Time as a Measurable Quantity

Before delving into the effects of time on us, it's essential to define what time actually is. At its core, time is a measurable quantity, tracked using clocks, stopwatches, and calendars. It progresses in seconds, minutes, and hours—or even in alternative units like the Mayan Baktun. However, it is not something we can physically touch or observe; we cannot encapsulate it in a test tube.

Time is fundamentally a one-directional process, governed by the Second Law of Thermodynamics, which states that the entropy of a closed system can never decrease. Considering our universe as a system, we can only move forward in time. Yet, this concept is not as simple as it seems.

Experiments involving time dilation reveal that time does not flow uniformly. Clocks in motion tick more slowly compared to stationary ones. While this may seem perplexing, it leads to fascinating phenomena, as depicted in the movie Interstellar (revisit those extraordinary moments). This principle is also pivotal in technologies such as GPS (learn more about it).

Where does time originate from? The prevalent view is that "everything began with the Big Bang," a notion embraced by both scientists and fans of the sitcom The Big Bang Theory. Before this cosmic event, neither space nor time existed, a concept that challenges our fundamental understanding since our lives revolve around the passage of time. Thankfully, time persists, alleviating us from the need to grapple with its absence.

An intriguing fact: the official definition of a second is based on a specific atomic process that occurs nearly 10 billion times in one second. Thus, while we can estimate a second, its precise measurement relies on advanced experiments beyond our natural capacities.

Perception of Time

Photo by Jon Tyson on Unsplash

Time transcends mere measurement; it is a vital influence in our daily lives. Alarms prompt us to wake, work schedules dictate our days, and we eagerly await the moment we can finally leave our responsibilities behind. Our hunger cues and feelings of longing for loved ones are all intricately tied to the passage of time. Therefore, time should be considered a fundamental aspect of human behavior and existence.

Most major physical quantities are expressed through human-centric metrics: seconds (s), meters (m), and kilograms (kg). These base units, known as the International System of Units (SI Units), are defined in ways that are relatable to human experience. A meter is approximately the length of our bodies, a kilogram is something we can easily lift, and a second is a duration we can readily respond to.

But is our experience of time uniform? Just as humans come in various shapes and sizes, our perception of time also varies. While a short person may measure just over half a meter, the tallest individuals remain under three meters. It’s reasonable to utilize meters for our understanding, and the same holds true for our perception of time.

Time is often perceived as a sequence of events. But how many occurrences can we register in a single second? Research indicates that the average human brain processes about 60 distinct events per second. While this may seem substantial, it is, in reality, quite limited.

In 2014, researchers examined how different animals perceive events, revealing a wide range of perception rates—some animals perceive events up to four times slower or faster than humans (Small Animals Live in a Slow-Motion World). For example, turtles register around 15 events per second, while houseflies experience an impressive 250 events per second. This disparity explains why catching that pesky fly can be so challenging.

Inherent Human Limitations

Photo by Alina Grubnyak on Unsplash

Time is ultimately a matter of perception, and while we share a common experience of it, our biological limitations shape our understanding. Imagine a reality where time flows at different rates for different people—thankfully, that is not the case. So, how do we arrive at this shared perception?

We typically gauge our perception of time through reaction speed, which is the fastest response we can make to external stimuli. This speed essentially represents our maximum capacity for processing any events occurring around us.

Reaction speed can be broken down into three primary components:

1. Perception: Light must travel from an object to our eyes and then to our brains.
2. Processing: Once the signal reaches the brain, it must be interpreted and transformed into action.
3. Response: After processing, we generally execute a physical response, like a hand movement.

For instance, consider the moment we perceive a ball flying toward us and prepare to catch it. Let’s estimate how long it takes to 'see' the ball:

• Perception: Light travels from the ball to our eyes at 300,000 km/s, taking less than 10 nanoseconds.
• Processing: The signal, once received, is converted into a chemical signal that travels through the optic nerve to the brain, which takes a few milliseconds (see link).
• Sampling rate: We can only perceive objects every 20 milliseconds.

Total time: 10 nanoseconds + 1 millisecond + 20 milliseconds = 20 milliseconds.

Processing is more intricate due to varying neural firing rates. Generally, signals travel at about 10 m/s along an average axon, taking approximately 0.1 milliseconds to traverse 1 mm. Given possible loops in processing, we can estimate processing to take hundreds of milliseconds.

Total time: 20 milliseconds + 100 milliseconds = 100 milliseconds.

The response time is similar to perception speed, constrained by the nervous system's and muscles' performance (see link). Collectively, we can assume reaction speed is around 0.2 seconds, a figure consistent with various reaction time assessments such as The Human Benchmark. Test your own reaction speed!

The most common reaction time is 225ms as measured by the Human Benchmark.