The Curvature of Space

You can't really think about space without thinking about the four d structure that it its inmage of space time. One way to measure the curvature of space is to look at the path of two photons. And if you are in a parabola, then they appear to away from each other. Its equivalent to saying that a triangle on that surface has angles less than a hundred an 80 degrees. That's what it means for space to be flat, right?