What fictional universes ideas are most plausible and likely to be true within our (actual) universe??

Question: What fictional universes ideas are most plausible and likely to be true within our (actual) universe??
- Keywords:
  fiction,
  universe
Asked by anon-223038 to Sam on 19 Nov 2019.
- Sam Lawrence answered on 19 Nov 2019:
  
  A lot of the physics in the movie “Interstellar” are scientifically accurate, besides the part where he enters a black hole (sorry for the spoilers). We currently don’t know what happens as one travels inside of a black hole. However if you fell with your feet towards the black hole, you would experience “spaghettification” where you would be stretched like a long string of spaghetti. Time dilation is a real phenomena: if an identical twin travels around the universe at light-speed and returns to the Earth, they will be younger than their twin. Mind-blowing!

Question: What fictional universes ideas are most plausible and likely to be true within our (actual) universe??