The Speed of Light

Imagine an XY plane where time is Y and distance is X. A stationary object will occupy a vertical line. A traveling object is a line with non-zero slope. A purely horizontal line would be an object traveling at infinite speed, which is to say it's literally everywhere all at once. A stationary object and an infinitely fast object meet at a right angle.

But infinite speed is impossible, because you can't have anything that's everywhere all at once! It would occupy all the space! So you have to have some maximum—that is, the slightest possible slope. The smallest available Y for any given distance X. And that's the speed of light.

An object traveling at the speed of light meets a stationary object damn close to a right angle, but you can never get to 90° (because that's infinity, which we just outlawed a moment ago).

So what happens to two objects that meet, if both are going the speed of light? As Einstein said, the Y-axis itself has to stretch until they meet at less than a right angle. So: speed is a slope, yes, but relative speed (two different slopes) are an angle that can never quite approach 90 degrees.

And of course two stationary objects occupy parallel vertical lines, effectively a relative angle of zero.