The definition of metre based on velocity of light is considered to be absolutely constant, why?

Explanation

To understand why the definition of a meter based on the velocity of light is considered absolutely constant, we can break it down into a few key points:

### Step 1: Definition of a Meter
The meter is defined as the distance that light travels in a vacuum in a specific amount of time, specifically in 1/299,792,458 of a second.

### Step 2: Nature of Light in a Vacuum
The speed of light in a vacuum is approximately 299,792,458 meters per second. This speed is a fundamental constant of nature, denoted as 'c'.

...