> Can the Lobachevsky plane be embedded into R^3 ? > (The Lobachevsky metric must be induced by > the standard eucledean metric in R^3). > I have heard that the answer is "no". If so, anybody knows what are > the main ideas of the proof?
No, with the euclidean metric, but yes, with later non-euclidean metrics in R^3, after more advanced/general hyperbolic space models were developed and proposed with definition of corresponding geodesics also incorporated from H^2.The advent came about some 18 centuries after Euclid's euclidean metric ds^2 = dx^2 + dy^2.
In 1868, (in Essay on an interpretation of non-Euclidean geometry) Beltrami gave the first model of hyperbolic geometry. In Beltrami's model, lines of hyperbolic geometry are represented by geodesics on the pseudosphere. Thus, Beltrami attempted to prove that Euclid's parallel postulate could not be derived from the other axioms of Euclidean geometry; this proof fails however since the pseudosphere is only a small portion of the hyperbolic plane.
In the same year, however, Beltrami went much farther and gave a correct proof of the equiconsistency of hyperbolic and Euclidean geometry, by defining what are now known as the Klein model, the Poincaré disk model, and the Poincaré half-plane model, in his paper Teoria fondamentale degli spazii di curvatura costante. For the half- plane model, Beltrami cited a note by Liouville in a book by Monge on differential geometry.