According to Clifford Algebra: A Visual Introduction,
- A Clifford Algebra over $\mathbb{R}^3$ may describe the rigid motions in space (namely, conjugation acts as a reflection by a plane).
- A Clifford Algebra over $\mathbb{R}^4$ may describe the projective geometry in space.
- A Clifford Algebra over $\mathbb{R}^5$ may describe the conformal geometry in space.
Where could be found an intuitive explanation for the last two items?