The term “spacetime” and the concept of time being the “fourth dimension” appear to contradict each other. Is time actually a 4th dimension, or are all dimensions captured in time?
In: 22
Spacetime is a structural quality we use to conceptually represent what we refer to as the gravitational field. To accomplish this we use mathematics.
Pull out a clock and measure how long it takes you to read this sentence. You call this value time. Pull out a ruler and measure how long your keyboard is. You call this value length. These are simply coordinates. Indices. Values to organize and study the universe and their interactions with each other.
In SI units we define the meter relative to what a “second” is and the speed of light, however in general relativity we **define** both dimensions of space and time to be the same thing (called geometrized units). This is why *c* takes on the value of 1 in cosmological contexts. Historically we failed to recognize that the units for time and space should be the same, so it’s preferable to view *c* in SI units as a conversion factor.
In this way you might colloquially view it as a fourth dimension because they are defined as the same units. Having said all this, spacetime only has three spatial dimensions but is a “4-vector”. Events happen in the universe at a specific location at a specific time, so unsurprisingly we require four coordinates to describe them. Despite having the same units, time and space aren’t literally identical.
Not quite sure if any of this helped. Your question was fairly open-ended.
Latest Answers