I’ve written about 1D space + 3D time before, such as *here* and *here*.

Time is measured in terms of the annual calendar and the daily clock. Clocks are based on the apparent motion of the Sun and other celestial bodies across the sky, divided into 24 hours. The calendar is based on the annual cycle of the Sun’s declination (the angular distance north or south of the celestial equator), divided into 12 months and 365 (or 366) days. Thus time is measured in terms of the Earth’s orbital and rotational periods.

Length may be measured similarly. The original definition of the metre (meter) in 1793 was one ten-millionth of the distance from the equator to the North Pole. What is required to measure 1D space is a natural periodic motion whose travel distance may be accumulated indefinitely. What corresponds to the clock could be the motion of the night shadow across the face of the Earth at the equator:

*So the evening and the morning were the [Nth] day. Genesis 1*

The circumference of the Earth is 40,075,000 m. This is the distance moved by the edge of the day-night boundary in 24 hours. Then one hour is equivalent to 1,669,792 m and one second is equivalent to 464 m. The shadow motion may be accumulated indefinitely to make 1D length, similar to 1D time.

Whichever dimension is limited to 1D is the measure of a motion from the perspective of the object in motion, whether this is measured by the distance or duration. Since the 1D variable is the independent variable, this is selected as a standard motion available (in principle) to everyone. So the 1D variable becomes a universal length or time against which to measure motions in 3D of time or space, respectively.

*Related*