space-time
The space-time concept is the most difficult to explain or understand in the entirety of human knowledge. We perceive reality in terms of up and down, left and right, even jokes are made like: "He doesn't know up from down." For we view things in relativistic terms, and dualisms. Does up exist by itself? Does left exist by itself? Are they continuum's? Can an event exist as a non-event. Are space and time inseparable dualities? How many dimensions are there--one, two, three, four, five, six, seven, eight, nine, ten, then eleven.  Black holes, white holes event horizon, helix, super galactic, sub-atomic, worldlines. string-like, super-strings, quarks, gluon's, tachyons, big-bang, big-bang plus 1 x 10 minus 18th second. An event in terms of x,y, and z with respect to a rotational helix with a velocity equal to c on the worldline so long as it occurs outside the event-horizon and stays within the worldline.  That's why they messed up the Philadelphia experiment.
You are playing God when you mess with the space-time continuum.