Giuseppe Arcidiacono (Acireale, 1927 – Rome, 1998) was an Italian physicist, mathematician, and cosmologist, primarily known for his contributions to the field of relativity. A student and close collaborator of Luigi Fantappiè, he continued and expanded upon his research, particularly the "theory of syntons." His most significant work concerns the development of projective relativity, an extension of special relativity based on the Fantappiè group, which describes the De Sitter universe. This theory introduces an alternative cosmological model capable of explaining phenomena such as cosmological redshift without resorting to the expansion of the universe. A professor of Advanced Mechanics at the University of Perugia, he authored over one hundred and fifty scientific publications and several monographs, including *Relativity and Cosmology* and *The De Sitter Universe*. Although his theories did not become part of the mainstream of contemporary physics, his original approach earned him a prominent place in the Italian scientific debate of the 20th century, receiving recognition from institutions such as the Accademia dei Lincei.