Unanswered questions

One of the things I really enjoyed about being a high-school teacher was being able to ask the Science teachers all manner of interesting questions. One of the things I love thinking about are extremes, for example:

• The highest mountain (Everest 8,848m)
• The deepest ocean trench (Mariana Trench, 11,000m)
• The smallest particles (subatomic particles)
  
• The distance at which the Earth's atmosphere ends (outer edge of the exosphere 190,000 km, half way to the moon, where the remaining atmospheric particles are overwhelmed by the gravitational pull of the solar wind)

However I still have lots of outstanding questions, for example:

• The largest known object in the universe?
• Is it possible to have a coldest possible theoretical temperature, what would be the limits?
• Can disorders like say Autism occur on a spectrum and if so what's the name for non-medically treated part of the spectrum?
• Are Bell curves the only types of 2D curves for data?