Physics May Need 11 Dimensions. We Can Only Find 4

String theory's big cousin, M-theory, needs 11 dimensions. We can only find 4: three of space and one of time. So where would the other seven hide? We climb the whole ladder, from a single point to the 11th dimension: the 1884 book Flatland, why time counts as the 4th dimension, your "spacetime worm", the famous thought experiment behind dimensions 5 to 10, and what physics actually says, and has tested, about extra dimensions. Chapters 0:00 Where are the missing dimensions? 0:33 0D: a single point 0:53 1D: the line 1:24 2D: Flatland 2:11 3D: you 3:03 4D: time 4:07 The thought experiment 4:31 5D: every choice 5:04 6D: moving between lives 5:35 7D: different beginnings 6:10 8D: stacked infinities 6:41 9D: different laws 7:06 10D: everything 7:36 11D: what physics actually says 8:54 Back to Flatland #dimensions #physics #stringtheory