Science4All (english)'s video: Curved-space geometry Relativity 10

There's a fine line between straight and curved lines... Or is there not? What's a straight line (in a curved space)? What's wrong with that map? Spherical Geometry | Science4All 9 https://www.youtube.com/watch?v=SZsz3EchTA0 What's the geometry of my underpants? Hyperbolic Geometry | Science4All 11 https://www.youtube.com/watch?v=PBDcMrq-BSQ What's Einstein's gravity? General relativity explained! Science4All 15 https://www.youtube.com/watch?v=zZDoSpiIxs0 Is gravity acceleration or curvature? Follow-up clarifications | Science4All 16 https://www.youtube.com/watch?v=WbhUsPuioN8 What proved general relativity? Einstein's heart palpitations | Science4All 17 https://www.youtube.com/watch?v=IxS_4Z6_wBA What's the destiny of the universe? Einstein's biggest blunder | Science4All 18 https://www.youtube.com/watch?v=ZAiVf4zA6KI Spacetime of General Relativity | Science4All Article http://www.science4all.org/le-nguyen-hoang/spacetime-of-general-relativity/