Sweden

Oskar Benjamin Klein (Swedish) was a Swedish theoretical physicist. Klein is credited for inventing the idea, part of Kaluza–Klein theory, that extra dimensions may be physically real but curled up and very small, an idea essential to string theory / M-theory.

Gustaf Arrhenius was an oceanographer at Scripps Institution of Oceanography at the University of California San Diego whose varied research considered the earliest life on Earth and origins of the solar system.

Alfvén was the founder of the modern field of plasma physics, the study of electrically conducting gases. Plasma is the dominant state of matter in the universe, although it is rare on earth—stars, galaxies and the space between them are filled with plasma. Plasmas have widespread applications in technology, the most exciting being their potential use in controlled thermonuclear fusion, a potentially clean, cheap and unlimited source of energy. Alfvén’s ideas and research in studying the behaviour of plasma are routinely used in the many applications of plasma physics, as is shown by the many concepts that bear his name—Alfvén wave, Alfvén speed, Alfvén limit and so on.