Universe has three continuous space dimensions and one continuous time dimension, and they unite symmetrically in four-dimensional space-time {space-time, relativity}|. Time and space are not separate and independent physical properties.
events
All particles and objects move through space-time at light speed. Observers and objects move through time as well as space.
Space-time has events, not independent times and spatial positions. Observers and objects move through space-time events. Objects travel through space-time along four-dimensional-vector paths {world line}, along geodesics.
units
Space-time coordinates have the same units for time and space. Because distance equals time times velocity, distance unit can be time unit times light speed: c*t. Because time equals distance divided by velocity, time unit can be distance unit divided by light speed: x/c. Time unit can use one oscillation over one distance unit: 1 / cm = cm^-1.
relativity
Though relatively moving observers calculate different lengths and times, because lengths and times shorten in same proportion, space-time separation between two space-time events is constant for all uniformly moving observers.
regions
Different space-time regions behave differently. Regions can be inside gravity or electromagnetic sources. Vacuum regions can be near sources. Regions, such as flat space-time, can have weak fields. Regions can have weak fields but have radiation.
time coordinate as imaginary numbers
Relatively moving observers have different reference frames and relative space-times. Relative space-times differ by relative velocity (boost), which causes three-dimensional rotations into time. The complex plane and space-time coordinate system have the same properties, so time coordinate is like imaginary-number coordinate.
Physical Sciences>Physics>Relativity>Space-Time
5-Physics-Relativity-Space-Time
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Date Modified: 2022.0224