Then there's the matter of reference frames. In physics, a reference frame simply denotes where an observer happens to be standing; it's similar in concept to a point of view.
In Einstein's equations, there is no such thing as a universal, stationary frame of reference because every object in the universe is constantly moving through time and space.
The laws of physics still apply equally in every individual frame of reference, and the speed of light is constant in all frames of reference. But strange things start to happen near the speed of light - e.g., moving away from an object at those velocities means you will perceive that object as being closer. Weird, right?
Also, whenever an object with mass is in motion, its measured length will shrink in proportion to its speed; the faster it goes, the more its length will shrink - the aforementioned length contraction. No object with mass can reach exactly light speed, but if it did, it would shrink to nothing.
Because time and space are linked, something similar happens with time: it slows down with motion - time dilation - until time, too, dilates to nothing. None of this is apparent to the object that is moving, only to an outside observer in a different reference frame.
Length contraction and time dilation mean that there can be no such thing as two simultaneous events, when each is viewed from a different frame of reference.
Space and time are not fixed. The distance between two points in space, and the time between two events, depends upon the observer's point of view.
Confused yet? If you haven't encountered these concepts before, special relativity can be a bit of a conceptual challenge. A Slower Speed of Light lets you see how relativistic principles play out in a virtual sphere.
The objective of the game is to collect 100 orbs as you move through the game space, except with every orb you collect, the speed of light gets slower. That's when things get interesting. Per Ethan Siegel at Starts With a Bang:
The colors start to change, distances start to appear counterintuitive, and, well, you're challenged to develop an intuition for moving at relativistic speeds, because the speed of light has slowed! When you've successfully collected all 100 orbs, you're rewarded with the red/blueshifts turned off, and you merely observe the effects of the Lorentz transformations, which are still incredibly freaky!
It's a little tricky at first to figure out the controls, but worth the effort in the end to see what the world of relativity looks like from the perspective of, say, a photon, or an accelerated particle in the Large Hadron Collider. It's available for both Mac (here) and PC (here).