If the above physical definition of time is correct, people may still have the following questions:

(1) Understanding Time Before Human Existence

People often say: Humans have only lived on Earth for about a million years, while Earth itself formed 4.6 billion years ago. So time existed before humans - how can it be a human sensation?

Past and future are defined relative to our present time. In other words, wherever there is a present, there must be a past and future. If Earth never had humans, there would be no past or future. Without humans, how could there be time "before humans" or "after humans"? You can't first exclude humans, then use humans to define something.

Time's sequence (before/after/now) is like geographical directions (east/west/north/south) - none are absolute, all are relative to humans. Think about it: without humans, how could there be east/west/north/south? Up/down/left/right? Before/after?

(2) Could Time Be Animals' Sensation?

Some ask: Could time be a sensation of pigs, cattle, or other animals? If so, how can we precisely define it as humans' sensation of spatial position changes? Or should we call it pigs' sensation of spatial position changes? If not, why not? Just because pigs' brains aren't as smart as humans'?

Actually, time's definition can be broadly understood as: a sensation of spatial position changes by any being capable of perceiving motion. Humans express this sensation with the word "time," while pigs might express it with grunts.

(3) How Time Links to Moving Objects

When describing an object's motion through space, at the most basic level we need to understand how far it moves in a certain time period. While this wasn't problematic when we were unclear about time's nature, once we recognize time as merely a human sensation, questions naturally arise:

Can this moving object connect with our sensation? Or stepping back: if we're not present in that situation, can't the object's motion be described? Or does it lack a definite form of motion?

When an object appears stationary to us observers, we can completely consider this object unified with us as one object, even though we humans have flesh and blood, developed brains, and chemical properties that may be vastly different from the object.

It's entirely possible for us to describe one object's motion relative to another object.

Humanity's consistent approach has been: when describing an object's change in spatial position, if an observer is present, they will say how far the object traveled in a certain time period.

When observers aren't present, they will always seek a reference object, silently equating themselves with it, considering this reference object unified with the observer as one.

This is actually what everyone does - when we describe an object's motion, we always specify how its position changes relative to us as observers, or how it changes relative to what we consider a stationary object

(4) The Common Measure of Time

Time could be Zhang San's sensation of surrounding spatial changes, or Li Si's sensation of surrounding spatial changes. With so many people on Earth, how can there be a common measure of time?

All moving observers and perceivers naturally record their sensations of surrounding spatial changes in their minds, then equate these with Earth's rotation, Moon's motion, Sun's motion, cesium atom vibrations, pulse beats, etc. Finally, everyone agrees to equate their surrounding spatial changes with one particular motion, like Earth's rotation, creating a common measure of time.

(5) Viewing Time as Just a Process

Some argue: Objectively analyzing, time is just a process - this judgment can't be wrong, thus proving wrong the view that time is human sensation.

The continuous change in observers' surrounding spatial positions is indeed a process. Viewing time as a process isn't wrong, but this understanding of time's nature is just unclear and insufficient, not contradictory to other views.