  This paper concerns the so-called cosmological constant problem. In order to
solve it, we propose a toy model providing an extension of the dimensionality
of spacetime, with an additional spatial dimension which is macroscopically
unobservable. The toy model introduces no corrections to most predictions of
the "standard" general relativity regarding, among others, the so-called "five
tests of general relativity". However, it seems that the toy model could
provide an explanation to the flatness of circular velocity curves of spiral
galaxies without introducing any dark matter. The proposed model has quite
important cosmological consequences. By introducing certain corrections to
Friedmann's currently accepted model(s), the toy model allows one to solve
problems related to the present density of matter in the Universe and, finally,
it does not contain the initial singularity.
