Is time a real fourth dimension, or did Einstein invent it?

First, there is no fourth dimension, and no fifth; by Euclidean geometry there are only three, and Euclid is not going to change. The so-called fourth dimension was invented by Einstein through special relativity. His rule is that anything moving is contracted in its length, because he had to keep the earth moving in the Michelson-Morley experiment, where the measuring device supposedly shrank just enough to mask the earth's motion around the sun and give a false positive for a fixed earth. But if the moving object shrinks, it takes more time to get from point A to point B, so you have to dilate the time to compensate; that is time dilation. Once length and time are intertwined this way, you cannot separate them, and you get spacetime, which is not a substance you can put your hand through, just a mathematical device to fuse Euclidean geometry with time. Einstein tried to make everything relative, and the only way to do that is to remove the distinctions and make them one. But there is no fourth dimension; it is only a term used to make it look like there is another dimension.