The development of the first nuclear bomb, often referred to as the Manhattan Project led by Robert Oppenheimer, relied heavily on principles from nuclear physics, quantum mechanics, and engineering. Here are some key scientific concepts that were employed: 1. Nuclear Fission: This is the splitting of a large atomic nucleus into smaller ones, which releases tremendous energy. The principle applied in the bomb involved Uranium-235 or Plutonium-239, which are suitable for fission. When a free neutron strikes the nucleus of these atoms, they split, producing both enormous energy and additional free neutrons that can induce more fissions, creating a chain reaction. 2. Chain Reaction: The release of additional neutrons in a fission process can cause those neutrons to induce further fissions, leading to a rapid multiplication of the fission process and hence energy production. In a nuclear bomb, this chain reaction is uncontrolled and happens very fast, resulting in an explosion. 3. Mass-energy Equivalence: This principle presented by Einstein's famous equation, E=mc^2, shows that mass can be converted into energy. In the context of a nuclear bomb, a small amount of matter converted can generate a large amount of energy, contributing to the bomb’s explosive power. 4. Critical mass: This is the minimum amount of fissile material needed to sustain a nuclear chain reaction. To create an efficient and effective bomb, Oppenheimer and his team had to carefully calculate and obtain this critical mass for the bomb's nuclear material. 5. Implosion Method: Instead of just assembling sub-critical pieces of nuclear fuel to achieve critical mass as in "gun-type" designs, the bomb developed under Oppenheimer used an "implosion-style" mechanism. A shell of conventional explosives around a sub-critical sphere of fissile material was detonated symmetrically, compressing the fissile material into a supercritical state, thereby initiating the nuclear chain reaction. 6. Quantum Mechanics: The atomic and subatomic behaviors needed for the bomb's functioning require a solid understanding of quantum mechanics. Particularly, principles like quantum tunneling are vital in understanding how neutrons can penetrate atomic nuclei to trigger fission. These principles, among other technical aspects and engineering challenges, were addressed during the development of the first atomic bomb. The project not only marked a significant advance in military technology but also brought about profound changes in the field of nuclear physics and engineering.