[jobigoud]

An actual 4D printer could be trivial though. Just like the 3D printer discretize the height in several layers, the 4D printer would slice the fourth dimension in several hyper-layers and print a 3D object for each slice. We already have the software to create 3D slices out of 4D objects.

The trick will be to reassemble the slices into a 4D object :-)

Just looking at these cross sections could be interesting. Also printing the same object at different resolutions along the fourth dimension could be insightful.

[dekhn]

There's more than one dimension- any real parameter is considered a dimension in this context.

In this case, as the PR specifically says, the fourth dimension is time: they are encoding a temporal path within the object.