Why Does Time Fly When You're an Adult? Another Dimension Not Explained by Jentsch's Rule

Everyone knows "Janeway's Law," but what lies beyond it?

"It's December already?"

Every year as an adult, I find myself saying the same thing. The year, which felt so long when I was a child, speeds up with each passing birthday.

This phenomenon has a name. It's called the Janer's Law.

This is a law proposed by French philosopher Paul Janet in the 19th century, which states that the perceived length of time is determined by its ratio to one's entire life lived up to that point. For a 5-year-old, one year is one-fifth of their life. For a 50-year-old, one year is one-fiftieth of their life. The older one gets, the smaller the relative weight of a year becomes, and time accelerates.

A common background reason cited is the decrease in new experiences. First-time experiences are remembered for a long time, while familiar repetitions pass by quickly. The road to a new place feels long, but the way back feels short. A child's every day is filled with first experiences, while an adult's every day is made up of known repetitions.

So, the standard countermeasures become this: Challenge new things. Go to places you've never been. If you bring freshness back into your daily life, you can extend your perceived time, they say.

Up to this point, this is the standard explanation that you can find anywhere with a search.

And now, for the main point.

Where does the axis of subjective time exist?

Jenkin's Rule explains "why subjective time seems to shrink."

However, it does not answer the question that precedes it.

Where does the axis of "perceived time" actually exist?

The time on a clock moves forward at the same speed for everyone. A year for a 50-year-old and a year for a 5-year-old are exactly 365 days on the clock. Yet, the perceived length is vastly different. This means we live another kind of time, one that stretches and shrinks independently of the clock's time.

The law of Jane is merely a description of the pattern of this expansion and contraction, predicated on the existence of this "other time." The axis that expands and contracts remains outside the scope of the law.

The dimension of thickness ── T = t + it

Thirty minutes of a boring meeting and thirty minutes of being engrossed. On the clock, it's the same thirty minutes, but in terms of experience, they have completely different depths.

This thickness cannot be achieved no matter how finely you divide the clock face. Only a series of dimensionless moments align on the time axis t, and there is no space to inscribe the difference between a "dense 30 minutes" and a "sparse 30 minutes."

On the clock's timeline, there is no place for perceived time.

If that's the case, then perceived time expands in a direction different from the t-axis—a direction orthogonal to the t-axis.

The fifth thesis, "Imaginary Time," by Murai, directly formulates this structure. A complete description of time is given as a composition of the real time axis $t$ and the imaginary time axis $it$ orthogonal to it, $T = t + it$. The expansion and contraction of experienced time are recontextualized not as phenomena on the $t$-axis, but as changes in thickness in the $it$ direction.

A child's day doesn't feel long because the length of the t-axis is different, but because the depth is different.

The meaning of "to make time longer" changes

Seen in this new light, the meaning of "making time longer" also changes.

Increasing new experiences isn't about filling your schedule with activities. In fact, everyone has had a year that felt like it flew by because they were so busy. No matter how much you fill your schedule, time without depth remains shallow. Conversely, quiet time spent doing nothing can have an unforgettable depth to it.

The year passes quickly not because of aging or a mere illusion.

As long as you only consider clock time as time, another dimension will wither away. Behind Janet's Law lies a deeper structure of time. We welcome anyone interested in exploring this.

↓Yuma Murakami's Fifth Paper "Imaginary Time - Non-closure of Description and the Principle of Minimal Extension" is here↓

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