The fine-structure constant measures how strongly light and matter interact. Its value, about 1/137, has no units: aliens using completely different measurements would find the same number. Nobody knows why it has this value. Richard Feynman called it one of the great mysteries of physics. If it were slightly different, the chemistry of stars and atoms would change.
Cooled below −183 °C, oxygen turns into a pale blue liquid. Pour it between the poles of a strong magnet and, instead of flowing away, it hangs suspended between them. The reason lies in its unpaired electrons, which respond to the magnetic field. Liquid nitrogen, by contrast, is colourless and pours straight through.
In 2012, Felix Baumgartner jumped from a capsule hanging beneath a balloon, about 39 kilometres up. In that extremely thin air almost nothing slowed him down, and he reached around 1,358 km/h in free fall, or Mach 1.25. He became the first person to exceed the speed of sound with nothing but his own body.