Some science fiction weapons are plausible, but do not currently exist. Others use imaginary or physically impossible technologies.
Some real-world weapons initiatives such as the American Strategic Defense Initiative have clearly been inspired by science fiction weapons. Science fiction has also drawn on real-world scenarios, such as the idea of a Doomsday machine, which was seriously contemplated by Cold War nuclear strategists.
One reason that many of these weapons are currently fictional is due to the likely energy requirements. Existing methods of storing, conducting, transforming and directing energy are inadequate to produce a convenient hand-held weapon. Existing energy weapons, such as lasers, require large amounts of energy and also require large amounts of cooling equipment because they are relatively inefficient. The quantities of energy that the speculated weapons might require to obtain the anticipated effects would mean that energy storage and conversion systems would need to be almost 100% efficient.
Examples of science fiction weapons include: