Full Idea
Cantor's 'continuum hypothesis' is the assertion that there are no infinite cardinalities strictly between the size of the natural numbers and the size of the real numbers.
Gist of Idea
The Continuum Hypothesis says there are no sets between the natural numbers and reals
Source
report of George Cantor (works [1880]) by Stewart Shapiro - Thinking About Mathematics 2.4
Book Reference
Shapiro,Stewart: 'Thinking About Mathematics' [OUP 2000], p.42
A Reaction
The tricky question is whether this hypothesis can be proved.