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Human overpopulation. Human overpopulation (or human population overshoot) describes a concern that human populations may become too large to be sustained by their environment or resources in the long term. The topic is usually discussed in the context of world population, though it may concern individual nations, regions, and cities.
Population inversion. In physics, specifically statistical mechanics, a population inversion occurs while a system (such as a group of atoms or molecules) exists in a state in which more members of the system are in higher, excited states than in lower, unexcited energy states. It is called an "inversion" because in many familiar and commonly ...
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a frequency, polarization, and direction of ...
Nuclear meltdown. A simulated animation of a core melt in a light-water reactor after a loss-of-coolant accident. After reaching an extremely high temperature, the nuclear fuel and accompanying cladding liquefies and flows to the bottom of the reactor pressure vessel. Three of the reactors at Fukushima I overheated because the cooling systems ...
An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated by a slower expansion that would normally not be forceful, but is not allowed to expand, so that when ...
t. e. In physical cosmology, Big Bang nucleosynthesis (also known as primordial nucleosynthesis, and abbreviated as BBN) [1] is the production of nuclei other than those of the lightest isotope of hydrogen ( hydrogen-1, 1 H, having a single proton as a nucleus) during the early phases of the universe. This type of nucleosynthesis is thought by ...
Nuclear holocaust. Mushroom cloud from the 1954 explosion of Castle Bravo, the largest nuclear weapon detonated by the U.S. A nuclear holocaust, also known as a nuclear apocalypse, nuclear annihilation, nuclear armageddon, or atomic holocaust, is a theoretical scenario where the mass detonation of nuclear weapons causes widespread destruction ...
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. [1] It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies ...