# What is Time?

## Background

We all have a sense of what time is. We know how to measure it with devices we call clocks but we don’t understand what creates our sense of time.

The operational definition from Wikipedia states that time is created from a certain number of repetitions in a standard cyclical event. Whether it’s the rotation of the Earth, the swing of the pendulum or the frequency of cesium, it is repetitive nature that allows us to count and measure time. ## Explanation

Energy flows in waves, which are cycles. These cycles are the repetitions that create our sense of time. Everything beats at the same rate. Time literally flows through every particle and thus every atom and molecule. Our DNA that tells our bodies when to lose our baby teeth or turn our hair grey is not based on the clocks in our bedroom or the rotation of the Earth. Time comes from every particle within our bodies, including our DNA that is made of these same atoms and particles. Time is the frequency of longitudinal energy waves. However, time is not constant.  It changes with motion. The evidence for time’s relation to wave frequency is based on Einstein’s relativity.  If the wave’s frequency changed today, we would not know the difference.  Our perception of time would still be the same; clocks would still run and would appear normal to us.  However, if we had two clocks measuring two different wave frequencies, then we would notice a difference and can establish wave frequency as the mechanism for time.

### Time Dilation

We know that time dilation is real. When an object is moving faster relative to another object, their clocks will not agree.  The commonly used example is a Person A who is on Earth.  Person B flies in a spaceship near the speed of light to the edge of our solar system and back to Earth.  Person A is considerably older – his clock has witnessed many cycles.  Person B has hardly aged – her clock slowed considerably because of her velocity.  This is time dilation.  The slowing of clocks at relativistic speeds.

Particles based on waves can explain time dilation.  When a particle is in motion, it experiences the Doppler effect.  Much like the sound you hear in a passing car, the Doppler effect compresses waves on the leading edge in the direction of travel and elongates the waves on the trailing edge. The same is true of energy waves. ### Derivation of Time Dilation

The derivation is similar to the momentum-energy derivation, in which the Doppler effect is considered on particles.  The first portion of this derivation is repeated showing the calculation of the leading and trailing edge frequencies form the Doppler equations. The geometric mean of these frequencies is taken to calculate the change in the particle’s frequency. The denominator in the above is also known as the Lorentz factor. Combining the two equations above, it is shown that the Lorentz factor applies to frequency at relativistic speeds of a particle because of the Doppler effect.  If we assume time (t) is frequency, we obtain the equation for time dilation. ## Video – What is Time?

The following video is an explanation of time based on wave theory, including relativity concepts.  The video is narrated by Kyle Yee, a fifth grader at the time of the video’s production.