The electromagnetic force is one of the four fundamental forces of our universe. It is responsible for the flow of electron through wires, the magnetic field surrounding our planet, and the repulsive force between atom nuclei. The nuclei of atoms are comprised of protons and neutrons and are positively charged. As two atom nuclei approach each other, the opposing positive charges of the atoms push the nuclei apart, preventing them from getting close enough to allow the strong nuclear force from binding the nuclei. At great temperatures and pressures, atoms are forced close enough together that the latent repulsive force of the atoms is overcome, allowing the strong nuclear force to fuse the atom nuclei together, releasing energy and producing a heavier atom nucleus. This interaction is known as nuclear fusion and is the process by which all stars turn lighter elements like hydrogen and helium into heavier elements.