Combine the speed of light, the gravitational constant and Planck's constant, and you get a length of about 1.6 × 10⁻³⁵ metres: the Planck length. A proton is roughly a hundred billion billion times larger. At that scale, gravity and quantum mechanics should merge, and no current theory can describe what happens there.
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.