Eli5: why is time considered to be the fourth dimension
In: Physics
Because it’s one of four values we use to describe the position of a point.
Think of it this way. You want to describe a particular object. You can define where it is left to right. You can define where it is back and forth. You can define where it is up and down. And you can define *when* it is. Present, future, or past.
Time is a dimension in the sense that is a value in describing the existence of a particular point. A point has four values. Where it is up/down. Where it is left/right. Where it is forward/backwards. And *when it is*.
A “dimension” in the sense of a value defining an object is not necessarily something that said object can freely move within. Time is a mono-directional dimension. Objects only move through it in one direction, for a whole bunch of reasons, chief among them is that if an object *could* move bi-directionally through time then the whole concept of “causality” breaks down and the universe would be something radically different than the one in which we live.
But time is a dimension because a point’s temporal position is defined along the “time” dimension axis. And all points are defined by X, Y, Z, and T values.
If time *wasn’t* considered a dimension then you get weird superpositioning values, as two separate points can have identical X, Y, and Z values. Which is impossible as two points can’t exist in the same place *at the same time*. The “t” value is treated as a separate 4th dimension to account for this.
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