fiction becomes reality, it is the only connection to time travel we have. 

Is time created by the brain?

Time isn’t created by the brain per se, but it is often considered a product of human perception. Instead of saying that time is “created” by the brain, it might be more accurate to say that the brain enables the sensation of time passing to occur. The brain even has an internal clock, likely located in the right prefrontal cortex, to estimate how much time has passed. 

Despite the brain’s neural mechanisms for tracking time, human perception of time isn’t always accurate. A person’s sense of time is not always prioritized in their consciousness; “time blindness” is a frequent occurrence in people who are highly engaged in a task at their job or home. It occurs when a person’s feeling of the passage of time is not present.  In that sense, the brain also has some control over time, or at least how important its perception is at a given moment. 

Is time finite or infinite?

Time is infinite. It is not a resource to be consumed or a physical reserve that can be depleted. The human perception of time is simply a way to conceptualize changes in the physical world. Consider a cup of liquid water. The water molecules are constantly moving and colliding, and it is that energy that lets the water stay in its liquid state. 

Now, let’s introduce some science fiction. Imagine you have a magical button that, when pressed by your research partner, stops time for everything and everyone except the two of you.  You also have magical goggles that let you zoom in on the water molecules in the cup until you can see them individually. At this scale of the goggles, you can’t see anything but the molecules and how they interact with each other. Progressively, you lower the water’s temperature until it reaches absolute zero, or the temperature where all molecular motion stops.

From your perspective, while wearing the goggles, how would you know whether your fellow researcher had hit the “stop time” button or if you had reached absolute zero? In both cases, you would perceive that all motion among the water molecules stops. Without change (in this case, motion), perceiving time is impossible, but time hasn’t “run out.” When the water is re-warmed from absolute zero, motion will resume, and time will appear to “restart.” That is why time is infinite. In any system (including all of existence), the length of time between states will always be measurable as long as there is enough energy for change to occur.  

Why did Einstein say time is an illusion?

When Einstein spoke of time being an illusion, he was referring to the relative nature of time. The way an object experiences time depends on what reference frame that object has. Consider two cars traveling down the highway side-by-side. Car A is traveling 60 miles per hour, and Car B is traveling 65 miles per hour. From the reference frame of an observer standing on the side of the road, both cars appear to be traveling around 60 MPH. However, from Car A’s reference frame, Car B appears to be moving around five miles per hour. 

This is the illusion Einstein's words refer to. Depending on where you’re observing from, the cars appear to be moving at drastically different rates. Of course, both cars were moving at a constant velocity; the relative speed difference was solely based on the observer's reference frame. 

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