![Image source: California Institute of Technology The Flatness Problem Image source: California Institute of Technology](http://www.timeone.ca/wp-content/uploads/2013/06/051-the-flatness-problem.jpg)
Image source:
California Institute of Technology
Spacetime being 4-D means the universe is curved in four dimensions and that’s harder to imagine.
Image source:
California Institute of Technology
Spacetime being 4-D means the universe is curved in four dimensions and that’s harder to imagine.