At 12:00, the room is empty. At 12:05, a point-sized tetrahedron appears in the 
middle of the room, which keeps growing with constant speed, until at 12:15, it
simply disappears. What you just witnessed was a HyperPentahedron (if my four-dimensional intuition is right :-) --FalkBruegmann ''Someone has read FlatLand.''

Of course this is assuming it is aligned with the time axis, and its height is about 10 minutes. :-) --HaskoHeinecke

10 minutes = 111600000 miles as Einstein flies. You better hope that thing ain't spinning. Or that it's a verrrry BigRoom.

''I've read FlatLand, and I say that Einstein's air speed is largely irrelevant. We get to assume that the HyperPentahedron exists for all time, but took 10 minutes to pass through our three-dimensional slice of FourSpace. -- IanKjos''

Mathematicians call this a 4-simplex. (A tetrahedron is a 3-simplex, a triangle is a 2-simplex, a line segment is a 1-simplex, a point is a 0-simplex.)
----
CategoryMath