exfret wrote:Wait, so time is a dimension, right? Then how many meters are in a second of time dimension?

In physics, we do sometimes use the same units for time and distance. In which case, the speed of light is the conversion factor.

So 1 second would be 3x10^8m... or more generally, distance=time*c.

This is sometimes called 'letting c=1'. A common way to choose your units in advanced physics such that there are a)no c's in your equations, and b)there's a lot more symmetry and elegance in the equations.

So instead of E=mc^2, you get E=m. (Which also means that energy and mass have the same units in this system! If you go down the rabbit hole it gets really mind boggling.) You never do this in high school, or standard physics classes. But if you're dealing with a lot of relativistic stuff, it's a helpful shorthand.

As a further note, even when we *aren't* going out of our way to change units like this (and letting c=1) -- the same idea holds true. There are equations where you have to add space and time units. For example, finding the distance between two events. In normal 3D Newtonian space, spatial distance is just d^2 = x^2+y^2+z^2 (assuming one of the things is at the origin, of course). But in relativity, you want the distance to include the *time* dimension, too. In which case, the equation becomes d^2 = x^2+y^2+z^2-(c*t)^2

So to get the units to be the same, here, too, 'c' gets multiplied onto the time variable. (The negative sign is a whole 'nother can of worms)